不同屠宰工艺(剥皮和烫毛)对猪胴体表面微生物的多样性影响及关键点的控制研究

应用变性梯度凝胶电泳(Denaturinggradientgelelectrophoresis(DGGE))和经典微生物培养相结合的方法研究了剥皮和烫毛工艺中猪胴体表面污染的微生物数量和细菌多样性的变化以及3.5%乳酸处理后细菌总数和大肠菌群的变化。结果显示:不同猪胴体屠宰工艺中的微生物种类并不完全一致,微生物的污染多是由于前期的屠宰工艺引入;与剥皮工艺相比,烫毛后污染的微生物种类多,初始污染程度也较为严重;乳酸处理显著降低了剥皮工艺中的细菌总数,使出库猪胴体表面细菌总数降低到2.95logCFU/cm2,完全达到HACCP微生物的控制要求,但是没有降低烫毛工艺出库时的细菌总数,因此对不同的屠宰工艺应采取不同的关键点控制措施。     

应用DGGE技术研究玉米储藏过程中的霉菌群落时空分布特征

研究储粮过程中霉菌污染的发生规律,旨在减少霉菌及真菌毒素的污染,提高我国粮食安全。利用变性梯度凝胶电泳研究粮库中不同储藏时间和空间的玉米样品中霉菌群落的特点。结果表明,本研究中储藏玉米的霉菌污染以青霉、曲霉和毛霉为主,其霉菌群落的变化与储藏时间具有较强的相关性,而与其在粮库中的空间位置相关性较小。在储藏时间方面,储藏1a和3a的样品中霉菌群落具有较大的差异,而储藏2a样品的霉菌群落处于过渡期状态。本实验探究储藏玉米中霉菌群落的时空分布特征,可以为建立准确可靠的霉菌群落模型提供理论支持和数据支持。     

大鼠粪便中细菌基因组DNA提取方法的比较

为获得高质量的肠道细菌基因组DNA,用于研究肠道菌群的多样性,本实验分别采用改良的溶菌酶法和两种试剂盒DNA提取法提取大鼠粪便中的细菌基因组DNA,通过DNA浓度和纯度的测定、PCR-变性梯度凝胶电泳技术（PCR-DGGE技术）对提取效果进行比较,以找到适合于粪便中细菌基因组DNA的提取方法。结果表明,改良的溶菌酶法提取的DNA质量好,纯度高,而且具有菌群多样性丰富等特点,更适合用于肠道微生物菌群后续分子生物学研究。      

基于DGGE方法分析低氯化钠浓度对发酵白菜原核微生物群落结构的影响

为了探究氯化钠浓度对发酵白菜体系中微生物群落结构的影响。以4%、6%和8%氯化钠浓度发酵白菜,通过DGGE(denaturing gradient gel electrophoresis)方法及Quantity One软件分析原核微生物群落结构;通过回收DGGE电泳中荧光强度强、不同时间差异的电泳带,经克隆后测定碱基序列、与Gen Bank库序列对比鉴定。结果表明6%氯化钠浓度发酵白菜微生物多样性指数H(Shannon)、丰富度指数R(Species Richness)在发酵全过程中低于4%、8%组,均匀度指数E(Species Evenness)较4%、8%组的稳定。说明氯化钠浓度6%的发酵泡菜在整个发酵期微生物群落结构相对稳定且微生物种类小于氯化钠浓度4%、8%组。从DGGE电泳带荧光强度和存在的时间可知:在氯化钠浓度6%的发酵白菜体系中,Leuconostoc citreum(柠檬明串珠菌)、Uncultured bacterium(非培养细菌)、Leuconostoc mesenteroides(肠系膜明串珠菌)是白菜发酵中期、后期的优势微生物,Leuconostoc citreum(柠檬明串珠菌)、Leuconostoc mesenteroides(肠系膜明串珠菌)是乳酸菌。氯化钠浓度4%和8%发酵白菜中乳酸菌未成为优势微生物。说明氯化钠浓度6%较4%和8%发酵白菜原核微生物群落的变化接近于自然发酵蔬菜微生物变化规律,研究结果表明6%氯化钠浓度有利于白菜的发酵。      

Spatial and temporal changes in Actinobacterial dominance in experimental artificial groundwater recharge

