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\"Hundreds of million tonnes of agricultural and food waste are produced each year around the world, most of which is just that, waste. Anaerobic digestion, biogas and the heat and electricity that can be produced from it is still a nascent industry in many countries, yet the benefits of AD spread throughout the community: - Gives good financial returns to farmers and eco-entrepreneurs. - Helps community leaders meet various policies and legislative targets. - Offers an environmentally sensitive waste disposal option. - Provides a local heat and power supply, & creates employment opportunities - Reduces greenhouse gas emissions, as well as providing an organic fertilizer. Although the process of AD itself is relatively simple there are several system options available to meet the demands of different feedstocks. This book describes, in simple, easy to read language the five common systems of AD; how they work, the impact of scale, the basic requirements, the costs and financial implications, and how to get involved in this rapidly growing green industry\"--Provided by publisher.

The obstacle to optimal utilization of biogas technology is poor understanding of biogas microbiomes diversities over a wide geographical coverage. We performed random shotgun sequencing on twelve environmental samples. Randomized complete block design was utilized to assign the twelve treatments to four blocks, within eastern and central regions of Kenya. We obtained 42 million paired-end reads that were annotated against sixteen reference databases using two ENVO ontologies, prior to β-diversity studies. We identified 37 phyla, 65 classes and 132 orders. Bacteria dominated and comprised 28 phyla, 42 classes and 92 orders, conveying substrate’s versatility in the treatments. Though, Fungi and Archaea comprised 5 phyla, the Fungi were richer; suggesting the importance of hydrolysis and fermentation in biogas production. High β-diversity within the taxa was largely linked to communities’ metabolic capabilities. Clostridiales and Bacteroidales , the most prevalent guilds, metabolize organic macromolecules. The identified Cytophagales , Alteromonadales , Flavobacteriales , Fusobacteriales , Deferribacterales , Elusimicrobiales , Chlamydiales , Synergistales to mention but few, also catabolize macromolecules into smaller substrates to conserve energy. Furthermore, δ-Proteobacteria , Gloeobacteria and Clostridia affiliates syntrophically regulate P H2 and reduce metal to provide reducing equivalents. Methanomicrobiales and other Methanomicrobia species were the most prevalence Archaea , converting formate, CO 2(g) , acetate and methylated substrates into CH 4(g) . Thermococci , Thermoplasmata and Thermoprotei were among the sulfur and other metal reducing Archaea that contributed to redox balancing and other metabolism within treatments. Eukaryotes, mainly fungi were the least abundant guild, comprising largely Ascomycota and Basidiomycota species. Chytridiomycetes , Blastocladiomycetes and Mortierellomycetes were among the rare species, suggesting their metabolic and substrates limitations. Generally, we observed that environmental and treatment perturbations influenced communities’ abundance, β-diversity and reactor performance largely through stochastic effect. Understanding diversity of biogas microbiomes over wide environmental variables and its’ productivity provided insights into better management strategies that ameliorate biochemical limitations to effective biogas production.

The defining trait of obligate anaerobes is that oxygen blocks their growth, yet the underlying mechanisms are unclear. A popular hypothesis was that these microorganisms failed to evolve defences to protect themselves from reactive oxygen species (ROS) such as superoxide and hydrogen peroxide, and that this failure is what prevents their expansion to oxic habitats. However, studies reveal that anaerobes actually wield most of the same defences that aerobes possess, and many of them have the capacity to tolerate substantial levels of oxygen. Therefore, to understand the structures and real-world dynamics of microbial communities, investigators have examined how anaerobes such as Bacteroides, Desulfovibrio, Pyrococcus and Clostridium spp. struggle and cope with oxygen. The hypoxic environments in which these organisms dwell — including the mammalian gut, sulfur vents and deep sediments — experience episodic oxygenation. In this Review, we explore the molecular mechanisms by which oxygen impairs anaerobes and the degree to which bacteria protect their metabolic pathways from it. The emergent view of anaerobiosis is that optimal strategies of anaerobic metabolism depend upon radical chemistry and low-potential metal centres. Such catalytic sites are intrinsically vulnerable to direct poisoning by molecular oxygen and ROS. Observations suggest that anaerobes have evolved tactics that either minimize the extent to which oxygen disrupts their metabolism or restore function shortly after the stress has dissipated.Hypoxic environments in which anaerobes dwell experience episodic oxygenation, which can be toxic to these organisms, yet many anaerobes have the capacity to tolerate substantial levels of oxygen. In this Review, Lu and Imlay explore the molecular mechanisms by which oxygen impairs anaerobic bacteria and the degree to which anaerobic bacteria protect themselves from oxidative stress.

