Saturday, January 4, 2020

Microbial Interactions

Microbial Interactions
Microorganisms are ubiquitous in their occurrence. However, in natural environment they interact among themselves with plants, with animals, and, moreover, with their niches. Finally, different types of interrelations are established. Reasons for microbial interactions are the competition for nutrients (including oxygen) and space in an ecological niche. Baker and Cook (1974) pointed out that a microbe may not affect the other, or may affect by one or more of the following ways:

(a) by stimulation of growth and development of associate,

(b) by inhibition of growth and development of the associate,

 (c) by stimulating the formation of resting bodies by the associate,

 (d) by inhibiting the formation of resting bodies by the associate,

(e) by enforcing the dormancy of the associate,

 (f) by causing lysis of the associate,

(g) by harming the population of plants,

 (h) by directly benefiting the plants, and

 (i) by getting influenced by its own micro-environmental factors. Some of the possible microbial interactions have been discussed in this section.

However, on the basis of relative advantage to each partner i.e. hosts and microorganisms. the relationships are basically of three types :

(a)neutralism (where host remains unaffected by the microbe),
(b)mutualism (where both partners get benefits from the association), and
(c)parasitism (where one partner gets benefits and the second suffers from damages).

Clay-Humus-Microbe Interaction

Clay mineral (and humic substances) affect the activity, ecology and population of microorganisms in soil. Clays modified  the physicochemical environment of the microbes which either enhance or attenuate the growth of individual microbial population. After release from clays, the organic materials is either degrade by microorganisms or again bind to clays. Microorganisms have a negative charge at  pH of most microbial habitat.

The magnitude of electronegativity on cell walls of bacteria and fungi is regulated by pH, amino acid residues and changes in wall composition(Archibald et al, 1973).

Clay mineral get adsorb and bind with proteins, amino acids, small and humic substrates.

Nutrient used for growth and activity directly from clay-protein, clay-amino acids or peptides, and clay-humic substrate complexes. high level of clay interferes and restricts infection of banana rootlets by Fusarium oxysporum and thus exerts natural biological control of panama disease. The clay and humic colloids influence the distribution and activity of Streptomyces, Nocardia and Micromonospora (Goodfellow and Williams, 1983).

Clay particles (e.g. kaolinite) is known to reduce the toxicity of cadmium (Cd) on Macrophomina phaseolina (Dubey and Dwivedi, 1985).

Plant-Microbe Interactions

 The above ground such as foliage and below ground such as roots of plants are constantly interact with a large number of microorganisms(e.g. bacteria, actinomycetes, fungi, amoebae, nematodes, and algae) and viruses, and develops several types of inter-relationships.Moreover, considering the result of interactions, it may develop destructive, neutral, symbiotic or beneficial association with plants.

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