Harriott O T, Khairallah L, Benson D R
Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269-3044.
J Bacteriol. 1991 Mar;173(6):2061-7. doi: 10.1128/jb.173.6.2061-2067.1991.
Frankia vesicles are differentiated during nitrogen starvation; they contain nitrogenase whether produced by free-living frankiae or by frankiae in actinorhizal root nodules. Vesicles are surrounded by envelopes of several monolayers of uncharacterized lipid. It has been suggested that the envelope limits diffusion of O2 into the vesicle cytoplasm, thereby preventing inactivation of nitrogenase. Whole vesicles were prepared on sucrose gradients and sonicated, and vesicle envelopes were isolated on top of a cushion of 40% sucrose. Transmission electron microscopy of potassium permanganate-fixed envelopes confirmed the purity of these preparations. Only the outer and inner envelope layers were visible in permanganate-fixed intact vesicles; the laminae were not visible in aldehyde-osmium-fixed, lead citrate-uranyl acetate-stained whole vesicles. However, the laminated nature of the envelope was clearly evident in sonicated vesicles and in envelope fragments fixed with KMnO4. The observations indicate that partial disruption of the vesicle envelope enables its visualization with permanganate fixation, and these observations open the way for further studies on the relationship of the vesicle surface to environmental conditions.
弗兰克氏菌泡囊在缺氮期间分化；无论其由自由生活的弗兰克氏菌产生，还是由放线菌根瘤中的弗兰克氏菌产生，泡囊中都含有固氮酶。泡囊被几层性质未明的脂质包膜所包围。有人提出，这种包膜限制了氧气向泡囊细胞质的扩散，从而防止固氮酶失活。在蔗糖梯度上制备完整泡囊并进行超声处理，然后在40%蔗糖垫层上分离泡囊包膜。用高锰酸钾固定的包膜进行透射电子显微镜观察，证实了这些制剂的纯度。在高锰酸钾固定的完整泡囊中，仅可见外层和内层包膜层；在醛锇固定、柠檬酸铅-醋酸双氧铀染色的完整泡囊中，片层不可见。然而，在超声处理的泡囊和用高锰酸钾固定的包膜碎片中，包膜的层状性质明显可见。这些观察结果表明，泡囊包膜的部分破坏使其能够通过高锰酸钾固定进行观察，这些观察结果为进一步研究泡囊表面与环境条件的关系开辟了道路。
