Identification of significant live bacterial community shifts in different reclaimed waters during ozone and chlorine disinfection

Genomic insights into chlorine resistance of a Mycobacterium sp. strain isolated from treated wastewater effluent

Chlorine is the principal microbial disinfectant used for water treatment. However, chlorine-resistant bacteria such as Mycobacterium spp., can survive chlorine treatment and even grow in the presence of chlorine, posing potential public health risks. In this study, we isolated a Mycobacterium sp. strain from treated effluent and investigated its chlorine resistance and recovery using transcriptomic analyses. Specifically, isolate M1, showing 94.58 % average nucleotide identity (ANI) with Mycobacterium massilipolynesiensis type genome, was exposed to 1 ppm HOCl for 30 min and subjected to RNA sequencing. Genes identified as upregulated compared to control conditions (no HOCl) were involved in detoxification (toxic compound degradation; nemA; log2 fold-change [FC]: 7.41), redox homeostasis (COQ5; quinone synthesis; log2 FC 5.70, rosB; riboflavin synthesis; log2 FC 5.61), protein homeostasis (cysHKO, moeZ cysteine biosynthesis, and arg complex; arginine metabolism), and lipid metabolism (cpnA; 6.95 FC) suggesting a multifaceted adaptation to oxidative stress. Levels of a few membrane transport proteins (czcD, and bcr) were also upregulated, highlighting their role in chlorine exposure. Overall, this study broadens the understanding of chlorine resistance strategies employed by Mycobacterium sp. to combat oxidative stress and the resulting toxic intracellular compounds, and has implications for adjusting water treatment technologies toward eliminating mycobacteria.

Identification of correlation relationships and establishment of regression models among multiple microbial indicators in reclaimed waters

Monitoring and controlling microbial water quality is crucial for ensuring water reuse safety. In particular, existing water reuse guidelines and regulations normally prescribed coliform bacteria as microbial indicators. However, the use of non-unified coliform groups may bring difficulties to compare and optimize the conformity efforts on microbial surveillance. This study has identified the correlation relationships in each pair of four microbial indicators in reclaimed waters, namely the heterotrophic plate counts (HPCs), total coliforms (TC), fecal coliforms (FC) and E. coli (r = 0.861-0.987). Ultimately, the built regression model for internal conversion is expressed as: log10HPC (MPN/mL) = 0.737 × log10TC (MPN/L) = 0.830 × log10FC (MPN/L) = 0.872 × log10E. coli (MPN/L) with further verification and validation. The developed model can be used to help water reuse regulators and practitioners improve the efficiency in universal microbial risk detection and management. Besides, the resistant microbes in HPCs (e.g. disinfection resistant bacteria and pathogens) after reclaimed water treatment and disinfection also call for future attention.

Effects of tea polyphenols disinfectant on microbial communities and potential pathogenic bacteria in water

The structural and abundance changes in water disinfected by tea polyphenols were investigated in high-abundance microbial communities (HAMC), medium-abundance microbial communities (MAMC), and low-abundance microbial communities (LAMC), also included the interactions within and between these communities. The antibacterial effect of tea polyphenols was observed at concentrations of 20-300 mg/L. If the tea polyphenols concentration is greater than or equal to 200 mg/L, it can continue to inhibit the growth of bacteria, and keep the total number of bacteria in 48 hours no more than100 CFU/ml, and this reflected the continuity of tea polyphenols disinfectant in the pipe network. The relative abundance of some chlorine-resistant bacteria such as Blastomonas, Sphingomonas and Pseudomonas decreased significantly after disinfection with tea polyphenols, which indicates that tea polyphenols have the advantage of removing some chlorine-resistant bacteria. Samples of HAMC, MAMC and LAMC showed similar structure. Co-occurrence network analysis within microbial communities revealed the most complex interrelationships in HAMC. Co-occurrence network analysis between microbial communities showed that HAMC and MAMC were most closely related. In the co-occurrence network, 8 key bacteria genera were identified, in which 5 key genera belonged to medium-abundance and low-abundance. Potential pathogens were identified in the study and potential pathogens were Aerococcus and Staphylococcus were pointed out after tea polyphenols disinfection as the key potential pathogen genera by co-occurrence network analysis. The co-occurrence relationship between these key potential pathogens and other potential pathogens indicates that water quality safety can be controlled by the number of key potential pathogens.

Non-thermal plasma decontamination of microbes: a state of the art

Microbial decontamination is a critical concern in various sectors, from healthcare to food processing. Traditional decontamination methods, while effective to a degree, present limitations in terms of environmental impact, efficiency, and potential harm to the target material. This review investigates the emerging realm of non-thermal plasma (NTP) as a promising alternative for microbial decontamination, emphasizing its mechanisms, reactor designs and applications. The mechanism decomposed into physical, chemical and biological effects of plasma, are elaborated upon to provide a foundational understanding of the intrinsic principles of plasma decontamination. Except for the generation type of NTP, reactors and other parameters by which NTP achieves microbial decontamination, emphasizing the design considerations and parameters that influence its efficacy. Moreover, the latest applications of NTP in decontaminating air, water, and surfaces, supported by the latest research findings in each domain are explored. Additionally, the perspectives on the future research tendencies of NTP decontamination and disinfection are highlighted with potential avenues for exploration and innovation. Through this comprehensive review, the aim is to underscore the potential of NTP, particularly DBD plasma, as a versatile, efficient, and environmentally friendly method for microbial decontamination.

