Identification by MALDI-TOF Mass Spectrometry of Mercury-resistant Bacteria Associated with the Rhizosphere of an Apple Orchard

Abstract

ABSTRACTIn this work, mercury-resistant bacterial strains were isolated from the rhizosphere of an apple orchard, growing in a soil with high levels of mercury (Nuevo San Joaquin, Queretaro State, Mexico). Analysis of the soil in this region by the Cold Vapor Atomic Absortion Spectroscopy method showed that it contained 637 ± 51 mg mercury per kg. Mercury accumulation by fresh apples from this orchard amounted to 15.44 ± 4.33 mg/kg. The bacterial isolates were identified by application of proteomic technique of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). They were found to be strains of Bacillus muralis and Bacillus simplex. All strains showed the ability to catalyze the volatilization of Hg as measured via the nonradioactive X-ray method. In all strains merR and merA genes were detected by polymerase chain reaction. Nucleotide sequence analysis showed that merR from B. simplex was 435 bp in length and that its sequence was similar to merR sequences reported for other bacteria such as Cupriavidus, Ralstonia, Pseudomonas and Serratia. To our knowledge, this is the first report of mercury-resistant Bacillus strains isolated from the rhizosphere of an apple orchard and the first merR gene sequence from such Bacilli.