Pure culture techniques

Pure culture techniques

Aim

To learn the pure culture techniques and to isolate pure culture of bacteria

Principle

The microbial population in our environment, air, soil, water, etc is large and include many species of bacteria, fungi, algae, etc. For studying these populations, it is necessary to isolate them as pure cultures. Pure culture represents a population of organism of a single species or more precisely growth derived from single cell or spore.  There are various techniques for preparing microbes as pure cultures from mixed population.  Aseptic techniques or the sterile techniques are the processes required for transferring a microbial culture from one container to another without contaminating the culture or the environment.  For successful aseptic technique, the work area should be wiped with an antiseptic, the instruments, medium and containers should be sterile and the procedure should be done quickly to minimize the time of exposure.

The commonly used methods are streak plate, spread plate and pour plate technique.  These techniques involve thinning of organisms and immobilization on or in a nutrient medium.

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Isolation of pure culture by Streak Plate technique

Streak plate technique is used for the isolation of organisms, mostly bacteria, into pure culture from mixed population.  The inoculum is streaked over the agar surface in such a way that it “thins out” the bacteria and individual bacterial cells are separated and well-spaced from each other. The sample is diluted by streaking it through successive quadrants. While streaking in successive areas of the plate, the inoculum is diluted to the point where there is only one bacterial cell deposited every few millimeters on the surface of the agar plate.  When these bacterial cells divide and give rise to thousands of new bacterial cells, an isolated colony is formed.   Usually by the third or fourth quadrant individual isolated colonies will be formed. Pure cultures can be obtained by picking well isolated colonies and re-streaking these on fresh agar plates. 

Materials required

Bacterial culture, Inoculation loop, Bunsen burner, Nutrient Agar plates

Procedure

1. The inoculating loop was sterilized in the bunsen burner by putting the loop into the flame until it is red hot and it was allowed to cool.
2. Using the loop, a loopful of culture was drawn from the culture and spreaded it over the first quadrant (approximately 1/4 of the plate) and spread using close parallel streaks.
3. The loop was flame sterilized, cooled down and streaked gently over a quarter of the plate starting from the previous inoculated area using a back and forth motion.
4. The loop was again flame sterilized, cooled down and the streaks from the step 3 are extended in to next quarter
5. The loop was again flamed and allowed to cool and the streaks from the step 4 are extended in to next quarter.
6. The loop was flamed again and allowed to cool. The streak area of step 5 are extended into the center area of the plate.  The loop was flamed loop once more.
7. The plates are incubated in an inverted position in the incubator at 37^o C for 24 hours.

Results

A confluent growth was seen at the initial streak lines and the growth was less dense at the later streak lines.  Any growth not present on the streak line is considered as a contamination.  Well isolated colonies were observed towards the last streak lines.

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Enumeration of microbial cells by pour plate and spread plate technique

Aim

To Enumerate of microbial cells by pour plate and spread plate technique

Principle

Pour-plate method and Spread-plate method are pure culture techniques as well as are used enumeration of bacterial sample. These techniques need the sample to be serially diluted prior to plating. In serial dilution technique, the inoculum from a mixed culture is subjected to serial transfer through a sterile liquid.  The aim is to dilute the microbial suspension so that the final tubes in the series contain lesser number and varieties of microorganisms.

In pour plate technique, diluted samples are mixed with melted agar medium and then poured into sterile petri dishes. Here, 1 ml dilutions of bacteria is mixed with melted agar medium maintained in the liquid state at a temperature of 42-45°C (agar solidifies below 42°C). The bacteria and the melted medium are mixed well in separate Petri plates, allowed to solidify, and then incubated. The bacterial colonies develop, both within the agar medium (subsurface colonies) and on the medium (surface colonies). Pour plate method has certain disadvantages such as, the subsurface colonies needs digging them out of the agar medium and the microbes must be able to withstand temporary exposure to the 42-45° temperature of the liquid agar medium.

In spread plate technique 0.1 ml of the serially diluted mixed culture is placed on the center of an agar plate and spread evenly over the surface by means of a sterilized bent-glass-rod and the medium is then incubated. The colonies develop on the surface of the agar plates and the microorganisms are not exposed to temperature of the melted agar medium.

