Table_4_Characterization and Salt Response in Recurrent Halotolerant Exiguobacterium sp. SH31 Isolated From Sediments of Salar de Huasco, Chilean Altiplano.xlsx

Poly-extremophiles microorganisms have the capacity to inhabit hostile environments and can survive several adverse conditions that include as variations in temperature, pH, and salinity, high levels UV light and atmospheric pressure, and even the presence of toxic compounds and the formation of reactive oxygen species (ROS). A halotolerant Exiguobacterium strain was isolated from Salar de Huasco (Chilean Altiplano), a well-known shallow lake area with variable salinity levels, little human intervention, and extreme environmental conditions, which makes it ideal for the study of resistant mechanisms and the evolution of adaptations. This bacterial genus has not been extensively studied, although its cosmopolitan location indicates that it has high levels of plasticity and adaptive capacity. However, to date, there are no studies regarding the tolerance and resistance to salinity and osmotic pressure. We set out to characterize the Exiguobacterium sp. SH31 strain and describe its phenotypical and genotypical response to osmotic stress. In this context, as a first step to characterize the response to the SH31 strain to salinity and to establish the bases for a molecular study, we proposed to compare its response under three salt conditions (0, 25, and 50 g/l NaCl). Using different physiology, genomic, and transcriptomic approaches, we determined that the bacterium is able to grow properly in a NaCl concentration of up to 50 g/l; however, the best growth rate was observed at 25 g/l. Although the presence of flagella is not affected by salinity, motility was diminished at 25 g/l NaCl and abolished at 50 g/l. Biofilm formation was induced proportionally with increases in salinity, which was expected. These phenotypic results correlated with the expression of related genes: fliG and fliS Motility); opuBA and putP (transport); glnA, proC, gltA, and gbsA (compatible solutes); ywqC, bdlA, luxS y pgaC (biofilm and stress response); and therefore, we conclude that this strain effectively modifies gene expression and physiology in a differential manner when faced with different concentrations of NaCl and these modifications aid survival.

多重极端嗜极微生物（Poly-extremophiles microorganisms）能够栖息于严苛环境，可在多种不利条件下存活，这些条件包括温度、pH值与盐度的波动、高强度紫外线辐射、大气压力异常，乃至有毒化合物的存在与活性氧簇（reactive oxygen species, ROS）的生成。本研究从智利阿尔蒂普拉诺高原的瓦斯科盐沼（Salar de Huasco）中分离得到一株耐盐极小杆菌（Exiguobacterium）菌株。该区域为知名浅湖区域，盐度波动剧烈、人类干预极少且环境条件极端，非常适合开展抗性机制与适应性演化研究。尽管该菌属的分布范围广泛，具备极强的可塑性与适应能力，但目前针对该属的研究仍相对匮乏。然而截至目前，尚无针对该菌株盐度与渗透压耐受性及抗性的相关研究。本研究旨在对极小杆菌属SH31菌株（Exiguobacterium sp. SH31）进行表型与基因型特征分析，并阐明其在渗透压胁迫下的响应机制。基于上述背景，为明确SH31菌株对盐度的响应并为后续分子研究奠定基础，本研究设定了三种盐浓度条件（0、25及50 g/L氯化钠），对菌株的响应进行对比分析。通过生理学、基因组学与转录组学等多种研究手段，本研究证实该菌株可在最高50 g/L的氯化钠浓度下正常生长，但其最优生长浓度为25 g/L。尽管盐度不会影响鞭毛的合成，但菌株的运动能力在25 g/L氯化钠条件下会受到抑制，在50 g/L条件下则完全丧失。生物膜的形成随盐度升高呈正比诱导，这与预期结果一致。上述表型结果与相关基因的表达水平显著相关：fliG与fliS（运动相关）、opuBA与putP（物质转运相关）、glnA、proC、gltA与gbsA（相容性溶质合成相关）、ywqC、bdlA、luxS及pgaC（生物膜形成与胁迫响应相关）。因此本研究得出结论：该菌株可针对不同浓度的氯化钠胁迫，通过差异化方式调控基因表达与生理状态，从而提升自身存活能力。