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Haloalkane dehalogenases (HLDs) convert halogenated compounds to corresponding alcohols, halides, and protons. They belong to α/β-hydrolases, and their principal catalytic mechanism is S N 2 nucleophilic substitution followed by the addition of water. Since HLDs generally have broad and different substrate specificities, they have various biotechnological applications. HLDs have previously been believed to be present only in bacterial strains that utilize xenobiotic halogenated compounds, and three archetypal HLDs, i.e., DhlA, DhaA, and LinB, have been intensively investigated by biochemical, structural, and computational analyses. Furthermore, by using the resulting data and target-selected random mutagenesis approaches, these HLDs have been successfully engineered to improve their substrate specificities and activities. In addition, important insights into protein evolution have been obtained by studying these HLDs. At the same time, the genome and metagenome information has revealed that HLD homologues are widely distributed in many bacterial strains, including ones that have not been reported to degrade halogenated compounds. Some of these cryptic HLD homologues have been experimentally confirmed to be “true” HLDs with unique substrate specificities and enantioselectivities. Although their biological functions and physiological roles remain mysterious, these potential HLDs are considered promising materials for the development of new biocatalysts.

The red macroalgae (seaweed) Asparagopsis spp. has shown to reduce ruminant enteric methane (CH 4 ) production up to 99% in vitro . The objective of this study was to determine the effect of Asparagopsis taxiformis on CH 4 production (g/day per animal), yield (g CH 4 /kg dry matter intake (DMI)), and intensity (g CH 4 /kg ADG); average daily gain (ADG; kg gain/day), feed conversion efficiency (FCE; kg ADG/kg DMI), and carcass and meat quality in growing beef steers. Twenty-one Angus-Hereford beef steers were randomly allocated to one of three treatment groups: 0% (Control), 0.25% (Low), and 0.5% (High) A . taxiformis inclusion based on organic matter intake. Steers were fed 3 diets: high, medium, and low forage total mixed ration (TMR) representing life-stage diets of growing beef steers. The Low and High treatments over 147 days reduced enteric CH 4 yield 45 and 68%, respectively. However, there was an interaction between TMR type and the magnitude of CH 4 yield reduction. Supplementing low forage TMR reduced CH 4 yield 69.8% ( P <0.01) for Low and 80% ( P <0.01) for High treatments. Hydrogen (H 2 ) yield (g H 2 /DMI) increased ( P <0.01) 336 and 590% compared to Control for the Low and High treatments, respectively. Carbon dioxide (CO 2 ) yield (g CO 2 /DMI) increased 13.7% between Control and High treatments (P = 0.03). No differences were found in ADG, carcass quality, strip loin proximate analysis and shear force, or consumer taste preferences. DMI tended to decrease 8% ( P = 0.08) in the Low treatment and DMI decreased 14% ( P <0.01) in the High treatment. Conversely, FCE tended to increase 7% in Low ( P = 0.06) and increased 14% in High ( P <0.01) treatment compared to Control. The persistent reduction of CH 4 by A . taxiformis supplementation suggests that this is a viable feed additive to significantly decrease the carbon footprint of ruminant livestock and potentially increase production efficiency.

Non-targeted analysis (NTA) and suspect screening analysis (SSA) are powerful techniques that rely on high-resolution mass spectrometry (HRMS) and computational tools to detect and identify unknown or suspected chemicals in the exposome. Fully understanding the chemical exposome requires characterization of both environmental media and human specimens. As such, we conducted a review to examine the use of different NTA and SSA methods in various exposure media and human samples, including the results and chemicals detected. The literature review was conducted by searching literature databases, such as PubMed and Web of Science, for keywords, such as “non-targeted analysis”, “suspect screening analysis” and the exposure media. Sources of human exposure to environmental chemicals discussed in this review include water, air, soil/sediment, dust, and food and consumer products. The use of NTA for exposure discovery in human biospecimen is also reviewed. The chemical space that has been captured using NTA varies by media analyzed and analytical platform. In each media the chemicals that were frequently detected using NTA were: per- and polyfluoroalkyl substances (PFAS) and pharmaceuticals in water, pesticides and polyaromatic hydrocarbons (PAHs) in soil and sediment, volatile and semi-volatile organic compounds in air, flame retardants in dust, plasticizers in consumer products, and plasticizers, pesticides, and halogenated compounds in human samples. Some studies reviewed herein used both liquid chromatography (LC) and gas chromatography (GC) HRMS to increase the detected chemical space (16%); however, the majority (51%) only used LC-HRMS and fewer used GC-HRMS (32%). Finally, we identify knowledge and technology gaps that must be overcome to fully assess potential chemical exposures using NTA. Understanding the chemical space is essential to identifying and prioritizing gaps in our understanding of exposure sources and prior exposures.Impact statementThis review examines the results and chemicals detected by analyzing exposure media and human samples using high-resolution mass spectrometry based non-targeted analysis (NTA) and suspect screening analysis (SSA).

