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Herein we report the isolation of a novel actinomycete, strain MCCB 268T, from the sediment sample collected from a high Arctic fjord Kongsfjorden. MCCB 268T showed greater than 97% 16S rRNA gene sequence similarity with those of Pseudonocardia konjuensis LM 157T (98.06%), Pseudonocardia soli NW8-21 (97.22%) Pseudonocardia endophytica YIM 56035 (97.08%) and Pseudonocardia nantongensis KLBMP 1282 (97.34%) showing that the strain should be assigned to the genus Pseudonocardia. DNA–DNA hybridization with Pseudonocardia konjuensis LM 157T showed only 41.5% relatedness to strain MCCB 268T. The whole genome of the strain MCCB 268T was sequenced. Whole-genome average nucleotide identity, dDDH (%) and genome tree analysis demonstrated that strain significantly differed from other Pseudonocardia species. The G + C content was 70.5 mol%. MCCB 268T exhibited in vitro cytotoxicity and through bioassay guided fractionation followed by HPLC separation a cytotoxic compound (I) was isolated. The compound (I) was identified as 1-acetyl-β-carboline through NMR spectra and high-resolution mass spectrometry. Compound (I) showed cytotoxicity against lung cancer cell line and mode of anticancer activity was found to be through the induction of apoptosis. Based on the genotypic and phenotypic features, MCCB 268T ought to be classified as a novel species under the genus Pseudonocardia for which the name Pseudonocardia cytotoxica sp. nov. is proposed (= CCUG72333T = JCM32718T).

The Southwest Indian Ridge (SWIR) is one of the least explored mid-ocean ridges and contains a high frequency of hydrothermal vents. We examined the bacterial community structure and metabolic potential of surface sediments collected from a sea mount at 2681 m depth and a ridge-flank at 3776 m in SWIR. High throughput 16S rRNA amplicon sequencing combined with Community Level Physiological Profiling (CLPP) revealed that hydrothermal sediments hosted a diverse microbial community with significant difference in structure and function between seamount and ridge-flank. The ridge-flank community was primarily comprised of facultative chemoautotrophic members of Burkholderiales (43.0%) while copiotrophic members of Alteromonadales (56.9%) and Oceanospirillales (14.6%) were dominant in seamount sample. These results coincided with CLPP of microbial community with higher utilization of carbohydrates such as D-cellobiose, β-methyl-D-glucoside, glucose 1-phosophate and pyruvic acid methyl ester observed in seamount. Culture-dependent approach using array of nutrient media enabled the isolation of heterotrophic genera that exhibited ability to degrade refractory organic matter such as phenanthrene, anthracene, pyrene, fluorene and fluoranthene. These results indicate that bacterial community present in the deep-sea hydrothermal sediment can act as bioreactor for mineralization of refractory organic matter. Thus our study emphasize on the significance of polyphasic approach in comprehensive and rapid assessment of physiological and taxonomic characteristics of the deep seabed bacterial community and further suggested that the bacterial community can act as ecological indicators of the metabolic sources prevalent in the ridge environment.

The bacterial reduction of mercury is one of the transformation processes where ionic form (Hg2+) converts into elemental form (Hg0). The biological reduction of mercury is facilitated by the mercuric reductase (merA) gene. The significance of understanding the role of microbial mercury reduction in the Arctic during the changing climate conditions is high as it acts as the sink as well as a source of mercury. The present study was carried out to assess the prevalence of mercury tolerant bacteria and to know the distribution of merA in the Arctic bacterial communities. Citrobacter freundii strain MM7, a psychrotrophic, gram-negative, facultative anaerobic, non-traditional sulphate-reducing bacterium, isolated from the sediments of Kongsfjorden showed tolerance to mercury up to 10.0 mg/L in vitro. Mercury removal experiment confirmed the removal of ∼80% of mercury mediated by plasmid-borne merA gene. Studies using Fourier transform infrared (FTIR) showed the metabolic changes incited by mercury, and the spectroscopic differences reflected that the functional groups like alkynes, aromatic phosphates, organic phosphates, methyl, methylene, and amide groups present in the bacterial surface owe a significant part in Hg biosorption and removal. The present study provides insights on the mercury resistance in an Arctic bacterial strain and suggests the potential application of Citrobacter freundii strain MM7 in the bioremediation of mercury from the natural environment.

