小花棘豆生物碱对表皮葡萄球菌的抗菌作用及生物膜形成的影响

探讨小花棘豆生物碱对表皮葡萄球菌的抗菌作用及其对细菌生物膜的抑制作用。以表皮葡萄球菌为研究对象,通过微量肉汤稀释法测定最小抑菌浓度(MIC)和最小杀菌浓度(MBC),微量板半定量法测定其对表皮葡萄球菌生物膜形成的影响,以去离子水和氯化钠检测小花棘豆生物碱对细菌细胞壁的渗透能力影响。结果表明,小花棘豆生物碱对表皮葡萄球菌的抑菌作用较强,其MIC和MBC分别为1.6mg/mL和3.2mg/mL,1~1/4MIC的小花棘豆生物碱可明显抑制表皮葡萄球菌生物膜的形成,而且1~1/8MIC的小花棘豆生物碱对表皮葡萄球菌细胞壁的渗透能力有一定的影响。说明小花棘豆生物碱对表皮葡萄球菌具有抗菌作用,对其生物膜形成具有明显的抑制作用。     

大肠埃希菌生物被膜研究进展

细菌生物被膜指多个细菌黏附于机体或物体表面,分泌胞外多聚物将其自身包裹其中而形成的结构。研究表明人类许多细菌感染与生物被膜有关,生物被膜具有极高的抗药性和免疫逃逸能力,这也是许多细菌感染难以根除的重要原因之一,近年来已成为医学界关注的热点。大肠埃希菌是最重要的条件致病菌之一,论文从大肠埃希菌生物被膜的形态结构、检测方法、耐药机制、应对策略4个方面综述了大肠埃希菌生物被膜研究的进展。     

Unstable green fluorescent protein for study of Xanthomonas citri subsp. citri survival on citrus

Xanthomonas citri subsp. citri (Xac) is the causal agent of citrus bacterial canker, an important disease for the citrus industry. Studies of Xac survival in environments outside of the lesion performed in the past may have underestimated the viable population because the recovery was based on the ability of the bacterium to grow on culture media. This study monitored survival of Xac that express green fluorescent protein (GFP) in two different forms: the native protein, and a protein that is unstable due to a specific oligopeptide tail targeted by proteases within the bacterium. Transformed strains of Xac were verified to be stable in their expression of GFP and to show no differences in virulence and fitness compared to wild type strains. Evaluation of protein stability confirmed that strains with unstable GFP only expressed and fluoresced in metabolically active cells, and not in dead bacteria. Fluorescence of unstable GFP strains under confocal microscopy was used to track bacterial survival and biofilm formation on leaf and fruit surfaces. After spray inoculation, aggregates of fluorescing cells of unstable GFP strains formed biofilms on leaves and fruit. Bacterial cells that aggregated on the surfaces only survived when protected from desiccation. Aggregation of viable bacteria in biofilms confirms their role in pathogen survival outside of lesions and protection from bactericide treatments in the field or in the fruit disinfection process.     

Virulence factors analysis of native isolates of Xanthomonas albilineans and Xanthomonas sacchari from Tucumán,Argentina, reveals differences in pathogenic strategies

Xanthomonas albilineans (Xa) and X. sacchari (Xs) are both sugarcane pathogens. Xa is the causal agent of leaf scald disease, but there is limited information about the pathogenicity of Xs. The aim of this work was to study virulence factors of native strains of Xa (Xa32, Xa33, and XaM6) and Xs (Xs14 and Xs15) previously isolated from sugarcane with leaf scald symptoms, to gain insight into the biology of each microorganism. We analysed epiphytic survival, sensitivity to oxidative stress, extracellular degradative enzymes, cell motilities, exopolysaccharide (EPS) characteristics, cell adhesion, biofilm development, and control of stomatal regulation of the five strains. We observed that each species presented similar phenotypes for every factor analysed. Xa strains appeared to be more sensitive to oxidative stress and presented lower epiphytic survival than Xs. All strains presented endoglucanase activity; however, we could only detect protease and amylase activities in Xs strains. Swimming and sliding were higher in Xs, but twitching was variable among species. We also observed that only Xs strains produced a xanthan-like EPS, presented a strong cell adhesion, and structured biofilm. We detected some intraspecific variations showing that higher amounts of EPS produced by Xs14 correlated with its higher sliding motility and its homogenous and more adhesive biofilm. In addition, EPSs of Xs14 and Xs15 presented differences in strand height and acetyl percentage. Finally, we found that strains of both species were able to interfere with stomatal aperture mechanism. All these differences could influence the colonization strategies and/or disease progression in each species.     

Use of Quorum Sensing Inhibition Strategies to Control Microfouling

Interfering with the quorum sensing bacterial communication systems has been proposed as a promising strategy to control bacterial biofilm formation, a key process in biofouling development. Appropriate in vitro biofilm-forming bacteria models are needed to establish screening methods for innovative anti-biofilm and anti-microfouling compounds. Four marine strains, two Pseudoalteromonas spp. and two Vibrio spp., were selected and studied with regard to their biofilm-forming capacity and sensitivity to quorum sensing (QS) inhibitors. Biofilm experiments were performed using two biofilm cultivation and quantification methods: the xCELLigence^® system, which allows online monitoring of biofilm formation, and the active attachment model, which allows refreshment of the culture medium to obtain a strong biofilm that can be quantified with standard staining methods. Although all selected strains produced acyl-homoserine-lactone (AHL) QS signals, only the P. flavipulchra biofilm, measured with both quantification systems, was significantly reduced with the addition of the AHL-lactonase Aii20J without a significant effect on planktonic growth. Two-species biofilms containing P. flavipulchra were also affected by the addition of Aii20J, indicating an influence on the target bacterial strain as well as an indirect effect on the co-cultured bacterium. The use of xCELLigence^® is proposed as a time-saving method to quantify biofilm formation and search for eco-friendly anti-microfouling compounds based on quorum sensing inhibition (QSI) strategies. The results obtained from these two in vitro biofilm formation methods revealed important differences in the response of biosensor bacteria to culture medium and conditions, indicating that several strains should be used simultaneously for screening purposes and the cultivation conditions should be carefully optimized for each specific purpose.     

