Laboratory of Plant Biotechnology, Faculty of Sciences of Sfax, University of Sfax, Route Sokra BP 1171, 3000 Sfax, Tunisia.
Labiris Research Institute, Avenue Emile Gryzon 1, 1070 Brussels, Belgium.
Biomed Res Int. 2020 Jul 23;2020:6047528. doi: 10.1155/2020/6047528. eCollection 2020.
is a ubiquitous Gram-negative bacterium able to survive in diverse environments such as soil, plants, freshwater, and seawater. can be an opportunistic pathogen to humans when their immune system is deficient. Its pathogenicity may be linked to the production of virulence factors. We isolated strain RBS from the saltern of Sfax in Tunisia. In this study, we characterized the halotolerance, antibiotic susceptibility, and some virulence factors of strain RBS. High NaCl concentrations inhibited growth and motility. However, biofilm formation was enhanced to protect bacteria against salt stress. Among the 18 antibiotics tested, quinolones and tetracycline showed a significant inhibitory effect on growth, motility, and biofilm formation of strain RBS. -Lactams, however, did not have any inhibitory effect on neither bacterial growth nor motility. In some cases, resistance was due, in part, to biofilm formation. We also showed that RBS produces two proteases, LasB and AprA, which have been shown to be implicated in host infection. LasB was further characterized to study the role of metal ions in enzyme stability. It possesses two distinct metal ion-binding sites coordinating a calcium and a zinc ion. The effect of metal ion chelation was evaluated as well as substitutions of residues involved in metal ion binding. Impairing metal ion binding of LasB led to a loss of activity and a sharp decrease of stability. Our findings suggest that the binding of both metal ions is interdependent as the two metal ions' binding sites are linked via a hydrogen bond network.
是一种普遍存在的革兰氏阴性菌，能够在土壤、植物、淡水和海水等多种环境中生存。当人体免疫系统较弱时，它可能成为机会性病原体。其致病性可能与产生毒力因子有关。我们从突尼斯斯法克斯的盐田分离出了 RBS 菌株。在这项研究中，我们描述了 RBS 菌株的耐盐性、抗生素敏感性和一些毒力因子。高浓度的 NaCl 抑制了生长和运动性。然而，生物膜的形成得到了增强，以保护细菌免受盐胁迫。在测试的 18 种抗生素中，喹诺酮类和四环素类对 RBS 菌株的生长、运动性和生物膜形成有显著抑制作用。然而，-内酰胺类药物对细菌的生长和运动性没有任何抑制作用。在某些情况下，耐药性部分是由于生物膜的形成。我们还表明，RBS 产生两种蛋白酶，LasB 和 AprA，它们已被证明与宿主感染有关。进一步对 LasB 进行了表征，以研究金属离子在酶稳定性中的作用。它具有两个独特的金属离子结合位点，分别协调一个钙离子和一个锌离子。评估了金属离子螯合的效果以及参与金属离子结合的残基的取代。LasB 的金属离子结合受损导致活性丧失和稳定性急剧下降。我们的研究结果表明，两个金属离子的结合是相互依赖的，因为两个金属离子的结合位点通过氢键网络连接。
