Mercury resistance and volatilization by Pseudoxanthomonas sp. SE1 isolated from soil

• Pseudoxanthomonas sp. SE1 can resist and volatilize inorganic Hg from solution.
• The isolated bacterial strain harboured mercuric reductase gene and produced mercuric reductase enzyme.
• Demonstration of volatilization of Hg from solution due to bacterial reduction.
• The strain is a potential Hg-remediation bio-agent.

A mercury resistant bacterial strain SE1 isolated from contaminated soil was identified as Pseudoxanthomonas based on 16s rRNA sequencing. The Hg resistance was examined in both nutrient-rich media as well as low nutrient media and expressed as EC50 and MIC values. Estimated EC50 and MIC values in nutrient-rich media and low nutrient media had the following respective recordings — 22.6 mg L−1; 23.1 mg L−1 and 1.4 mg L−1 and 1.7 mg L−1. The isolate was able to volatilize inorganic mercury demonstrated by a modified photographic film experiment and subsequently revealed its ability to remove mercury from the solution. The ICP-QQQ-MS analysis of SE1 inoculated solution showed almost 60% of 1.5 mg L−1 mercury was volatilized in 6 h and almost 40% were accumulated in cell pellets. The mercuric reductase gene merA was identified in the genome of isolate SE1 and sequenced. The deduced amino acid sequence of merA gene indicated a sequence homology with different organisms from the alpha proteobacteria group and eukaryotic fungi. merA encoded enzyme mercuric reductase activity was evident in the crude protein of the isolate. The isolate’s ability to resist Hg, it’s Hg volatilization potential and the presence of merA gene and mercuric reductase enzyme demonstrates the potential application of this strain in mercury bioremediation.