Structure and Species Composition of Mercury-Reducing Biofilms

Abstract

Mercury-reducing biofilms from packed-bed bioreactors treating nonsterile industrial effluents were shown to consist of a monolayer of bacteria by scanning electron microscopy. Droplets of several micrometers in diameter which accumulated outside of the bacterial cells were identified as elemental mercury by electrondispersive X-ray analysis. The monospecies biofilms of Pseudomonas putida Spi3 initially present were invaded by additional strains, which were identified to the species level by thermogradient gel electrophoresis (TGGE) and 16S rDNA sequencing. TGGE community fingerprints of the biofilms showed that they were composed of the effluent bacteria and did not contain uncultivable microorganisms. Of the 13 effluent bacterial strains, 2 were not mercury resistant, while all the others had resistance levels similar to or higher than the inoculant strain.

Spatially Oscillating Activity and Microbial Succession of Mercury-Reducing Biofilms in a Technical-Scale Bioremediation System

“…The metallic mercury is retained in the matrix of the bioreactor in the form of mercury droplets (3,30). This energy-dependent reaction is an ancient and ubiquitous mechanism of bacteria to detoxify their surrounding environment (11,16,18,24).…”

“…Mercury-reducing bioreactors operated with nonsterile chloralkali wastewater have been shown to be colonized by invading mercury-resistant bacteria, and they exhibited increased microbial diversity and stable performance (7,28,30). To better understand the structure and activity of microbial communities in response to an invasion of Hg(II)-resistant or Hg(II)-sensitive bacteria and in response to the selection pressure of the pollutant, the culture-independent 16S-23S ribosomal DNA intergenic spacer polymorphism analysis (RISA) was applied to examine the bacterial community on the strain level.…”

Microbial Characterization of Mercury-Reducing Mixed Cultures Enriched with Different Carbon Sources

“…The biological mercury reduction mechanism has been applied for the detoxification of mercury-contaminated wastewater (6,31,32) and drinking water (19). The reduced form of mercury can then be removed by stripping into the gaseous phase and subsequent adsorption (8).…”

“…Mercury is the most toxic heavy metal, with no associated biological function (31). Mercury pollution arises from sources such as the chlor-alkali industry, coal burning and gold mining, and is one of the most frequently found heavy metals in industrial wastewater (11).…”

“…The reduced form of mercury can then be removed by stripping into the gaseous phase and subsequent adsorption (8). These studies have generally employed pure cultures (30,31), although mixed cultures are advantageous in wastewater treatment due to the difficulty in maintaining aseptic conditions. Biological mercury reduction requires an external carbon source to industrial wastewater in order to promote bacterial growth.…”