Materials required

Bacterial culture, Inoculation loop, Bunsen burner, Nutrient Agar, sterile petri dishes, 9 ml sterile water blanks, sterile pipettes

Procedure – Serial dilution

1     1 ml of sample was aseptically added to first test tube containing sterile 9 ml water and the tube was marked as 10^-1. 

2     1 ml sample from the 10^-1 tube was added aseptically to another 9 ml sterile water blank marked as 10^-2 and repeated until 10^-9.

Procedure –pour plate technique

1     sterile petri dishes were inoculated with 1.0 mL of diluted sample from the tubes marked 10^-5, 10⁶, 10^-7, 10^-8 and 10^-9.

2     15-20 ml sterile molten agar kept at water bath at 45°C was poured into each Petri dish and the dish was rotated gently to mix the culture and the medium thoroughly and to ensure that the medium covers the plate evenly. 

3     The agar was allowed to solidify, and the plate was incubated in an inverted position at 37°C for 24-48 hours.

Procedure – Spread plate technique

1. sterile petri dishes were poured with sterile nutrient agar and allowed to solidify.
2. The plates were inoculated with 0.1 mL of diluted sample from the tubes marked 10^-5, 10⁶, 10^-7, 10^-8 and 10^-9.  The sample was pipetted onto the center of the surface of an agar plate.
3. The L-shaped glass spreader was dipped in alcohol, and flamed over a bunsen burner.
4. The sample was spread evenly over the surface of agar using the sterile glass spreader.
5. The plates were incubated in an inverted position at 37°C for 24 -48 hours.

Observation

The number of colonies and colony morphology was observed in the plates after incubation.  The colony forming unit (CFU) was calculated.

CFU/ml = (no. of colonies x dilution factor) / volume plated. 

Result

CFU from pour plate was ……………

CFU from spread plate was ……………

The predominant colonies were found to be …………………… ……………………………………………………………………………………………….……………………………………………………………………………………………………………….…………………. in plates after pour plate technique and ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. in plates after spread plate technique.

 

 

                                                              Serial dilution technique

 

Bacterial Staining

Bacterial Staining

Visualization of microorganisms in the living state is quite difficult, not only because they are minute, but also because they are transparent and practically colourless when suspended in an aqueous medium.  To study their properties and to divide microorganisms into specific groups for diagnostic purposes stains and staining procedures in conjunction with light microscopy have become a major tool in microbiology.

Chemically, a stain or dye may be defined as an organic compound containing a benzene ring plus a chromophore and auxochrome group.

The ability of the stain to bind to macromolecular cellular components such as proteins or nucleic acids depend on the electrical charge found on the chromogen portions as well as on the cellular component to be stained. 

Acidic dyes are anionic, which means that on ionization of the stain, the chromogen portion exhibits a negative charge and therefore has a strong affinity for the positive constituent of the cell.  Proteins, positively charged cellular components, will readily bind to and accept the color of the negatively charged anionic chromogen of an acidic stain.  Example for acidic dyes are picric acid and nigrosine.

Basic dyes are cationic because on ionization the chromogen portion exhibits a positive charge and therefore has a strong affinity for the negative constituents of the cell.  Nucleic acids, negatively charged cellular components, will readily bind to and accept the color of the positively charged cationic chromogen of a basic stain.  Examples for basic stain is Methylene blue.

Basic dyes are more commonly used in bacterial staining.  The presence of negative charge on the bacterial surface acts to repel most acidic dyes and thus prevent their penetration into the cell.  Numerous staining techniques are available for visualization, differentiation and separation of bacteria in terms of morphological characteristics and cellular structures.

 

 

Batch, Fed Batch and Continuous Fermentation

Batch, Fed Batch and Continuous Fermentation

Fermentation may be carried out as batch, continuous or fed-batch processes.  Batch growth involves a closed system where all nutrients are present at the start of the fermentation in a fixed volume. There may be further additions that limit to acids or bases for pH control, or gases for aeration, etc.

In fed-batch systems fresh medium or medium components are fed continuously, intermittently or are added as a single supplement.  Here the volume of the system increases with time.

