Walzer Gil, Rosenberg Eugene, Ron Eliora Z
Department of Molecular Microbiology and Biotechnology, Life Sciences, Tel-Aviv University, Tel-Aviv, Israel 69978.
Environ Microbiol. 2006 Jun;8(6):1026-32. doi: 10.1111/j.1462-2920.2006.00994.x.
Acinetobacter strains use hydrophobic carbon sources and most of them are efficient oil degraders. They secrete a variety of emulsifiers which are efficient in producing and stabilizing oil-in-water emulsions. The bioemulsifier of Acinetobacter radioresistens KA53 (Alasan) is a high-mass complex of proteins and polysaccharides. The major emulsification activity of this complex is associated with a 45 kDa protein (AlnA), which is homologous to the outer membrane protein OmpA. The emulsification ability of AlnA depends on the presence of hydrophobic residues in the four loops spanning the transmembrane domains. The finding of a secreted OmpA was unexpected, in view of the fact that this protein is essential in all Gram-negative bacteria, has four trans-membrane domains and is considered to be an integral structural component of the outer membrane. However, secretion of an OmpA with emulsifying ability could be of physiological importance in the utilization of hydrophobic substrates as carbon sources. Here we examined the possibility that secretion of OmpA with emulsifying activity is a general property of the oil-degrading Acinetobacter strains. The results indicate that OmpA is secreted in five strains of Acinetobacter, including strain Acinetobacter sp. ADP1 whose genome has been sequenced. The ompA genes of ADP1 and an additional strain, Acinetobacter sp. V-26 were cloned and sequenced. Structure analysis of the sequence of the two proteins indicated the existence of the hydrophobic regions, previously shown to be responsible for the emulsification activity of AlnA. Further examination of the recombinant OmpA proteins indicated that they are, indeed, strong emulsifiers, even when produced in Escherichia coli. The finding that Acinetobacter OmpA has emulsifying activity and that it is secreted in five strains of Acinetobacter may be physiologically significant and suggests the involvement of this protein in biodegradation of hydrophobic substrates, including hydrocarbons.
不动杆菌菌株利用疏水性碳源，并且它们中的大多数都是高效的石油降解菌。它们分泌多种乳化剂，这些乳化剂在制备和稳定水包油乳液方面很有效。抗辐射不动杆菌KA53（阿拉桑）的生物乳化剂是一种蛋白质和多糖的高质量复合物。这种复合物的主要乳化活性与一种45 kDa的蛋白质（AlnA）相关，该蛋白质与外膜蛋白OmpA同源。AlnA的乳化能力取决于跨越跨膜结构域的四个环中疏水残基的存在。鉴于这种蛋白质在所有革兰氏阴性细菌中都是必需的，具有四个跨膜结构域并且被认为是外膜的一个不可或缺的结构成分，所以分泌型OmpA的发现是出乎意料的。然而，具有乳化能力的OmpA的分泌在利用疏水性底物作为碳源方面可能具有生理重要性。在这里，我们研究了具有乳化活性的OmpA的分泌是否是石油降解不动杆菌菌株的一个普遍特性。结果表明，OmpA在五种不动杆菌菌株中分泌，包括其基因组已被测序的不动杆菌ADP1菌株。克隆并测序了ADP1和另一个菌株——不动杆菌V-26的ompA基因。对这两种蛋白质序列的结构分析表明存在疏水区域，先前已证明这些区域负责AlnA的乳化活性。对重组OmpA蛋白的进一步研究表明，即使在大肠杆菌中产生，它们确实也是强力乳化剂。不动杆菌OmpA具有乳化活性并且在五种不动杆菌菌株中分泌这一发现可能具有生理意义，并表明该蛋白质参与包括烃类在内的疏水性底物的生物降解。
