Question

How are protozoa helpul to us

Answer 1

Protozoa play important roles in the fertility of soils. By grazing on soil bacteria, they regulate bacterial populations and maintain them in a state of physiological youth-i.e., in the active growing phase. This enhances the rates at which bacteria decompose dead organic matter. Protozoa also excrete nitrogen and phosphorus, in the form of ammonium and orthophosphate, as products of their metabolism, and studies have shown that the presence of protozoa in soils enhances plant growth.
Protozoa play important roles in wastewater treatmentprocesses, in both activated sludge and slow percolating filter plants. In both processes, after solid wastes are removed from the sewage, the remaining liquid is mixed with the final sludge product, aerated, and oxidized by aerobic microorganisms to consume the organic wastes suspended in the fluid. In the former process, aerobic ciliates consume aerobic bacteria, which have flocculated; in the latter process, substrates are steeped in microorganisms, such as fungi, algae, and bacteria, which provide food for oxidizing protozoa. In the final stages of both processes, solids settle out of the cleaned effluent in the settlement tank. Treatment plants with no ciliates and only small numbers of amoebas and flagellates produce turbid effluents containing high levels of bacteria and suspended solids. Good-quality, clean effluents are produced in the presence of large ciliated protozoan communities because they graze voraciously on dispersed bacteria and because they have the ability to flocculate suspended particulate matter and bacteria.
Protozoa probably play a similar role in polluted natural ecosystems. Indeed, there is evidence that, by feeding on oil-degrading bacteria, they increase bacterial growth in much the same way they enhance rates of decomposition in soils, thereby speeding up the breakdown of oil spillages.