Taxonomic description and genome sequence of Salinicoccus sediminis sp. nov., a halotolerant bacterium isolated from marine sediment

Delving into the lifestyle of Sundarban Wetland resident, biofilm producing, halotolerant Salinicoccus roseus: a comparative genomics-based intervention

BACKGROUND

Microbial community played an essential role in ecosystem processes, be it mangrove wetland or other intertidal ecologies. Several enzymatic activities like hydrolases are effective ecological indicators of soil microbial function. So far, little is known on halophilic bacterial contribution and function on a genomic viewpoint of Indian Sundarban Wetland. Considering the above mentioned issues, the aims of this study was to understand the life style, metabolic functionalities and genomic features of the isolated bacterium, Salinicoccus roseus strain RF1H. A comparative genome-based study of S. roseus has not been reported yet. Henceforth, we have considered the inclusion of the intra-species genome comparison of S. roseus to gain insight into the high degree of variation in the genome of strain RF1H among others.

RESULTS

Salinicoccus roseus strain RF1H is a pink-red pigmented, Gram-positive and non-motile cocci. The bacterium exhibited high salt tolerance (up to 15% NaCl), antibiotic resistance, biofilm formation and secretion of extracellular hydrolytic enzymes. The circular genome was approximately 2.62978 Mb in size, encoding 574 predicted genes with GC content 49.5%. Presence of genomic elements (prophages, transposable elements, CRISPR-Cas system) represented bacterial virulence and multidrug-resistance. Furthermore, genes associated with salt tolerance, temperature adaptation and DNA repair system were distributed in 17 genomic islands. Genes related to hydrocarbon degradation manifested metabolic capability of the bacterium for potential biotechnological applications. A comparative pangenome analysis revealed two-component response regulator, modified C4-dicarboxylate transport system and osmotic stress regulated ATP-binding proteins. Presence of genes encoding arginine decarboxylase (ADC) enzyme being involved in biofilm formation was reported from the genome. In silico study revealed the protein is thermostable and made up with ~ 415 amino acids, and hydrophilic in nature. Three motifs appeared to be evolutionary conserved in all Salinicoccus sequences.

CONCLUSION

The first report of whole genome analysis of Salinicoccus roseus strain RF1H provided information of metabolic functionalities, biofilm formation, resistance mechanism and adaptation strategies to thrive in climate-change induced vulnerable spot like Sundarban. Comparative genome analysis highlighted the unique genome content that contributed the strain's adaptability. The biomolecules produced during metabolism are important sources of compounds with potential beneficial applications in pharmaceuticals.

Persistence and spread of tetracycline resistance genes and microbial community variations in the soil of animal corrals in a semi-arid planted forest

At the spring, goat and sheep herds are transferred to planted forests, in a semi-arid region in the northern Negev Desert, Israel, to reduce herbaceous biomass and, fire risk. The herds are held overnight in corrals for about 4 months, enriching the soil with organic matter and nitrogen. This research examined the effect of these enrichments on soil bacterial community structure (BCS) and the abundance of tetracycline resistance genes (TRGs) in active and abandoned corrals (1-10-years-old). Based on 16S rRNA gene sequences, the Proteobacteria and Actinobacteria phyla dominated the soil of all corrals. The Actinobacteria were less abundant in the active and 1-year-old corrals (23-26%) than in the other corrals and the control (33-38%). A principal component analysis showed that, the BCS in the active and the 1-year-old abandoned corrals was significantly different from that in the older corrals and the control. The Firmicutes phylum constituted 28% of the BCS in the active corrals, 12.5% in the 1-year-old corrals and 2% in the older corrals and the control. In contrast, the Acidobacteria phylum was hardly detected in the active and 1-year-old abandoned corrals and constituted 10% of the BCS in the older corrals. Genes conferring resistance to tetracycline were detected in high numbers. The tetG and tetW genes were detected in the active and abandoned corrals (1-10 years). The tetQ gene was detected only in the active and 1-year-old abandoned corrals. None of the genes were detected in the control soil. The three genes were detected outside an active corral, in the downstream section of an ephemeral tributary. The results prove that abandoned and unobserved periodic animal corrals are an environmental reservoir for TRGs.

Salinicoccus cyprini sp. nov., isolated from the gut of mirror carp, Cyprinus carpio var. specularis

