Microbial diversity in polyextreme salt flats and their potential applications

Recent geological, hydrochemical, and mineralogical studies performed on hypersaline salt flats have given insights into similar geo-morphologic features on Mars. These salt-encrusted depressions are widely spread across the Earth, where they are characterized by high salt concentrations, intense UV radiation, high evaporation, and low precipitation. Their surfaces are completely dry in summer; intermittent flooding occurs in winter turning them into transitory hypersaline lakes. Thanks to new approaches such as culture-dependent, culture-independent, and metagenomic-based methods, it is important to study microbial life under polyextreme conditions and understand what lives in these dynamic ecosystems and how they function. Regarding these particular features, new halophilic microorganisms have been isolated from some salt flats and identified as excellent producers of primary and secondary metabolites and granules such as halocins, enzymes, carotenoids, polyhydroxyalkanoates, and exopolysaccharides. Additionally, halophilic microorganisms are implemented in heavy metal bioremediation and hypersaline wastewater treatment. As a result, there is a growing interest in the distribution of halophilic microorganisms around the world that can be looked upon as good models to develop sustainable biotechnological processes for all fields. This review provides insights into diversity, ecology, metabolism, and genomics of halophiles in hypersaline salt flats worldwide as well as their potential uses in biotechnology.

Oceanobacillus salinisoli sp. nov., a bacterium isolated from saline soil of Turpan city in Xinjiang province, north-west China

YIM B00359^T, a novel bacterial strain was isolated from the saline soil of Turpan city in Xinjiang province, north-west China. The strain was Gram-stain-positive, motile, aerobic, produced oval subterminal endospores in swollen sporangia. The whole-cell hydrolysates contain meso-diaminopimelic acid as the cell-wall diamino acid, with xylose, glucose, and ribose as the major whole-cell sugars. The phospholipids are diphosphatidylglycerol, phosphatidylglycerol, unidentified phospholipids, unidentified glycolipids, and one unidentified glycophospholipid. The predominant menaquinone is MK-7. The major fatty acids are anteiso-C_15:0, iso-C_14:0, iso-C_15:0, and iso-C_16:0. The DNA G + C content of the type strain is 37.5 mol%. Phylogenetic analysis indicated that the isolate belongs to the genus Oceanobacillus. However, it differed from its closest relatives, Oceanobacillus halophilus DSM 23996 ^T and Oceanobacillus senegalensis Marseille-P3587^T in many physiological and chemotaxonomic characteristics. Based on comparative analysis of polyphasic taxonomic data, strain YIM B00359^T represents a novel species of the genus Oceanobacillus, for which the name Oceanobacillus salinisoli sp. nov. is proposed. The type strain is YIM B00359^T (= CGMCC 1.17509^T = KCTC 43185^T).

Actinomyces wuliandei sp. nov., Corynebacterium liangguodongii sp. nov., Corynebacterium yudongzhengii sp. nov. and Oceanobacillus zhaokaii sp. nov., isolated from faeces of Tibetan antelope in the Qinghai-Tibet plateau of China

Eight Gram-stain-positive, rod-shaped bacterial strains were isolated from faeces of Tibetan antelopes on the Tibet-Qinghai Plateau of China. Genomic sequence analysis showed that the strains belong to the genera Actinomyces (strains 299^T and 340), Corynebacterium (strains 2184^T, 2185, 2183^T and 2189) and Oceanobacillus (strains 160^T and 143), respectively, with a percentage of similarity for the 16S rRNA gene under the species threshold of 98.7 % except for strains 160^T and 143 with Oceanobacillus arenosus CAU 1183^T (98.8 %). The genome sizes (and genomic G+C contents) were 3.1 Mb (49.4 %), 2.5 Mb (64.9 %), 2.4 Mb (66.1 %) and 4.1 Mb (37.1 %) for the type strains 299^T, 2183^T, 2184^T and 160^T, respectively. Two sets of the overall genome relatedness index values between our isolates and their corresponding closely related species were under species thresholds (95 % for average nucleotide identity, and 70 % for digital DNA-DNA hybridization). These results, together with deeper genotypic, genomic, phenotypic and biochemical analyses, indicate that these eight isolates should be classified as representing four novel species. Strain 299^T (=CGMCC 1.16320^T=JCM 33611^T) is proposed as representing Actinomyces wuliandei sp. nov.; strain 2184^T (=CGMCC 1.16417^T=DSM 106203^T) is proposed as representing Corynebacterium liangguodongii sp. nov.; strain 2183^T (=CGMCC 1.16416^T=DSM 106264^T) is proposed as representing Corynebacterium yudongzhengii sp. nov.; and strain 160^T (=CGMCC 1.16367^T=DSM 106186^T) is proposed as representing Oceanobacillus zhaokaii sp. nov.

Insights Into the Microbiology of the Chaotropic Brines of Salar de Atacama, Chile