Konjac glucomannan (KGM) has been shown to relieve constipation, which could be associated with increased stool bulk and improved colonic ecology. This placebo-controlled study consisted of a 21-d placebo period, a 7-d adaptation period when volunteers consumed KGM progressively, and a 21-d KGM-supplemented period (1.5 g/meal, 4.5 g/d). Eight healthy adults consumed 7-d cycle menus of typical low-fiber Chinese food throughout the study. The gastrointestinal response was monitored daily. Stools were fully collected on days 15 to 21 of placebo and KGM periods to determine the fecal mass, components, microflora, and short-chain fatty acid contents. The KGM supplement significantly increased the mean defecation frequency (number/day), wet stool weight, and dry stool weight (g/d) by ∼27.0% ( P < 0.05), 30.2% ( P < 0.05), and 21.7% ( P < 0.05), respectively. The dry fecal mass increased mainly in the plant and soluble material, whereas bacterial mass tended to increase from 12.9 ± 1.6 to 13.6 ± 2.7 g/d ( P > 0.05). However, KGM significantly promoted the fecal concentrations (log counts/g wet feces) of lactobacilli ( P < 0.05) and total bacteria ( P < 0.05), and promoted the daily output (log counts per day) of bifidobacteria ( P < 0.05), lactobacilli ( P < 0.05), and total bacteria ( P < 0.05) as evaluated by the fluorescence in situ hybridization method. KGM supplement also promoted colonic fermentation as shown in the decreased fecal pH ( P < 0.05) and increased fecal short-chain fatty acid concentrations ( P < 0.05). Supplementation of KGM into a low-fiber diet promoted the defecation frequency in healthy adults, possibly by increasing the stool bulk, thus promoting the growth of lactic acid bacteria and colonic fermentation.

Key Points Acetogenic bacteria are an anaerobic group of microorganisms that use the Wood–Ljungdahl pathway (WLP) to live from the conversion of two molecules of carbon dioxide (CO 2 ) to acetate. The WLP is suggested to be one of the oldest biochemical pathways and is the only pathway that couples the fixation of inorganic carbon to energy conservation. In acetogenic bacteria, the WLP is not directly involved in energy conservation but is coupled to one of two membrane-bound enzyme complexes. Acetogenic bacteria use either the Rnf complex (a ferredoxin–NAD + oxidoreductase) or potentially an Ech hydrogenase (a ferredoxin–H 2 oxidoreductase) for chemiosmotic energy conservation. The coupling ion can be either Na + or H + . The actual energy equivalent in the acetogenic metabolism is the iron–sulphur cluster of the small protein ferredoxin. The metabolism is focused on transferring electrons to this soluble electron carrier. Acetogenic bacteria should be classified as Rnf- and Ech-containing acetogens according to the bioenergetic differences between organisms in these two groups. Acetogenic bacteria rely on the reduction of CO 2 to acetate by the Wood–Ljungdahl pathway to couple energy conservation and biomass production. However, how energy is conserved in acetogens has been an enigma. Here, Schuchmann and Müller describe recent insights into the biochemistry and genetics of the energy metabolism of model acetogens, highlight how these bacteria link CO 2 fixation to energy conservation and propose a new bioenergetic classification for acetogens. Life on earth evolved in the absence of oxygen with inorganic gases as potential sources of carbon and energy. Among the alternative mechanisms for carbon dioxide (CO 2 ) fixation in the living world, only the reduction of CO 2 by the Wood–Ljungdahl pathway, which is used by acetogenic bacteria, complies with the two requirements to sustain life: conservation of energy and production of biomass. However, how energy is conserved in acetogenic bacteria has been an enigma since their discovery. In this Review, we discuss the latest progress on the biochemistry and genetics of the energy metabolism of model acetogens, elucidating how these bacteria couple CO 2 fixation to energy conservation.

