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Himalayan glaciers are receding at an exceptional rate, perturbing the local biome and ecosystem processes. Understanding the microbial ecology of an exclusively microbe-driven biome provides insights into their contributions to the ecosystem functioning through biogeochemical fluxes. Here, we investigated the bacterial communities and their functional potential in the retreating East Rathong Glacier (ERG) of Sikkim Himalaya. Amplicon-based taxonomic classification revealed the dominance of the phyla Proteobacteria, Bacteroidota, and candidate Patescibacteria in the glacial sites. Further, eight good-quality metagenome-assembled genomes (MAGs) of Proteobacteria, Patescibacteria, Acidobacteriota, and Choloflexota retrieved from the metagenomes elucidated the microbial contributions to nutrient cycling. The ERG MAGs showed aerobic respiration as a primary metabolic feature, accompanied by carbon fixation and complex carbon degradation potentials. Pathways for nitrogen metabolism, chiefly dissimilatory nitrate reduction and denitrification, and a complete sulphur oxidation enzyme complex for sulphur metabolism were identified in the MAGs. We observed that DNA repair and oxidative stress response genes complemented with osmotic and periplasmic stress and protein chaperones were vital for adaptation against the intense radiation and stress conditions of the extreme Himalayan niche. Current findings elucidate the microbiome and associated functional potentials of a vulnerable glacier, emphasizing their significant ecological roles in a changing glacial ecosystem. [ABSTRACT FROM AUTHOR]

The melting of glaciers due to global warming leads to the formation of proglacial water bodies such as streams and lakes in their downstream environment. Triloknath glacier in the North-Western Himalayas has retreated unprecedently at a rate of 180 m /decade, forming similar water bodies. Glacier meltwater is considered the primary source of microbial diversity in downstream water bodies. Documentation of such diversity is crucial to retrieve the specialized microbial population because of the shift in the aquatic system due to deglaciation. In the current study, bacterial community structure based on V3-V4 region amplicons of 16S rRNA gene of two proglacial lakes and the glacial stream of Triloknath glacier was compared. Proglacial lake I site represents the ice-contacted proglacial lake while the proglacial lake II represents an ice-distal proglacial lake generally said to be evolved from the former. Proteobacteria was the most abundant phylum across the three sites. The prevalence of Proteobacteria in the proglacial lake I, proglacial lake II and glacial stream was 43.58%, 49.91%, and 40.08%, respectively. The highest species richness based on Chao I index (656) was observed in glacial stream while, the highest species diversity based on the Shannon index (8.95) was observed in proglacial lake I. The physiochemical conditions of glacial stream and proglacial lake II were closer than the lake I. These findings were corroborated with microbial diversity results as beta diversity analysis based on the Bray-curtis matrix indicated the closeness of glacier stream and proglacial lake II ecosystem and these sites also shared maximum bacterial genera.16S rRNA gene-based functional analysis showed the occurrence of xenobiotics degrading genes exposing the presence of pollutants in glacier ecosystem. The current study generated baseline information about the change in bacterial diversity due to deglaciation and hydrological connectivity of downstream water bodies with the glacier. The study documented residential microbial population of sensitive ecological niche of proglacial water bodies of Triloknath glacier ecosystem. • Bacterial community study of proglacial water bodies of Triloknath glacier ecosystem • Shift in bacterial community due to deglaciation and altered hydrological connectivity • Occurrence of xenobiotic degrading genes exposed presence of pollutants in glacier ecosystem. [ABSTRACT FROM AUTHOR]

[Display omitted] • Potentially novel species of Mucilaginibacter was isolated from the proglacial site. • Production of exopolysaccharide was statistically optimized yielding 26.4 mg/mL EPS. • Structural analysis of EPS revealed linear polysaccharide with glucose. • EPS showed cryoprotective activity and metal ion biosorption activity. • First report of EPS production and characterization from the genus Mucilaginibacter. Mucilaginibacter sp. is known as an exopolysaccharide (EPS) producer. In this study, a potentially novel species of genus Mucilaginibacter was used to extract EPS. Statistical optimisation by Response surface methodology produced 26.4 mg/mL EPS at 20℃, pH 7.4 using 47 mg carbon source/mL. The molecular weight of the extracted EPS was 3045.09 Da as determined by MADI-TOF/TOF-MS. Structural characterisation by monosaccharide composition, methylation, Fourier-transform infrared spectroscopy, and Nuclear magnetic resonance analysis revealed that the EPS was a linear polysaccharide with the sugar backbone of α-D-Glciv(1→4)α-D-Glciii(1→3)β-D-Glcii(1→6)α-D-Glci. The extracted EPS provided 97.91 % viability to mesophilic Escherichia coli under freezing conditions (-80℃) for up to 7 days. Additionally, extracted EPS showed metal ion biosorption ability for Cu2+ (8.36 mg/g), Fe2+ (4.47 mg/g), Mn2+ (0.12 mg/g), and Zn2+ (0.103 mg/g). Owing to these properties, the extracted EPS can be explored for its application as a cryoprotective agent and as a medium to remove toxic metal ions. To the best of our knowledge, this is the first report on the extraction and characterisation of EPS from the genus Mucilaginibacter. [ABSTRACT FROM AUTHOR]

