FabF is required for piezoregulation of cis-vaccenic acid levels and piezophilic growth of the deep-sea bacterium Photobacterium profundum strain SS9

To more fully explore the role of unsaturated fatty acids in high-pressure, low-temperature growth, the fabF gene from the psychrotolerant, piezophili c deep-sea bacterium Photobacterium profundum strain SS9 was characterized and its role and regulation were examined. An SS9 strain harboring a disrup tion in the fabF gene (strain EA40) displayed growth impairment at elevated hydrostatic pressure concomitant with diminished cis-vaccenic acid (18:1) production. However, growth ability at elevated pressure could be restored to wild-type levels by the addition of exogenous 18:1 to the growth medium. Transcript analysis did not indicate that the SS9 fabF gene is transcripti onally regulated, suggesting that the elevated 18:1 levels produced in resp onse to pressure increase result from posttranscriptional changes. Unlike m any pressure-adapted bacterial species such as SS9, the mesophile Escherich ia coli did not regulate its fatty acid composition in an adaptive manner i n response to changes in hydrostatic pressure. Moreover, an E. coli fabF st rain was as susceptible to elevated pressure as wild-type cells. It is prop osed that the SS9 fabF product, beta-ketoacyl-acyl carrier protein synthase II has evolved novel pressure-responsive characteristics which facilitate SS9 growth at high pressure.