一株拮抗菌C-5 的分离及鉴定

针对目前海参养殖中水产微生态制剂品种单一、施用效果不稳定等现状,作者从地瓜参(Acaudina molpadioidea)肠道分离土著肠杆菌(Enterobacter),筛选到1株具有较好拮抗作用的海洋细菌C-5,该菌对副溶血弧菌(Vibrio parahaemolyticus)、溶藻弧菌(Vibrio alginolyticus)、杀鲑气单胞菌(Aeromonas salmonicida)等7种细菌有拮抗作用;通过形态观察、生理生化和16S rDNA基因序列分析鉴定为霍肠杆菌(Enterobacter hormaechei);通过卤虫(Artemia)和药敏实验检测该菌具有安全性,其对卤虫的72 h半致死浓度(LC50)为108cfu/m L,只对20种常规抗生素中的5种产生耐药性;对C-5的发酵条件进行优化,该菌优化后的发酵条件为:温度30℃,pH 7.0,盐度2%。结果表明,C-5有望作为一种益生菌应用于海水养殖病害控制。     

罗氏沼虾(Macrobrachium rosenbergii)幼体新暴发病病原阴沟肠杆菌的分离鉴定

2010 年, 浙江湖州部分罗氏沼虾(Macrobrachium rosenbergii)育苗场在幼体培育阶段, 暴发 了幼体大规模发病死亡的新病害。从2 个育苗场6 个发病育苗池的发病幼体匀浆液中分离得到6 株 优势生长菌株(编号为NTH01、NTH02、NTH03、316D、316X、316C), 菌落形态较为一致。取代表 菌株NTH01, 以浸泡方式进行人工回感, 结果菌株NTH01 能够导致幼体发病死亡, 且症状与生产表 现一致。经形态学观察、生理生化鉴定、16S rRNA 与gyr B 基因序列系统发育关系构建, 鉴定菌株 NTH01 为阴沟肠杆菌(Enterobacter cloacae).以阴沟肠杆菌omp A 基因片段为靶序列, 建立了PCR 检测方法, 对另外5 株优势菌进行检测, 结果该5 株菌都是阴沟肠杆菌。2011 年, 对4 个发病育苗场 幼体与亲虾进行检测, 结果发病幼体中分离的优势菌检测呈阳性, 亲虾肝胰腺与肠道组织检测到该 菌存在, 但亲虾不表现病症。对30 种抗生素的药敏试验结果表明, 菌株NTH01 对恩诺沙星、氧氟 沙星、庆大霉素等6 种抗生素敏感, 对发病幼体进行针对性用药, 效果明显。本试验结果表明, 阴沟 肠杆菌是导致罗氏沼虾育苗期间幼体大规模发病死亡的致病菌。     

Accumulation of hexavalent chromium by an exopolysaccharide producing marine Enterobacter cloaceae

An exopolysaccharide producing Enterobacter cloaceae (AK-I-MB-71a) was tested for its Cr (VI) tolerance. This isolate was not only resistant to this heavy metal but also showed enhanced growth and exopolysaccharide production in the presence of Cr (VI) at 25, 50 and 100 ppm concentrations. XRF analysis of both the biomass as well as the exopolysaccharide revealed that a sum total of about 60-70% chromium was accumulated by this bacterium. This indicated that this organism could prove to be a potential candidate in the field of bioremediation with respect to chromium removal.     

Isolation and characterization of AHL-degrading bacteria from fish and pond sediment

Quorum sensing (QS) disruption is considered as a potential alternative strategy to combat bacterial diseases in aquaculture. In this study, we isolated and identified bacteria degrading QS molecules from pond sediment and fish intestine. A total of 132 strains were obtained in the enrichment culture, of which two strains were identified as Enterobacter sp. f003 and Staphylococcus sp. sw120, being isolated from the fish intestine and pond sediment, respectively. We found that strains f003 and sw120 could degrade acyl-homoserine lactones (AHLs) and cause no hemolysis of sheep red blood cells. The AHL lactonase (aiiA) homologous gene in the two strains was detected in PCR amplification and the high-degrading activity to N-hexanoyl-L-homoserine lactone (C6-HSL) and AHLs secreted from pathogenic Aeromonas hydrophila was assessed. Meanwhile, the artificial infection of cyprinid Carassius auratus gibelio with intraperitoneal injection showed that the two strains were avirulent. Therefore, the obtained indigenous bacteria are candidate probiotics against pathogenic A. hydrophila in aquaculture.     

一株耐盐性阴沟肠杆菌生长产氢对微量元素的需求

用单因素分析法研究在培养基中缺乏铁、镁、微量元素液、维生素液时对阴沟肠杆菌 XA-2生长的影响。实验发现,铁和镁对该菌的生长影响显著,而缺乏微量元素液、维生素液对该菌的生长影响不明显。缺铁培养时该菌在稳定期的菌浊浓度 OD600nm为1.2586,缺镁培养时菌浊浓度为0.6988,仅为完全培养时菌浊浓度的三分之一,其中,镁对该菌生长的影响更显著。产氢实验表明,各因素对产氢情况的影响显著,依次为：铁>镁>维生素液>微量元素液。当该菌利用缺铁培养基产氢时,其累计产氢量仅为44 mL/L ,铁元素的缺乏严重影响该菌的产氢活动。