Mercury Reduction and Methyl Mercury Degradation by the Soil Bacterium Xanthobacter autotrophicus Py2

ABSTRACTTwo previously uncharacterized potential broad-spectrum mercury (Hg) resistance operons (mer) are present on the chromosome of the soilAlphaproteobacteriaXanthobacter autotrophicusPy2. These operons,mer1andmer2, contain two features which are commonly found inmeroperons in the genomes of soil and marineAlphaproteobacteria, but are not present in previously characterizedmeroperons: a gene for the mercuric reductase (MerA) that encodes an alkylmercury lyase domain typical of those found on the MerB protein, and the presence of an additional gene, which we are callingmerK, with homology to glutathione reductase. Here, we demonstrate that Py2 is resistant to 0.2 μM inorganic mercury [Hg(II)] and 0.05 μM methylmercury (MeHg). Py2 is capable of converting MeHg and Hg(II) to elemental mercury [Hg(0)], and reduction of Hg(II) is induced by incubation in sub toxic concentrations of Hg(II). Transcription of themerAgenes increased with Hg(II) treatment, and in both operonsmerKresides on the same polycistronic mRNA asmerA. We propose the use of Py2 as a model system for studying the contribution ofmerto Hg mobility in soil and marine ecosystems.

Kinetics Approach of Biodegradation of Petroleum Contaminated Soil by using Indigenous Isolated Bacteria

The bioremediation of petroleum contaminated soil was investigated using a microscale Landfarming. The Indigenousbacteria, Pseudomonas pseudoalcaligenes, Bacillus megaterium, and Xanthobacter autotrophicus were isolated from the contaminated sites Sungai Lilin Jambi Pertamina Ltd and used further in the bioremediation experiments. The biodegradation rates of petroleum contaminated soil in the presence of the isolated bacteria were studied by using the chemical kinetics approach. The reaction orders were studied by using the differential method and the reaction rate constants were studied by using the integral method. The results showed that the reaction orders were 1.0949, 1.3985, 0.8823, and the reaction rate constants were 0.0189, 0.0204, 0.0324 day-1, respectively. Considering the values of reaction orders and reaction rate constants, the biodegradation rate of contaminated soil by usingeach bacteria had significantly different value; Xanthobacter Autotrophicus bacteria could degrade the petroleumoil sludge fastest than the others.Keywords: Biodegradation, indigenous bacteria, kinetics, petroleum oil