Microbial life inhabiting hypersaline environments belong to a limited group of extremophile or extremotolerant taxa. Natural or artificial hypersaline environments are not limited to high concentrations of NaCl, and under such conditions, specific adaptation mechanisms are necessary to permit microbial survival and growth. Argentina, Bolivia, and Chile include three large salars (salt flats) which globally, represent the largest lithium reserves, and are commonly referred to as the Lithium Triangle Zone. To date, a large amount of information has been generated regarding chemical, geological, meteorological and economical perspectives of these salars. However, there is a remarkable lack of information regarding the biology of these unique environments. Here, we report the presence of two bacterial strains (isolates LIBR002 and LIBR003) from one of the most hypersaline lithium-dominated man-made environments (total salinity 556 g/L; 11.7 M LiCl) reported to date. Both isolates were classified to the Bacillus genera, but displayed differences in 16S rRNA gene and fatty acid profiles. Our results also revealed that the isolates are lithium-tolerant and that they are phylogenetically differentiated from those Bacillus associated with high NaCl concentration environments, and form a new clade from the Lithium Triangle Zone. To determine osmoadaptation strategies in these microorganisms, both isolates were characterized using morphological, metabolic and physiological attributes. We suggest that our characterization of bacterial isolates from a highly lithium-enriched environment has revealed that even at such extreme salinities with high concentrations of chaotropic solutes, scope for microbial life exists. These conditions have previously been considered to limit the development of life, and our work extends the window of life beyond high concentrations of MgCl2, as previously reported, to LiCl. Our results can be used to further the understanding of salt tolerance, most especially for LiCl-dominated brines, and likely have value as models for the understanding of putative extra-terrestrial (e.g., Martian) life.

Cell envelop is the key site for Cr(Ⅵ) reduction by Oceanobacillus oncorhynchi W4, a newly isolated Cr(Ⅵ) reducing bacterium

The Cr(Ⅵ) removal way and Cr(Ⅵ) reducing site of Oceanobacillus oncorhynchi W4, a novel Cr(Ⅵ) reducing bacterium, were investigated in this study. Results showed that about 74.2% of Cr(Ⅵ) was removed from solution by growing cells within 72 h. Moreover, heating-killed resting cells had little Cr(Ⅵ) removal capacity, which was significantly lower than that of resting cells, which reached nearly 80% removal rate, suggesting that the way of Cr(Ⅵ) removal mainly relied on biological reduction rather than biosorption. And the Cr(Ⅵ) reduction was found to be significantly enhanced by some electron donors, especially glycerin, which further verified enzyme-mediated biological reduction as the way for Cr(Ⅵ) removal. Experiments of Cr(Ⅵ) removal by permeable cells indicated that there was no significant difference in chromium reduction between the impermeable cells and the permeable cells. The cell envelop fraction had a Cr(Ⅵ) removal rate of 82.9%, apparently higher than cytoplasmic fraction (11.1%), indicating that the cell envelop was the main location for Cr(Ⅵ) reduction, which were further demonstrated by Scanning Electron Microscope and Transmission electron microscopy plus EDS analysis. Furthermore, analysis of X-ray photoelectron spectroscopy manifested that CO, C-OH and C-OC groups on the surfaces played major roles in correlation with chromium species.

Diversity of Bacillus-like bacterial community in the rhizospheric and non-rhizospheric soil of halophytes (Salsola stocksii and Atriplex amnicola), and characterization of osmoregulatory genes in halophilic Bacilli

Salinity is one of the major abiotic stresses; a total of 3% of the world’s land mass is affected by salinity. Approximately 6.3 million hectares of land in Pakistan is affected by salinity to varying degrees, and most of the areas are arid to semiarid with low annual precipitation. The aim of the present study is to identify and characterize Bacillus and Bacillus-derived bacterial genera from the rhizospheric and non-rhizospheric soil samples from the Khewra Salt Mine, Pakistan, by using culture-independent and -dependent methods. Seven Bacillus-like bacterial genera, Bacillus, Halobacillus, Virgibacillus, Brevibacillus, Paenibacillus, Tumebacillus, and Lysinibacillus, were detected by using pyrosequencing analysis, whereas only four genera, Bacillus, Halobacillus, Oceanobacillus, and Virgibacillus, were identified by culture-dependent methods. Most of the Bacillus-like isolates identified in this study were moderately halophilic, alkaliphilic, and mesophilic bacteria and were considered a good source of hydrolytic enzymes because of their ability to degrade proteins, carbohydrates, and lipids. Eight Bacillus-like strains from the genera Bacillus, Halobacillus, Oceanobacillus, and Virgibacillus showed positive results for the presence of ectABC gene cluster (ectoine), six strains could synthesize betaine from choline, and six strains tested positive for the synthesis of proline from either glutamate or ornithine by using proline dehydrogenase enzyme.

Microbial community structure and diversity within hypersaline Keke Salt Lake environments

Keke Salt Lake is located in the Qaidamu Basin of China. It is a unique magnesium sulfate-subtype hypersaline lake that exhibits a halite domain ecosystem, yet its microbial diversity has remained unstudied. Here, the microbial community structure and diversity was investigated via high-throughput sequencing of the V3-V5 regions of 16S rRNA genes. A high diversity of operational taxonomic units was detected for Bacteria and Archaea (734 and 747, respectively), comprising 21 phyla, 43 classes, and 201 genera of Bacteria and 4 phyla, 4 classes, and 39 genera of Archaea. Salt-saturated samples were dominated by the bacterial genera Bacillus (51.52%-58.35% relative abundance), Lactococcus (9.52%-10.51%), and Oceanobacillus (8.82%-9.88%) within the Firmicutes phylum (74.81%-80.99%), contrasting with other hypersaline lakes. The dominant Archaea belonged to the Halobacteriaceae family, and in particular, the genera (with an abundance of >10% of communities) Halonotius, Halorubellus, Halapricum, Halorubrum, and Natronomonas. Additionally, we report the presence of Nanohaloarchaeota and Woesearchaeota in Qinghai-Tibet Plateau lakes, which has not been previously documented. Total salinity (especially Mg²⁺, Cl^-, Na⁺, and K⁺) mostly correlated with taxonomic distribution across samples. These results expand our understanding of microbial resource utilization within hypersaline lakes and the potential adaptations of dominant microorganisms that allow them to inhabit such environments.