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

Abstract

To more fully explore the role of unsaturated fatty acids in high-pressure, low-temperature growth, the fabF gene from the psychrotolerant, piezophilic deep-sea bacterium Photobacterium profundum strain SS9 was characterized and its role and regulation were examined. An SS9 strain harboring a disruption 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 transcriptionally regulated, suggesting that the elevated 18:1 levels produced in response to pressure increase result from posttranscriptional changes. Unlike many pressure-adapted bacterial species such as SS9, the mesophile Escherichia coli did not regulate its fatty acid composition in an adaptive manner in response to changes in hydrostatic pressure. Moreover, an E. coli fabF strain was as susceptible to elevated pressure as wild-type cells. It is proposed 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.

FIG. 1

Northern analysis of fabF expression in P. profundum strains EA40 (fabF) and DB110 (wild type). Cells were grown to late exponential phase for total RNA isolation and probed using internal fragment of SS9 fabF as described in Materials and Methods. Lanes: 1, EA40 at 4°C; 2, EA40 at 15°C; 3, DB110 at 4°C; 4, DB110 at 15°C; 5, DB110 at 28 MPa (9°C); 6, DB110 at 0.1 MPa (9°C).

FIG. 2

Growth characteristics of fabF disruption mutant P. profundum strain EA40 and strain DB110 as a function of temperature (A) and pressure (B). (A) ●, DB110 at 15°C; ○, EA40 at 15°C; ■, DB110 at 4°C; □, EA40 at 4°C. (B) ●, DB110 at 28 MPa; ○, EA40 at 28 MPa; ■, DB110 at 0.1 MPa; □, EA40 at 0.1 MPa.

FIG. 3

Nutritional complementation of P. profundum fabF mutant EA40 at elevated pressure (28 MPa, 9°C). ●, plus 18:1 supplementation; ○, minus 18:1.

FIG. 4

Growth characteristics of E. coli fabF disruption mutant MR86 and parental strain SJ16 as a function of pressure. See Materials and Methods for cultivation conditions. Pressure experiments were conducted at a temperature of 37°C. ●, SJ16 at 30 MPa; ○, MR86 at 30 MPa; ■, SJ16 at 0.1 MPa; □, MR86 at 0.1 MPa.