Formation of odorant haloanisoles and variation of microorganisms during microbial O-methylation in annular reactors equipped with different coupon materials

First evidence of off-flavour haloanisoles production by dormant fungal spores in drinking water: Formation pattern, influencing factors and transcriptome analysis

Fungi are major producers of off-flavour haloanisoles (HAs) in drinking water supply systems. However, evidence of HA production by dormant fungal spores remains unclear. This study investigated the microbial O-methylation of dormant spores of a fungus Aspergillus sp. from drinking water treatment plants. Dormant spores were capable of O-methylating 2,4,6-trichlorophenol (2,4,6-TCP) to produce 2,4,6-trichloroanisole (2,4,6-TCA). A pronounced linear correlation was identified between the precursor load and the 2,4,6-TCA formation capability, with a function lg(y)= 0.542lg(x) - 4.28 (R2 = 0.838). The effects of metal ions on fungal spore O-methylation were multifaceted and highly concentration-dependent. Natural organic matters could inhibit 2,4,6-TCA formation. NH2Cl presented higher efficacy than free chlorine in inhibiting spore O-methylation. However, O-methylation inhibition rates were lower than spore inactivation rates, suggesting spores in viable but non-culturable state still possessed partial ability to form 2,4,6-TCA. Transcriptome analysis revealed that 50 nM 2,4,6-TCP treatment had no impact on the spore's transcriptional profile, whereas 1 mM Cu2+ treatment significantly inhibited O-methylation process by down-regulating genes involved in ATP generation. This study provides a first evidence that dormant fungal spores are capable of producing 2,4,6-TCA, raising concerns about the potential off-flavour risk and the development of targeted control strategies in drinking water systems.

Novel and Simple Method for Quantification of 2,4,6-Trichlorophenol with Microbial Conversion to 2,4,6-Trichloroanisole

Contamination with 2,4,6-trichloroanisole (TCA) often causes taste and odor (T&O) problems in drinking water due to its low odor threshold concentration. Microbial O-methylation of the precursor 2,4,6-trichlorophenol (TCP) would be the dominant mechanism for TCA formation. Simple and rapid measurement of TCP in the low concentration range is necessary to control the problems induced by TCA. In this study, the combination of microbial conversion and instrumental analysis was proposed as a method of TCP quantification. Fungi and bacteria were isolated from various water samples and examined for their ability to produce TCA from TCP. As a result, a strain exhibiting quantitative TCA production and a high growth rate was obtained and named Mycolicibacterium sp. CB14. The conversion rate of TCP to TCA by this strain was found to be high and stable (85.9 ± 5.3%), regardless of the applied TCP concentration, although within the range of 0.1-10 µg/L. The limits of detection and quantification for TCP by this proposed method were determined to be 5.2 ng/L and 17.3 ng/L, respectively. By improving the methods, Mycolicibacterium sp. CB14 could be used for the quantification of TCP at very low concentration levels, which is sufficient to manage the T&O problem caused by TCA.

Early succession of biofilm bacterial communities in newly built drinking water pipelines via multi-area analysis

Biofilms inhabiting pipeline walls are critical to drinking water quality and safety. With massive pipeline replacement underway, however, biofilm formation process in newly built pipes and its effects on water quality are unclear. Moreover, differences and connections between biofilms in newly built and old pipes are unknown. In this study, early succession (≤ 120 days) of biofilm bacterial communities (abundance and diversity) in upper, middle and bottom areas of a newly built cement-lined ductile iron pipeline were evaluated using improved Propella™ biofilm reactor and multi-area analysis. A comparison with old pipelines (grey cast iron, 10 years) was performed. In the newly built pipeline, the abundance of biofilm bacteria did not change significantly between 40 and 80 days, but increased significantly between 80 and 120 days. The biofilm bacterial abundance (per unit area) in the bottom area was always higher than that in the upper and middle areas. Based on alpha diversity index and PCoA results, biofilm bacterial community richness, diversity and composition did not change significantly during the 120-day operation. Besides, biofilm shedding from the walls of newly built pipeline significantly increased bacterial abundance in the outlet water. Opportunistic pathogen-containing genera, such as Burkholderia, Acinetobacter and Legionella, were identified in both water and biofilm samples from newly built pipelines. The comparison between new and old pipelines suggested a higher bacterial abundance per unit area at the middle and bottom areas in old pipelines. Moreover, the bacterial community composition of biofilms in old pipelines was similar to that of newly built pipelines. These results contribute to accurate prediction and management of biofilm microbial communities in drinking water pipelines, ensuring the biosafety of drinking water. KEY POINTS: • Biofilm bacterial communities in different areas of pipe wall were revealed. • The abundance of biofilm bacteria increased significantly between 80 and 120 days. • Biofilm bacterial community compositions of newly built and old pipes were similar.

