Unwarranted accumulation of halogenated compounds in the rivers and streams has in recent years emerged due to the widespread use agricultural pesticides. The presence of these halogenated compounds in the water does not only suppress the immune system of fish but adversely induce serious morbidity and mortality among cultured stocks. Importantly, gradual accumulation of these compounds in the system of cultured and wild freshwater fish species cultured in ponds and floating net-cages in dams and rivers, respectively, poses some risks to humans, the end users. In this study, we attempted to isolate bacteria from the gut of pond-reared rohu <i>(Labeo rohita)</i> in Myanmar, screened the isolated bacteria for dehalogenase gene using molecular technique and tested the ability of these bacteria to degrade halogenated compounds in vitro. The eight bacterial strains studied were identified as <i>Enterobacter mori</i> strain MK- 121001, <i>Enterobacter cloacae</i> strains MK121003, MK-121004, MK121010, <i>Ralstonia solanacearum</i> strain 121002, <i>Acinetobacter baumannii</i> strain MK121007, <i>Chromobacterium violaceum</i> strain MK121009 and <i>Pantoea vagans</i> strain 121011. Only three bacterial strains (MK121002, MK121007 and MK121009) were capable of degrading 2,2-dichloropropionic acid (2,2-DCP) as the sole carbon source up to a final substrate concentration of 20 mM. Their mean growth doubling time ranging from 6-23 hours with the maximum of chloride ion released of 85%. PCR amplifica- tion with oligonucleotide primers designed from group I dehalogenase revealed the presence of deha- logenase genes in all isolates suggesting dehalogenase gene in strains 121001, 121003, 121004, 121010 and 121011 were silenced. In contrast, group II dehalogenase primers did not show any PCR amplification. These results suggest that MK121002, MK121007 and MK121009 only encode a group I dehalogenase and its non-stereoselectivity is in agreement with previoulsly described group I haloacid dehalogenase. The partial gene sequences were blasted but no significant sequence identity was observed. Therefore, it suggest the 2-haloacid dehalogenase of MK121002, MK12-1007 and MK121009 might be a novel group I 2-haloacid dehalogenase. The results indicated a broad distribution of dehalogenation genes in many micro- bial genomes that harbor dehalogenase(s) due to the exposure of the microorganisms to the naturally occurring or man-made halogenated compounds in the environmental systems. So far, microorganisms capable of producing dehalogenases were mainly isolated from soil and scarcely from aquatic animals and their environments. To the authors’ knowledge, this is the first report on the isolation of dehalogenase-producing bacteria from the gut of pond-reared freshwater fish, Labeo rohita, in Myanmar
Aims:The goal of the study is to isolate species of bacteria that capable of utilizing 2,2-dichloropropionic acid (2,2-DCP) as sole carbon source from soil sample collected from surrounding lake water located in Universiti Teknologi Malaysia, Skudai Johor. Methodology and Result: Genomic DNA from bacterium SE1 was extracted and PCR amplification was carried out using universal primers, Fd1 (5' -AGA GTT TGA TCC TGGCTC AG -3') and rP1 (5'-ACG GTC ATA CCT TGT TAC GAC TT -3') before sending for sequencing. The 16S rDNA nucleotide sequences were compared with Basic Local Alignment Search Tool nucleotide (BLASTn) and further analyzed using phylogenetic tree of Neighbour-Joining method (MEGA 5). Phylogenetic analysis indicated that SE1 strain clearly shared 97% homology to the genus of Serratia marcescens and therefore designated as Serratia marcescens sp. SE1. SE1 exhibited the ability to utilize 2,2-DCP as sole carbon source at 20 mM concentration with cell doubling time of 5 h and maximum chloride ion release of 38μmolCl-/ml. This result suggests that the dehalogenase enzyme present in the bacteria has high affinity towards the substrate. Based on morphological and partial biochemical characteristics, strain SE1 was a non-motile Gram-negative bacterium with red colonies,that gave a catalase positive reaction. Conclusion, significance and impact of study: A better understanding of dehalogenases enzyme produce by this Serratia marcescens sp. SE1 in general will be useful to be used as bioremediation tools for environmental management. This is the first reported case that Serratia sp. has the ability to degrade halogenated compound.
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