Continuous fermentations are open systems where fresh medium is continuously fed into the fermentation vessel and spent medium and cells are removed at the same rate and thus the volume remains constant.

Batch fermentation

This is a closed culture system which contains an initial, limited amount of nutrients. The microorganisms from the inoculum will pass through a number of phases, lag phase, log or exponential phase, stationary phase and death or decline phase.

Lag phase is immediately after inoculation when no apparent growth takes place and this is considered as a time of adaptation. The length of the lag phase should be reduced as much possible in a commercial process to be economical.  Following lag phase, the logarithmic or log phase ensues, this is the period during which the growth rate of cells gradually increases, the cells grow at a Constant, maximum, rate possible.  The exponential phase may be described as

                         dx/dt = µx

Where x is the concentration of microbial biomass, t is time in hours and µ is the specific growth rate. 

The production of primary metabolites occurs during the log phase and this phase is known as the trophophase.  Examples of primary metabolites are amino acids, nucleotides, vitamins, citric acid, acetic acid, ethanol, etc.

 

The growth of the organism results in the consumption of nutrients and the excretion of microbial products. Thus, after a certain time the growth rate of the culture decreases until growth ceases. This may be due to the depletion of essential nutrients in the medium (substrate limitation) or accumulation of toxic products by organism (toxin limitation) or both these factors.

The nature of the limitation of growth can be studied by growing the organism in the presence of different concentrations of substrates and plotting the biomass concentration at stationary phase against the initial substrate concentration. 

It can be seen that with initial increase in substrate concentrations a proportional increase in the biomass produced occurs.  The situation may be explained as

                          x = Y(S-S_R)

Where x is the concentration of biomass produced,

Y is the yield factor (g biomass produced/ substrate consumed),

S is the initial substrate concentration, and

S_R is the residual substrate concentration.

The yield factor is a measure of the efficiency of substrate conversion into biomass.

After stationary phase, death phase occurs. The decrease in growth rate and the cessation of growth due to the depletion of substrate, may be explained using Monod equation,

                       µ = µ_max s/(K_s+s)

Where s is the residual substrate concentration, µ is the specific growth rate, µ_max is the maximum specific growth rate and K_s is substrate utilization constant, which is equal to substrate concentration when µ is half µ_max and this is a measure of the affinity of the organism for the substrate.

Secondary metabolites are produced during the stationary phase and this phase is also known as idiophase.  Secondary metabolites are organic compounds that are not directly involved in the normal growth, development or reproduction of an organism. Microbial secondary metabolites include antibiotics, pigments, toxins, etc.

A primary metabolite is considered as growth-linked and secondary metabolites are non-growth-linked products.

Application of batch fermentation

Batch fermentation may be used to produce biomass, primary metabolites and secondary metabolites. For biomass production, cultural conditions supporting the fastest growth rate and maximum population would be used.  For primary metabolite production conditions to extend the exponential phase and for secondary metabolite production, conditions giving a short exponential phase and an extended production phase will be used.

A batch fermentation possess disadvantages since several distinct practical stages are associated with the operation of a batch fermentation as follows,

1. Charging or filling the fermenter with fresh medium;
2. Sterilization of the fermenter and medium;
3. Inoculation of the fermenter;
4. Production of microbial products;
5. Harvesting of biomass and spent fermentation broth; and
6. Cleaning of the vessel.

This has major economic implications since for a considerable period of time, the fermenter vessel is not producing microbial products, but is being cleaned, filled, sterilized, etc. The non-productive period is referred to as the down-time of the fermenter.  The down time is very high for a batch fermentation.

Fed batch Fermentation

Fed-batch culture is a batch culture which is fed continuously, or sequentially, with medium, without the removal of culture fluid. It is established initially in batch mode and is then fed according to either one of the following strategies:

i) The same medium used to establish the culture is added - result in an increase in volume.

(ii) A solution of the limiting substrate at the same concentration as that in the initial medium is added - result in an increase in volume.

(iii) A concentrated solution of the limiting substrate is added - result in an increase in volume.

iv) A very concentrated solution of the limiting substrate is added – does not result in an increase in volume.

