Unusual Rise in Mercury-Resistant Bacteria in Coastal Environs

Abstract

A sharp rise in mercury-resistant bacteria (MRB) capable of tolerating very high concentration of Hg was observed over the last 3-4 years in the coastal environs of India. While none or negligible colony-forming units (CFU) of bacteria were counted on seawater nutrient agar with 0.5 ppm ( 2.5 microM) Hg (II) as HgCl2 until 1997, from 13 to over 75% of the CFU grew on 20 times higher, 50 microM, Hg concentrations from almost every recently examined marine sample. Although exceptionally high counts of MRB (96% of CFU) were recorded from samples collected from the polluted zones off Mumbai, the MRB capable of growth on seawater nutrient agar with 50 microM Hg were quite abundant in most samples collected from many locations with few or no pollution effects. We noticed for the first time the occurrence of aerobic heterotrophic bacterial isolates capable of growth with 250 microM Hg. Such MRB grew with higher concentrations of many other toxic xenobiotics than the Hg sensitive ones. Based on the unusually high populations of viable MRB and some simple experiments, we propose that many marine bacterial species are selected, possibly through acquisition of plasmids and/or transposable elements and modifying Hg, whose concentration, according to recent studies, is on the rise in marine habitats.

Effects of Deposition of Heavy-Metal-Polluted Harbor Mud on Microbial Diversity and Metal Resistance in Sandy Marine Sediments

“…In addition, the collection bacteria from IFD contained the lowest percentage of Cu-and Cd-sensitive bacteria. Elevated levels of metal-tolerant Bacteria in soils and sediments after exposure to heavy metals have been described previously (Diaz-Ravina and Baath 1996;Ramaiah and De 2003;Rasmussen and Soerensen 1998), but not in combination with detailed metal analyses indicating such localized and short-term metal exposure.…”

Abundance of sewage-pollution indicator and human pathogenic bacteria in a tropical estuarine complex

“…In order to quantify and understand their relationship with relevant environmental factors, several investigators have examined distribution of these groups of bacteria and certain viruses in coastal waters (Colwell et al 1977;Marchand 1986;Patti et al 1987;Piccolomini et al 1987;Ramaiah and Chandramohan 1993;Ruiz et al 2000;Ramaiah and De 2003). Mortality and survival rates of fecal contamination indicator Escherichia coli in the marine regimes have also been studied (Thom et al 1992;Darakas 2001).…”

Evaluation of mercury biotransformation by heavy metal-tolerant Alcaligenes strain isolated from industrial sludge

“…Till date, there is no data available for such high tolerance of mercury in aerobic bacteria. Frischmuth et al (1993) and Ramaiah and De (2003) reported several bacterial strains with tolerance up to 100 lg/g for mercuric chloride in solid and liquid medium.…”