Marine fungi produce many halogenated metabolites with a variety of structures, from acyclic entities with a simple linear chain to multifaceted polycyclic molecules. Over the past few decades, their pharmaceutical and medical application have been explored and still the door is kept open due to the need of new drugs from relatively underexplored sources. Biological properties of halogenated compounds such as anticancer, antiviral, antibacterial, anti-inflammatory, antifungal, antifouling, and insecticidal activity have been investigated. This review describes the chemical structures and biological activities of 217 halogenated compounds derived mainly from Penicillium and Aspergillus marine fungal strains reported from 1994 to 2019.

Deuterium labeling is of great value in organic synthesis and the pharmaceutical industry. However, the state-of-the-art C–H/C–D exchange using noble metal catalysts or strong bases/acids suffers from poor functional group tolerances, poor selectivity and lack of scope for generating molecular complexity. Herein, we demonstrate the deuteration of halides using heavy water as the deuteration reagent and porous CdSe nanosheets as the catalyst. The deuteration mechanism involves the generation of highly active carbon and deuterium radicals via photoinduced electron transfer from CdSe to the substrates, followed by tandem radicals coupling process, which is mechanistically distinct from the traditional methods involving deuterium cations or anions. Our deuteration strategy shows better selectivity and functional group tolerances than current C–H/C–D exchange methods. Extending the synthetic scope, deuterated boronic acids, halides, alkynes, and aldehydes can be used as synthons in Suzuki coupling, Click reaction, C–H bond insertion reaction etc. for the synthesis of complex deuterated molecules. Developing convenient deuterium labeling procedures is important in organic synthesis and the pharmaceutical industry. Here, the authors report a mild photocatalytic strategy for controllable deuteration of halides using D 2 O as the reagent and porous CdSe nanosheets as the catalyst.

Fastidious anaerobic bacteria play critical roles in environmental bioremediation of halogenated compounds. However, their characterization and application have been largely impeded by difficulties in growing them in pure culture. Thus far, no pure culture has been reported to respire on the notorious polychlorinated biphenyls (PCBs), and functional genes responsible for PCB detoxification remain unknown due to the extremely slow growth of PCB-respiring bacteria. Here we report the successful isolation and characterization of three Dehalococcoides mccartyi strains that respire on commercial PCBs. Using high-throughput metagenomic analysis, combined with traditional culture techniques, tetrachloroethene (PCE) was identified as a feasible alternative to PCBs to isolate PCB-respiring Dehalococcoides from PCB-enriched cultures. With PCE as an alternative electron acceptor, the PCBrespiring Dehalococcoides were boosted to a higher cell density (1.2 × 10⁸ to 1.3 × 10⁸ cells per mL on PCE vs. 5.9 × 10⁻ to 10.4 × 10⁻ cells per mL on PCBs) with a shorter culturing time (30 d on PCE vs. 150 d on PCBs). The transcriptomic profiles illustrated that the distinct PCB dechlorination profile of each strain was predominantly mediated by a single, novel reductive dehalogenase (RDase) catalyzing chlorine removal from both PCBs and PCE. The transcription levels of PCB-RDase genes are 5-60 times higher than the genome-wide average. The cultivation of PCB-respiring Dehalococcoides in pure culture and the identification of PCB-RDase genes deepen our understanding of organohalide respiration of PCBs and shed light on in situ PCB bioremediation.