Fed-batch systems employing strategies i) and (ii) are variable volume fed batch system. System employing strategy (iv) is fixed volume fed batch system. The use of strategy (iii) gives a culture intermediate between the variable and fixed volume systems.

Continuous Fermentation

Exponential growth in batch culture may be prolonged by the addition of fresh medium to the vessel.  Fresh medium is continuously added and an equal volume of spent fermentation broth and cells are displaced at same rate. Exponential growth will proceed and steady state will be achieved, that is, formation of new biomass by the culture is balanced by the loss of cells from the vessel.

The flow of medium into the vessel is related to the volume of the vessel by the dilution rate, D, defined as

                       D=F/V

where F is the flow rate and V is the volume of the vessel.

The net change in cell concentration over a time would be

                    dx/dt  = growth - output

                    dx/dt  = µx - Dx

Under steady state concentrations, dx/dt will be zero, then

                    µx = Dx

                    µ = D

So under steady state conditions the specific growth rate is controlled by the dilution rate, up to a maximum value equal to µ max.  If the dilution rate is increased above µmax, complete washout of the cells occurs, as the cells have insufficient time to divide before being washed out of the reactor via the overflow. The dilution rate at which this problem of washout is just avoided is termed as the critical dilution rate (D_crit).

The controlling effect of the dilution rate on microbial growth can be explained by the Monod equation,

                   µ = µ_max s/(K_s+s)

At steady state, µ = D, so

                  D = µ_max ŝ / (K_s+ŝ), where ŝ is steady state concentration of substrate

                  ŝ = KsD / (µ_{max -} D)

So the substrate concentration is influenced by the dilution rate.  Thus biomass growth depends upon substrate concentration and thereby on dilution rate. 

Growth of cells is controlled by the availability of a rate-limiting nutrient. Th system, where the concentration of the rate-limiting nutrient entering the system is fixed, is termed as a chemostat. In a chemostat the substrate concentration is held constant. The other type is a turbidostat, where nutrients in the medium are not limiting. In this case turbidity or absorbance of the culture is monitored and maintained at a constant value, here the cell concentration is held constant.

Continuous Fermenter

The concentration of cells in the chemostat at steady state is described by the equation:

                  ẍ = Y (S_R- S_r)

where ẍ is the steady-state cell concentration in the chemostat, SR is the substrate concentration of inflowing medium, Sr is the steady-state residual substrate concentration in the reactor and Y is the yield factor.

Therefore, the biomass concentration under steady state conditions is controlled by the substrate feed concentration and the operating dilution rate.

Advantages and disadvantages of continuous fermentation system

The down time of fermenter is much less and is thus more economic.  The fermenter can be more easily automated thus requiring less labor.  But the chances of contamination and loss of productivity of the microorganism (strain deterioration) is more.  The control operations are more complicated.  There will be problems in the licensing of a continuous process product since it may not be always possible to trace a consignment of product to a batch of raw materials.  This is due to the fact that in a long continuous process several different batches of media will be used and thus associating product with a batch of raw material will be impossible.

These three modes of fermentations are used in various microbial fermentative productions.  The choice of the mode of operation, that is batch, fed-batch or continuous fermentation, depends upon the product being produced.

 

References

Industrial Microbiology: An Introduction, M J. Waites, N L. Morgan, J S. Rockey, G Higton

Principles of fermentation technology, PF Stanbury, A Whittakker, SJ Hall, 1995, Butterworth-Heinemann publications

 

 

Biodiversity in Plants and Animals

 Biodiversity in Plants and Animals

The term biodiversity was coined by Walter G. Rosen in the year 1986. Biodiversity is the diversity or variability of living organisms present on earth and other species undergone extinction million years ago. In other words, it is the Biological diversity which denotes the total number of different living species, living within a particular region including the microbes, plants, animals, and ecosystems such as coral reefs, forests, rainforests, deserts etc. In biodiversity, every single living species has an equally important role in the ecosystem. It is the totality of genes, species and ecosystems in a defined area.

According to the Convention of Biological Diversity (CBD), biological diversity – or biodiversity – means “the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. This includes diversity within species, between species and of ecosystems”.

All living organisms can be divided into five kingdoms, Animals, Plants, Fungi, Protists and Bacteria.