We report the complete genome sequence of Arthrobacter sp. ERGS1:01, a novel bacterium which produces industrial enzymes at low temperature. East Rathong glacier in Sikkim Himalayas is untouched and unexplored for microbial diversity though it has a rich source of glaciers, alpine and meadows. Genome sequence has provided the basis for understanding its adaptation under harsh condition of Himalayan glacier, its ability to produce cold active industrial enzymes and has unlocked opportunities for microbial bioprospection from East Rathong glacier. [ABSTRACT FROM AUTHOR]

• First complete genome of a prodigiosin-producing Janthinobacterium sp. • Potentially novel species based on phylogenomic analysis and genome indices. • Upregulated cold stress-responsive genes highlighted cold-adaptation in ERMR3:09. • Genome analysis revealed unique genes and gene cluster for prodigiosin biosynthesis. • Extracted pigment can find application as a natural antioxidant agent. Janthinobacterium from cold niches has been studied broadly for bioactive violacein production. However, reports on the atypical red-pigmented Janthinobacterium strains are shallow. The bioactive red prodigiosin pigment has immense pharmacological significance, including antioxidant, antimicrobial and anticancer potential. Here, we report the first complete genome of a prodigiosin-producing Janthinobacterium sp. ERMR3:09 from Sikkim Himalaya in an attempt to elucidate its cold adaptation and prodigiosin biosynthesis. Nanopore sequencing and Flye assembly of the ERMR3:09 genome resulted in a single contig of 6,262,330 bp size and 62.26% GC content. Phylogenomic analysis and genome indices indicate that ERMR3:09 is a potentially novel species of the genus Janthinobacterium. The multicopy cold-responsive genes and gene upregulation under cold stress denoted its cold adaptation mechanisms. Genome analysis identified the unique genes, gene cluster and pathway for prodigiosin biosynthesis in ERMR3:09. Considering the notable antioxidant activity, it can be the next powerhouse of bioactive prodigiosin production. [ABSTRACT FROM AUTHOR]

• Microbes at sites near glacier terminus are richer and diverse than sites away. • Sites near glacier terminus are rich in autotrophic and chemolithotrophic microbes. • Sites away from the glacier terminus are abundant in heterotrophic microbes. Climate change has caused an unimaginable upsurge in glacier retreats. The melted ice exposes bare areas offering sites for new ecosystem development where primary microbial succession initiates the build-up of organic mass for plant colonisation. Chhota Shigri glacier is one such glacier that has retreated immensely and provides an ideal site for microbial succession studies. Here, we studied the shift in microbial communities and their functional traits along the glacier forefield from bare glacier snout to mature vegetated foreland through amplicon and whole metagenome sequencing approaches. The forefield sites closer to the glacier snout were abundant in the microbial phyla, such as Patescibacteria, Gemmatimonadota, Proteobacteria, Bacteroidota, Chloroflexi, Cyanobacteria, Verrucomicrobiota and Myxococcota that have potential in carbon (C), nitrogen (N), and sulphur (S) cycling. The sites away from glacier snout were abundant in the phyla Actinobacteria and Acidobacteriota, which are heterotrophic and help in organic carbon recycling. The microbes at the sites closer to the glacier terminus were richer and more diverse than those away from the terminus. The abundance and diversity of the microbes were primarily affected by the local soil's temperature, followed by pH and elements concentration (Calcium (Ca), Phosphorous (P), Potassium (K), Iron (Fe), Copper (Cu), Zinc (Zn), Lead (Pb)). Moreover, the whole-genome metagenome study revealed the prevalence of genes associated with N, C and S cycling. Additionally, the microbes and genes involved in xenobiotics compounds (Aminobenzoate, Benzoate, Caprolactam) degradation are also observed in the forefield soils. This study pointed out microbial successional gradients, the effect of local environmental factors in driving microbial succession and the role of glacier microbes in nutrients cycling and xenobiotics degradation along glacier forefield, helping our understanding of microbial succession and functional roles played by the microbes at nutrient-poor glacial soil. [ABSTRACT FROM AUTHOR]

