Chen Shaoxing, Sun Siqi, Wang Rui, Feng Hongli, Xiang Hua
College of Life Sciences, Anhui Normal University, No.1 Beijing East Road, Wuhu 241000, China
College of Life Sciences, Honghe University, No.1 Xuefu Road, Mengzi 661100, China.
Appl Environ Microbiol. 2021 Apr 15;87(8). doi: 10.1128/AEM.02889-20. Epub 2021 Feb 12.
Halolysins, which are subtilisin-like serine proteases of haloarchaea, are usually secreted into the extracellular matrix via the twin-arginine translocation pathway. A small number of activated molecules can greatly affect cell growth owing to their proteolytic activity. It is, however, unclear as to whether this proteolysis-based growth inhibition by halolysins conveys antagonistic or defensive effects against other resident abd potentially competitive microorganisms. Here, we report that halolysin R4 (HlyR4), encoded by the R4 gene, is the key enzyme in the initial steps of extracellular protein utilization in HlyR4 shows significant antagonistic activity against other haloarchaeal strains. Deletion of R4 completely halts the inhibition activity of towards other haloarchaea, while correspondingly, complementation of R4 almost completely restores the inhibition activity. Furthermore, strains containing R4 showed a certain amount of resistance to halocins and halolysins in milieu, and this function of R4 is reproducible in The versatility of HlyR4 enables its host to outcompete other haloarchaea living in the same hypersaline environment. Intriguingly, unlike the growth phase-dependent halolysins SptA and Nep, it is likely that HlyR4 may be secreted independent of growth phase. This study provides a new peptide antibiotics candidate in haloarchaea, as well as new insight towards a better understanding of the ecological roles of halolysins. This study shows that halolysin R4 from provides its host antagonistic and defensive activities against other haloarchaea, which expands our knowledge on the traditional function of haloarchaeal extracellular proteases. Haloarchaeal extracellular serine proteases have been previously discussed as growth-phase-dependent proteins, whereas our study reports constitutive expression of halolysin R4. This work also clearly reveals a hidden diversity of extracellular proteases from haloarchaea. Studies on multifunctional halolysins reveal that they play an important ecological role in shaping microbial community composition and provide a new perspective towards understanding the intricate interactions between haloarchaeal cells in hypersaline environments. HlyR4 can lyse competing cells living in the same environment, and the cell debris may probably be utilized as nutrients, which may constitute an important part of nutrient cycling in extremely hypersaline environments.
嗜盐菌素是嗜盐古菌中类似枯草杆菌蛋白酶的丝氨酸蛋白酶，通常通过双精氨酸转运途径分泌到细胞外基质中。少数活化分子因其蛋白水解活性可极大地影响细胞生长。然而，尚不清楚嗜盐菌素基于蛋白水解的生长抑制作用对其他常驻且可能具有竞争性的微生物是具有拮抗作用还是防御作用。在此，我们报告由R4基因编码的嗜盐菌素R4（HlyR4）是嗜盐栖热菌细胞外蛋白利用初始步骤中的关键酶，HlyR4对其他嗜盐古菌菌株表现出显著的拮抗活性。R4基因的缺失完全消除了嗜盐栖热菌对其他嗜盐古菌的抑制活性，而相应地，R4基因的互补几乎完全恢复了抑制活性。此外，含有R4的嗜盐栖热菌菌株在环境中对嗜盐菌素和嗜盐菌素表现出一定程度的抗性，并且R4的这种功能在嗜盐栖热菌中是可重复的。HlyR4的多功能性使其宿主能够胜过生活在相同高盐环境中的其他嗜盐古菌。有趣的是，与生长阶段依赖性嗜盐菌素SptA和Nep不同，HlyR4可能独立于生长阶段分泌。本研究提供了一种新的嗜盐古菌肽抗生素候选物，以及对更好理解嗜盐菌素生态作用的新见解。本研究表明，嗜盐栖热菌的嗜盐菌素R4为其宿主提供了针对其他嗜盐古菌的拮抗和防御活性，这扩展了我们对嗜盐古菌细胞外蛋白酶传统功能的认识。嗜盐古菌细胞外丝氨酸蛋白酶以前被认为是生长阶段依赖性蛋白，而我们的研究报告了嗜盐菌素R4的组成型表达。这项工作还清楚地揭示了嗜盐古菌细胞外蛋白酶隐藏的多样性。对多功能嗜盐菌素的研究表明，它们在塑造微生物群落组成方面发挥着重要的生态作用，并为理解高盐环境中嗜盐古菌细胞之间复杂的相互作用提供了新的视角。HlyR4可以裂解生活在同一环境中的竞争细胞，细胞碎片可能被用作营养物质，这可能构成极端高盐环境中营养循环的重要组成部分。
