Institute for Applied Microbiology, University of Tennessee, Knoxville, TN 37932.
Proc Natl Acad Sci U S A. 1989 May;86(9):3399-403. doi: 10.1073/pnas.86.9.3399.
When growing on N(2), actinomycetes from the genus Frankia form multicellular structures that contain nitrogenase. The structures are referred to as vesicles and are indistinguishable from vesicles formed when Frankia sp. are in root-nodule symbioses. Vesicles isolated from N(2)-grown cells of Frankia sp. strain CpI1 had a significantly higher amount and different composition of fatty acids than did vegetative cells recovered from NH(4) (+)-containing medium. Lipids from vesicles, whole cells grown on N(2), and whole cells grown on NH(4) (+) were fractionated by silicic acid chromatography into neutral lipids, glycolipids, and polar lipids. The fatty acids were transesterified by methanolysis and analyzed by gas chromatography and mass spectrometry. Vesicles had considerably higher amounts of fatty acids in the neutral and glycolipid fractions but lower amounts of polar lipid fatty acids than did vegetative cells. Polar lipids from vesicles had a higher proportion of mono-unsaturated and cyclopropane fatty acids and a lower proportion of isobranched fatty acids than did polar lipids from NH(4) (+)-grown or N(2)-grown cells. The neutral lipid and glycolipid fractions contained several long-chain compounds with molecular ions at m/z 408 and 410. The proportions of these compounds were significantly higher in the lipids from vesicles than from vegetative cells. These results suggest that lipids in vesicles might be involved in the protection of nitrogenase from O(2) and suggest a parallel with the glycolipids involved in protecting nitrogenase from O(2) in the cyanobacterial heterocysts.
在 N(2)上生长时，弗兰克氏放线菌属的放线菌形成含有固氮酶的多细胞结构。这些结构被称为泡囊，与弗兰克氏菌属在根瘤共生时形成的泡囊无法区分。从弗兰克氏菌 CpI1 的 N(2)生长细胞中分离出的泡囊，其脂肪酸含量和组成与从含 NH(4) (+)的培养基中回收的营养细胞有显著差异。从泡囊、在 N(2)上生长的完整细胞和在 NH(4) (+)上生长的完整细胞分离出的脂质，通过硅胶色谱法分为中性脂质、糖脂和极性脂质。通过甲醇解对脂肪酸进行酯交换，并通过气相色谱和质谱分析。与营养细胞相比，泡囊中中性和糖脂部分的脂肪酸含量明显更高，但极性脂质脂肪酸含量较低。泡囊的极性脂质中，单不饱和和环丙烷脂肪酸的比例较高，异支链脂肪酸的比例较低，而 NH(4) (+)生长或 N(2)生长细胞的极性脂质则相反。中性脂质和糖脂部分含有几种具有 m/z 408 和 410 的分子离子的长链化合物。这些化合物在泡囊脂质中的比例明显高于营养细胞。这些结果表明，泡囊中的脂质可能参与固氮酶免受 O(2)的保护，并表明与蓝细菌异形胞中参与保护固氮酶免受 O(2)的糖脂有类似之处。