The bacterial community composition of a valley glacier in Svalbard, its pro-glacial channels, and the associated downstream fjord ecosystem was investigated so as to figure out the degree to which downslope transport of microbes from the glacier systems along a hydrological continuum impose an effect on the patterns of diversity in the fjord system. A combination of culture based and high-throughput amplicon sequencing approach was followed which resulted in significant variation (R = 0.873, p = 0.001) in the bacterial community structure between these ecosystems. Dominance of sequences belonging to class β-Proteobacteria was seen in the glacier snow, ice and melt waters (MW) while a relatively higher abundance of OTUs belonging to α-Proteobacteria and Verrucomicrobiae demarcated the fjord waters. Similarity percentage (SIMPER) analysis of the Operational Taxonomic Units (OTUs) showed that OTU 1,105,280 (9.15%) and OTU 331 (6.5%) belonging to Burkholderiaceae (β-proteobacteria) and OTU 101,660 (5.76%) and OTU 520 (5.07%) belonging to Rhodobacteraceae (α-proteobacteria) contributed maximum to the overall dissimilarity between the sampling sites. The bacterial community from the MWs were found to be true signatures of the glacier ecosystem while the Kongsfjorden bacterial fraction mostly represented heterotrophic marine taxa influenced by warm Atlantic waters and presence of organic matter. Significant presence of unknown taxa in the MWs suggests the need to study such unexplored, transient niches for a better understanding of the associated microbial processes. Among the various environmental parameters measured, nutrients (NO3− and SiO42−) were found to exhibit strong association with the MW bacterial community while temperature, trace metals, Cl− and SO42− ions were found to influence the fjord bacterial community. The significant differences in the bacterial community composition between the glacier and the fjord ecosystem suggest the unique nature of these systems which in turn is influenced by the associated environmental parameters.

Bacterial production, respiration and metabolic diversity were measured up to 120 m depth in the Sub-Antarctic Front (SAF) and Polar Fronts I and II (PFI and PFII) of the Indian Ocean sector of the Southern Ocean during 2010 Austral Summer. Prokaryotic cell count was maximum at PFI and PFII (~109 cells L−1) and minimum at SAF (~107 cells L−1). Furthermore, integrated bacterial production was higher at PFI (1.07 mg C m−2 h−1) and PFII (0.72 mg C m−2 h−1) compared to SAF (0.61 mg C m−2 h−1). At PFII, integrated bacterial growth efficiency was higher (8.96) compared to PFI (7.42) and SAF (7.17), signifying that the net contribution of PFII to the microbial loop could be relatively pronounced. Enhanced cell numbers and production at polar fronts indicate that the dissolved organic matter could be converted to secondary biomass through the microbial loop. However, integrated bacterial respiration rate at PFII (0.83 mg C m−2 h−1) was lower than that at PFI (1.84 mg C m−2 h−1) resulting in higher growth efficiency at PFII. Metabolic flexibility at SAF was clearly brought about by utilization of carboxylic acids like D-malic acid and itaconic acid, and carbohydrates like N-acetyl D-glucosamine, D-cellobiose and D-lactose. Utilization of amino acids like glycyl L-glutamic acid and L-threonine, and an amine, phenylethylamine, was critical in determining the metabolic variability at PFI. PFII hosted microbes that utilized phenolic compounds (2-hydroxy benzoic acid and 4-hydroxy benzoic acid) and polymers (like Tween 80). Utilization of polyols over carbohydrates in polar waters indicates a niche with lesser influence of the Antarctic melt waters on the bacterioplankton metabolism.