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It has been estimated that there are around 8.7 million species of plants and animals in existence among which only around 1.2 million species are identified and described so far. Millions of other organisms remain a complete mystery to us.  The various forms of life on the planet included 7.8 million species of animal, 298,000 species of plant and 611,000 species of mushrooms, mould and other fungi along with 36,400 species of protozoa, single-celled organisms, and 27,500 species of algae with no estimate on the number of bacteria.

Plant Biodiversity

Algae: More than 40,000 species of algae are known and described and another 360,000 species are believed to exist.  Most of these yet to be described and identified algae are expected to be present in barks, rocks, marine environment, Polar Regions, etc.

Most of the green algae are cosmopolitan and are present in marine, brackish, fresh water and soil environments.  They are distributed in about 1040 species and 170 genera and 8 orders.  Cladophoraceae is the largest family among green algae and this family contains about 300 species.

Brown algae are mainly present in ocean and there are 265 genera and more than 1500 species in about 14 orders.    They are found in maximum diversity at Japanese region of Pacific and North Atlantic. 

Red algae are the largest group of algae and they are also found mainly in ocean.  There are about 555 genera and they are in maximum diversity at Japanese region of Pacific and North Atlantic and in South Australia. 

The microalgae such as desmids, diatoms, etc are difficult to be surveyed.

Bryophytes: More than 14,000 to 16,000 species of bryophytes are known.  Among this 8000-9000 species coming under 425 genera are mosses and 6000-7000 are liverworts.  It is expected that about 30,000 more species are yet to be discovered.  Majority of bryophytes are reported from cooler regions especially in tropical forest and temperate woodlands.  The Indo Australian archipelago and South America are the areas where bryophytes are richly distributed followed by South Australia, North America, North-east Asia, Himalayas, East Africa and Europe.  The largest genera among bryophytes are Plagiochila (500 species) and Frullania (400 species).

Pteridophytes: These are vascular land plants and along with gymnosperms and angiosperms they dominate the terrestrial environment. There are about 15,000 species of pteridophytes which are native in tropical forest.  It consists of Psilophytales, Lycophytales and Sphenophytales.  Psilophytales contain two genera, Lycophytales have 5 genera and Sphenophytales have 1 genus.  These are diverse group and exhibit diverse sizes, from very tiny to very large tree ferns.  12.5% of the total world fern species are found in Papua New Guinea. 

Gymnosperms: Gymnosperms are mostly trees and a few are shrubs.  There are 500 species of Conifers, 100 species of Cycads and 71 species of Gnetales identified.  Ginkgo biloba is known as living fossil and is native to China.  Conifers are predominant over temperate and alpine regions of tropics. 

Angiosperms: These constitute flowering plants.  There are about 235,000 to 300,000 species in this category.  Almost 500,000 species are yet to be discovered.  The species of these plants are grouped in 17,000 genera under 200-600 families.  Orchidaceae (25,000 to 35,000 species) and Leguminosae (15,000 species) are the largest families.  Angiosperms are the most dominant plant element in earth.  The size of plants in this category range in size from 1 mm (Wolffia) to over 100 meters (Eucalyptus)

Animal Biodiversity

Animals are the eaters of Earth.  They are heterotrophs and depend directly or indirectly for their nourishment on plants, photosynthetic protists, algae or autotrophic bacteria.  Animals vary diversely in their size.  They range from too small to be observed with naked eye to enormously large whales and giant squids

Animal kingdom includes 35 phyla and most of them occur in sea. Fewer phyla occur in fresh water and very few are present in land.  Three phyla such as Arthropoda (spiders and insects), Mollusca (snails) and Chordata (Vertebrates) dominates animal world.

Almost all animals (98%) are invertebrates, that is they lack back bone.  Only 2% animals are vertebrates, that is having back bone. 

The invertebrates are divided into seven phyla. The invertebrate phyla are Molluscs (snails and octopuses), Arthropods (insects, spiders and crabs), Echinoderms (sea urchins and starfish), Cnidaria (jellyfish), Porifera (sponges), Annelids (segmented worms) and Platyhelminthes (flatworms).

