symbiosis and antibiosis among microbial populations

 Symbiosis and Antibiosis among microbial populations.

Microorganisms interact them selves and lead to beneficial and harmful relationships some of the interactions and inter relations are mentioned below.

a) Symbiosis(a beneficial association)

It is a interaction of two different species and both the partners of the association get benefits.

Example: Lichens( association of algae and fungi): Lichen is a thallus of dual organisms i,e a fungus and an algae that form a self supporting combination. The fungal components is called mycobiant and the algal partner is known as phycobiant. The two groups of organisms live in a colony in which fungus forms thalus while algae(5-10%) forms mass of thalus.

A mycelium fungus forms a network of tissue and alga cells embed in the network of fungus to form lichen. In lichen, mycelium derives nutrition from the alga inturn it provides mineral nutrients to alga by digesting rocks with the help of enzymes. The algal cells produce the food by themselves and or fix nitrogen from the atmosphere which then diffuse into fungal network. Thus alga provides food to fungus and fungus provides shelter and mineral nutrients to alga.

The fungal partners forming a lichen are the members of Ascomycetes and 2 to three genera of Basidiomycetes. The member of alga forming lichen belonging to cyanobacteria or chlorophyta.

b) Antagonism( a harmful association)

The composition of microflora or microfauna of any habitat is governed by the biological balance created through interactions and association of all individuals present in the community. Any inhibitory effect of an organism created by any means to the other organisms is known as antagonism. Antagonism is a balancing wheel of the nature, by which biological equilibrium is maintained. Antagonism is devided into three main types

i) Amensalism

ii) Competition

iii) Parasitism and predation 

i) Amensalism( Antibiosis and lysis)

It is the phenomenon in which one microbiabial species is adversely affected by the another species and the another species is not affected by the first one. It is occur due to secretion of antimicrobial metabolites by the organism A which inhibit the organism B but organism A is unaffected. Antimicrobial metabolites like antibiotics, siderophores or enzymes produced by  A microbe, it penetrate the cell wall and inhibit metabolic activities of B microbe due to its toxicity.

For example: Trichoderma harzianum and T viridae secrete cell wall lysing enzymes and mycelium cells lysed due to enzyme effect.

ii) Competition:

Among the microbes the competition exist for nutritions, oxygen and space but not for water temprature and pH. The competition ability for substrate by any particular species is determined by competitive saprophytic ability and survivability of that species based on fallowing characteristics:

1. Rapid germination and rapid growth of fungi, in response to nutrients.
2. Appropriate enzymes for degradation and obtaining carbon constituents of plant tissue
3. Secretion of fungistatic and bacteriostatic product
4. Tolerance of fungistatic substance produced by competitive microbes.  

Thus competition exist for limiting sources, especially inadequate amount of carbon causes competition. At low level of carbon, the fast growers hold slow growers in check when both are added to sterilized soil. But no check of slow growers observed when carbon supplied inadequately.

iii) Parasitism and Predation:

It is a phenomenon in which one organism consumes other organism i,e a living organism is mechanically attack by other which leads to the death of former organism. It is voilent and destructive relationship.

Example: i) Fungus-Fungus interaction(Mycoparasitism):

 When one fungus is parasitized by other fungus then this process is called mycoparasitism. In inter fungus interactions, several events occur which lead to predation i,e coiling penetration resting body formation, barrier formation to check the entry of pathogen and lysis of host cell. The parasite dissolve cell wall of host but sometimes host develops a resistance to prevent penetration and proliferation of parasite in the body.

Example ii) Mycophagy:

It means feeding upon fungi by amoeba. Many amoeba known to feed on pathogenic fungi. These amoeba interact with fungal hyphae and make perforations. Ameoba feeds on fungi in three steps: Attachment- Ameoba attach to fungus by choumotoxis process

-Engulfing: The fungal hyphae based on its size, are fully engulfed by amoeba.

-Digestion: Completely/partially engulfed fungi are digested into a large central vacoules.

Example iii) Nematophagy:

The phenomenon of eating nematodes by fungi is known as nematophagy. Fungi are mechanically attack and kill the nematodes resulting in consumption of nematodes. Over 50 species of fungi are known to attack nematodes different developmental stages of nematodes are known to attacked by different species of fungi.