Microbial oils are proposed as a suitable alternative to petroleum‐based chemistry in terms of environmental preservation. These oils have traditionally been studied using sugar‐based feedstock, ...which implies high costs, substrate limitation, and high contamination risks. In this sense, low‐cost carbon sources such as volatile fatty acids (VFAs) are envisaged as promising building blocks for lipid biosynthesis to produce oil‐based bioproducts. VFAs can be generated from a wide variety of organic wastes through anaerobic digestion and further converted into lipids by oleaginous yeasts (OYs) in a fermentation process. These microorganisms can accumulate in the form of lipid bodies, lipids of up to 60% wt/wt of their biomass. In this context, OY is a promising biotechnological tool for biofuel and bioproduct generation using low‐cost VFA media as substrates. This review covers recent advances in microbial oil production from VFAs. Production of VFAs via anaerobic digestion processes and the involved metabolic pathways are reviewed. The main challenges as well as recent approaches for lipid overproduction are also discussed.
Microbial oil are proposed as a suitable alternative to petroleum‐based chemistry in terms of environmental preservation. These oils have traditionally been studied using sugar‐based feedstock. VFAs rich digestate (VFAs) is envisaged as promising low‐cost substrate reducing process cost as well as allowing wastes valorisation.
Microalgae are regarded as a potential biomass source for biofuel purposes. With regard to bioethanol production, microalgae seem to overcome traditional substrate drawbacks. Enzymatic activities are ...responsible for carbon allocation and hence for carbohydrate profiles. Enzyme activities may be manipulated by metabolic engineering; however, this goal may also be achieved by controlling environmental conditions of the culture system. We outline the key-enzymes as well as the main operational conditions applied to microalgae growth (inorganic nutrient supplementation, irradiance and temperature) that affect carbohydrate synthesis on microalgae and cyanobacteria. Normally, harsh conditions are needed for such a goal and thus, arrested microalgae growth may occur. Potential strategies to avoid arrested growth, while enhancing carbohydrate accumulation, were also pointed out in this review.
This study assessed the feasibility of melon and watermelon residues for the co-production of short-chain fatty acids (SCFAs) and hydrogen (H2) via single-stage anaerobic fermentation. The high ...content of carbohydrates and readily biodegradable organic matter in the wastes, along with the acid pH (5.6–5.8) imposed in the reactors, were key factors to reach high SCFAs and H2 co-production efficiencies. Mentioned conditions promoted a specialized microbial community dominated by Ruminococcus involved in the prevalence of the reverse β-oxidation pathway. This microbial metabolism caused the accumulation of isobutyric and caproic acids (76% of total SCFAs), resulting in a SCFAs production efficiency higher than 40% with concomitant high H2 production yields (395.5 and 62.7 mL H2/g volatile solids influent for melon and watermelon fermentation). A high hydraulic retention time (HRT) of 27 days, an organic loading rate of 3 g of volatile solids per day and liter of working volume and a fermentation temperature of 25 °C were also crucial for maximizing H2 production at acid pH. Overall, melon and watermelon wastes bioconversion efficiencies into H2 and SCFAs reached 64.0 and 58.7%, demonstrating the successful co-production of different bioproducts in a single-stage fermentation by establishing proper operational conditions.
•Single-stage fermentation successfully co-produced H2 and organic acids.•Isobutyric (41–44%) and caproic acids (32–35%) were the most abundant organic acids.•Reverse β-oxidation pathway prevalence resulted in high H2 and longer acids yields.•Reverse β-oxidation was mediated by Ruminococcus presence.•Operation conditions allowed the system to reach 58–64% efficiencies.
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•A new Lactobacillus pentosus strain was obtained by adaptive evolution.•Lactic acid yield from xylose at initial pH 7, 6 and 5 was enhanced by 2-fold.•Increase in xylose consumption ...rate was also shown when pH was set at 7.•Lactic acid productivity from wheat straw hydrolysate was increased by 1.4-fold.
Since xylose is the second most abundant sugar in lignocellulose, using microorganisms able to metabolize it into bio-based chemicals like lactic acid is an attractive approach. In this study, Lactobacillus pentosus CECT4023T was evolved to improve its xylose fermentation capacity even at acid pH by adaptive laboratory evolution in repeated anaerobic batch cultures at increasing xylose concentration. The resulting strain (named MAX2) presented between 1.5 and 2-fold more xylose consumption and lactic acid production than the parental strain in 20 g L−1 xylose defined media independently of the initial pH value. When the pH was controlled in bioreactor, lactic acid productivity at 16 h increased 1.4-fold when MAX2 was grown both in xylose defined media and in wheat straw hydrolysate. These results demonstrated the potential of this new strain to produce lactic acid from hemicellulosic substrates at low pH, reducing the need of using neutralizing agents in the process.