Halogenated organic compounds (organohalides) are globally prevalent, recalcitrant toxic, and carcinogenic environmental pollutants. Select microorganisms encode enzymes known as reductive dehalogenases (EC 1.97.1.8) that catalyze reductive dehalogenation reactions resulting in the generation of lesser-halogenated compounds that may be less toxic and more biodegradable. Recent breakthroughs in enzyme structure determination, elucidation of the mechanisms of reductive dehalogenation, and in heterologous expression of functional reductive dehalogenase enzymes have substantially increased our understanding of this fascinating class of enzymes. This knowledge has created opportunities for more versatile (in situ and ex situ) biologically-mediated organohalide destruction strategies. Reductive dehalogenases catalyze reactions for potential organohalide destruction, which is a pressing global environmental problem. Recent crystal studies have shed light on structure–function relationships of these enzymes. Structure–function relationship and homology modeling will play a pivotal role in the full characterization of these enzymes moving forward. A summary of characterized and identified reductive dehalogenases is reported in this review, revealing the diversity of substrates and preferred electron donors for microorganisms capable of reductive dehalogenation. Recombinant expression of functional dehalogenases is a new breakthrough in this field, overcoming the problems of slow growth and low biomass densities of ORB, which will facilitate a rapid increase in the understanding of the biology and application of these enzymes.

Seaweeds are broadly distributed and represent an important source of secondary metabolites (e.g., halogenated compounds, polyphenols) eliciting various pharmacological activities and playing a relevant ecological role in the anti-epibiosis. Importantly, host (as known as basibiont such as algae)–microbe (as known as epibiont such as bacteria) interaction (as known as halobiont) is a driving force for coevolution in the marine environment. Nevertheless, halobionts may be fundamental (harmless) or detrimental (harmful) to the functioning of the host. In addition to biotic factors, abiotic factors (e.g., pH, salinity, temperature, nutrients) regulate halobionts. Spatiotemporal and functional exploration of such dynamic interactions appear crucial. Indeed, environmental stress in a constantly changing ocean may disturb complex mutualistic relations, through mechanisms involving host chemical defense strategies (e.g., secretion of secondary metabolites and antifouling chemicals by quorum sensing). It is worth mentioning that many of bioactive compounds, such as terpenoids, previously attributed to macroalgae are in fact produced or metabolized by their associated microorganisms (e.g., bacteria, fungi, viruses, parasites). Eventually, recent metagenomics analyses suggest that microbes may have acquired seaweed associated genes because of increased seaweed in diets. This article retrospectively reviews pertinent studies on the spatiotemporal and functional seaweed-associated microbiota interactions which can lead to the production of bioactive compounds with high antifouling, theranostic, and biotechnological potential.

In studying indoor air quality, the concentration of volatile organic compounds (VOCs) emitted from wood-based panels and products is considered a main influencing factor. VOCs with low concentrations, even below the detection limit, can also have negative effects. Herein, VOCs emitted from particleboards and laminated boards were collected and analysed by GC-MS, and key odorous VOCs were identified using the odor activity value. Compared with laminated boards, particleboards showed higher concentration of total volatile organic compound (TVOC). Halogenated compounds, esters, and aromatic hydrocarbons were main contributors to total VOC emissions, which could relate to the addition of additives used during panel manufacturing. Eleven VOCs were identified that listed as hazardous air pollutants in the US Clean Air Act. Aldehydes were the major contributor to the OAV; most aldehydes have unpleasant odors, such as fatty acids, which contribute to the smell of surrounding air. Octanal was the dominant odorant in the aldehyde compounds.

Variation of volatile organic compound (VOC) concentration and composition in an active landfill were monitored by a developed static chamber for 2 years. The landfill gas from 82 sampling points including 70 points on working face, 8 points on geomembrane (GMB), and 4 points on final cover were analyzed for VOCs by GC-MS. Twenty-eight types of VOCs were detected, including terpenes, sulfur compounds, aromatics, hydrocarbon, oxygenated compounds, aldehyde compounds, and halogenated compounds. Terpenes were the dominant VOCs recorded in the spring, autumn, and winter seasons, whereas sulfur compounds dominated in the summer season. Limonene, ethyl alcohol, and acetone were identified as the main VOCs emitted from the waste working face of the landfill. Limonene dominated the terpenes with a maximum concentration of 43.29 μg m −3 in the autumn season. Limonene was also the dominant VOC escaping from the defects of geomembrane temporary cover reaching an average concentration 38 μg m −3 . The defects of geomembranes can be a great emission source of VOCs. Emission rate of limonene was 2.24 times higher than that on the working face. VOC concentrations on the final cover can be 166 times less than those obtained on the working face. VOC emitted from the landfill did not represent a health threat for human health. However, concentrations of methyl mercaptan and ethanethiol on the working face were 3.4–22.8 times greater than their odor threshold, which were the main compounds responsible for odor nuisance. Results obtained from CALPUFF model indicated that methyl mercaptan and ethanethiol would not be a nuisance for the residents around the landfill. However, these compounds are harmful to the workers on the landfill.