A novel orange to pink coloured bacterial strain designated as CT19^T was isolated from the gastrointestinal tract of mirror carp, Cyprinus carpio var. specularis (Lacepède, 1803) collected from the Gobind Sagar reservoir at village Lathiani, Una, Himachal Pradesh, India. Cells of the strain were found to be aerobic, Gram-stain-positive, non-motile and non-spore-forming coccoids. Based on the 16S rRNA gene sequence, the strain was closely related to Salinicoccus hispanicus J-82^T (=DSM 5352^T; 97.4 %), followed by S. sesuvii CC-SPL15-2^T (=DSM 23267^T; 96.4 %), S. amylolyticus JC304^T (=KCTC 33661^T; 95.6 %) and S. roseus DSM 5351^T (95.4 %). Identity with all other members of the genus were <94.5 %. The draft genome of strain CT19^T was assembled to 2.4 Mbp with a G+C content of 47.9 mol%. Average nucleotide identity and digital DNA-DNA hybridization values between strain CT19^T and S. hispanicus J-82^T were found to be 85.9 and 31.3% respectively which is far below the threshold for species delineation. Iso-C_15 : 0, anteiso-C_15 : 0, iso-C_17 : 0, C_16 : 0 and anteiso-C_17 : 0 were the major cellular fatty acids of strain CT19^T. Major polar lipids were diphosphatidylglycerol, phosphatidylgylcerol and an unidentified glycolipid. Respiratory quinone system was composed of menaquinone-6 and major cell wall amino acid was l-lysine. Based on phylogenomic, physiological and biochemical characteristics, strain CT19^T represents a novel species of the genus Salinicoccus for which the name Salinicoccus cyprini sp. nov. is proposed. The type strain is CT19^T (=KCTC 43022^T =CCM 8886^T=MCC 3834^T).

Fictibacillus aquaticus sp. nov., isolated from downstream river water

A Gram-stain-positive, facultatively anaerobic bacterial strain, GDSW-R2A3^T, was isolated from a downstream water sample collected from the river Ganges, India. Analysis of the 16S rRNA gene sequence of strain GDSW-R2A3^T revealed its affiliation to the family Bacillaceae. Further analysis using a polyphasic approach revealed that strain GDSW-R2A3^T was most closely related to the genus Fictibacillus. Analysis of the almost-complete (1488 bp) 16S rRNA gene sequence of strain GDSW-R2A3^T revealed the highest level of sequence similarity with Fictibacillus phosphorivorans CCM 8426^T (98.3 %) and Fictibacillus nanhaiensis KCTC 13712^T (98.3 %) followed by Fictibacillus barbaricus DSM 14730^T (98.0 %). The digital DNA-DNA hybridization and average nucleotide identity (ANI) values between strain GDSW-R2A3^T and the most closely related taxon, F. phosphorivorans CCM 8426^T, were 20.3 and 78.2 %, respectively. The DNA G+C content of the strain was 44.2 mol%. The cell-wall amino acid was meso-diaminopimelic acid. Polar lipids present were phosphatidylglycerol, phosphatidylethanolamine, diphosphatidylglycerol, three aminophospholipids, two phospholipids and one unidentified lipid; the major menaquinone was MK-7; iso-C14 : 0, iso-C15 : 0 and anteiso-C15 : 0 were the major fatty acids. On the basis of the phenotypic, chemotaxonomic and phylogenetic data, it can be concluded that strain GDSW-R2A3^T represents a novel species of the genus Fictibacillus, for which the name Fictibacillus aquaticus sp. nov. is proposed. The type strain is GDSW-R2A3^T (=VTCC-B-910015^T=CCM 8782^T).

Development of the first gene expression system for Salinicoccus strains with potential application in bioremediation of hypersaline wastewaters

Salinicoccus salsiraiae IM408 (=CGMCC13032) is a novel halophilic bacterium that we isolated from the saline soil of Da Gang Oilfield. It tolerates 60 g/l sodium chloride and up to 123 g/l (1.5 M) sodium acetate and has shown a potential application in bioremediation of wastewater with high salt and high chemical oxygen demand (COD). Two plasmids, pS408-1 and pS408-2, were identified in S. salsiraiae IM408, and the sequences and copy numbers of the plasmids were determined. Based on these plasmids, two shuttle vectors containing a replicon for Escherichia coli, ampicillin, and chloramphenicol resistance genes, as well as the replicon from pS408-1 or pS408-2, were constructed and named as pTCS101 and pTCS201, respectively. A suitable host strain, named S. salsiraiae PE01, was also developed from the wild-type by plasmid elimination. Using the plasmid pTCS101 as an expression vector, L-lactate dehydrogenase from Staphylococcus aureus was expressed successfully in S. salsiraiae PE01. This is the first gene expression system for the Salinicoccus genus. It has provided the potential for expression of desired proteins or for establishment of desired pathways in Salinicoccus strains, which would make these halophiles more advantageous in future biotechnological applications.

Halophiles: biology, adaptation, and their role in decontamination of hypersaline environments

The unique cellular enzymatic machinery of halophilic microbes allows them to thrive in extreme saline environments. That these microorganisms can prosper in hypersaline environments has been correlated with the elevated acidic amino acid content in their proteins, which increase the negative protein surface potential. Because these microorganisms effectively use hydrocarbons as their sole carbon and energy sources, they may prove to be valuable bioremediation agents for the treatment of saline effluents and hypersaline waters contaminated with toxic compounds that are resistant to degradation. This review highlights the various strategies adopted by halophiles to compensate for their saline surroundings and includes descriptions of recent studies that have used these microorganisms for bioremediation of environments contaminated by petroleum hydrocarbons. The known halotolerant dehalogenase-producing microbes, their dehalogenation mechanisms, and how their proteins are stabilized is also reviewed. In view of their robustness in saline environments, efforts to document their full potential regarding remediation of contaminated hypersaline ecosystems merits further exploration.