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

Abstract

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.

Genomic Variation and Arsenic Tolerance Emerged as Niche Specific Adaptations by Different Exiguobacterium Strains Isolated From the Extreme Salar de Huasco Environment in Chilean – Altiplano

“…In our study, arsenic concentration and salinity are the two most prominent factors with the greatest variation (Figure 1). Moreover, salinity variation correlates with previous reports for H0, H1 and H4 sites (Dorador et al, 2008;Remonsellez et al, 2018), even they found that H0 and H1 sites exhibited more similarities, contrasting with the remaining sites. Hence, the effects of the five SH niche conditions (arsenic specifically), over the micro-diversity of inhabitant Exiguobacterium strains is of great interest.…”

“…Exiguobacterium is a bacterial genus initially described by Collins et al (1983) , as Gram positive, pigmented rods, facultative aerobic with a wide range of temperature and tolerance. These bacteria have also been characterized as halo-, psychro- and thermo-tolerant and some even resist highly toxic arsenic ( Vishnivetskaya et al, 2007 ; Belfiore et al, 2013 ; Remonsellez et al, 2018 ; Castro-Severyn et al, 2019 ). Different strains from this genus have been isolated from multiple extreme environments that vary from marine water, permafrost, deserts, salt flats and even stromatolites ( Rodrigues et al, 2006 ; Ordoñez et al, 2013 ; Tang et al, 2013 ; Vishnivetskaya et al, 2014 ; Zhang et al, 2015 ).…”

“…The Salar de Huasco is a poly-extreme ecosystem located on the Chilean Altiplano (Northern Region) where cultivable members of the Exiguobacterium genus are ubiquitous ( Remonsellez et al, 2018 ). This area is subjected to major climatic oscillations ( Cortés-Albayay et al, 2019 ), namely: temperature, salinity, high levels of solar radiation, negative water balance and the presence of arsenic ( Dorador et al, 2008 ; Herrera et al, 2009 ; Hernández et al, 2016 ; Pérez et al, 2017 ; Remonsellez et al, 2018 ; Castro-Severyn et al, 2019 ). Another relevant aspect of the Salar de Huasco is the great microbial diversity that has been little explored ( Dorador et al, 2010 , 2013 ; Molina et al, 2016 ; Castro-Severyn et al, 2017 ).…”

“…Previously, we carried out a study of three Exiguobacterium strains focusing on the high levels of arsenic tolerance presented by isolates from the Salar de Huasco sediments. Through sequencing, genomic and proteomic analyzes of these strains, we found several markers directly related tolerance arsenic, as well as the response to oxidative and overall stress ( Castro-Severyn et al, 2017 , 2019 ; Remonsellez et al, 2018 ). In this study, we tested whether genotypic variability of Exiguobacterium isolates correlates with their capacity to tolerate arsenic and with specific properties of their habitat, which could drive genus divergence.…”

Pan‐genome analysis of Exiguobacterium reveals species delineation and genomic similarity with Exiguobacterium profundum PHM 11

“…Exiguobacterium is a large genus of gram‐positive, facultative anaerobic, nonspore‐forming bacillus. Members of this genus are biochemically and morphologically diverse and are found in diverse habitats such as soil, rhizosphere and survive under extreme environmental conditions (Vishnivetskaya et al ., 2009; Remonsellez et al ., 2018). Exiguobacterium genus comprises halophilic, psychrotrophic and moderate thermophilic species (Vishnivetskaya et al ., 2014; Kasana and Pandey, 2018), with noticeable morphological diversity depending on species, strain and environmental conditions.…”