ywbB基因对枯草芽胞杆菌NCD-2菌株生物膜形成和根际定殖能力的影响

为明确枯草芽胞杆菌Bacillus subtilis NCD-2菌株生物膜形成相关基因及其在生物膜形成、根际定殖中的作用,采用转座子插入技术,从4000余株NCD-2突变子中获得6株生物膜形成能力降低的突变子。在生物膜形成能力丧失的突变子M3中,转座子以单拷贝的形式插入到ywbB基因内部。通过基因同源重组技术对ywbB基因进行缺失突变,获得ywbB基因缺失突变菌株NCD-2(ΔywbB),与野生菌株相比,突变子丧失了生物膜形成能力。进一步比较发现,突变菌株NCD-2(ΔywbB)显著降低了在棉花根际的群体数量,同时也降低了对棉花立枯病的防治效果。研究证明,ywbB是NCD-2菌株生物膜形成途径中的重要基因,且生物膜形成与NCD-2菌株根际定殖和生防效果呈正相关。     

The undiscovered potential of dehydroproline as a fire blight control option

The non‐protein amino acid 3,4‐dehydro‐l ‐proline (DHP) significantly reduced the incidence of fire blight infection on immature pear fruits infected with wildtype Erwinia amylovora. DHP also inhibited biofilm formation in both streptomycin‐sensitive and ‐resistant strains of E. amylovora and induced dispersal of preformed biofilms in the streptomycin‐sensitive strain. The investigations shed light on the hitherto undiscovered ability of DHP to inhibit bacterial biofilms and its potential as a chemical control option for fire blight.     

海水循环水养殖系统生物膜快速挂膜试验

循环水养殖系统生物膜的挂膜成熟是一个比较耗时的过程,通常需要30～40d。为解决这一技术瓶颈,该文在一个大型海水循环水养殖厂的生物滤池内进行了生物膜快速挂膜的中试试验。该养殖厂循环水养殖系统有并联的生物滤池4个,单个为跑道式2级串联结构,总容量为800m3,采用毛刷状聚乙烯丝为生物载体。试验设计为预先培养水质净化菌的种子液,制备经200目筛绢过筛后质量比为4:1的黏土和沸石粉超细颗粒混合物悬液,然后按103cfu/mL和5g/L的浓度在两级滤池中分别加入4种不同水质净化菌的种子液和"黏土-沸石粉"混合物悬液,静水充气培养8d后,生物载体上能够形成较为牢固的生物膜。打开循环水系统运行2d后,连续5d检测生物滤池进、出水口的氨氮、硝酸盐、亚硝酸盐和COD(化学需氧量)含量,其5d平均消除率分别为:52.04%、17.24%、26.82%和62.94%。结果表明,与传统生物膜自然培养方法相比,该文所采用的挂膜方法将海水循环水养殖系统生物膜的挂膜成熟提前了20d以上,起到了增速效果,在生产上也是可行的。     

Pilot research on micropollutants removal in the raw water by combined process of water-lifting aeration and oligotrophic biofilm

Under the operation of multifunctional device for water lifting and aeration(MDWLA), in situ simulation experiment is made by use of the oligotrophic biofilm process for pretreatment of micro-polluted raw water in order to investigate the removal effects of nitrogen and organic matter. The experimental results show that the combined technique of water-lifting aeration and oligotrophic biofilm process is feasible, and the removal rate of ammonia, nitrate, total nitrogen and TOC in steady running period range from 82%~100%, 62%~79%, 71%~80% and 73%~80%, respectively, under the condition of temperature 10~23 ℃, dissolved oxygen 4.0~6.0 mg/L, NH +4-N 0.230 mg/L, NO -2-N 0.010 mg/L, NO -3-N 1.125 mg/L, TN 2.010 mg/L, CODMn 3.140 mg/L and BOD5 1.540 mg/L for source water, also the nitrite is poorly detected and the ratio of BOD5 to CODMn is in the range of 0.05 to 0.20. Obviously, the nitrogen removal effects can meet the requirements of class Ⅲ of surface water quality according to GB3838—2002 and the biological stability can be improved under stable operation condition of the combined process. Lastly, the changes of oligotrophic denitrifying bacteria number and biological phase, and water purifying mechanism of oligotrophic biofilm system are also discussed.     

一种新型竹纤维生物膜载体的制备与性能

以竹纤维为主要原料制备得到一种新型竹纤维生物膜载体.载体比表面积达5393m2·m-3,亲水性能良好,30min后基本浸湿完全.研究了竹纤维生物膜载体在低浓度生活污水处理中的挂膜性能,结果表明:载体挂膜速率快,7天后载体表面即出现大量黏性黄褐色生物膜,第12天基本完成挂膜,膜厚达3～5mm.生物相观察表明:以固着型纤毛虫为主的后生动物数量较稳定,生物膜趋于成熟.载体生物膜耐水力剪切冲击能力和恢复能力强,对CODCr和NH4+-N的去除率在80％以上.