Ethidium bromide (EtBr) is a carcinogenic and mutagenic agent which is widely used in research laboratories to probe nucleic acids by gel electrophoresis. It is generally buried underground (for solid waste) or disposed of pouring it down the sink (in case of liquid waste). Soil or drain microbial community may be able to take care of such substance else it will lead to contamination of our underground resources or others through defined and undefined routes. In view of the above assumption and literature reports the present study was undertaken to isolate and evaluate bacteria for removal, by bioaccumulation and /or biotransformation, of EtBr from contaminated sources and wastes, before their disposal to the environment. Two distinct bacteria both motile BR3 and BR4 could be identified from agarose-gel-waste containing 0.5-1.0 g/ml ethidium bromide. Both bacteria were found to grow on EtBr-NA plate (Nutrient-Agar supplemented with EtBr at a concentration of 30 g/ml) however only BR3 isolate showed large non-fluorescent-halo zone (characteristic to degradation of EtBr) when exposed to trans-UV light. Other isolate BR4 could accumulate EtBr within the colony biomass but did not show clear (non-fluorescent) hallow zone around it. However the bacterium was not able to utilize the EtBr as a sole carbon source.

Microcystins (MCs) are toxic cyclic heptapeptides produced by few toxic cyanobacteria and generally form blooms in eutrophic surface fresh water bodies. They cause acute to chronic poisoning and other health related problems mainly by irreversible inhibition of protein phosphatases (PP1 and PP2A) and increased formation of reactive oxygen species (ROS). Due to limitation of non-biological methods of water treatments the exploration of MCs degrading bacteria is emerging at a quite pace to address, through bioremediation, the problems posed by MCs in water and water-bodies. Report and study of MCs biodegrading bacteria from India were lacking. However it was evident, from our previous study, that microcystin degradation can be achieved by indigenous microcystin degrading bacterial population in its natural place where microcystin producing blooms occur. This study has presented isolation and characterization of indigenous microcystin degrading bacteria from holy ponds in Utter Pradesh of India. Overall 20 bacterial isolates were isolated from Microcystis infested different ponds. Out of these 13 isolates were mlrA positive by PCR and were found to be distinct isolates by amplified ribosomal DNA restriction analysis (ARDRA). However, ARDRA analysis revealed overall four bacterial groups. On the basis of 16S-rRNA gene sequence the Gram-positive-rod isolate PM1 was identified, with 99% identity, as Bacillus licheniformis which was shown earlier to cluster with microcystin degrading bacterium B. subtilis. Thus the present study revealed, for the first time, probable microcystin degrading bacteria in water-bodies from India. The potential and the metabolic pathway of PM1 and other mlrA positive isolates need to be further studied and validated to confirm their application in microcystin bioremediation.

Ethidium bromide (EtBr) is widely used in most laboratories to detect nucleic acids in gel electrophoresis applications. It is a well-known carcinogenic and mutagenic agent, which can affect biotic components of the place in which it is disposed. Usually the gel-waste is either buried in the ground or incinerated, whereas the liquid waste is disposed of down the sink following the recommended methods of treatment. The recommended methods do not involve biological potential, but rather make use of chemicals, which may further deteriorate soil and water quality. The present study identifies and characterizes the EtBr-degrading bacterial isolates BR3 and BR4. A bibliographic review of the risk status of using these isolates for the treatment of lab waste in laboratory settings is also presented. BR3 was identified as Proteus terrae N5/687 (LN680103) and BR4 as Morganella morganii subsp. morganii ATCC 25830 (AJ301681) with 99.9% and 99.48% similarity, respectively, using an EzBioCloud microbial identifier. The literature revealed the bacterium Proteus terrae as a non-pathogenic and natural microflora of humans, but Morganella morganii as an opportunistic pathogen. These organisms belong to risk group II. Screening the sensitivity of these isolates to antibiotics revealed a sufficient number of antibiotics, which can be used to control them, if required. BR3 and BR4 exhibited resistance to individual antibiotics, ampicillin and vancomycin, whereas only BR3 was resistant to tetracycline. The current investigation, along with earlier reported work on these isolates, identifies BR3 as a useful isolate in the industrial application for the degradation of EtBr. Identical and related microorganisms, which are available in the culture collection repositories, can also be explored for such potential to formulate a microbial consortium for the bioremediation of ethidium bromide prior to its disposal.