Objective: The aim of the present study is to investigate the effect of antioxidant polyphenol-rich pomegranate juice (PJ) supplementation for 5 weeks on patients with stable chronic obstructive pulmonary disease (COPD), since the oxidative stress plays a major role in the evolution and pathophysiology of COPD. Design: A randomized, double-blind, placebo-controlled trial was conducted. Subjects: A total of 30 patients with stable COPD were randomly distributed in two groups (15 patients each). Interventions: Both groups consumed either 400 ml PJ daily or matched placebo (synthetic orange-flavoured drink) for 5 weeks. Trolox Equivalent Antioxidant Capacity (TEAC) of PJ, blood parameters (14 haematological and 18 serobiochemical), respiratory function variables, bioavailability of PJ polyphenols (plasma and urine) and urinary isoprostane (8-iso-PGF₂(α)) were evaluated. Results: The daily dose of PJ (containing 2.66 g polyphenols) provided 4 mmol/l TEAC. None of the polyphenols present in PJ were detected in plasma or in urine of volunteers. The most abundant PJ polyphenols, ellagitannins, were metabolized by the colonic microflora of COPD patients to yield two major metabolites in both plasma and urine (dibenzopyranone derivatives) with no TEAC. No differences were found (P>0.05) between PJ and placebo groups for any of the parameters evaluated (serobiochemical and haematological), urinary 8-iso-PGF₂(α), respiratory function variables and clinical symptoms of COPD patients. Conclusions: Our results suggest that PJ supplementation adds no benefit to the current standard therapy in patients with stable COPD. The high TEAC of PJ cannot be extrapolated in vivo probably due to the metabolism of its polyphenols by the colonic microflora. The understanding of the different bioavailability of dietary polyphenols is critical before claiming any antioxidant-related health benefit. Sponsorship: 'Fundación Séneca' (Murcia, Spain), Project PB/18/FS/02 and Spanish CICYT, Project AGL2003-02195.

The succession from aerobic and facultative anaerobic bacteria to obligate anaerobes in the infant gut along with the differences between the compositions of the mucosally adherent vs. luminal microbiota suggests that the gut microbes consume oxygen, which diffuses into the lumen from the intestinal tissue, maintaining the lumen in a deeply anaerobic state. Remarkably, measurements of luminal oxygen levels show nearly identical pO₂ (partial pressure of oxygen) profiles in conventional and germ-free mice, pointing to the existence of oxygen consumption mechanisms other than microbial respiration. In vitro experiments confirmed that the luminal contents of germ-free mice are able to chemically consume oxygen (e.g., via lipid oxidation reactions), although at rates significantly lower than those observed in the case of conventionally housed mice. For conventional mice, we also show that the taxonomic composition of the gut microbiota adherent to the gut mucosa and in the lumen throughout the length of the gut correlates with oxygen levels. At the same time, an increase in the biomass of the gut microbiota provides an explanation for the reduction of luminal oxygen in the distal vs. proximal gut. These results demonstrate how oxygen from the mammalian host is used by the gut microbiota, while both the microbes and the oxidative chemical reactions regulate luminal oxygen levels, shaping the composition of the microbial community throughout different regions of the gut.

