Community analysis and characterization of humic substances-degrading bacteria from Alaska tundra soil

Abstract

Soil humic substances are widely distributed in cold natural environments such as alpine areas, the Arctic, and the Antarctic and are known as an important fraction of soil organic carbon. Currently, however, little is known about humic substances-degrading bacteria in cold environments, which led us to initiate the present study. A total of 143 bacterial strains were isolated on minimal agar plates containing humic acids or oat spelt xylan, commercially available, from 66 different soil samples in Nome, Alaska (August, 2011). They were identified based on their 16S rRNA sequence similarity using EzTaxon program, with Firmicutes (82.5%) and γ-Proteobacteria (14.7%) comprising the largest portion. A detailed analysis of the 16S rRNA sequences of 45 good humic acids or xylan-degraders showed that they are affiliated to several taxa: Pseudomonas spp., 15 strains; Paenibacillus spp., 27 strains; Rhodococcus spp., 2 strains; Serratia sp., 1 strain. The selected strains were tested on their degradability for various monocyclic aromatics, and then further examined for putative degradative metabolites of humic substances. Finally, two bacterial strains (Pseudomonas sp. PAMC 26793 and Paenibacillus sp. 26794) were selected as excellent humic substances-degraders and characterized to have different pathway(s) for degradation of humic substances. The changes between the initial and final structures substances-degrading bacteria in cold environments, which led us to initiate the present study. A total of 143 bacterial strains were isolated on minimal agar plates containing humic acids or oat spelt xylan, commercially available, from 66 different soil samples in Nome, Alaska (August, 2011). They were identified based on their 16S rRNA sequence similarity using EzTaxon program, with Firmicutes (82.5%) and γ-Proteobacteria (14.7%) comprising the largest portion. A detailed analysis of the 16S rRNA sequences of 45 good humic acids or xylan