strain ACAM 342 produced a range of polyunsaturated fatty acids (PUFA) including 18:2ω6, 18:3ω3, 18:3ω6, 18:4ω3 and 20:5ω3 (EPA). Under culture in Zobell's broth at 15 °C exponential-phase cultures produced 3.2 + 0.3% EPA, or 1.2 + 0.2 mg (g bacterial dry wt). Alteration of growth phase, addition of biotin to the medium or a 10-fold decrease in nutrient levels had no significant effect (>0.05) on levels of EPA. Growth in 7.0% NaCl medium markedly decreased the overall degree of fatty acid unsaturation (<0.01), while growth on acetate as the sole carbon source increased the level of 18:2.6 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). This bacterium represents a model organism to study bacterial PUFA production. The -monounsaturated fatty acid 16:1ω7t was also produced under all culture conditions, together with four other -isomers, namely 14:1ω5t, 15:1ω6t, 17:1ωt and 18:1ω7t. Although the relative levels of -acids also changed under various culture conditions, there was no evidence that they were produced as a starvation or stress response.


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