ABSTRACT
Severalotherreportsdocumenttheoccurrenceofintracytoplasmicstructuresresemblinghydrocarboninclusions.Bertrandetal.' 0describeddisc-shaped,electron-transparentcytoplasmic"vesicles"inthinsectionsandinnegativelystainedpreparations ofahexadecane-grownmarinebacterium.Thesevesiclesarenotobservedinacetategrowncells.Infreeze-etchedpreparationswithfracturesthroughtheintracytoplasmic vesicles,thevesiclesappeartobemembranelimited.Theinternalstructureofthevesicleappearstohaveasmoothtofinelygranulartexture,indicatingthepossiblehydrocarbonorlipoidalnatureoftheenclosedmaterial.Althoughthenatureofthematerial sequesteredintheseinclusionswasnotdetermined,hexadecane-growncellswere showntocontain20-foldmorenonsaponifiablelipidthanacetate-growncells.Results wereinconclusiveastowhetherthesecytoplasmicvesiclescontainhexadecane,since nodistinctionwasmadebetweenexternallyabsorbedandinternallyaccumulatedhexadecane.Thermomicrobiumfosteri,anobligatethermophilecapableofgrowthonhydrocarbons,containselectron-transparentintracytoplasmicinclusionsresultingfrom
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B. Intracytoplasmic Membranes The second ultrastructural feature unique to alkane-grown Acinetobacter is the pre-
Such extensive intracytoplasmic membrane systems have been noted in only one other hydrocarbon-utilizing bacterium, a cyclohexane-grown Nocardia sp. ' 3 Mesosome-like membranes have been reported for unidentified bacteria grown on ethane, propane, or butane;" n-butane-grown Arthrobacter strain AK19; 14 heptadecanegrown Thermomicrobium fosteri sp. nov.;" and hexadecane-and nonalkane-grown Acinetobacter sp. HOI-N. 4 Whether these mesosome-like membranes are related to hydrocarbon metabolism is not known.
