UV-B Halotolerant Bacteria from Marakkanam Saltpan and Biology of UV-B Tolerant Pontibacillus salipaludis Based on Whole Genome Sequencing

Abstract

Saltpans in South India experience intense sunlight and ultraviolet radiation (UV). Therefore, it was hypothesized that halophilic bacteria living there could tolerate UV radiation. To test this, sediment and water samples from the Marakkanam Saltpan were collected and exposed to an artificial UV-B lamp. After irradiation, an aliquot of the sample was spread on nutrient agar (prepared in sterilized source water), and two bacterial strains were obtained, named SBO and SBY. Based on 16S rRNA gene phylogeny, these strains were identified as Bacillus sp. and Pontibacillus salipaludis, respectively. Another aliquot of the UV-B-exposed sample was inoculated into the nutrient broth (in sterilized source water), and incubated for a week in the dark. Later, it was subjected to Illumina MiSeq-based sequencing for the V3-V4 region (16S rRNA gene). Results revealed the presence of 13 bacterial phyla. However, the phylum Bacillota (48.59%) and Pseudomonadota (27.36%) accounted for more than 75% of the diversity. Pontibacillus was the most abundant genus, accounting for 44% of total bacterial diversity. The whole genome of P. salipaludis was sequenced on Illumina HiSeqX to decipher possible genes and pathways involved in UV-B tolerance. The genome size was estimated to be 4.05 MB, with a mean G + C content of 40.82%. RASTtk-based genome annotation revealed 4217 coding sequences and 78 RNAs. Related to the UV-B tolerance, sixteen genes involved in carotenoid and prodigiosin biosynthetic pathways were found. antiSMASH showed the presence of terpene-type carotenoids. More than sixty genes involved in various DNA repair pathways were found.