Isolation and Characterization of Humic Substances-Degrading Bacterial Strains from Alaska Soil

Abstract

A total of 143 bacterial strains was isolated from 66 different soil samples from Council, Nome, Alaska, as commercial humic acid or xylan-degrader and classified into three types (dominant-, good growth-, or unique morphology-type). Subsequently, they were tested on their degradability for various monocyclic aromatic compounds. They were identified based on 16S rRNA sequences using EzTaxon program, showing that Firmicutes (82.5%) and γ-Proteobacteria (14.7%) comprise the large portion. A detailed analysis of the 16S rRNA sequences of 45 good humic acid or xylan-degrader indicated that they are affiliated into several taxa: Pseudomonas spp., 15 strains; Paenibacillus spp., 27 strains; Rhodococcus spp., 2 strains; Serratia sp., 1 strain. Also, we further re- examined for their degradability against putative metabolites from humic substances, selecting four bacterial strains (PAMC 26793, 26794, 26821, and 26823) as excellent degraders. Since the humic sunstances-degraders are believed to play an important role in the cycle of soil organic carbon, as the first step, we initiated the study on their degradative pathway(s) for humic substances. At present, one strain (PAMC 26793), which has an excellent ability to degrade various kinds of aromatic compounds including the putative metabolites from humic substances, is subjected to the genome sequencing for its catabolic genes. This work was ubsequently, they were tested on their degradability for various monocyclic aromatic compounds. They were identified based on 16S rRNA sequences using EzTaxon program, showing that Firmicutes (82.5%) and γ-Proteobacteria (14.7%) comprise the large portion. A detailed analysis of the 16S rRNA sequences of 45 good humic acid or xylan-degrader indicated that they are affiliated into several taxa: Pseudomonas spp., 15 strains; Paenibacillus spp., 27 strains; Rhodococcus spp., 2 strains; Serratia sp., 1 strain. Also, we further re-examined for their degradability against putative