An FDA microbiologist working in a biosafety laboratory tests for high risk pathogens in food. Irvine, California, 2009. A microbiologist is a person who investigates things or studies in the field microbiology. Microbiologists investigate the growth and characteristics of microscopic organisms such as bacteria, algae, or fungi. Most microbiologists specialize in the environmental, food, agricultural or medical aspects in either medical or industrial microbiology.