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Microorganisms, as the name suggests, are extremely minute organisms which are impossible to be observed by the naked eyes. Due to their size, they are mostly interpreted as being single-celled organisms and include different types of organisms in their classification bacteria, viruses, fungi, archaea and protists. Also, there are some animals which are so small that they need to be visualised under microscope for their structure to be determined, hence are termed as microscopic animals. While most of the microorganisms, due to their ability to interrupt with the normal cellular activities of other living organisms, are considered mostly as being pathogenic, they are also advantageous in a huge number of ways and their role in nature makes them crucial for the balance of the ecosystem.
When different kinds of organisms interact with each other for living, the process of symbiosis occurs. The symbiosis can occur through the fusion of one organism into the other known as endosymbiosis or just through the extracellular communication of the organisms known as ectosymbiosis. The interaction among these organisms can occur in different forms such as mutualism where both of the organisms associate to benefit from each other, commensalism where one organism is in an advantageous stage while the other remains neutral with no gain or loss and parasitism where an organism takes the benefits for its survival by harming the other organism it is attached with (Prescott, 1999).
The symbiotic behaviour of the microorganisms which helps them in forming different kind of relationships such as mutualism and commensalism with different kinds of animals has proved to be very beneficial for them. One of the significant benefits has been the aid provided by the microorganisms during the digestion of food in the intestinal tract of the animals. For example the presence of the microbial ecology inside the body of ruminant animals has played a huge role in the food digestion process within their rumen. Ruminant animals, which depend mainly on grasses and other fibre-rich plants, gain cellulose after food consumption to supply their high demand for energy. However, the lack of natural enzyme within their bodies can be counter effective during the cellular activities of these animals. This problem is overcome by different microorganisms found inside the rumen of the ruminants such as ciliated protozoa, anaerobic fungi and many bacterial species such as Fibrobacter succinogenes and Ruminococcus albus which provide enzymes for breaking down cellulose to various carbon products such as glucose for energy. These organisms which create carbon cycle within the body of ruminants are important in providing organic compounds, proteins and vitamins to the animals (Wallace, 2008). Also, there are other organisms such as leaf-cutting insects which heavily rely on different types of bacteria for their nutrition. These bacteria belonging to different families such as Enterobacteriacaea and different genera such as Prevotella, Ruminococcus, Klebsiella, etc., which together form a fungal population, acquire the capability of degrading the fibres that constitute the cell walls of the plant. These polymers are hydrolysed into smaller monomers due to the fungal activities and are very useful for these leaf-cutting insects such as ants to achieve energy for survival. The relationship of the fungus and the leaf-cutting insects is mutual as the insects which cultivate the fungus help the microorganisms by sheltering them in a safe and facilitated environment within the leaves (Suen et.al. 2010).
Not only animals, but microorganisms, with their efficiency in creating symbiosis with different living creatures, have been very helpful for the growth and maintenance of huge variety of plants in many numbers of ways. The roots are the main pathways for the absorption of different nutritional components needed for the plants to survive and grow. To do so, they come in contact with the soil hence fixing the plants into stationary position. This area of the interaction of the plant roots and the soil is called the rhizosphere. The rhizosphere contains a number of microorganisms which form mutualistic relationship with the plants, therefore allowing both of the plants and the microorganisms to exist and function normally. Different types of microorganisms such as the fungal strain, Trichoderma viride, are very important in protecting the soil against pathogens by producing antibiotics. This is crucial for the plants as it helps them to avoid different diseases. Besides this, plants absorb different molecules synthesised by different microorganisms present in the region to support their development. Some of the molecules include plant hormones such as gibberellic acid produced by the fungus, Gibberella fujikuro, cytokinins, auxins, etc., along with various other components such as amino acids, sugars and vitamins which help the plants to grow and maintain their structure (Starkey, 1958). Along with different organic molecules, several inorganic factors are also needed for ensuring the growth of plants. Among these, nitrogen is considered to be a vital aspect for the plant development. Nitrogen gases, which dominate the earthâ€™s atmosphere, cannot be used directly by the plant materials and so need to be converted into various nitrogen containing compounds. During this process of nitrogen fixing, different microorganisms come into play making it possible for the plants to absorb the compounds.
Among different types of plants, leguminous plants use different bacteria such as Rhizobium and Bradyrhizobium for the fixing of nitrogen. These bacteria enter into the plants by piercing through the walls and the epidermis of the root cells and ultimately giving rise to the nodules. After the entry, the microorganisms become active for nitrogen fixation at the site called bacteroids present within the nodule. The nodules also contain leghemoglobin which have features similar to that of haemoglobin in human beings. The ability of these molecules to provide oxygen is very important for the bacteroids to maintain their ATP level and also for the nodules to give their red colour. The darkness of the nodule helps in determining the degree of N2 fixation. Besides the symbiotic relation of Rhizobium and leguminous plants, the interaction between the bacteria and other non-leguminous plants such as Parasponia andersonii also occurs to fix the nitrogen. Apart from Rhizobium, several other bacteria such as Frankia form symbiotic relationship with various dicotyledonous plants for the formation of the nodules. These nodules, in presence of sufficient oxygen, increase their nitrogenous activity and help in fixing nitrogen required for the growth and development of plants (Burris et.al. 1992).
