Redox-mediator-free degradation of sulfathiazole and tetracycline using Phanerochaete chrysosporium

Degradation of tetracycline, oxytetracycline & ampicillin by purified multiple copper oxidase like laccase from Stentrophomonas sp. YBX1

Multiple copper oxidase (MCO) like laccase is widely distributed in higher plant, fungi and bacteria. This study identified MCO like laccase producing bacterium isolated from a wastewater treatment plant based on 16S rRNA sequence analysis, and they were further confirmed by phylogenetic reconstruction. Biochemical and gene characterization of MCO like laccase from Stenotrophomonas sp. YBX1 is presented. Purification of MCO like laccase was carried out by ion exchange HQ Trap column and followed by gel filtration spheracryl S-100 column. The purified MCO like laccase from Stenotrophomonas sp. YBX1 shows a total activity of 1252 units and specific activity 391.2 U/mg and protein concentration 0.32 mg/mL. In SDS PAGE, the approximate molecular mass was found at 66 kDa and further confirmed from an MS spectrum of MALDI-TOF. The purified MCO like laccase is capable of degradation of antibiotics such as tetracycline completely, whereas oxytetracycline (78%) and ampicillin (62%) degraded within 96 min without any redox mediators at pH 5 and 30 ºC. Its degradation pathway was based on identification of metabolites by LC-MS spectrum. The enzymatic degradation may be used in advanced treatment of antibiotics containing wastewater.

Oxidation of chlortetracycline and its isomers by Botrytis aclada laccase in the absence of mediators: pH dependence and identification of transformation products by LC-MS

Tetracyclines are antibiotics considered emerging pollutants and currently, wastewater treatment plants are not able to remove them efficiently. Laccases are promising enzymes for bioremediation because they can oxidize a wide variety of substrates. The aim of this study was to evaluate the Botrytis aclada laccase for the oxidation of chlortetracycline and its isomers in the absence of a mediator molecule, at a pH range between 3.0 to 7.0, and to characterize the transformation products by LC-MS. Chlortetracycline and three isomers were detected in both, controls and reaction mixtures at 0 h and in controls after 48 h of incubation but in different proportions depending on pH. An additional isomer was also detected, but only in the presence of BaLac. Based on the transformation products identified in the enzymatic reactions and information from literature, we assembled a network of transformation pathways starting from chlortetracycline and its isomers. The spectrometric analysis of the products indicated the probable occurrence of oxygen insertion, dehydrogenation, demethylation and deamination reactions. Four new products were identified, and we also described a novel transformation product without the chloro group. We observed that increasing pH led to higher diversity of main products. This is the first study using the laccase from fungi Botrytis aclada to oxidate chlortetracycline and its isomers and it can be considered as an ecological alternative to be used in bioremediation processes such as wastewater.

A comprehensive review on biodegradation of tetracyclines: Current research progress and prospect

The release of tetracyclines (TCs) in the environment is of significant concern because the residual antibiotics may promote resistance in pathogenic microorganisms, and the transfer of antibiotic resistance genes poses a potential threat to ecosystems. Microbial biodegradation plays an important role in removing TCs in both natural and artificial systems. After long-term acclimation, microorganisms that can tolerate and degrade TCs are retained to achieve efficient removal of TCs under the optimum conditions (e.g. optimal operational parameters and moderate concentrations of TCs). To date, cultivation-based techniques have been used to isolate bacteria or fungi with potential degradation ability. Moreover, the biodegradation mechanism of TCs can be unveiled with the development of chemical analysis (e.g. UPLC-Q-TOF mass spectrometer) and molecular biology techniques (e.g. 16S rRNA gene sequencing, multi-omics sequencing, and whole genome sequencing). In this review, we made an overview of the biodegradation of TCs in different systems, refined functional microbial communities and pure isolates relevant to TCs biodegradation, and summarized the biodegradation products, pathways, and degradation genes of TCs. In addition, ecological risks of TCs biodegradation were considered from the perspectives of metabolic products toxicity and resistance genes. Overall, this article aimed to outline the research progress of TCs biodegradation and propose future research prospects.

Combined utilization of metabolic inhibitors to prevent synergistic multi-species biofilm formation

Biofilm is ubiquitous in industrial water systems, causing biofouling and leading to heat transfer efficiency decreases. In particular, multi-species living in biofilms could boost biomass production and enhance treatment resistance. In this study, a total of 37 bacterial strains were isolated from a cooling tower biofilm where acetic acid and propionic acid were detected as the main carbon sources. These isolates mainly belonged to Proteobacteria and Firmicutes, which occupied more than 80% of the total strains according to the 16S rRNA gene amplicon sequencing. Four species (Acinetobacter sp. CTS3, Corynebacterium sp. CTS5, Providencia sp. CTS12, and Pseudomonas sp. CTS17) were observed co-existing in the synthetic medium. Quantitative comparison of biofilm biomass from mono- and multi-species showed a synergistic effect towards biofilm formation among these four species. Three metabolic inhibitors (sulfathiazole, 3-bromopyruvic acid, and 3-nitropropionic acid) were employed to prevent biofilm formation based on their inhibitory effect on corresponding metabolic pathways. All of them displayed evident inhibition profiles to biofilm formation. Notably, combining these three inhibitors possessed a remarkable ability to block the multi-species biofilm development with lower concentrations, suggesting an enhanced effect appeared in simultaneous use. This study demonstrates that combined utilization of metabolic inhibitors is an alternative strategy to prevent multi-species biofilm formation.

37 bacterial strains were isolated and identified from a cooling tower biofilm.

Synergistic effect of biofilm formation was observed among four species.

Three metabolic inhibitors showed effective inhibition against biofilm formation.

Targeting cellular metabolism is an effective way to inhibit biofilm formation.

Biotransformation of Tetracyclines by Fungi: Challenges and Future Research Perspectives

Tetracycline antibiotics are used worldwide in human and veterinary medicine. On the basis of low metabolization and through organic fertilizers, tetracyclines enter the environment in a biologically active form. This can have toxic effects on microbial communities and promote the selection of resistant strains. The use of fungi could be a promising approach to deactivate tetracyclines by degradation or derivatization as a result of their particular enzyme endowment. Here, we highlight the current analytical and biotechnological challenges associated with the bioconversion of tetracyclines by fungi and propose research approaches to advance the technology for wastewater and manure treatment.