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.

Microbiome of seventh-century old Parsurameswara stone monument of India and role of desiccation-tolerant cyanobacterium Lyngbya corticicola on its biodeterioration.

The Parsurameswara stone monument, built in the seventh century, is one of the oldest stone monuments in Odisha, India. Metagenomic analysis of the biological crust samples collected from the stone monument revealed 17 phyla in the microbiome, with Proteobacteria being the most dominant phylum, followed by cyanobacteria. Eight cyanobacteria were isolated. Lyngbya corticicola was the dominant cyanobacterium in all crust samples and could tolerate six months of desiccation in vitro. With six months of desiccation, chlorophyll-a decreased; however, carotenoid and cellular carbohydrate contents of this organism increased in the desiccated state. Resistance to desiccation, high carotenoid content, and effective trehalose biosynthesis in this cyanobacterium provide a distinct advantage over other microbiomes. Comparative metabolic profiles of the biological crust and L. corticicola show strongly corrosive organic acids such as dichloroacetic acid, which might be responsible for the biocorrosion of stone monuments.

Mycosporine-alanine, an oxo-mycosporine, protect Hassallia byssoidea from high UV and solar irradiation on the stone monument of Konark.

Mycosporine-like amino acids (MAAs) are small natural molecules having potent UV-absorbing and antioxidant properties. Hassallia byssoidea is one dominant cyanobacterium found all over the Konark stone monument, a UNESCO World Heritage site. We characterized mycosporine-alanine for the first time from H. byssoidea and studied its biosynthetic pathway from the whole genome data. We found D-alanyl-D-alanine carboxypeptidase, which might convert mycosporine-glycine to mycosporine-alanine by replacing glycine with alanine or by separate methylation, the mycosporine-glycine is converted to mycosporine-alanine. Our in vitro UV-B exposure experiment and exposure of H. byssoidea to natural sunlight show an increase in biosynthesis of mycosporine-alanine with 12 h of UV-B irradiation and high natural sunlight. We also found mycosporine-alanine to have good free radical scavenging activity with an IC50 value of 1.98 mg/ml. Our results show due to the presence of mycosporine-alanine H. byssoidea probably tolerate the UV and high solar radiation and continue to colonize on the Konark stone monument as a dominant cyanobacterium.

Salinity induced synthesis of UV-screening compound scytonemin in the cyanobacterium Lyngbya aestuarii.

Lyngbya aestuarii is the dominant cyanobacterium in Chilika lagoon occurring in all the seasons irrespective of variation in the salinity regime ranging from 3 to 28 ppt. The organism possess the UV screening scytonemin pigment, which was maximum when grown at 56 ppt salinity. Three different forms of scytonemin were detected in L. aestuarii with retention time (RT) 1.76, 2.42 and 2.94 min, however, occurrence of these forms was influenced by the salinity. Scytonemin with RT 2.42 was sensitive to higher salinity and its maximum concentration was obtained at 28 ppt salinity correlated with the highest salinity level of Chilika. Formation of multilayer colored sheath around the trichome was prominently observed at the salinity of the culture from 28 to 56 ppt. But at salinity below 7 ppt and also at more than 56 ppt salinity degradation of sheath with corresponding decrease in scytonemin was observed.

Adaptation strategies of the sheathed cyanobacterium Lyngbya majuscula to ultraviolet-B.

Lyngbya majuscula is a dominant organism in the east coast of India forming characteristic mat in dried saline soils simultaneously exposed to solar radiation of the tropics. Studies on the growth response, changes in the spectral properties of the methanolic extract and protein profile of this estuarine sheathed cyanobacterium to UV-B revealed existence of effective adaptation mechanism to withstand prolonged UV-B radiation. Carotenoids along with MAAs of the organism was increased with increase in UV irradiation. Increase in thickness of the mucilaginous sheath layer as well as cellular carbohydrate content was observed upon exposure to prolonged UV-B dose. Induction of 21 and 33 kDa low molecular weight proteins, and a 99 kDa protein together with formation of distinct multilayered sheath embedding trichomes with granulated cells were the adaptive features of the organism to cope with UV-B stress. The organism was considerably revived after incubating the irradiated cells in mineral medium under florescent light and in the dark suggesting existence of photoreactivation and dark repair in this cyanobacterium. However more experiments are needed to establish the existence of photoreactivation and dark repair mechanism in the studied cyanobacterium.