Predation of Microbes by Animals

Predation of Microbes by Animals

	Predation of Microbes by Animals Many invertebrates satisfy part of their food requirements by preying on microbes 105-107 times smaller in biomass than themselves. This is accomplished by two feeding strategies:
Grazing This is a common feeding strategy of aquatic invertebrates like snails and sea urchins. They scrape and ingest the microbial crust from submerged surfaces where the microbial populations are able to reach high densities because of the physical absorption of dissolved nutrients on these surfaces. The size difference between the predator and prey becomes relatively unimportant in this feeding process (grazing) because the predator pursues masses of millions of microbes rather than individual prey.
Various members of the marine habitat, secrete slime trails which bacterial, fungal and algal populations colonise. These slime trails provide nutrition for the microbial population. They adhere to the slime which acts as mucous traps. The animals then retrace their tracks and graze on the microbial population that are entrapped in the mucous slime trails
Filter feeding Many sessile benthic (sediment) invertebrates that are permenantly attached underwater exhibit this mechanism to exploit suspended planktonic microbial prey. These animals remain stationary and filter the prey out of suspension. This process is energetically advantageous to the predators which maintain a flow of water using cilia through which the microbes are filtered. For example, sponges, bivalve molluscs and barnacles exhibit this kind of feeding.
	The microbes associated with faecal pellets are an important source of food for many aquatic and terrestrial animals. Digestion of food during passage through the alimentary canal is usually incomplete leaving the cellulose portion undigested. The excreted faecal pellets are further decomposed by the remnants of intestinal microbes and additional microbes from the environment when the recalcitrant plant polymers are solubilised and converted to microbial biomass.

Re-ingestion of the faecal pellets by the same animal or other animal population allows a more complete utilisation of the food resource. In addition, the microbes also supply critical vitamins than otherwise would be absent in the diet. In the terrestrial habitat, certain rodents (rabbits) are coprophagous (re-ingest their own faecal matter).

Most herbivorous animals are unable to digest the cellulosic parts of the plant materials they consume. They rely on the enzymatic capabilities of microbes to degrade this material and to produce substances that they can assimilate

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