O'Connell M, Henry S, Shapiro L
J Bacteriol. 1986 Oct;168(1):49-54. doi: 10.1128/jb.168.1.49-54.1986.
Fatty acid degradation was investigated in Caulobacter crescentus, a bacterium that exhibits membrane-mediated differentiation events. Two strains of C. crescentus were shown to utilize oleic acid as sole carbon source. Five enzymes of the fatty acid beta-oxidation pathway, acyl-coenzyme A (CoA) synthase, crotonase, thiolase, beta-hydroxyacyl-CoA dehydrogenase, and acyl-CoA dehydrogenase, were identified. The activities of these enzymes were significantly higher in C. crescentus than the fully induced levels observed in Escherichia coli. Growth in glucose or glucose plus oleic acid decreased fatty acid uptake and lowered the specific activity of the enzymes involved in beta-oxidation by 2- to 3-fold, in contrast to the 50-fold glucose repression found in E. coli. The mild glucose repression of the acyl-CoA synthase was reversed by exogenous dibutyryl cyclic AMP. Acyl-CoA synthase activity was shown to be the same in oleic acid-grown cells and in cells grown in the presence of succinate, a carbon source not affected by catabolite repression. Thus, fatty acid degradation by the beta-oxidation pathway is constitutive in C. crescentus and is only mildly affected by growth in the presence of glucose. Tn5 insertion mutants unable to form colonies when oleic acid was the sole carbon source were isolated. However, these mutants efficiently transported fatty acids and had beta-oxidation enzyme levels comparable with that of the wild type. Our inability to obtain fatty acid degradation mutants after a wide search, coupled with the high constitutive levels of the beta-oxidation enzymes, suggest that fatty acid turnover, as has proven to be the case fatty acid biosynthesis, might play an essential role in membrane biogenesis and cell cycle events in C. crescentus.
在新月柄杆菌（Caulobacter crescentus）中研究了脂肪酸降解，该细菌表现出膜介导的分化事件。已证明两株新月柄杆菌能够利用油酸作为唯一碳源。鉴定出了脂肪酸β-氧化途径的五种酶，即酰基辅酶A（CoA）合酶、巴豆酸酶、硫解酶、β-羟酰基辅酶A脱氢酶和酰基辅酶A脱氢酶。这些酶在新月柄杆菌中的活性显著高于在大肠杆菌中观察到的完全诱导水平。与在大肠杆菌中发现的50倍葡萄糖阻遏相比，在葡萄糖或葡萄糖加油酸中生长会降低脂肪酸摄取，并使参与β-氧化的酶的比活性降低2至3倍。外源二丁酰环磷酸腺苷可逆转酰基辅酶A合酶的轻度葡萄糖阻遏。结果表明，在油酸生长的细胞和在琥珀酸（一种不受分解代谢物阻遏影响的碳源）存在下生长的细胞中，酰基辅酶A合酶活性相同。因此，β-氧化途径的脂肪酸降解在新月柄杆菌中是组成型的，仅受到葡萄糖存在下生长的轻度影响。分离出了在油酸作为唯一碳源时无法形成菌落的Tn5插入突变体。然而，这些突变体能够有效地转运脂肪酸，并且β-氧化酶水平与野生型相当。经过广泛搜索后我们无法获得脂肪酸降解突变体，再加上β-氧化酶的高组成水平，这表明脂肪酸周转可能在新月柄杆菌的膜生物合成和细胞周期事件中发挥重要作用，正如脂肪酸生物合成的情况所证明的那样。
