Laboratory of Protein Function, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, 1-1-1 Tsushima-naka, Kitaku, Okayama, Japan.
Microbiol Immunol. 2012 May;56(5):295-307. doi: 10.1111/j.1348-0421.2012.00445.x.
Aeromonas have been isolated from a wide variety of aquatic environments. However the number of Aeromonas in sea water is extremely small compared to that in fresh water. In in vitro culture, Aeromonas can grow in mediums containing NaCl at a concentration of 3.0%, this concentration corresponding to that of sea water. It is unclear why the number of Aeromonas is low in sea water. Exoproteins of bacteria are thought to be important for bacterial growth and survival in the environment. Previously, the present authors have shown that mediums containing 3.0% NaCl suppress production of two proteases, serine protease and metalloprotease. In this experiment, other exoproteins whose production is influenced by the amount of NaCl in the medium were analyzed. A protein whose production is repressed in medium containing 3.0% NaCl was found and purified. Biological assay of the purified protein showed that it degrades tributyrin and hydrolyzes para-nitrophenyl-fatty acylesters. These results show that the protein is a lipase. Subsequently, the nucleotide sequence of the gene encoding the lipase was determined and the amount of mRNA of the lipase gene in the cells measured. It was found that transcription of the gene is not inhibited by NaCl in the medium. This result indicates that the lipase might be synthesized, but the folding process to become an active structure does not progress smoothly in a medium containing 3.0% NaCl.
气单胞菌已从各种水生环境中分离出来。然而，与淡水相比，海水中的气单胞菌数量极其稀少。在体外培养中，气单胞菌可以在含有 3.0%NaCl 的培养基中生长，这一浓度与海水相当。目前尚不清楚为什么海水中的气单胞菌数量较少。细菌的胞外蛋白被认为对细菌在环境中的生长和存活很重要。先前，本作者已经表明，含有 3.0%NaCl 的培养基会抑制两种蛋白酶（丝氨酸蛋白酶和金属蛋白酶）的产生。在本实验中，分析了其他受培养基中 NaCl 含量影响的胞外蛋白。发现并纯化了一种在含有 3.0%NaCl 的培养基中产量受抑制的蛋白质。对纯化蛋白的生物测定表明，它可以降解三丁酸酯并水解对硝基苯脂肪酸酯。这些结果表明该蛋白是一种脂肪酶。随后，确定了编码脂肪酶的基因的核苷酸序列，并测量了细胞中脂肪酶基因的 mRNA 量。结果发现，基因的转录不受培养基中 NaCl 的抑制。这一结果表明，脂肪酶可能被合成，但在含有 3.0%NaCl 的培养基中，其折叠成具有活性结构的过程并不顺利。
