The identification of carbamazepine biodegrading phylotypes and phylotypes sensitive to carbamazepine exposure in two soil microbial communities

Abstract

Carbamazepine (CBZ), an antiepileptic drug, has been introduced into agricultural soils via irrigation with treated wastewater and biosolids application. Such contamination is problematic because CBZ is persistent and the risks to ecosystems or human health are unknown. The current study examined CBZ biodegradation in two agricultural soils (soil 1 and 2) and the effects on the soil microbial communities during CBZ exposure. The experimental design involved three CBZ concentrations (50, 500, 5000ng/g), under aerobic as well as anaerobic conditions. CBZ concentrations were determined using solid phase extraction and LC MS/MS. The effect of CBZ on the soil microbial community was investigated using high throughput sequencing and a computational approach to predict functional composition of the metagenomes (phylogenetic investigation of communities by reconstruction of unobserved states, PICRUSt). The most significant CBZ biodegradation occurred in soil 1 under aerobic conditions. In contrast, CBZ biodegradation was limited under anaerobic conditions in soil 1 and under both conditions in soil 2. For soil 1, several phylotypes were enriched following CBZ degradation compared to the controls, including unclassified Sphingomonadaceae, Xanthomonadaceae and Rhodobacteraceae, as well as Sphingomonas, Aquicella and Microvirga. These phylotypes are considered putative CBZ degraders as they appear to be benefiting from CBZ biodegradation. PICRUSt revealed that soil 1 contained a greater abundance of xenobiotic degrading genes compared to soil 2, and thus, this analysis method offers a potential valuable approach for predicting CBZ attenuation in soils. PICRUSt analysis also implicated Sphingomonadaceae and Xanthomonadaceae in drug metabolism. Interestingly, numerous phylotypes decreased in abundance following CBZ exposure and these varied with soil type, concentration, duration of exposure, and the availability of oxygen. For three phylotypes (Flavobacterium, 3 genus incertae sedis and unclassified Bacteroidetes), the relative abundance was reduced in both soils, indicating a notable sensitivity to CBZ for these microorganisms.