Nocelli Natalia, Bogino Pablo C, Banchio Erika, Giordano Walter
Departamento de Biología Molecular, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Río Cuarto, Córdoba X5804BYA, Argentina.
Materials (Basel). 2016 May 26;9(6):418. doi: 10.3390/ma9060418.
Bacterial surface components and extracellular compounds, particularly flagella, lipopolysaccharides (LPSs), and exopolysaccharides (EPSs), in combination with environmental signals and quorum-sensing signals, play crucial roles in bacterial autoaggregation, biofilm development, survival, and host colonization. The nitrogen-fixing species () produces two symbiosis-promoting EPSs: succinoglycan (or EPS I) and galactoglucan (or EPS II). Studies of the alfalfa symbiosis model system have revealed numerous biological functions of EPSs, including host specificity, participation in early stages of host plant infection, signaling molecule during plant development, and (most importantly) protection from environmental stresses. We evaluated functions of EPSs in bacterial resistance to heavy metals and metalloids, which are known to affect various biological processes. Heavy metal resistance, biofilm production, and co-culture were tested in the context of previous studies by our group. A range of mercury (Hg II) and arsenic (As III) concentrations were applied to wild type strain and to mutant strains defective in EPS I and EPS II. The EPS production mutants were generally most sensitive to the metals. Our findings suggest that EPSs are necessary for the protection of bacteria from either Hg (II) or As (III) stress. Previous studies have described a pump in that causes efflux of arsenic from cells to surrounding culture medium, thereby protecting them from this type of chemical stress. The presence of heavy metals or metalloids in culture medium had no apparent effect on formation of biofilm, in contrast to previous reports that biofilm formation helps protect various microorganism species from adverse environmental conditions. In co-culture experiments, EPS-producing heavy metal resistant strains exerted a protective effect on AEPS-non-producing, heavy metal-sensitive strains; a phenomenon termed "rescuing" of the non-resistant strain.
细菌表面成分和胞外化合物，特别是鞭毛、脂多糖（LPS）和胞外多糖（EPS），与环境信号和群体感应信号相结合，在细菌自聚集、生物膜形成、存活和宿主定殖中发挥关键作用。固氮物种（）产生两种促进共生的EPS：琥珀聚糖（或EPS I）和半乳葡聚糖（或EPS II）。苜蓿共生模型系统的研究揭示了EPS的多种生物学功能，包括宿主特异性、参与宿主植物感染的早期阶段、植物发育过程中的信号分子以及（最重要的）抵御环境胁迫。我们评估了EPS在细菌对重金属和类金属抗性中的功能，已知这些重金属和类金属会影响各种生物过程。在我们小组之前研究的背景下，测试了重金属抗性、生物膜产生和共培养情况。将一系列汞（Hg II）和砷（As III）浓度应用于野生型菌株以及EPS I和EPS II缺陷的突变菌株。EPS产生突变体通常对这些金属最敏感。我们的研究结果表明，EPS对于保护细菌免受Hg（II）或As（III）胁迫是必要的。先前的研究描述了中一种导致砷从细胞外流到周围培养基中的泵，从而保护细胞免受这种化学胁迫。与之前报道生物膜形成有助于保护各种微生物物种免受不利环境条件影响相反，培养基中重金属或类金属的存在对生物膜形成没有明显影响。在共培养实验中，产生EPS的重金属抗性菌株对不产生AEPS的重金属敏感菌株发挥了保护作用；这种现象被称为非抗性菌株的“拯救”。
