Functional profiling of mercuric reductase (<it>mer </it>A) genes in biofilm communities of a technical scale biocatalyzer

• Main Authors: von Canstein Harald, Pauling Björg V, Fehr Wanda, Felske Andreas DM, Wagner-Döbler Irene
• Format: Article
• Language: English
• Published: BMC 2003-10-01
• Series: BMC Microbiology
• Online Access: http://www.biomedcentral.com/1471-2180/3/22

<p>Abstract</p> <p>Background</p> <p>Bacterial mercury resistance is based on enzymatic reduction of ionic mercury to elemental mercury and has recently been demonstrated to be applicable for industrial wastewater clean-up. The long-term monitoring of such biocatalyser systems requires a cultivation independent functional community profiling method targeting the key enzyme of the process, the <it>merA </it>gene coding for the mercuric reductase. We report on the development of a profiling method for <it>merA </it>and its application to monitor changes in the functional diversity of the biofilm community of a technical scale biocatalyzer over 8 months of on-site operation.</p> <p>Results</p> <p>Based on an alignment of 30 <it>merA </it>sequences from Gram negative bacteria, conserved primers were designed for amplification of <it>merA </it>fragments with an optimized PCR protocol. The resulting amplicons of approximately 280 bp were separated by thermogradient gelelectrophoresis (TGGE), resulting in strain specific fingerprints for mercury resistant Gram negative isolates with different <it>merA </it>sequences. The <it>merA </it>profiling of the biofilm community from a technical biocatalyzer showed persistence of some and loss of other inoculum strains as well as the appearance of new bands, resulting in an overall increase of the functional diversity of the biofilm community. One predominant new band of the <it>merA </it>community profile was also detected in a biocatalyzer effluent isolate, which was identified as <it>Pseudomonas aeruginosa</it>. The isolated strain showed lower mercury reduction rates in liquid culture than the inoculum strains but was apparently highly competitive in the biofilm environment of the biocatalyzer where moderate mercury levels were prevailing.</p> <p>Conclusions</p> <p>The <it>merA </it>profiling technique allowed to monitor the ongoing selection for better adapted strains during the operation of a biocatalyzer and to direct their subsequent isolation. In such a way, a predominant mercury reducing <it>Ps. aeruginosa </it>strain was identified by its unique mercuric reductase gene.</p>