MANIPULATION OF POLYUNSATURATED, BRANCHED-CHAIN AND TRANS-FATTY ACID PRODUCTION IN SHEWANELLA-PUTREFACIENS STRAIN ACAM-342

Shewanella putrefaciens strain ACAM 342 produced a range of polyunsaturated fatty acids (PUFA) including 18:2 omega 6, 18:3 omega 3, 18:3 omega 6, 18:4 omega 3 and 20:5 omega 3 (EPA). Under culture in Zobell's broth at 15 degrees C exponential-phase cultures produced 3.2 +/- 0.3 % EPA, or 1.2 +/- 0.2 mg (g bacterial dry wt)(-1). Alteration of growth phase, addition of biotin to the medium or a 10-fold decrease in nutrient levels had no significant effect (P > 0.05) on levels of EPA. Growth in 7.0% NaCl medium markedly decreased the overall degree of fatty acid unsaturation (P < 0.01), white growth on acetate as the sole carbon source increased the level of 18:2 omega 6 from 0.4 +/- 0.1 % to 7.1 % of total fatty acids through inhibition of branched-chain fatty acid synthesis. Addition of desaturase cofactors to the growth medium increased the proportion of EPA from 3.2 +/- 0.3 % to 4.6 %, but decreased the quantitative yield from 1.2 +/- 0.2 to 0.9 mg (g bacterial dry wt)(-1). This bacterium represents a model organism to study bacterial PUFA production. The trans-monounsaturated fatty acid 16:1 omega 7t was also produced under all culture conditions. together with four other trans-isomers. namely 14:1 omega 5t. 15:1 omega 6t, 17:1 omega 8t and 18:1 omega 7t. Although the relative levels of trans-acids also changed under various culture conditions, there was no evidence that they were produced as a starvation or stress response.