YOGESWARAN JAGADEESAN , RAHAMATHUNNISHA BASHEER AND BALAIAH ANANDARAJ
Abstract
Cyanobacteria exist under a variety of climatic, nutrients and physical conditions, and are likely to form blooms. This distinct group of bacteria is photosynthetic and produce several metabolites that include a number of endotoxins, of which are commonly found in mass occurrences of cyanobacteria, especially under eutrophic conditions. Microcystins (MCs) are well-studied cyanobacterial cyclic peptide hepatotoxins predominantly produced by Freshwater cyanobacteria, including species of Microcystis, Anabaena, Nostoc and Planktothrix. Potential chronic toxicity from MC led the WHO to establish a guideline value of 1 µgLâ1 as a maximum concentration of MC-LR in drinking water. Furthermore, MC-LR was classified as a possible human carcinogen (group 2B). However, only very less data on the occurrence of microbial degradation of MC are available in the world. In the present study, bacterial strain capable of degrading MC-LR was isolated from an eutrophic lake present in Kalugumalai, Thirunelveli district and the PCR based detection of the microcystin degrading genes was carried out. A total of 15 bacterial isolates from two different eutrophic lakes, only the isolate 14 showed the presence of the mlrA gene encoding for an enzyme microcystinase which is important in MC-LR biodegradation which was confirmed by the sequence based approach. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the new isolate belong to the Stenotrophomonas sp. and was designated as Stenotrophomonas maltophilia AR14 under GenBank accession number KC773842. The BLAST result shows 99% similarity with the Stenotrophomonas EMS strain which has mlrA gene. The amplified PCR product of mlrA gene was submitted for gene sequencing. The BLAST results shows, 93% similarity with Sphingomonas sp. ACM-3962 MlrA (mlrA) gene, partial cds (AF411068.2), 93% with Novosphingobium sp. THN1 mlr gene cluster, partial sequence (HQ664118.1) and 93% with Sphingomonas sp. ACM-3962 MlrC and MlrA genes, partial cds (DQ423533.1).