Screening for heavy metal tolerance of isolated facultative methylotrophic (FM) bacteria from Pasig and Tullahan River soil sediments

Four facultative methylotrophic bacterial isolates were obtained from the soil sediment samples of Pasig and Tullahan River. Morphological and biochemical characterization were performed in all isolates. For the morphological characterization, colonial and microscopic characterization were done. The FM isolates were observed to have large, cream to pink colonies and were translucent. All FM isolates were found to be rod-shaped and they exhibited Gram- negative reaction except for one which was Gram-positive bacteria. For the biochemical characterization, catalase test was done in a conventional manner and in the study, FM isolates were found to be catalase positive bacteria. Meanwhile, the rest of the biochemical tests using API 20 NE & E bioMeriéux kit were used to determine the species of all of the four isolates. Included in the kit, oxidase test revealed that all isolates were oxidase positive except for one which is the unknown spp. Only three isolates were identified and two of them were identified as Sphingomonas paucimobilis and the other one as Rhizobium radiobacter. Afterwards, Heavy metal tolerance of the four isolates were determined. This test showed that all isolates were able to tolerate Cadmium up to 10 ppm (mg/L) only. Furthermore, Rhizobium radiobacter was able to tolerate Lead and Nickel up to 100 ppm (mg/L) while it can only to tolerate Cobalt up to 80 ppm (mg/L). At the same time, Sphingomonas paucimobilis was able to tolerate Cobalt, Lead, and nickel up to 100 ppm (mg/L). On one hand, bacterial colonies of each isolates were decreasing as concentration of heavy metal increases