Explain the role of small organisms, such as yeast, in our environment. how could pollutants influence this?

The role of microorganisms such as yeast in the environment is that these contain bacteria which are the workhorses of biological processes such as fermentation to produce metabolites that are beneficial to the body. An example of this is the fermentation of any fruit (or substances containing sugar) to produce metabolites such as alcohol, aldehydes, acids (lactic or acetic acid) and many more via the action of yeast bacteria, commonly Saccharomyces cerevisiae. Pollutants affect the functions of yeast as they play as contaminants of the living workhorses.Pollutants can introduce disturbances which affect how yeasts strive in the environment. This affects the production of metabolites as well. 

Ithink due to shortage of water