Likewise, different microorganisms also play huge role in the area of biotechnology. The use of the biotechnology which has great impact in different fields such as medicine, agriculture, engineering, etc. make use of biological organisms and are involved in some sort of industrial processes. This also includes food technology which has been hugely influenced by the use of microorganisms during the process. One of the important aspects of the food technology where microorganisms are utilised includes fermentation. Fermentation is the process of oxidising the sugar molecules such as carbohydrates for the formation of smaller molecules such as alcohol and carbon dioxide which are simultaneously reduced in an oxygen deprived environment. So, the fermentation process has been used for the production of different kinds of alcohol such as wine where different strains of yeast such as Saccharomyces cerevisiae or Saccharomyces ellipsoideus are used to extract the alcoholic content from the carbohydrates as well as beer which are produced by the fermentation of starch obtained from cereals using other strains of yeast such as Saccharomyces carlsbergensis (Prescott, 1999).
Besides producing alcohol, milk can also be fermented to produce lactic acid which is useful in dairy products such as yogurt, cream, cheese, butter, etc. To synthesise these products, different lactic acid bacteria belonging to various genera such as Lactococcus, Lactobacilli, Enterococci, Streptococci, etc. are used during the fermentation process. Different strains of these bacteria are used in different ways to achieve the desired product such as the bacteria Lactobacilli bulagricus and Streptococcus thermophilus provide the milk with good texture and flavour giving yogurt as the end product. However, the inability of some other bacteria such as Lactobacillus acidophilus to provide texture leaves the milk only with considerable acidity (Acidophilus milk). This is one of the useful products of milk fermentation (Vuyst 2000). Also, the process of bread making is highly affected by the bacterial strain Saccharomyces cerevisiae which ferment different saccharides such as glucose and fructose present naturally in the dough, sucrose added by the baker and maltose produced through the breakdown of starch into acids. The fermentation converts the sugars into acids such as CO2, hence providing the bread with the needed texture, taste and odour (Attfield et.al. 2001). In addition to these, fermentation industry has been proved to be very advantageous to meet the high demand of antibiotics whilst maintaining the economy during their production. These antibiotics are generated from the growth of microorganisms such as different strains of fungus Penicillium and are known as secondary metabolites. This rapid production of antibiotics is useful in different areas ranging from human bodies to soil to combat different pathogens and other harmful microbes (Wilkinson, 1975).
Along with the use of the microorganisms in different fields of biotechnology, rapid development has been observed in the genetic engineering where the DNA of an organism is modified using several means such as enzymes and vectors and recombinant DNA is obtained that is used to for benefits. Microorganisms have been modified for different medical purposes. The proteins that have the potential of treating certain diseases or illness have been extracted through the genetically modified microorganisms. The alternation of genes in an organism to treat diseases known as gene therapy makes great use of different strains of bacteria such as Salmonella, Shigella, Listeria as well as Escherichia coli and certain types of yeast (Vassaux et.al. 2005). Among these, there has been significant achievement in the cancer treatment through the use of modified microorganisms. Various microorganisms such belonging to the strains of Clostridium, Bifidobacterium, Salmonella, Mycobacterium, Bacillus and Listeria, which are either obligate anaerobic or facultative anaerobic, have the ability of supressing the tumour growth by acting as anticancer agents and hence targeting the overgrowing cells (Bernades et.al. 2010). Similarly, the use of vaccines has been very important to treat different diseases such as small pox, measles, mumps, polio, etc. These vaccines which are inserted into organismsâ€™ bodies carry several antigens and so induce the immune response within the body systems. The production of these useful antigens is possible through the different microbial strains of bacteria and viruses such as StaphylococcusÂ carnosus, Salmonella enterica, Listeria monocytogenes, etc. which are weakened and are used as carriers for the antigens. This causes the antibodies against certain pathogens to be produced inside the living body of the organisms (Schoen et al. 2007).
The technique of genetically modifying microorganisms has been of great use in the field of agriculture. Different bacteria such as Agrobacterium tumefaciens are used to produce recombinant DNA with desired gene and are transferred into the plants in order to produce different plant growth hormones and hence increase crop productivity. Also, the genes from other bacteria such as Bacillus thuringiensis have been transformed using recombinant DNA technology and inserted into the plant cells of different types such as tomato and tobacco enabling them to resist against diseases caused by the pests. Besides different pests, fungi and insects, the frost formation can also disturb the normal functioning of cells in many agricultural crops. There are several biological agents that can induce in the nucleation of ice layer in the leaf surfaces. To reduce the effects of these agents, several microorganisms such as ice-minus strain of Pseudomonas syringae bacteria, Pseudomonas fluorescens, Erwinia herbicola, etc. are used to protect the plants against ice formation (Atlas, 1998).
With so many benefits and many more such as in treatment of sewages and wastes, energy recovery through large production of biomass that are brought through the use of microorganisms, they can hardly be considered as disease causing agents. All the advantages are very necessary to maintain the equilibrium of the environment and to benefit human beings during daily survivals. While the pathogenic organisms that carry diseases need to be controlled from growth, attempt of eradicating the microorganisms completely from the ecosystem needs to be avoided as this can counter balance the positive effects carried by them and can induce a serious threat to the survival of some other organisms in the living system.