Soil Bacterial Consortia and Previous Exposure Enhance the Biodegradation of Sulfonamides from Pig Manure

Abstract

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 12C- and 14C-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 α, β and γ classes of Proteobacteria, Firmicutes, Bacteroidetes and Acidobacteria. Proteobacteria (α, β and γ), 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 14C-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.

Characterization of pure cultures isolated from sulfamethoxazole-acclimated activated sludge with respect to taxonomic identification and sulfamethoxazole biodegradation potential

“…Finally, also for the group Brevundimonas spp. some literature data exist proving that these organisms might play a role in the removal of antibiotics [44]. …”

Long-term antibiotic exposure in soil is associated with changes in microbial community structure and prevalence of class 1 integrons

“…Islas-Espinoza et al (2012) observed an increase in species richness as determined by Shannon-Wiener and Margalef indexes in a soil supplemented with sulfamethazine. Shade et al (2013), using a 16S rRNA gene sequencing approach, compared soil bacterial communities under apple trees (Malus domestica) that had undergone spray treatments with streptomycin sulphate.…”

“…This has been previously undertaken using Density Gradient Gel Electrophoresis (DGGE) (Jechalke et al, 2014;Kopmann et al, 2013;Reichel et al, 2013;Westergaard et al, 2001), or Terminal Restriction Fragment Length Polymorphism (T-RFLP) (Islas-Espinoza et al, 2012) analysis of fragments of the 16S rRNA gene. Westergaard et al (2001) demonstrated a decrease in diversity (as indicated by reduced banding complexity resolved by DGGE) in soils treated with tylosin as well as an increased abundance of some taxa, the identity of which were not determined.…”

Antibiotic residues and resistance in the environment

“…Sulfonamide adapted bacterial cultures however, were able to degrade sulfonamides very rapidly (0.2 to 3 days) (Ingerslev and Halling-Sørensen, 2000). The accelerating effect of previous exposure was also shown in a study in pig manure (Islas-Espinoza, 2012). It has been suggested that little or no biodegradation occurs whenever there are other easily biodegradable sources of carbon and nitrogen present (Drillia, 2005), which is obviously the case in manure and manure amended soils.…”