The chlorinated nitroaromatic antibiotic chloramphenicol (CAP) is a refractory contaminant that is widely present in various environments. However, few CAP-mineralizing bacteria have been documented, and a complete CAP catabolism pathway has yet to be identified. In this study, the bacterial strain Sphingobium sp. CAP-1 was isolated from an activated sludge sample and was shown to be capable of aerobically subsisting on CAP as the sole carbon, nitrogen, and energy source while simultaneously and efficiently degrading CAP. p-Nitrobenzoic acid (PNBA), p-nitrobenzaldehyde (PNBD), protocatechuate (PCA), and the novel side chain C 3 -hydroxy-oxygenated product of CAP (O-CAP) were identified during CAP degradation. Strain CAP-1 was able to convert O-CAP to intermediate product PNBA. The putative functional genes associated with PNBA catabolism into the tricarboxylic acid cycle via PCA and floc formation were also identified by genome sequencing and comparative proteome analysis. A complete pathway for CAP catabolism was proposed. The discovery of a novel CAP oxidation/detoxification process and a complete pathway for CAP catabolism enriches the fundamental understanding of the bacterial catabolism of antibiotics, providing new insights into the microbial-mediated fate, transformation, and resistance risk of CAP in the environment. The molecular basis of CAP catabolism and floc formation in strain CAP-1 also offers theoretical guidance for the enhanced bioremediation of CAP-containing environments.

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A new white-rot fungus SYBC-L1, which could produce an extracellular laccase, was isolated from a decayed Elaeocarpus sylvestris. The strain was identified as Pycnoporus sp. SYBC-L1 according to the morphological characteristics and ribosomal ITS1-5.8S-ITS2 RNA genomic sequence analysis. The highest laccase activity of 24.1 U ml(-1), which was approximately 40-fold than that in basal medium, was achieved in optimal culture medium in submerged fermentation. The laccase produced by Pycnoporus sp. SYBC-L1 was not only a cold adaptation enzyme with a relative catalytic activity of 30.2% at 0 degrees C but also a high thermostable enzyme. The half-lives at 60, 70 and 80 degrees C were 85.5, 37.2, and 2.6 h, respectively. The laccase could effectively decolorize weak acid blue AS and diamond black PV up to 88% and 74.7%, respectively, within 2 h in the absence of any redox mediators. The results suggested Pycnoporus sp. SYBC-L1 was a potential candidate for laccase production and industrial application.

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h i g h l i g h t sFeeding with glucose obtained higher AYR decolorization efficiency than acetate. Diverse cathodic bacterial communities were observed with different co-substrates. Glucose-fed condition was dominated with Citrobacter, Enterococcus and Alkaliflexus. Acetate-fed condition was dominated with Acinetobacter and Achromobacter. Co-substrate types impacted performance and the cathodic bacterial communities. a r t i c l e i n f o t r a c tSelective enrichment of cathodic bacterial community was investigated during reductive decolorization of AYR fedding with glucose or acetate as co-substrates in biocathode. A clear distinction of phylotype structures were observed between glucose-fed and acetate-fed biocathodes. In glucose-fed biocathode, Citrobacter (29.2%), Enterococcus (14.7%) and Alkaliflexus (9.2%) were predominant, and while, in acetate-fed biocathode, Acinetobacter (17.8%) and Achromobacter (6.4%) were dominant. Some electroactive or reductive decolorization genera, like Pseudomonas, Delftia and Dechloromonas were commonly enriched. Both of the higher AYR decolorization rate (k AYR = 0.46) and p-phenylenediamine (PPD) generation rate (k PPD = 0.38) were obtained fed with glucose than acetate (k AYR = 0.18; k PPD = 0.16). The electrochemical behavior analysis represented a total resistance in glucose-fed condition was about 73.2% lower than acetate-fed condition. The different co-substrate types, resulted in alteration of structure, richness and composition of bacterial communities, which significantly impacted the performances and electrochemical behaviors during reductive decolorization of azo dyes in biocathode.

Chloramphenicol (CAP) is a frequently detected environmental pollutant. In this study, an electroactive biofilm for CAP reduction was established by initially in the anode and then inverting to the cathode. The established biocathode could enhance the reduction of CAP to the nitro-group reduced CAP (AMCl2) and further dechlorinated form (AMCl), both had lost the antibacterial activity. The phylogenetic diversity of the acclimated biofilm was decreased after the polar inversion. Proportions of functional bacterial genera, including Geobacter, Desulfovibrio and Pseudomonas responsible for the bidirectional electron transfer and nitroaromatics reduction, had increased 28%, 104% and 43% in the cathode. The relatively high abundances (over 50%) of Geobacter in anode and cathode were rarely detected for the nitroaromatics reduction. This study provides new insights into the electroactive biofilm structure improvement by the polarity inversion strategy for refractory antibiotics degradation.

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