Bacterial communities and functional genes stimulated during phenanthrene degradation in soil by bio-microcapsules

In this study, a taxonomic and functional metagenomic method was used to investigate the difference produced between degrading bacteria immobilized in layer-by-layer assembly (LBL) microcapsules or not during the bioremediation of a soil polluted with phenanthrene (PHE). Bioaugmentation with LBL microcapsule immobilized degrading bacteria could result in different changes of native microbial communities, shifting the functional gene constructions of polluted soils. The LBL treatment enhanced PHE degradation (initial concentration of 100 mg kg^-1 dry soil) by 60% after 25 d compared to the free bacteria (FB). The enhancing effect of PHE degradation produced by the LBL treatment was found to be significantly associated with some crucial phyla (e.g., Bacteroides, Gemmatimonadetes and Acidobacteria) and genera including Streptomyces, Ramlibacter, Mycobacterium, Phycicoccus, Gemmatirosa, Flavisolibacter, Micromonospora, Acid_Candidatus_Koribacter and Gemmatimonas. The main differences of functional metagenomics between LBL and FB treatments were observed in higher levels in metabolism of aromatic hydrocarbons and its related functions or enzymes in the former, e.g., membrane transport systems, binding, substrate transporter, cleavage enzymes, dehydrogenation, oxidase, esterase and glycosidase, greatly favoring PHE mineralization. Therefore, our results provide useful findings on understanding of how immobilization strategies can influence the taxonomic and functional gene composition in soils, as well as polycyclic aromatic hydrocarbons (PAH) degradation.