Pontiella agarivorans sp. nov., a novel marine anaerobic bacterium capable of degrading macroalgal polysaccharides and fixing nitrogen.

Marine macroalgae produce abundant and diverse polysaccharides, which contribute substantially to the organic matter exported to the deep ocean. Microbial degradation of these polysaccharides plays an important role in the turnover of macroalgal biomass. Various members of the Planctomycetes-Verrucomicrobia-Chlamydia (PVC) superphylum are degraders of polysaccharides in widespread anoxic environments. In this study, we isolated a novel anaerobic bacterial strain NLcol2T from microbial mats on the surface of marine sediments offshore Santa Barbara, CA, USA. Based on 16S ribosomal RNA (rRNA) gene and phylogenomic analyses, strain NLcol2T represents a novel species within the Pontiella genus in the Kiritimatiellota phylum (within the PVC superphylum). Strain NLcol2T is able to utilize various monosaccharides, disaccharides, and macroalgal polysaccharides such as agar and É©-carrageenan. A near-complete genome also revealed an extensive metabolic capacity for anaerobic degradation of sulfated polysaccharides, as evidenced by 202 carbohydrate-active enzymes (CAZymes) and 165 sulfatases. Additionally, its ability of nitrogen fixation was confirmed by nitrogenase activity detected during growth on nitrogen-free medium, and the presence of nitrogenases (nifDKH) encoded in the genome. Based on the physiological and genomic analyses, this strain represents a new species of bacteria that may play an important role in the degradation of macroalgal polysaccharides and with relevance to the biogeochemical cycling of carbon, sulfur, and nitrogen in marine environments. Strain NLcol2T (= DSM 113125T = MCCC 1K08672T) is proposed to be the type strain of a novel species in the Pontiella genus, and the name Pontiella agarivorans sp. nov. is proposed.IMPORTANCEGrowth and intentional burial of marine macroalgae is being considered as a carbon dioxide reduction strategy but elicits concerns as to the fate and impacts of this macroalgal carbon in the ocean. Diverse heterotrophic microbial communities in the ocean specialize in these complex polymers such as carrageenan and fucoidan, for example, members of the Kiritimatiellota phylum. However, only four type strains within the phylum have been cultivated and characterized to date, and there is limited knowledge about the metabolic capabilities and functional roles of related organisms in the environment. The new isolate strain NLcol2T expands the known substrate range of this phylum and further reveals the ability to fix nitrogen during anaerobic growth on macroalgal polysaccharides, thereby informing the issue of macroalgal carbon disposal.

Metagenomics analysis yields assembled genomes from prokaryotic anaerobes with polymer-degrading potential.

Anaerobic microbial communities are often highly degradative, such as those found in the herbivore rumen and large-scale anaerobic digesters. Since the microbial communities in these systems degrade recalcitrant organic polymers, we hypothesize that some microbes in anaerobic environments may be involved in man-made plastic association, deformation, or even breakdown. While efforts have been put toward characterizing microbial communities, many microbes remain unidentified until they can be sufficiently cultivated to generate enough genetic material to assemble high-quality metagenome assemblies and reference genomes. In this study, microbial consortia from goat fecal pellets and anaerobic digester sludge were cultivated for over 6 weeks to assemble metagenomes from novel anaerobic taxa with potential degradative activity. To select for microbes with potential plastic-degrading abilities, plastic strips were included in culture, though the presence of plastic did not appear to enrich for particularly degradative consortia, yet it did select for novel species that otherwise may not have been characterized. Whole-genome shotgun sequencing enabled assembly of 72 prokaryotic metagenome-assembled genomes (MAGs) with >90% completion, <5% contamination, and an N50 >10,000 bp; 17 of these MAGs are classified as novel species given their lack of similarity to publicly available genomes and MAGs. These 72 MAGs vary in predicted carbohydrate-degrading abilities, with genes predicted to encode fewer than 10 or up to nearly 400 carbohydrate-active enzymes. Overall, this enrichment strategy enables characterization of less abundant MAGs in a community, and the MAGs identified here can be further mined to advance understanding of degradative anaerobic microbial consortia.

Microbial communities and their enzymes facilitate degradation of recalcitrant polymers in anaerobic digestion.

Microbial consortia efficiently degrade complex biopolymers found in the organic fraction of municipal solid waste (OFMSW). Through enzyme production and division of labor during anaerobic digestion, microbial communities break down recalcitrant polymers and make fermentation products, including methane. However, microbial communities remain underutilized for waste degradation as it remains difficult to characterize and predict microbial interactions during waste breakdown, especially as cultivation conditions change drastically throughout anaerobic digestion. This review discusses recent progress and opportunities in cultivating natural and engineered consortia for OFMSW hydrolysis, including how recalcitrant substrates are degraded by enzymes as well as the critical factors that govern microbial interactions and culture stability. Methods to measure substrate degradation are also reviewed, and we demonstrate the need for increased standardization to enable comparisons across different environments.

Improved soluble expression and use of recombinant human renalase.

Electrochemical bioreactor systems have enjoyed significant attention in the past few decades, particularly because of their applications to biobatteries, artificial photosynthetic systems, and microbial electrosynthesis. A key opportunity with electrochemical bioreactors is the ability to employ cofactor regeneration strategies critical in oxidative and reductive enzymatic and cell-based biotransformations. Electrochemical cofactor regeneration presents several advantages over other current cofactor regeneration systems, such as chemoenzymatic multi-enzyme reactions, because there is no need for a sacrificial substrate and a recycling enzyme. Additionally, process monitoring is simpler and downstream processing is less costly. However, the direct electrochemical reduction of NAD(P)+ on a cathode may produce adventitious side products, including isomers of NAD(P)H that can act as potent competitive inhibitors to NAD(P)H-requiring enzymes such as dehydrogenases. To overcome this limitation, we examined how nature addresses the adventitious formation of isomers of NAD(P)H. Specifically, renalases are enzymes that catalyze the oxidation of 1,2- and 1,6-NAD(P)H to NAD(P)+, yielding an effective recycling of unproductive NAD(P)H isomers. We designed several mutants of recombinant human renalase isoform 1 (rhRen1), expressed them in E. coli BL21(DE3) to enhance protein solubility, and evaluated the activity profiles of the renalase variants against NAD(P)H isomers. The potential for rhRen1 to be employed in engineering applications was then assessed in view of the enzyme's stability upon immobilization. Finally, comparative modeling was performed to assess the underlying reasons for the enhanced solubility and activity of the mutant enzymes.