Akkermansia muciniphila has evolved to specialize in the degradation and utilization of host mucus, which it may use as the sole source of carbon and nitrogen. Mucus degradation and fermentation by A. muciniphila are known to result in the liberation of oligosaccharides and subsequent production of acetate, which becomes directly available to microorganisms in the vicinity of the intestinal mucosa. Coculturing experiments of A . muciniphila with non-mucus-degrading butyrate-producing bacteria Anaerostipes caccae , Eubacterium hallii , and Faecalibacterium prausnitzii resulted in syntrophic growth and production of butyrate. In addition, we demonstrate that the production of pseudovitamin B 12 by E. hallii results in production of propionate by A. muciniphila , which suggests that this syntrophy is indeed bidirectional. These data are proof of concept for syntrophic and other symbiotic microbe-microbe interactions at the intestinal mucosal interface. The observed metabolic interactions between A . muciniphila and butyrogenic bacterial taxa support the existence of colonic vitamin and butyrate production pathways that are dependent on host glycan production and independent of dietary carbohydrates. We infer that the intestinal symbiont A. muciniphila can indirectly stimulate intestinal butyrate levels in the vicinity of the intestinal epithelial cells with potential health benefits to the host. IMPORTANCE The intestinal microbiota is said to be a stable ecosystem where many networks between microorganisms are formed. Here we present a proof of principle study of microbial interaction at the intestinal mucus layer. We show that indigestible oligosaccharide chains within mucus become available for a broad range of intestinal microbes after degradation and liberation of sugars by the species Akkermansia muciniphila . This leads to the microbial synthesis of vitamin B 12 , 1,2-propanediol, propionate, and butyrate, which are beneficial to the microbial ecosystem and host epithelial cells. The intestinal microbiota is said to be a stable ecosystem where many networks between microorganisms are formed. Here we present a proof of principle study of microbial interaction at the intestinal mucus layer. We show that indigestible oligosaccharide chains within mucus become available for a broad range of intestinal microbes after degradation and liberation of sugars by the species Akkermansia muciniphila . This leads to the microbial synthesis of vitamin B 12 , 1,2-propanediol, propionate, and butyrate, which are beneficial to the microbial ecosystem and host epithelial cells.

The herbivore digestive tract is home to a complex community of anaerobic microbes that work together to break down lignocellulose. These microbiota are an untapped resource of strains, pathways and enzymes that could be applied to convert plant waste into sugar substrates for green biotechnology. We carried out more than 400 parallel enrichment experiments from goat faeces to determine how substrate and antibiotic selection influence membership, activity, stability and chemical productivity of herbivore gut communities. We assembled 719 high-quality metagenome-assembled genomes (MAGs) that are unique at the species level. More than 90% of these MAGs are from previously unidentified herbivore gut microorganisms. Microbial consortia dominated by anaerobic fungi outperformed bacterially dominated consortia in terms of both methane production and extent of cellulose degradation, which indicates that fungi have an important role in methane release. Metabolic pathway reconstructions from MAGs of 737 bacteria, archaea and fungi suggest that cross-domain partnerships between fungi and methanogens enabled production of acetate, formate and methane, whereas bacterially dominated consortia mainly produced short-chain fatty acids, including propionate and butyrate. Analyses of carbohydrate-active enzyme domains present in each anaerobic consortium suggest that anaerobic bacteria and fungi employ mostly complementary hydrolytic strategies. The division of labour among herbivore anaerobes to degrade plant biomass could be harnessed for industrial bioprocessing. More than 400 parallel enrichment experiments from goat faeces are analysed using metagenomics to evaluate how substrate and antibiotic selection affect membership, activity, stability and chemical productivity of herbivore gut microbiomes.

Co-aggregation of anaerobic microorganisms into suspended microbial biofilms (aggregates) serves ecological and biotechnological functions. Tightly packed aggregates of metabolically interdependent bacteria and archaea play key roles in cycling of carbon and nitrogen. Additionally, in biotechnological applications, such as wastewater treatment, microbial aggregates provide a complete metabolic network to convert complex organic material. Currently, experimental data explaining the mechanisms behind microbial co-aggregation in anoxic environments is scarce and scattered across the literature. To what extent does this process resemble co-aggregation in aerobic environments? Does the limited availability of terminal electron acceptors drive mutualistic microbial relationships, contrary to the commensal relationships observed in oxygen-rich environments? And do co-aggregating bacteria and archaea, which depend on each other to harvest the bare minimum Gibbs energy from energy-poor substrates, use similar cellular mechanisms as those used by pathogenic bacteria that form biofilms? Here, we provide an overview of the current understanding of why and how mixed anaerobic microbial communities co-aggregate and discuss potential future scientific advancements that could improve the study of anaerobic suspended aggregates. Key points • Metabolic dependency promotes aggregation of anaerobic bacteria and archaea • Flagella, pili, and adhesins play a role in the formation of anaerobic aggregates • Cyclic di-GMP/AMP signaling may trigger the polysaccharides production in anaerobes