•Agroindustrial wastes as potential feedstock for volatile fatty acids production.•Anaerobic fermentation of agroindustrial wastes contributes to circular economy.•High bioconversion yields (50–60%) ...were reached in batch and continuous reactors.•Fermentation effluents with high content of long-chain VFAs.•Firmicutes was identify as key phylum for anaerobic fermentation of carbohydrates.
This study evaluated the feasibility of the anaerobic digestion as a sustainable valorisation strategy for volatile fatty acids production from agroindustrial waste (cucumber, tomato and lettuce). High bioconversion efficiencies were reached by operating the reactors at 25 °C, 3 g VS·d−1·L−1 with pH adjustment. Cucumber fermentation achieved the highest bioconversion (52.6%), whereas tomato degradation was the least efficient bioprocess (40.1%) due to the low pH (5.6) that partially inhibited the hydrolytic and acidogenic activities. In all cases, carboxylic acid profiles were mainly composed of volatile fatty acids with even carbon number. The developed microbial community exhibited high hydrolytic and acidogenic activities associated to carbohydrates degradation. This microbial population was dominated by Firmicutes phylum and showed a lack of acetogenic bacteria related with CH4 production, resulting in a remarkably high VFAs accumulation.
With increasing concerns regarding energy and environment, algae biofuel is generating considerable interest around the world. Nevertheless, the harvesting step required before downstream biomass ...processing is a major bottleneck. Commonly employed methods include addition of chemicals or use of mechanical equipment that increase dramatically the biofuel production cost. This review deals with naturally occurring processes that can help offset those costs by causing microalgae flocculation. Interaction theories are briefly reviewed. In addition, operational parameters such as pH, irradiance, nutrients, dissolved oxygen, and temperature effect on microalgae flocculation are evaluated. Finally, microalgae flocculation is also considered from an ecological point of view by taking advantage of their interaction with other microorganisms.
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•Successful acclimation of methanogenic culture to extreme ammonia levels in CSTR.•Efficient utilization of a 3rd generation biomass as biomethanation substrate.•The most abundant ...bacterium (Shinella spp.) was not affected by the ammonia levels.•C. ultunense increased significantly its abundance during the acclimation process.•Methanosarcina spp. was the most abundant methanogen at the highest ammonia levels.
Acclimatized anaerobic communities to high ammonia levels can offer a solution to the ammonia toxicity problem in biogas reactors. In the current study, a stepwise acclimation strategy up to 10g NH4+-N L−1, was performed in mesophilic (37±1°C) continuously stirred tank reactors. The reactors were co-digesting (20/80 based on volatile solid) cattle slurry and microalgae, a protein-rich, 3rd generation biomass. Throughout the acclimation period, methane production was stable with more than 95% of the uninhibited yield. Next generation 16S rRNA gene sequencing revealed a dramatic microbiome change throughout the ammonia acclimation process. Clostridium ultunense, a syntrophic acetate oxidizing bacteria, increased significantly alongside with hydrogenotrophic methanogen Methanoculleus spp., indicating strong hydrogenotrophic methanogenic activity at extreme ammonia levels (>7g NH4+-N L−1). Overall, this study demonstrated for the first time that acclimation of methanogenic communities to extreme ammonia levels in continuous AD process is possible, by developing a specialised acclimation AD microbiome.
The insulin-degrading enzyme (IDE) is a metalloendopeptidase with a high affinity for insulin. Human genetic polymorphisms in Ide have been linked to increased risk for T2DM. In mice, hepatic Ide ...ablation causes glucose intolerance and insulin resistance when mice are fed a regular diet.
These studies were undertaken to further investigate its regulatory role in glucose homeostasis and insulin sensitivity in diet-induced obesity.
To this end, we have compared the metabolic effects of loss versus gain of IDE function in mice fed a high-fat diet (HFD).
We demonstrate that loss of IDE function in liver (L-IDE-KO mouse) exacerbates hyperinsulinemia and insulin resistance without changes in insulin clearance but in parallel to an increase in pancreatic β-cell function. Insulin resistance was associated with increased FoxO1 activation and a ~2-fold increase of GLUT2 protein levels in the liver of HFD-fed mice in response to an intraperitoneal injection of insulin. Conversely, gain of IDE function (adenoviral delivery) improves glucose tolerance and insulin sensitivity, in parallel to a reciprocal ~2-fold reduction in hepatic GLUT2 protein levels. Furthermore, in response to insulin, IDE co-immunoprecipitates with the insulin receptor in liver lysates of mice with adenoviral-mediated liver overexpression of IDE.
We conclude that IDE regulates hepatic insulin action and whole-body glucose metabolism in diet-induced obesity via insulin receptor levels.
•Loss of hepatic IDE function exacerbates insulin resistance in mice fed a HFD.•Gain of hepatic IDE function improves insulin sensitivity in mice fed HFD.•Hepatic IDE appears to modulate insulin homeostasis via regulating β-cell function.
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