Himalayan niches provide unprecedented opportunities for finding novel microbes of commercial importance. The present study investigated the genome sequence of Glaciimonas sp. PCH181 isolated from the glacial stream of Indian trans-Himalaya. The draft genome sequence has six contigs with 5.3 Mb size, 51.1% G + C content, and possesses 4876 genes. Phylogenomic analysis revealed PCH181 as a putative novel bacterium in the genus Glaciimonas. Genomic insight showed Glaciimonas sp. PCH181 enriched with genes for diverse physiology, cold/stress adaptation, and industrial potential. The presence of genes for CO 2 fixation and hydrogen metabolism suggested for chemolithoautotrophy. However, genes for sugars and organic acids usage showed heterotrophy and validated by physiological experiments. Genes for the metabolism of phenol (up to 500 ppm) and biosynthesis of polyhydroxyalkanoate (25% of dry cell mass) were also verified. Collectively, we present the first whole genome sequencing in the genus Glaciimonas , a taxonomically, physiologically, and industrially noteworthy bacterium. • First genome sequencing report in the genus Glaciimonas isolated from Himalayan glacier. • Genomic insights revealed Glaciimonas sp. PCH181 taxonomically, physiologically, and industrially noteworthy bacterium. • Genes encoding enzymes for phenol degradation and polyhydroxyalkanoates biosynthesis were identified in the genome. • Glaciimonas sp. PCH181 metabolizes diverse carbon sources, synthesize polyhydroxybutyrate and degrade phenol. [ABSTRACT FROM AUTHOR]

Commercial biofertilizers tend to be ineffective in cold mountainous regions due to reduced metabolic activity of the microbial inoculants under low temperatures. Cold-adapted glacier bacteria with plant growth-promoting (PGP) properties may prove significant in developing cold-active biofertilizers for improving mountain agriculture. With this perspective, the cultivable bacterial diversity was documented from the East Rathong glacier ecosystem lying above 3900 masl of Sikkim Himalaya. A total of 120 bacterial isolates affiliated to Gammaproteobacteria (53.33%), Bacteroidetes (16.66%), Actinobacteria (15.83%), Betaproteobacteria (6.66%), Alphaproteobacteria (4.16%), and Firmicutes (3.33%) were recovered. Fifty-two isolates showed many in vitro PGP activities of phosphate solubilization (9–100 µg/mL), siderophore production (0.3–100 psu) and phytohormone indole acetic acid production (0.3–139 µg/mL) at 10 °C. Plant-based bioassays revealed an enhancement of shoot length by 21%, 22%, and 13% in ERGS5:01, ERMR1:04, and ERMR1:05, and root length by 14%, 17%, 11%, and 22% in ERGS4:06, ERGS5:01, ERMR1:04, and ERMR1:05 treated seeds respectively. An increased shoot dry weight of 4–29% in ERMR1:05 and ERMR1:04, and root dry weight of 42–98% was found in all the treatments. Genome analysis of four bacteria from diverse genera predicted many genes involved in the bacterial PGP activity. Comparative genome study highlighted the presence of PGP-associated unique genes for glucose dehydrogenase, siderophore receptor, tryptophan synthase, phosphate metabolism (phoH, P, Q, R, U), nitrate and nitrite reductase, TonB-dependent receptor, spermidine/putrescine ABC transporter etc. in the representative bacteria. The expression levels of seven cold stress-responsive genes in the cold-adapted bacterium ERGS4:06 using real-time quantitative PCR (RT-qPCR) showed an upregulation of all these genes by 6–17% at 10 °C, and by 3–33% during cold-shock, which indicates the cold adaptation strategy of the bacterium. Overall, this study signifies the psychrotrophic bacterial diversity from an extreme glacier environment as a potential tool for improving plant growth under cold environmental stress. [ABSTRACT FROM AUTHOR]