Actually, there are two major groups of microbiological contamination in diesel fuels; bacteria and fungi.
Bacteria are single-cell organisms that lack a membrane-bound nucleus.
In contrast, fungi do have a defined nucleus. The nucleus is the organelle which contains most of the cellís genetic material.
Below are lists of the bacteria and fungi most commonly recovered from diesel fuel and associated water in fuel tanks and distribution systems.
Hormoconis resinae (formerly classified as Cladosporium)
In some instances it can be important to differentiate between bacteria and fungi because they are structurally very different, and respond to treatment differently.
I believe most simply refer to them as "Bugs" though