Hello
my humble opinion or statement this happens a lot to us on the ships I work on slack tanks and condensation breed this bacteria there are biocides to kill this stuff as stated above by others. the down side to using the biocides is it is very toxic use caution that includes when changing the filters I instruct my coworkers to wear gloves and resperatiors on the fuel that has not been run thru a purifier and after the fuel has been thru a purifier to still use gloves. that stuff the biocides are really bad stuff.
good luck.
chris