Artificial groundwater recharge (AGR) is used in the drinking water industry to supplement groundwater resources and to minimise the use of chemicals in water treatment. This study analysed the spatial and temporal changes of microbial communities in AGR using two test systems: a nutrient-amended fluidized-bed reactor (FBR) and a sand column. Structural changes in the feed lake water (Lake Roine), FBR, and sand column bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) and the length heterogeneity analysis of amplified 16S rRNA genes (LH-PCR). Two clone libraries were created to link the LH-PCR results to the dominant bacterial groups. The lake water bacterial community was relatively stable, with three bands dominating in all LH-PCR products. The most dominant fragment accounted for up to 72% and was derived from Actinobacteria. Based on the clone libraries and LH-PCR data, Actinobacteria also dominated in the unattached bacterial community of the FBR, whereas several Proteobacterial groups were more abundant on the FBR carrier particles. In the stabilised AGR system a major change in the community structure of the lake water bacteria took place during passage within the first 0.6 m in the sand column as the community composition shifted from Actinobacteria-dominated populations to a diverse, mainly Proteobacterial communities. Concurrently, most of the dissolved organic carbon (DOC) was removed at this stage. In summary, the study showed that the make-up of microbial communities in experimental AGR systems responded to changes in their environment. LH-PCR showed potential as a method to determine microbial community dynamics in long-term studies at real-scale AGR sites. This is the first step to provide data on microbial community dynamics in AGR for drinking water production.     

Characterization of nitrifying granules produced in an aerobic upflow fluidized bed reactor

Since nitrification is the rate-determining step in the biological nitrogen removal from wastewater, many research studies have been conducted on the immobilization of nitrifying bacteria. In this research, granulation of nitrifying bacteria in an aerobic upflow fluidized bed (AUFB) reactor in a nitrification process for inorganic wastewater containing 500 g/m³ of NH₄⁺-N was investigated. It was observed that spherical, pseudocubic and elliptical granules with a diameter of 346 μm were produced at the bottom of the reactor after 300 days. Denaturing gradient gel electrophoresis analysis revealed that Nitrosomonas-like bacteria were the dominant ammonia-oxidizing species in the granules. Many colonies of Nitrosomonas-like bacteria were found in the outer part of the granules based on the spatial distribution analysis by fluorescence in situ hybridization. By stepwise reduction of the hydraulic retention time, the ammonia removal rate of the AUFB reactor containing these nitrifying granules finally reached 1.5 kg-N/m³/day. Results suggested that the use of granules realizes the retention of a large amount of nitrifying bacteria in the reactor, which guarantees a highly efficient nitrification.     

Exploiting olive oil mill effluents as a renewable resource for production of biodegradable polymers through a combined anaerobic–aerobic process

BACKGROUND: The performance of a three‐stage process for polyhydroxyalkanoate (PHA) bioproduction from olive oil mill effluents (OME) has been investigated. In the first anaerobic stage OME were fermented in a packed bed biofilm reactor into volatile fatty acids (VFAs). This VFA‐rich effluent was fed to the second stage, operated in an aerobic sequencing batch reactor (SBR), to enrich mixed cultures able to store PHAs. Finally, the storage response of the selected consortia was exploited in the third aerobic stage, operated in batch conditions. RESULTS: The anaerobic stage increased the VFA percentage in the OME from 18% to ～32% of the overall chemical oxygen demand (COD). A biomass with high storage response was successfully enriched in the SBR fed with the fermented OME at an organic load rate of 8.5 gCOD L^?1 d^?1, with maximum storage rate and yield (146 mgCOD gCOD^?1 h^?1 and 0.36 COD COD^?1, respectively) very similar to those obtained with a synthetic VFA mixture. By means of denaturing gradient gel electrophoresis (DGGE) analysis, different bacterial strains were identified during the two SBR runs: Lampropedia hyalina and Candidatus Meganema perideroedes, with the synthetic feed or the fermented OMEs, respectively. In the third stage, operated at increasing loads, the maximum concentration of the PHA produced increased linearly with the substrate fed. Moreover, about half of the stored PHAs were produced from substrates other than VFAs, mostly alcohols. CONCLUSION: The results obtained indicate that the process is effective for simultaneous treatment of OME and their valorization as a renewable resource for PHA production. Copyright © 2009 Society of Chemical Industry