Soil bacterial consortia and previous exposure enhance the biodegradation of sulfonamides from pig manure

Persistence or degradation of synthetic antibiotics in soil is crucial in assessing their environmental risks. Microbial catabolic activity in a sandy loamy soil with pig manure using C-12- and C-14-labelled sulfamethazine (SMZ) respirometry showed that SMZ was not readily degradable. But after 100 days, degradation in sulfadiazine-exposed manure was 9.2%, far greater than soil and organic manure (0.5% and 0.11%, respectively, p < 0.05). Abiotic degradation was not detected suggesting microbial catabolism as main degradation mechanism. Terminal restriction fragment length polymorphism showed biodiversity increases within 1 day of SMZ spiking and especially after 200 days, although some species plummeted. A clone library from the treatment with highest degradation showed that most bacteria belonged to alpha, beta and gamma classes of Proteobacteria, Firmicutes, Bacteroidetes and Acidobacteria. Proteobacteria (alpha, beta and gamma), Firmicutes and Bacteroidetes which were the most abundant classes on day 1 also decreased most following prolonged exposure. From the matrix showing the highest degradation rate, 17 SMZ-resistant isolates biodegraded low levels of (14) C-labelled SMZ when each species was incubated separately (0.2-1.5%) but biodegradation was enhanced when the four isolates with the highest biodegradation were incubated in a consortium (Bacillus licheniformis, Pseudomonas putida, Alcaligenes sp. and Aquamicrobium defluvium as per 16S rRNA gene sequencing), removing up to 7.8% of SMZ after 20 days. One of these species (B. licheniformis) was a known livestock and occasional human pathogen. Despite an environmental role of these species in sulfonamide bioremediation, the possibility of horizontal transfer of pathogenicity and resistance genes should caution against an indiscriminate use of these species as sulfonamide degraders

Impact of PhACs on Soil Microorganisms

International audienceThe use of reclaimed water in crop irrigation helps to mitigate water shortage. The fertilization of arable soils with sewage sludge, biosolids, or livestock manure reduces extensive application of synthetic fertilizers. However, both practices lead to the introduction of pharmaceutical active compounds (PhACs) in arable soil, known to host a wide range of living organisms, including microorganisms which are supporting numerous ecosystem services. In soils, the fate of PhACs is governed by different abiotic and biotic processes. Among them, soil sorption and microbial transformation are the most important ones and determine the fate, occurrence, and dispersion of PhACs into the different compartments of the environment. The presence of PhACs in soils can compromise the abundance, diversity, and activity of the soil microbial community which is one of the key players in a range of soil ecosystem services. This chapter reviews the current knowledge of the effects of PhACs, commonly found in wastewater effluents and derived organic fertilizers, on the soil microbial community