Sulfide oxidation under oxygen limitation by a thiobacillus thioparus isolated from a marine microbial mat

Abstract The colorless sulfur bacterium Thiobacillus thioparus T5, isolated from a marine microbial mat, was grown in continuous culture under conditions ranging from sulfide limitation to oxygen limitation. Under sulfide-limiting conditions, sulfide was virtually completely oxidized to sulfate. Under oxygen-limiting conditions, sulfide was partially oxidized to zerovalent sulfur (75%) and thiosulfate (17%). In addition, low concentrations of tetrathionate and polysulfide were detected. The finding of in vivo thiosulfate formation supports the discredited observations of thiosulfate formation in cell free extracts in the early sixties. In a microbial mat most sulfide oxidation was shown to take place under oxygen-limiting conditions. It is suggested that zerovalent sulfur formation by thiobacilli is a major process resulting in polysulfide accumulation. Implications for the competition between colorless sulfur bacteria and purple sulfur bacteria are discussed.     

凝固酶阴性葡萄球菌临床耐药性的连续性研究

目的了解凝固酶阴性葡萄球菌的耐药性情况。方法分析2008年至2010年沈阳军区总医院临床分离的484株凝固酶阴性葡萄球菌的药敏结果。结果 2008年至2010年凝固酶阴性葡萄球菌的分离率分别为4.7%、3.6%和3.1%。耐甲氧西林凝固酶阴性葡萄球菌（MRSCN）分别为76.6%、78.5%和79.9%。青霉素G、红霉素和苯唑西林的耐药率较高,平均分别为91.2%、87.5%和82.6%。万古霉素、替考拉宁和利奈唑胺的耐药率均为0。结论 2008年至2010年凝固酶阴性葡萄球菌检出率相对稳定,对常用抗菌药物的耐药率相对稳定,这为临床用药选择及加强感染控制提供了有力指导。     

连作对麦冬根际土壤细菌群落的影响

以中草药麦冬为研究对象,采用变性梯度凝胶电泳(DGGE)方法,考察连作对麦冬根际土壤细菌群落的影响。结果表明,重茬麦冬根际细菌群落的Shannon-Wiener指数从苗期至快速生长期、再到块根膨大期分别为3.36-3.40-3.69,丰富度指数为55.0-61.5-63.5,均匀度指数为0.84-0.82-0.89;而同期正茬根际细菌群落的上述指数值分别为3.66-3.33-3.72、67.5-53.5-63.5和0.87-0.84-0.90。通过对土壤细菌群落的DGGE图谱进行主成分分析,结果显示,上述各个时期重茬与正茬样本均发生显著分离,表明连作改变了麦冬根际细菌群落的多样性变化趋势和结构组成。进一步比较麦冬块根膨大期根际主要功能菌群的数量变化,发现连作后氨化细菌和好气性纤维素分解菌数量增加,而硝化细菌和固氮菌的数量减少。对比发现重茬麦冬的产量仅为正茬的70.6%,表明麦冬连作减产与其根际土壤细菌群落的变化相关。     

具有边疆时滞和扩散的非自治Holling捕食系统的持续生存

本文给出了在具有连续时滞和Ⅱ类功能性反应及扩散的非自治捕食系统中，种群持续自下而上，周期解存在及全局渐近稳定的充分条件。