This study addresses factors governing nitrification and denitrification rates, along with the abundance of the bacterial groups likely involved in these activities, in Kongsfjorden, an Arctic fjord at Ny-Alesund, Svalbard. The fjord was sampled three times during the month of March 2008 as day length and direct solar radiation increased. Although initially well mixed, cooler and more saline, the fjord became stratified, warmer and less saline during late March. The concentrations of NH4 + (4.4 ± 1.6 to 6 ± 1.6 μM) and NO2 − (1 ± 0.3 to 1.2 ± 0.4 μM) increased progressively with the decrease in NO3 − (6.1 ± 1.3 to 3.8 ± 1.5 μM), reflecting the onset of primary productivity. Nitrification rates and the culturable population of nitrifiers decreased significantly from 1.6 ± 0.9 to 0.4 ± 0.1 ng at NH4 +-N l−1 h−1 and 5.1 ± 0.3 × 102 to 29 ± 14 cells l−1, respectively. In contrast, denitrification rates increased (2.4 ± 0.5 to 4.6 ± 1.3 ng-at NO3 −-N l−1 h−1), although the abundance of culturable denitrifiers did not vary significantly. A significant correlation of nitrifiers with NO3 − during early March (p

The significance of freshwater systems in global manganese cycles is well appreciated. Yet, the polar systems, which encompass the largest freshwater repository in the world, have been least studied for their role in manganese cycling. Here, we present results from a study that was conducted in the brackish water lakes in the Larsemann Hills region (east Antarctica). The rate of in situ manganese oxidation ranged from 0.04 to 3.96 ppb day−1. These lakes harbor numerous manganese-oxidizing bacteria (105 to 106 CFU l−1), predominantly belonging to genera Shewanella, Pseudomonas and an unclassified genus in the family Oxalobacteriaceae. Experiments were conducted with representatives of predominant genera to understand their contribution to Mn cycling and also to assess their metabolic capabilities in the presence of this metal. In general, the total and respiring cell counts were stimulated to a maximum when the growth medium was amended with 10 mM manganese. The addition of manganese promoted the use of d-mannitol, maltose, etc., but inhibited the use of maltotriose, l-serine and glycyl l-glutamic acid. The bacterial isolates were able to catalyze both the redox reactions in manganese cycling. In vitro manganese oxidation rates ranged from 3 to 147 ppb day−1, while manganese reduction rates ranged from 35 to 213 ppb day−1. It was also observed that the maximum stimulation of manganese oxidation occurred in the presence of cobalt (81 ± 57 ppb day−1), rather than iron (37 ± 16 ppb day−1) and nickel (40 ± 47 ppb day−1). Our studies suggest that cobalt could have a more profound role in manganese oxidation, while nickel promoted manganese reduction in polar aquatic systems.

The phytoplankton pigment indices were used to characterize the spatial succession of the community composition in the frontal regions of the subtropical front (STF), sub-Antarctic front (SAF), and polar front (PF) in the Indian Ocean sector of the Southern Ocean during austral summer 2013. Diagnostic indices revealed that the flagellates were dominant in STF (51%) and progressively declined toward SAF (39%) and PF (11%). Similarly, the prokaryotes were highest in STF (43%) and decreased to SAF (32%) and PF (28%). In contrast, the diatoms were gradually increased from STF (6%) to SAF (29%) and PF (61%). The variability of flagellates and diatoms from the STF to PF is attributed to the variability of photosynthetically available radiation, sea surface temperature, and sea surface wind speed. The in-situ pigment indices were then compared to the NASA Ocean Biogeochemical model that shows the similar patterns of frontal community distribution except their magnitude. Similarly, the satellite retrieved phytoplankton biomass (chlorophyll a) was checked for its consistency after comparing with the in-situ observations and the result shows underestimation of satellite measured values. The result suggests that the conjunctive analysis of in-situ, satellite, and model archive is suitable to study the impact of climate variability on the structure of marine ecosystems.