Phenotypic plasticity in Bacillus cereus strains isolated from various Antarctic habitats

We studied five strains of psychrotolerant Bacillus cereus (B. cereus) isolated from Antarctic snow (BCsn), ice (BCic), lake water (BCwr), sediment (BCsd), and soil (BCsl) samples in terms of their growth, biochemical properties, and heat shock responses. Analyses of growth kinetics at 4℃ showed that BCsn had the fastest generation time (16.1 h), whereas BCwr had the slowest (30.8 h). Strain BCsd formed the largest zone of lipid hydrolysis (18 mm) whereas BCsn formed the smallest zone (3 mm).Only BCsd produced gelatinase. These physiological differences illustrate adaptations of B. cereus isolates to different niches. Strains BCsl and BCwr were resistant to all 12 of the antibiotics tested. Strains BCsn, BCic, and BCsd were resistant to cell wall synthesis inhibitors (penicillin and ampicillin) and susceptible to protein synthesis inhibitors (tetracycline and streptomycin). A carbon-substrate utilization assay revealed that BCsn, BCic, and BCwr could specifically utilize D-glucose-6-phosphate, salicin, and 2’-deoxyadenosine, respectively, indicating a degree of metabolic diversity among these Antarctic B. cereus strains. An analysis of heat shock proteins (HSPs) produced in response to a 60℃ heat treatment revealed significant variations in the amounts of HSP33 (p = 0.01, df = 4), HSP44 (p = 0.003, df = 4), and HSP60 (p = 0.04, df = 4) among the strains. This emphasizes the importance of HSPs in bacterial taxonomy. These results show that there are considerable adaptive variations among B. cereus strains from extremophilic environments. This could be significant in evaluating the taxonomy and evolution of this species

Editorial: Digitizing frozen earth—revealing microbial diversity and physiology in the cryobiosphere through “omics” tools, volume II

We thank Sentinel North (CFREF) and ArcticNet (NCE) for funding support for the T-MOSAiC workshop. Natural Sciences and Engineering Research Council of Canada (NSERC, #RGPIN-2020-06874). DV and SC were supported by CAMUAM funds (ref.: SI3-PJI-2021-00461

A characteristic study of humic acids isolated from Arctic fjord sediments

Humic substances are ubiquitous natural materials found in sediments as a product of biochemical transformation reactions representing a significant proportion of organic carbon cycle on earth. This study involves the analysis of humic substances with special emphasis on humic acids (HAs) in sediments collected from the Kongsfjorden System of Arctic region in June, 2017. The characterization of the isolated HAs were done using various spectroscopic techniques viz. UV-visible, Fluorescence, FTIR and NMR. Isolated HAs were also undergone for elemental analysis along with other characterization. The UV spectral analysis results with a lower E4/E6 ratio suggesting the presence of HAs with high degree of aromaticity and condensation. Indications for the presence of hydroxyl, methyl, methylene, carbonyl, carboxyl, phenol, alcohol and amide groups were obtained from the FTIR spectrums of HAs. NMR spectral characteristics also confirm the presence of OH group as well as the presence of CH protons adjacent to C=X, were X can be any electronegative element. This also confirms the presence of carbonyl group which is also evident in the FTIR spectral studies. Presence of aliphatic regions slightly more dominated with long chain and/or alicyclic moieties rather than methyl groups was also inferred from the results of NMR

Spatially resolved assembly, connectivity and structure of particle-associated and free-living bacterial communities in a high Arctic fjord

ABSTRACTThe assembly processes that underlie the composition and connectivity of free-living (FL) and particle-associated (PA) bacterial communities from surface to deep waters remain little understood. Here, using phylogenetic null modeling, we quantify the relative influence of selective and stochastic mechanisms that assemble FL and PA bacterial communities throughout the water column in a high Arctic fjord. We demonstrate that assembly processes acting on FL and PA bacterial communities are similar in surface waters, but become increasingly distinct in deep waters. As depth increases, the relative influence of homogeneous selection increases for FL but decreases for PA communities. In addition, dispersal limitation and variable selection increase with depth for PA, but not for FL communities, indicating increased residence time of taxa on particles and less frequent decolonization. As a consequence, beta diversity of PA communities is greater in bottom than in surface waters. The limited connectivity between these communities with increasing depth leads to highly distinct FL and PA bacterial communities in bottom waters. Finally, depth-related trends for FL and PA beta diversity and connectivity in this study are consistent with previous observations in the open ocean, suggesting that assembly processes for FL and PA bacterial communities may also be distinct in other aquatic environments.</jats:p