Vertebrates belong to the phylum Chordata. Vertebrates are subdivided into five classes, Fish, Amphibians, Reptiles, Birds and Mammals.  The largest group in vertebrates are bony fish.  Amphibians are animals that include salamanders, newts, caecilians, frogs and toads.  Most reptiles live on land while some, like crocodiles and turtles, and some snakes survive in water.  Birds come under two categories, either flightless birds or flying birds.  All mammals breathe using lungs, and therefore live on land and mammals that live in water, like whales and dolphins, come to the surface of the water to breathe.

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Invertebrates

Invertebrates lack a backbone, have an external skeleton for protection and as a supporting structure. Approximately 95% of all animal species are invertebrates such as insects.

Zooplankton

Mollusks - snails, clams, squid, and octopuses

Crustaceans - crabs, lobsters, and shrimp

Echinoderms - sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers

Arthropods -  insects, beetles; moths and butter flies; wasps, ants, and bees; flies and mosquitoes; grasshoppers and crickets; and cockroaches.

The insects possess enormous evolutionary success due to their small size, high reproductive rate and ability to adapt rapidly to environmental changes. These inhabit nearly every ecosystem except the polar regions and the oceans.

Vertebrates

Vertebrates have skeletal support and are relatively large. Most have two pairs of appendages: fins, limbs, or wings. Fish, amphibians, and reptiles are ectotherms, with body temperatures the

same as the surrounding environment. Birds and mammals are endotherms, able to keep their body temperatures nearly constant, independent of the temperature of their surroundings.

There are 50,000 species of vertebrates in seven classes:

·         Agnatha, Chondrichthyes, Osteichthyes (fish): These are ectothermic, aquatic vertebrates with gills, usually fins, and an elongated body covered with scales.

·         Amphibia (amphibian): Ectothermic vertebrates with aquatic larvae; adults live in land or water; includes frogs, toads, newts, salamanders, and caecilians

·         Reptilia (reptiles): Egg laying ectothermic vertebrates with scaly, dry skin.

·         Aves (birds): Endothermic, egg laying vertebrates with feathers for insulation, most can fly

·         Mammalia (mammals): Endothermic vertebrates are covered with hair or fur for insulation, nourish their young with milk from the mammary glands, and mostly give live birth to young.

Fish

Fish live in fresh or salt water of all depths and all temperatures and breathe through gills.

Cartilaginous fish (class Chondrichthyes), consisting of sharks, are extremely diverse and successful; they have remained nearly unchanged for 70 million years.

Bony fish (class Osteichthyes) are more diverse. Stream lined fish, such as tuna and mackerel, Flatfish, including sole and halibut, Elongate fish, such as eels, are examples. 

Amphibians

Amphibians need to live in or near water. Members of the order Caudata (salamanders and newts) have long tails and equal sized front and rear legs, similar to lizards.

Members of the order Anura (frogs and toads) have large, muscular hind legs for jumping, webbed feet for swimming, and no tail. Frogs absorb oxygen dissolved in water when they are in wet places and breathe through lungs when they are in land. Toads have stouter bodies and thicker skins, allowing them to live farther from water.

Reptiles

Reptiles are scaly, dry skinned, air breathers. Their lungs, water proof skin, and shelled eggs allow them to live away from water. The reptiles include Crocodilia (crocodiles, caimans, and alligators), Squamata (lizards and snakes), and Testudines (turtles).

Lizards have low bodies, long tails, and legs that extend outward from the sides of their bodies. Snakes (and legless lizards) have no limbs.

Turtles have a shell for protection. Dinosaurs (superorder Dinosauria), the most famous reptiles, have been extinct for 65 million years.

Birds

Birds are endotherms with feathers for insulation and hard shelled eggs and they can live in a wide range of environments.  They are the most diverse class of terrestrial vertebrates. Species range in size from tiny hummingbirds (order Trochiliformes) to enormous ostriches (order Struthioniformes).

Most birds can fly, although a few have lost the ability and have developed other adaptations such as running (ostriches) or swimming (penguins). Flying birds are lightweight, with a bony bill and hollow bony skeletons. Seabirds have webbed feet for swimming; long legs for

wading; fat deposits, light bones, and air sacs for buoyancy; an oily secretion for waterproofing feathers and providing insulation; highly developed eyesight for locating fish in the water; and a salt gland over the eye to eliminate excess salt.

