Plain jet fuel (Jet-A) does not contain any biocide. Fuels with added Prist (those with anti-ice inihibitor) does contain biocide, if I remember correctly. There is an additive called Biobor than can be added to jet fuel to keep any microorganisms at bay. We used it all the time and never had a bit of algae. Of course, if you fly your aircraft regularly, there shouldn't be any worries whatsoever.