Cultivation-dependent and cultivation-independent investigation of O-methylated pollutant-producing bacteria in three drinking water treatment plants

O-methylated pollutants (OMPs) are emerging contaminants in drinking water and mainly produced through bacterial O-methylation. However, the information of OMP-producing bacteria (OMPPB) in drinking water treatment plant (DWTP) is largely unknown so far. In this study, the OMPPB in water samples from three DWTPs (XL, JX and NX) were investigated by using cultivation-dependent and cultivation-independent technologies. Four OMPs were detected and their odor and toxicity risks were assessed. Formation potentials (FPs) of 2,4,6-trichloanisole, 2,3,6-trichloanisole, 2,4,6-tribromoanisole, pentachloroanisole and diclofenac methyl ester were determined in water samples and their values shifted significantly among DWTPs. A most probable number (MPN) method was established to quantify OMPPB numbers and the relationships between total haloanisole FPs (HAFPs) (y) and OMPPB numbers (x) in three DWTPs could be described by the following functions: y = 0.496×^0.373 (XL), y = 0.041×^0.465 (JX) and y = 0.218×^0.237 (NX). Several genera like Bacillus, Ralstonia, Brevundimonas, etc. were newly found OMPPB among the cultivable bacteria, and their OMP products were evaluated in terms of quantity and environment risks (odor, toxicity and bioaccumulation). High-throughput sequencing revealed treatment process was the main driving factor to shape the OMPPB community structures and Mantel test showed HAFP profile was significantly influenced by Mycobacterium and Pelomonas. PICURSt2 analysis discovered four phenolic O-methyltransferases (OMTs) and four carboxylic OMTs which might be responsible for OMP formation. Several strategies were recommended to assess risk and control contamination brought by OMPPB in DWTPs.

Management of biogenic taste and odour: From source water, through treatment processes and distribution systems, to consumers

Biogenic taste and odour (T&O) have become a global concern for water utilities, due to the increasing frequency of algal blooms and other microbial events arising from the combined effects of climate change and eutrophication. Microbially-produced T&O compounds impact source waters, drinking water treatment plants, and drinking water distribution systems. It is important to manage across the entire biogenic T&O pathway to identify key risk factors and devise strategies that will safeguard the quality of drinking water in a changing world, since the presence of T&O impacts consumer confidence in drinking water safety. This study provides a critical review of current knowledge on T&O-causing microbes and compounds for proactive management, including the identification of abiotic risk factors in source waters, a discussion on the effectiveness of existing T&O barriers in drinking water treatment plants, an analysis of risk factors for biofilm growth in water distribution systems, and an assessment of the impacts of T&O on consumers. The fate of biogenic T&O in drinking water systems is tracked from microbial production pathways, through the release of intracellular T&O by cell lysis, to the treatment of microbial cells and dissolved T&O. Based on current knowledge, five impactful research and management directions across the T&O pathway are recommended.

One-Pot Biocatalytic In Vivo Methylation-Hydroamination of Bioderived Lignin Monomers to Generate a Key Precursor to L-DOPA

Electron-rich phenolic substrates can be derived from the depolymerisation of lignin feedstocks. Direct biotransformations of the hydroxycinnamic acid monomers obtained can be exploited to produce high-value chemicals, such as α-amino acids, however the reaction is often hampered by the chemical autooxidation in alkaline or harsh reaction media. Regioselective O-methyltransferases (OMTs) are ubiquitous enzymes in natural secondary metabolic pathways utilising an expensive co-substrate S-adenosyl-l-methionine (SAM) as the methylating reagent altering the physicochemical properties of the hydroxycinnamic acids. In this study, we engineered an OMT to accept a variety of electron-rich phenolic substrates, modified a commercial E. coli strain BL21 (DE3) to regenerate SAM in vivo, and combined it with an engineered ammonia lyase to partake in a one-pot, two whole cell enzyme cascade to produce the l-DOPA precursor l-veratrylglycine from lignin-derived ferulic acid.

One-Pot Biocatalytic In Vivo Methylation-Hydroamination of Bioderived Lignin Monomers to Generate a Key Precursor to L-DOPA

Electron‐rich phenolic substrates can be derived from the depolymerisation of lignin feedstocks. Direct biotransformations of the hydroxycinnamic acid monomers obtained can be exploited to produce high‐value chemicals, such as α‐amino acids, however the reaction is often hampered by the chemical autooxidation in alkaline or harsh reaction media. Regioselective O‐methyltransferases (OMTs) are ubiquitous enzymes in natural secondary metabolic pathways utilising an expensive co‐substrate S‐adenosyl‐l‐methionine (SAM) as the methylating reagent altering the physicochemical properties of the hydroxycinnamic acids. In this study, we engineered an OMT to accept a variety of electron‐rich phenolic substrates, modified a commercial E. coli strain BL21 (DE3) to regenerate SAM in vivo, and combined it with an engineered ammonia lyase to partake in a one‐pot, two whole cell enzyme cascade to produce the l‐DOPA precursor l‐veratrylglycine from lignin‐derived ferulic acid.

