Isolation of a polyethylene-degrading bacterium, Acinetobacter guillouiae, using a novel screening method based on a redox indicator.

Plastic, a polymer synthesized from petrochemicals, is used worldwide. However, natural degradation of plastic is difficult, causing environmental pollution, with microplastics posing a serious threat to human health. In this study, we aimed to use a new screening method based on the oxidation-reduction indicator, 2,6-dichlorophenolindophenol, to isolate a polyethylene-degrading bacterium, Acinetobacter guillouiae, from insect larvae. Plastic-degrading strains are identified by the color change in the redox indicator from blue to colorless as plastic metabolism occurs. Polyethylene biodegradation by A. guillouiae was verified through weight loss, surface erosion, physiological evidence, and chemical changes on the plastic surface. In addition, we analyzed the characteristics of hydrocarbon metabolism in polyethylene-degrading bacteria. Results suggested that alkane hydroxylation and alcohol dehydrogenation were key steps in polyethylene degradation. This novel screening method will pave the way for high-throughput screening of polyethylene-degrading microorganisms and extending its application to other types of plastics may potentially address plastic pollution.

Effects of biochar addition on the fate of ciprofloxacin and its associated antibiotic tolerance in an activated sludge microbiome.

This study investigated the effects of adding biochar (BC) on the fate of ciprofloxacin (CIP) and its related antibiotic tolerance (AT) in activated sludge. Three activated sludge reactors were established with different types of BC, derived from apple, pear, and mulberry tree, respectively, and one reactor with no BC. All reactors were exposed to an environmentally relevant level of CIP that acted as a definitive selective pressure significantly promoting AT to four representative antibiotics (CIP, ampicillin, tetracycline, and polymyxin B) by up to two orders of magnitude. While CIP removal was negligible in the reactor without BC, the BC-dosed reactors effectively removed CIP (70-95% removals) through primarily adsorption by BC and biodegradation/biosorption by biomass. The AT in the BC-added reactors was suppressed by 10-99%, compared to that without BC. The BC addition played a key role in sequestering CIP, thereby decreasing the selective pressure that enabled the proactive prevention of AT increase. 16S rRNA gene sequencing analysis showed that the BC addition alleviated the CIP-mediated toxicity to community diversity and organisms related to phosphorous removal. Machine learning modeling with random forest and support vector models using AS microbiome data collectively pinpointed Achromobacter selected by CIP and strongly associated with the AT increase in activated sludge. The identification of Achromobacter as an important AT bacteria revealed by the machine learning modeling with multiple models was also validated with a linear Pearson's correlation analysis. Overall, our study highlighted Achromobacter as a potential useful sentinel for monitoring AT occurring in the environment and suggested BC as a promising additive in wastewater treatment to improve micropollutant removal, mitigate potential AT propagation, and maintain community diversity against toxic antibiotic loadings.

Anaerobic membrane bioreactor performance with varying feed concentrations of ciprofloxacin.

The anaerobic membrane bioreactor (AnMBR) has considerable potential for treating wastewater, although there is very little data on the effect of antibiotics on AnMBR performance. This study examined the effect of Ciprofloxacin (CIP) - an antibiotic that can occur at high concentrations, and has a substantial impact on ecosystems, on AnMBR performance. The long-term (44 days) presence of 0.5 mg/L CIP in the feed did not have a strong effect on COD removal, volatile fatty acid (VFA) accumulation, or methane yield, but did affect the pH, soluble microbial products (SMPs) and suspended solids. However, at 4.7 mg/L CIP, a significant effect on all the parameters tested was seen. 16S rRNA gene-based community analysis demonstrated that CIP changed the phylogenetic structure and altered the species richness and diversity. The relative abundance of various genera was also changed, and this explained much of the change in AnMBR behavior.

Ecological processes underpinning microbial community structure during exposure to subinhibitory level of triclosan.

Ecological processes shaping the structure and diversity of microbial communities are of practical importance for managing the function and resilience of engineered biological ecosystems such as activated sludge processes. This study systematically evaluated the ecological processes acting during continuous exposure to a subinhibitory level of antimicrobial triclosan (TCS) as an environmental stressor. 16S rRNA gene-based community profiling revealed significant perturbations on the community structure and dramatic reduction (by 20-30%) in species diversity/richness compared to those under the control conditions. In addition, community profiling determined the prevalence of the deterministic processes overwhelming the ecological stochasticity. Analysis of both community composition and phenotypes in the TCS-exposed communities suggested the detailed deterministic mechanism: selection of TCS degrading (Sphingopyxis) and resistant (Pseudoxanthomonas) bacterial populations. The analysis also revealed a significant reduction of core activated sludge members, Chitinophagaceae (e.g., Ferruginibacter) and Comamonadaceae (e.g., Acidovorax), potentially affecting ecosystem functions (e.g., floc formation and nutrient removal) directly associated with system performance (i.e., wastewater treatment efficiency and effluent quality). Overall, our study provides new findings that inform the mechanisms underlying the community structure and diversity of activated sludge, which not only advances the current understanding of microbial ecology in activated sludge, but also has practical implications for the design and operation of environmental bioprocesses for treatment of antimicrobial-bearing waste streams.

