Study of mercury (II) chloride tolerant bacterial isolates from Baghmati River with estimation of plasmid size and growth variation for the high mercury (II) resistant Enterobacter spp.

A total of three mercury resistant belonging to genus Enterobacter, Streptococcus and Pseudomonas were isolated from river banks of Baghmati in Kathmandu and were further categorized on the basis of their tolerance to mercury (II) chloride. Among all these isolates Enterobacter strain expressed highest degree of resistance towards Hg (II) chloride showing distinct growth in medium with upto 80 μg/ml of HgCl2 . Excessive slime production along with delayed pattern of growth and lower viability was observed for the isolate under increasing concentrations of Hg (II) supplemented liquid culture medium. Upon investigating total genetic content of this isolate, occurrence of plasmid with approximate 18 kb size and susceptible to mercuric chloride after plasmid curing suggests a plasmid mediated tolerance.