van Waasbergen L G, Hildebrand M, Tebo B M
Marine Biology Research Division and Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla 92093-0202, USA.
J Bacteriol. 1996 Jun;178(12):3517-30. doi: 10.1128/jb.178.12.3517-3530.1996.
The marine Bacillus sp. strain SG-1 forms spores that oxidize manganese(II) as a result of the activities of uncharacterized components of its spore coat. Nucleotide sequence analysis of chromosomal loci previously identified through insertion mutagenesis as being involved in manganese oxidation identified seven possible genes (designated mnxA to mnxG) in what appears to be an operon. A potential recognition site for the sporulation, mother-cell-specific, RNA polymerase sigma factor, sigmaK, was located just upstream of the cluster, and correspondingly, measurement of beta-galactosidase activity from a Tn917-lacZ insertion in mnxD showed expression at mid-sporulation to late sporulation (approximately stage IV to V of sporulation). Spores of nonoxidizing mutants appeared unaffected with respect to their temperature and chemical resistance properties and germination characteristics. However, transmission electron microscopy revealed alterations in the outermost spore coat. This suggests that products of these genes may be involved in the deposition of the spore coat structure and/or are spore coat proteins themselves. Regions of the deduced protein product of mnxG showed amino acid sequence similarity to the family of multicopper oxidases, a diverse group of proteins that use multiple copper ions to oxidize a variety of substrates. Similar regions included those that are involved in binding of copper, and the addition of copper at a low concentration was found to enhance manganese oxidation by the spores. This suggests that the product of this gene may function like a copper oxidase and that it may be directly responsible for the oxidation of manganese by the spores.
海洋芽孢杆菌属菌株SG-1形成的芽孢能够氧化锰（II），这是其芽孢衣中未知成分活动的结果。对先前通过插入诱变鉴定出的参与锰氧化的染色体位点进行核苷酸序列分析，在一个似乎是操纵子的结构中确定了七个可能的基因（命名为mnxA至mnxG）。在该基因簇的上游刚好定位到一个芽孢形成特异性的母细胞RNA聚合酶σ因子σK的潜在识别位点，相应地，对mnxD中Tn917-lacZ插入片段的β-半乳糖苷酶活性进行测定，结果显示在芽孢形成中期至后期（大约芽孢形成的IV至V阶段）有表达。非氧化突变体的芽孢在温度、化学抗性和萌发特性方面似乎未受影响。然而，透射电子显微镜显示其最外层芽孢衣有改变。这表明这些基因的产物可能参与芽孢衣结构的沉积和/或本身就是芽孢衣蛋白。mnxG推导的蛋白质产物区域显示出与多铜氧化酶家族的氨基酸序列相似性，多铜氧化酶是一组利用多个铜离子氧化多种底物的不同蛋白质。相似区域包括那些参与铜结合的区域，并且发现低浓度添加铜可增强芽孢对锰的氧化作用。这表明该基因的产物可能像铜氧化酶一样发挥作用，并且可能直接负责芽孢对锰的氧化。
