Halomonas alkalicola CICC 11012s can grow at pH 12.5, the highest pH at which the organisms in the genus Halomonas can grow. Genomic analysis reveals that H. alkalicola adapts to alkaline stress using a variety of adaptive strategies; however, the detailed mechanism for its growth at high-alkaline conditions has not been elucidated. Therefore, in this study, the adaptations of H. alkalicola in response to extreme alkaline stress were investigated. A sharp decrease of alkaliphilic tolerance was observed in mutants E. coli ΔEctonB and H. alkalicola ΔHatonB. Expressions of the gene clusters encoding TonB-dependent transport system and iron complex transport system in H. alkalicola grown under extreme alkaline conditions were markedly up-regulated. We then compared the intracellular ionic iron content and iron-chelating ability of mutant strain with those of wild-type strain to understand the influence of TonB-dependent transport system on the alkaline responses. The results indicated that the presence of TonB-dependent transport system increased the alkaline tolerance of H. alkalicola grown at high-alkaline conditions, but had no effects when the strain was grown at neutral pH and low-alkaline conditions. Meanwhile, the presence of this system increased the transport and accumulation of ionic irons to maintain intracellular metabolic homeostasis, which in turn could increase the tolerance of the strain to extreme alkaline conditions. Based on the results, we established a model representing the interactions between TonB-dependent transport system, alkaline tolerance, and intracellular ionic iron that could help deepen the understanding of the alkaline response mechanism of alkaliphilic bacteria.

盐单胞菌alkalicola中金公司11012s在pH 12.5成长，在其属中生物的pH值最高的盐单胞菌能生长。基因组分析表明，碱杆菌可通过多种适应策略适应碱性胁迫。然而，尚未阐明其在高碱性条件下生长的详细机制。因此，在这项研究中，研究了嗜盐链球菌对极端碱性胁迫的适应性。在突变体大肠杆菌ΔEctonB和嗜碱杆菌H-alkolaΔHatonB中观察到耐碱性急剧下降。编码TonB依赖性转运系统和铁络合物转运系统的基因簇在碱金属假丝酵母中的表达在极端碱性条件下生长的植物明显上调。然后，我们将突变菌株与野生型菌株的细胞内离子铁含量和铁螯合能力进行了比较，以了解TonB依赖性转运系统对碱性反应的影响。结果表明，依赖TonB的转运系统的存在增加了嗜碱链球菌的耐碱性在高碱性条件下生长，但是当菌株在中性pH和低碱性条件下生长时没有作用。同时，该系统的存在增加了离子铁的转运和积累，以维持细胞内代谢稳态，这反过来又可以增加菌株对极端碱性条件的耐受性。基于结果，我们建立了一个模型，代表了依赖TonB的转运系统，碱耐受性和细胞内离子铁之间的相互作用，这可能有助于加深对嗜碱细菌的碱性反应机理的了解。