Riverine antibiotic resistome along an anthropogenic gradient

The introduction of antibiotic-resistant bacteria into riverine systems through the discharge of wastewater treatment plant (WWTP) effluent and agricultural waste poses significant health risks. Even when not pathogenic, these bacteria can act as reservoirs for antibiotic resistance genes (ARGs), transferring them to pathogens that infect humans and animals. In this study, we used fluorescence in situ hybridization, qPCR, and metagenomics to investigate how anthropogenic activities affect microbial abundance and the resistome along the Holtemme River, a small river in Germany, from near-pristine to human-impacted sites. Our results showed higher bacterial abundance, a greater absolute and relative abundance of ARGs, and a more diverse ARG profile at the impacted sites. Overall, the ARG profiles at these sites reflected antibiotic usage in Germany, with genes conferring resistance to drug classes such as beta-lactams, aminoglycosides, folate biosynthesis inhibitors, and tetracyclines. There were also variations in the ARG profiles of the impacted sites. Notably, there was a high abundance of the oxacillin resistance gene OXA-4 at the downstream site in the river. In the metagenome assembly, this gene was associated with a contig homologous to small plasmids previously identified in members of the Thiotrichaceae. The likely in-situ host of the putative plasmid was a close relative of Thiolinea (also known as Thiothrix) eikelboomii, a prominent member of WWTP microbiomes worldwide. Our results show that the effluent from WWTPs can introduce bacteria into the environment that act as shuttle systems for clinically relevant ARG.

Assessment of microorganisms in drinking water disinfected by catalytic ozonation with fluorinated ceramic honeycomb and NaClO disinfectants under laboratory and pilot conditions

While sodium hypochlorite (NaClO) has long been used to disinfect drinking water, concerns have risen over its use due to causing potentially hazardous byproducts. Catalytic ozonation with metal-free catalysts has attracted increasing attention to eliminate the risk of secondary pollution of byproducts in water treatment. Here, we compared the disinfection efficiency and microbial community of catalytic ozone with a type of metal-free catalyst fluorinated ceramic honeycomb (FCH) and NaClO disinfectants under laboratory- and pilot-scale conditions. Under laboratory conditions, the disinfection rate of catalytic ozonation was 3∼6-fold that of ozone when the concentration of Escherichia coli was 1 × 106 CFU/ml, and all E. coli were killed within 15 s. However, 0.65 mg/L NaClO retained E. coli after 30 min using the traditional culturable approach. The microorganism inactivation results of raw reservoir water disinfected by catalytic ozonation and ozonation within 15 s were incomparable based on the cultural method. In pilot-scale testing, catalytic ozonation inactivated all environmental bacteria within 4 min, while 0.65 mg/L NaClO could not achieve this success. Both catalytic ozonation and NaClO-disinfected methods significantly reduced the number of microorganisms but did not change the relative abundances of different species, i.e., bacteria, viruses, eukaryotes, and archaea, based on metagenomic analyses. The abundance of virulence factors (VFs) and antimicrobial resistance genes (ARGs) was detected few in catalytic ozonation, as determined by metagenomic sequencing. Some VFs or ARGs, such as virulence gene 'FAS-II' which was hosted by Mycobacterium_tuberculosis, were detected solely by the NaClO-disinfected method. The enriched genes and pathways of cataO3-disinfected methods exhibited an opposite trend, especially in human disease, compared with NaClO disinfection. These results indicated that the disinfection effect of catalytic ozone is superior to NaClO, this finding contributed to the large-scale application of catalytic ozonation with FCH in practical water treatment.

Revealing the Viable Microbial Community of Biofilm in a Sewage Treatment System Using Propidium Monoazide Combined with Real-Time PCR and Metagenomics

Microbial community composition, function, and viability are important for biofilm-based sewage treatment technologies. Most studies of microbial communities mainly rely on the total deoxyribonucleic acid (DNA) extracted from the biofilm. However, nucleotide materials released from dead microorganisms may interfere with the analysis of viable microorganisms and their metabolic potential. In this study, we developed a protocol to assess viability as well as viable community composition and function in biofilm in a sewage treatment system using propidium monoazide (PMA) coupled with real-time quantitative polymerase chain reaction (qPCR) and metagenomic technology. The optimal removal of PMA from non-viable cells was achieved by a PMA concentration of 4 μM, incubation in darkness for 5 min, and exposure for 5 min. Simultaneously, the detection limit can reach a viable bacteria proportion of 1%, within the detection concentration range of 102-108 CFU/mL (colony forming unit/mL), showing its effectiveness in removing interference from dead cells. Under the optimal conditions, the result of PMA-metagenomic sequencing revealed that 6.72% to 8.18% of non-viable microorganisms were influenced and the composition and relative abundance of the dominant genera were changed. Overall, this study established a fast, sensitive, and highly specific biofilm viability detection method, which could provide technical support for accurately deciphering the structural composition and function of viable microbial communities in sewage treatment biofilms.

Do all algae grow faster in environments replenished by reclaimed water? Examples of two effluents produced in Beijing

Reclaimed water with nitrogen, phosphorus, and other contaminants may trigger algal blooms during its ecological utilization in replenishing rivers or lakes. However, the effect of reclaimed water on algal growth rates is not well understood. In this study, the growth potentials of algae in terms of Cyanophyta, Chlorophyta, and Bacillariophyta, as well as mixed algae in both regular culture medium and reclaimed water produced from treatment plants in Beijing with similar N and P concentrations, were compared to evaluate whether reclaimed water could facilitate algal growth. In addition, reclaimed water was also sterilized to verify the impact of bacteria's presence on algal growth. The results indicated that most algae grew faster in reclaimed water, among which the growth rate of Microcystis aeruginosa even increased by 5.5 fold. The growth of mixed algae in reclaimed water was not enhanced due to the strong adaptive ability of the community structure. Residual bacteria in the reclaimed water were found to be important contributors to algal growth. This work provided theoretical support for the safe and efficient utilization of reclaimed water.