Unveiling metabolic pathways involved in the extreme desiccation tolerance of an Atacama cyanobacterium

Role of exopolysaccharides of Anabaena sp. in desiccation tolerance and biodeterioration of ancient terracotta monuments of Bishnupur

Colonization of the cyanobacteria in the Bishnupur terracotta temples, one of the heritage sites of West Bengal, India is in an alarming state of deterioration now. Among the cyanobacteria Anabaena sp. (VBCCA 052002) has been isolated from most of the crust samples of terracotta monuments of Bishnupur. The identification was done using micromorphological characters and confirmed by 16S rRNA gene sequencing. The isolated strain produces enormous exopolysaccharides, which are extracted, hydrolyzed, and analyzed by HPLC. We have studied desiccation tolerance in this cyanobacterium and found biosynthesis of trehalose with an increase in durations of desiccation. The in vitro experiment shows that Chlorophyll-a and carotenoid content increase with fourteen days of desiccation, and cellular carbohydrates increase continuously. However, cellular protein decreases with desiccation. To gain insights into the survival strategies and biodeterioration mechanisms of Anabaena sp. in the desiccated conditions of the Bishnupur monuments, the present study focuses on the physiological aspects of the cyanobacteria under controlled in vitro conditions. Our study indicates that in desiccation conditions, trehalose biosynthesis takes place in Anabaena sp. As a result of the excessive sugar and polysaccharide produced, it adheres to the surface of the terracotta structure. The continuous contraction and expansion of these polysaccharides contribute to the biodeterioration of these monuments.

Geology defines microbiome structure and composition in nunataks and valleys of the Sør Rondane Mountains, East Antarctica

Understanding the relation between terrestrial microorganisms and edaphic factors in the Antarctic can provide insights into their potential response to environmental changes. Here we examined the composition of bacterial and micro-eukaryotic communities using amplicon sequencing of rRNA genes in 105 soil samples from the Sør Rondane Mountains (East Antarctica), differing in bedrock or substrate type and associated physicochemical conditions. Although the two most widespread taxa (Acidobacteriota and Chlorophyta) were relatively abundant in each sample, multivariate analysis and co-occurrence networks revealed pronounced differences in community structure depending on substrate type. In moraine substrates, Actinomycetota and Cercozoa were the most abundant bacterial and eukaryotic phyla, whereas on gneiss, granite and marble substrates, Cyanobacteriota and Metazoa were the dominant bacterial and eukaryotic taxa. However, at lower taxonomic level, a distinct differentiation was observed within the Cyanobacteriota phylum depending on substrate type, with granite being dominated by the Nostocaceae family and marble by the Chroococcidiopsaceae family. Surprisingly, metazoans were relatively abundant according to the 18S rRNA dataset, even in samples from the most arid sites, such as moraines in Austkampane and Widerøefjellet ("Dry Valley"). Overall, our study shows that different substrate types support distinct microbial communities, and that mineral soil diversity is a major determinant of terrestrial microbial diversity in inland Antarctic nunataks and valleys.