Removal of Chloroxylenol Disinfectant by an Activated Sludge Microbial Community.

Chloroxylenol (CHL) is an antimicrobial ingredient that is frequently used in antiseptics/disinfectants for skin (e.g. hand soap) and non-living surfaces. CHL is an alternative to triclosan and triclocarban, the use of which has recently been banned in some countries. Accordingly, the more widespread use of CHL may significantly increase its occurrence and level in aquatic environments in the near future, eventually resulting in potential ecological risks. Wastewater treatment plants (WWTPs) may be a point source of CHL in natural environments due to extensive discharge through urban waste stream disposal. While the satisfactory removal of CHL in WWTPs is critical for maintaining healthy aquatic ecosystems, the extent of CHL removal and whether CHL causes system upset/failure in WWTPs currently remain unknown. In the present study, we conducted bioreactor operation and batch experiments to investigate the fate and effects of CHL and elucidate the mechanisms underlying degradation at various levels from environmentally relevant to high levels (0.5-5 mg L-1). Bioreactors partially removed CHL (44-87%) via a largely biological route. Microbial association networks constructed using 16S rRNA gene sequencing data revealed selective enrichment and a correlation between Sphingobium and CHL, implying its involvement in the biological breakdown of CHL through dehalogenation and ring hydroxylation pathways. The present results provide insights into the behavior and effects of CHL in activated sludge communities and important information for the sustainable management of CHL that may be an emerging issue in the urban water cycle.

Microbial Community Enhances Biodegradation of Bisphenol A Through Selection of Sphingomonadaceae.

Bisphenol A (BPA) is a common ingredient in plastic wares and epoxy resins that are essential for our daily life. Despite the obvious benefits, BPA may act as an environmental endocrine disruptor, causing metabolic, reproductive, and/or developmental consequences and diseases in humans and other organisms. Although previous studies have yielded progress toward the microbial breakdown of BPA, the work has primarily been focused on pure cultures rather than complex microbial communities. In this study, we examined microbial communities in bioreactors that control the fate of BPA at various levels (up to 5000 µg L-1). Microbial communities rapidly increased removal rates of 500-5000 µg L-1 BPA from 23-29 to 89-99% during the first 2 weeks of the acclimation period, after which > 90% stable removal rates were maintained over 3 months. Biochemical assays demonstrated that BPA was removed by biodegradation, rather than other abiotic removal routes (e.g., adsorption and volatilization). The 16S rRNA gene-based community analysis revealed that 50-5000 µg L-1 of BPA exposure systematically selected for three Sphingomonadaceae species (Sphingobium, Novosphingobium, and Sphingopyxis). The Sphingomonadaceae-enriched communities acclimated to BPA showed a 7.0-L gVSS-1 day-1 BPA degradation rate constant, which is comparable to that (4.1-6.3) of Sphingomonadaceae isolates and is higher than other potential BPA degraders. Taken together, our results advanced the understanding of how microbial communities acclimate to environmentally relevant levels of BPA, gradually enhancing BPA degradation via selective enrichment of a few Sphingomonadaceae populations with higher BPA metabolic activity.

Metabolically engineered glucose-utilizing Shewanella strains under anaerobic conditions.

Comparative genome analysis of Shewanella strains predicted that the strains metabolize preferably two- and three-carbon carbohydrates as carbon/electron source because many Shewanella genomes are deficient of the key enzymes in glycolysis (e.g., glucokinase). In addition, all Shewanella genomes are known to have only one set of genes associated with the phosphotransferase system required to uptake sugars. To engineer Shewanella strains that can utilize five- and six-carbon carbohydrates, we constructed glucose-utilizing Shewanella oneidensis MR-1 by introducing the glucose facilitator (glf; ZMO0366) and glucokinase (glk; ZMO0369) genes of Zymomonas mobilis. The engineered MR-1 strain was able to grow on glucose as a sole carbon/electron source under anaerobic conditions. The glucose affinity (Ks) and glucokinase activity in the engineered MR-1 strain were 299.46 mM and 0.259 ± 0.034 U/g proteins. The engineered strain was successfully applied to a microbial fuel cell system and exhibited current generation using glucose as the electron source.