Agricultural soil and drilosphere as reservoirs of new and unusual assimilators of 2,4-dichlorophenol carbon

Abstract

2,4-Dichlorophenol (2,4-DCP) is a potential soil and groundwater contaminant. Earthworms modulate growth and activities of soil microbiota. Thus, active 2,4-DCP degraders in agricultural soil and drilosphere (i.e. burrow walls, gut content and cast) were identified by comparative amplicon pyrosequencing-based 16S rRNA stable isotope probing in soil columns. In situ relevant concentrations of [U-(13) C]2,4-DCP were consumed in soil within 19 and 41 days in the presence and absence of the endogeic earthworm Aporrectodea caliginosa, respectively. [U-(14) C]2,4-DCP mineralization was higher in cast, burrow wall and soil from columns with than without earthworms. [U-(14) C]2,4-DCP mineralization was lowest in gut contents. Data indicated a strong impact of earthworms on the active microbial community. Novosphingobium, Comamonas and Desulfitobacterium sp. assimilated 2,4-DCP-[(13)C] in the absence of earthworms. Pseudomonas, Flavobacterium and Clostridium sp. assimilated 2,4-DCP-[(13)C] in the drilosphere. Novosphingobium- and Variovorax-related taxa dominated [U-(13)C]2,4-DCP consumers in soil slurries with drilosphere and bulk soil material. 16S rRNA sequences suggested species level novelty. The collective data demonstrates that new Bacteroidetes and Alphaproteobacteria/Betaproteobacteria were involved in 2,4-DCP-C transformation and indicated that diverse and hitherto unknown microbes associated with carbon flow from 2,4-DCP are shaped by earthworms.