Biotransformation of halophenols into earthy-musty haloanisoles: Investigation of dominant bacterial contributors in drinking water distribution systems

Microorganisms in drinking water distribution systems (DWDSs) can O-methylate toxic halophenols (HPs) into earthy-musty haloanisoles (HAs). However, the dominant HA-producing bacterial species and their O-methylation properties are still unknown. In this study, eight bacterial strains from DWDS were isolated and the community abundances of the related genera in bulk water and biofilms as well as their O-methylation properties were investigated. Among the genera discovered in this study, Sphingomonas and Pseudomonas are dominant and play important roles in DWDSs. All bacteria could simultaneously convert five HPs to the corresponding HAs. Two Sphingomonas ursincola strains mainly produced 2,3,6-trichloroanisole (2,3,6-TCA) (2.48 × 10^-9-1.18 × 10^-8 ng/CFU), 2,4,6-trichloroanisole (2,4,6-TCA) (8.12 × 10^-10-3.11 × 10^-9 ng/CFU) and 2,4,6-tribromoanisole (2,4,6-TBA) (2.95 × 10^-9-3.21 × 10^-9 ng/CFU), while two Pseudomonas moraviensis strains preferred to generate 2-monochloroanisole (2-MCA) (1.19 × 10^-9-3.70 × 10^-9 ng/CFU) and 2,4-dichloroanisole (2,4-DCA) (3.81 × 10^-9-1.20 × 10^-8 ng/CFU). Among the chloramphenicol-susceptible strains, four strains contained inducible O-methyltransferases (OMTs), while the O-methylations of the others were expressed constitutively. All bacteria could use S-adenosyl methionine as methyl donor. Potential taste and odor (T & O) risks of five HAs in DWDS followed an order of 2,4,6-TBA > 2,4,6-TCA > 2,3,6-TCA > 2,4-DCA > 2-MCA. The recommended 2,4,6-TCP criteria for T & O control is 0.003-0.07 mg/L.

The effects of three different microplastics on enzyme activities and microbial communities in soil

Soils always receive microplastics (MPs) from plastic mulching, compost, and sewage irrigation, but the effects of MPs on soil environment remain largely unexplored. The objectives of this study were to investigate the effects of three MPs (membranous polyethylene (PE), fibrous polypropylene (PP), and microsphere PP) on enzyme activities and microbial community structure in one loamy and sandy soil. The concentration of microsphere PP (2 mg/g) was one-tenth of those of the other two MPs (20 mg/g). The results showed that the effects of three MPs on urease, dehydrogenase, and alkaline phosphatase activities followed the order: fibrous PP > membranous PE > microsphere PP, membranous PE > microsphere PP > fibrous PP and fibrous PP > microsphere PP > membranous PE, respectively. Results from high-throughput sequencing of 16S rRNA revealed that the membranous PE and fibrous PP raised the alpha diversities of the soil microbiota, whereas the diversity indexes of microbiota on MPs surfaces were significantly lower than those in the amended soils. MPs significantly altered the microbial community structure, especially for the enrichment of Acidobacteria and Bacteroidetes, the depletion of Deinococcus-Thermus and Chloroflexi. Aeromicrobium, Streptomyces, Mycobacterium, Janibacter, Nocardia, Arthrobacter were prone to inhabit on the MPs surfaces. PRACTITIONER POINTS: Three microplastics had different effects on soil enzyme activities. Fibrous PP had a more persistent effect on microbial activity. Membranous PE and fibrous PP raised the alpha diversities of soil microbiota. The effects of membranous PE and fibrous PP on microbial communities were similar. Distinct microbial communities were enriched on the surfaces of microplastics.

A review: The challenge, consensus, and confusion of describing odors and tastes in drinking water

Documentation exists for many chemicals that cause tastes and odors in water, however, water suppliers do not routinely monitor for these chemicals. Effective management of a taste-and-odor (T&O) problem in drinking water often requires good verbal description of the offending sensory experience. Experience demonstrates that obtaining verbal descriptions is challenging. To improve our understanding of communications, sensory science literature was reviewed to obtain descriptors for twenty-one chemicals acknowledged to cause T&O issues in drinking water. The review focused on pure chemicals above their odor threshold concentrations. Results reveal that descriptors follow four general categories. For select chemicals, strong consensus exists around a single or very few appropriate descriptors. Examples are "salty" for sodium and "chlorinous" for free chlorine. The next category has moderate agreement for several descriptors, with at least one major descriptor. For example the microbiological metabolite 2-methylisoborneol is most commonly described as "earthy/musty/moldy" but also "camphor, grass, and sweet". Some chemicals have weak agreement on their descriptors, but overall associate words with similar meaning. An example is the chemical toluene with descriptors of "solvent-like" words including "solvent", "gasoline", "paint-like", "cleaning fluid", and "etherish", but also "vinegar" and "sweet". The last chemical category possesses diverse descriptors with no consensus. For example, the oxylipin n-heptanal is described as "oily, fatty, chemical, musty/earthy/moldy, rancid, sweaty, grass, sickening, and stale". While descriptor diversity for select chemicals may not identify the cause of T&O, understanding that certain chemicals are perceived very differently aids in effective communications and eliminates confusion from expecting consumers or utility personnel to respond with consensus.