Biodegradation of microcystin-LR using acclimatized bacteria isolated from different units of the drinking water treatment plant

Highlights: • Filtration unit bacterial community showed maximum MC-LR degradation of 97%. • Acclimatized bacteria (MC-LR enriched) increased degradation rate by over 52%. • Degraded samples showed toxicity level well below 2.5% v/v DMSO (using Bioassay). • Pseudomonas fragi and Chryseobacterium sp. were identified as the novel MC-LR degraders. Bacterial community isolated from different units of a Drinking Water Treatment Plant (DWTP) including pre-ozonation unit (POU), the effluent-sludge mixture of the sedimentation unit (ESSU) and top-sand layer water sample from the filtration unit (TSFU) were acclimatized separately in the microcystin-leucine arginine (MC-LR)-rich environment to evaluate MC-LR biodegradation. Maximum biodegradation efficiency of 97.2 ± 8.7% was achieved by the acclimatized-TSFU bacterial community followed by 72.1 ± 6.4% and 86.2 ± 7.3% by acclimatized-POU and acclimatized-ESSU bacterial community, respectively. Likewise, the non-acclimatized bacterial community showed similar biodegradation efficiency of 71.1 ± 7.37%, 86.7 ± 3.19% and 94.35 ± 10.63% for TSFU, ESSU and POU, respectively, when compared to the acclimatized ones. However, the biodegradation rate increased 1.5-folds for acclimatized versus non-acclimatized conditions. The mass spectrometry studies on MC-LR degradation depicted hydrolytic linearization of cyclic MC-LR along with the formation of small peptide fragments including Adda molecule that is linked to the reduced toxicity (qualitative toxicity analysis). This was further confirmed quantitatively by using Rhizobium meliloti as a bioindicator. The acclimatized-TSFU bacterial community comprised of novel MC-LR degrading strains, Chryseobacterium sp. and Pseudomonas fragi as confirmed by 16S rRNA sequencing.