Mammals

Mammals are air breathing endotherms with hair or fur for insulation that allows them to live in nearly all environments.  Most species are terrestrial, a few are aquatic. The majority of mammals are placental.  Mammals are born from their mother’s body and fed mother’s milk when they are young.

Roughly half of all mammal species are in the order Rodentia, examples rats, Capybara

Bats (order Chiroptera) are the only true flying mammals.

Members of the order Carnivora include species of flesh eating mammals, such as cats, dogs, mongooses, bears, seals, and walrus.

Order Insectivora includes small animals such as shrews and moles.

The two orders of hoofed mammals are the odd toed Perissodactyla, which includes the horse and rhinoceros, and the even toed Artiodactyla, which includes the deer, antelope, camel, pig, and cow.

Whales, dolphins, and porpoises (order Cetacea) are marine mammals

Humans, monkeys, apes, and lemurs belong to the order Primates

With intelligence as an adaptive strategy, humans have colonized nearly every habitat on the land, from the coldest polar regions to the tropical jungles.

Importance of plant and animal biodiversity 

Biodiversity have a key role in human nutrition.  It safeguards the sustainable productivity of soil and provide the genetic resources for all crops and livestock species that we utilize as food. The diversity of plant and animal resources forms the basis for the wellbeing of society and serves as an important source of food and income. Plants and animals provide medicine, timber, biomass, energy, fertilizer, transport, etc so that our livelihoods and welfare are dependent on them.

Pants are an important resource for food, shelter, and agriculture and include bushes, grasses, herbs, shrubs, trees, vines, ferns, and mosses. They are the primary producers and provide us with the oxygen and carbohydrate.

There are several animal species which are trained, domesticated and used for food production, agriculture, livestock, etc. They play a vital role in food safety. 

Contribution to economies: Agriculture, including livestock and fishery, contribute to national economies.  Wild foods of both plant and animal origin are of considerable economic value and they also provide important ecosystem services that contribute significantly to national and global economies. Example, the herbal medicine, crop pollination by insects, etc.

Contribution to human nutrition and health: Plant and animal biodiversity provides nutritionally diverse food products in diverse food chains. This nutritional diversity is mainly observed at species level even though variety/cultivar/breed-level differences also exist.  Biodiversity provides support for drug discovery and the availability of medicinal resources.  about 80% of the world population depends on medicines from nature for primary healthcare.

Biodiversity loss is associated with global health implications where changes in biodiversity such as changes in populations and distribution of disease vectors, scarcity of fresh water, impacts on agricultural biodiversity and food resources etc increases infectious disease transmission.

Contributions to livelihoods of rural populations: Income and livelihoods, especially of poor people, are highly dependent on biodiversity, on wild or uncultivated natural ecosystems.

Livestock provide nutritional supplements to staple plant-based diets and provide manure for soil fertilization, fibre for clothes and serve as financial instruments and enhance social status.

Ecosystem services and functions: Ecosystem services are essential for human life as they provide provisioning services, regulating services, supporting services and cultural services. Ecosystem provide food and clean water (provisioning services), regulate floods, drought, land degradation and diseases (regulating services), support soil formation, nutrient cycling and pollination of crops (supporting services), and provide recreational, spiritual and cultural benefits (cultural services).

Both crop and livestock productions are interdependent with ecosystem services and thus biodiversity, resulting in both positive and negative impacts. On one hand, agricultural landscapes that contain significant areas of semi-natural lands are important for wildlife, such as breeding sites for birds and on the other hand, pesticides and habitat loss, degradation and fragmentation threaten natural pollinators.

 

References

• Textbook of Biodiversity, K V Krishnamurthy, Science Publishers
• Biology, 4^th Edition, Raven and Johnson, WCB Publishers
• https://www.nationalgeographic.org/encyclopedia
• https://www.theguardian.com/environment/2011/aug/23/species-earth-estimate-scientists
• https://www.siyavula.com/read/science/grade-7/biodiversity/02-biodiversity?id=toc-id-6