Abstract: Agro-industrial waste is highly nutritious in nature and facilitates microbial growth. Most agricultural wastes are lignocellulosic in nature; a large fraction of it is composed of carbohydrates. Agricultural residues can thus be used for the production of various value-added products, such as industrially important enzymes. Agro-industrial wastes, such as sugar cane bagasse, corn cob and rice bran, have been widely investigated via different fermentation strategies for the production of enzymes. Solid-state fermentation holds much potential compared with submerged fermentation methods for the utilization of agro-based wastes for enzyme production. This is because the physical–chemical nature of many lignocellulosic substrates naturally lends itself to solid phase culture, and thereby represents a means to reap the acknowledged potential of this fermentation method. Recent studies have shown that pretreatment technologies can greatly enhance enzyme yields by several fold. This article gives an overview of how agricultural waste can be productively harnessed as a raw material for fermentation. Furthermore, a detailed analysis of studies conducted in the production of different commercially important enzymes using lignocellulosic food waste has been provided.

Abstract: Microbial aromatic catabolism offers a promising approach to convert lignin, a vast source of renewable carbon, into useful products. Aryl-O-demethylation is an essential biochemical reaction to ultimately catabolize coniferyl and sinapyl lignin-derived aromatic compounds, and is often a key bottleneck for both native and engineered bioconversion pathways. Here, we report the comprehensive characterization of a promiscuous P450 aryl-O-demethylase, consisting of a cytochrome P450 protein from the family CYP255A (GcoA) and a three-domain reductase (GcoB) that together represent a new two-component P450 class. Though originally described as converting guaiacol to catechol, we show that this system efficiently demethylates both guaiacol and an unexpectedly wide variety of lignin-relevant monomers. Structural, biochemical, and computational studies of this novel two-component system elucidate the mechanism of its broad substrate specificity, presenting it as a new tool for a critical step in biological lignin conversion.

Abstract: Methane (CH4) is a potent greenhouse gas that is released from fossil fuels and is also produced by microbial activity, with at least one billion tonnes of CH4 being formed and consumed by microorganisms in a single year 1 . Complex methanogenesis pathways used by archaea are the main route for bioconversion of carbon dioxide (CO2) to CH4 in nature2–4. Here, we report that wild-type iron-iron (Fe-only) nitrogenase from the bacterium Rhodopseudomonas palustris reduces CO2 simultaneously with nitrogen gas (N2) and protons to yield CH4, ammonia (NH3) and hydrogen gas (H2) in a single enzymatic step. The amount of CH4 produced by purified Fe-only nitrogenase was low compared to its other products, but CH4 production by this enzyme in R. palustris was sufficient to support the growth of an obligate CH4-utilizing Methylomonas strain when the two microorganisms were grown in co-culture, with oxygen (O2) added at intervals. Other nitrogen-fixing bacteria that we tested also formed CH4 when expressing Fe-only nitrogenase, suggesting that this is a general property of this enzyme. The genomes of 9% of diverse nitrogen-fixing microorganisms from a range of environments encode Fe-only nitrogenase. Our data suggest that active Fe-only nitrogenase, present in diverse microorganisms, contributes CH4 that could shape microbial community interactions.

Abstract: This study aimed to determine the suitability of several organic waste substrates to be processed by the larvae of the black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) (BSFL) in a value-added bioconversion system. Three types of organic waste (brewer's waste, solid phase of pig manure, and semidigested grass) were tested and compared with a standard larval diet, broll (wheat middling). Larval survival and growth, chemical composition of the resulting prepupae, conversion ratios of nutrients and waste dry matter, and waste reduction rate were measured. Larval survival was high in all tested substrates. Compared with the larvae fed pig manure or semidigested grass, those fed standard diet or brewer's waste showed shorter development time, higher weight gain, and higher prepupal crude protein and crude fat content. BSFL also reduce more dry matter in the standard diet or in brewer's waste than in the other two substrates. On the other hand, larvae fed semidigested grass took 70 d to complete development and suffered fat loss. Thus, we suggest that brewer's waste is the most suitable substrate among the selected wastes for being processed by BSFL, whereas semidigested grass is an unsuitable substrate. We found that lignin had a significantly negative effect on larval growth, and emphasized the importance of applying lignin-digesting microorganisms to lignin-rich substrates being converted by BSFL. Moreover, a protein:fat:digestible carbohydrate ratio of 2:1:2 was hypothesized to benefit larval development.

Abstract: Okara is a by-product of soybean processing produced in large quantities, but under-used by the food industry. Strategies to increase its nutritional quality could contribute to the usage of this biomass. Fresh and heat-treated okara were subjected to solid-state fermentation (SSF) using S. cerevisiae and physicochemical parameters of quality, total phenolics, β-glucosidase activity, antioxidant activity and the biotransformation of isoflavone were evaluated. Fermentation contributed to the improvement of nutritional quality, promoting an increase in protein content, and increases in total phenolics, and antioxidant activity. SSF also promoted the bioconversion of isoflavone β-D-glucosides to aglycone forms through the action of β-glucosidases. Furthermore, SSF led to the reduction of raw fiber content with a potential improvement in digestibility. SSF was demonstrated to be a valuable tool in improving quality and functional attributes, and in adding value to okara, thus contributing to its better usage in the development of food products and supplements.

Abstract: The soaring levels of industrialization and rapid progress towards urbanization across the world have elevated the demand for energy besides generating a massive amount of waste The latter is responsible for poisoning the ecosystem in an exponential manner, owing to the hazardous and toxic chemicals released by them In the past few decades, there has been a paradigm shift from “waste to wealth”, keeping the value of high organic content available in the wastes of biological origin The most practiced processes are that of anaerobic digestion, leading to the production of methane However; such bioconversion has limited net energy yields Industrial fermentation targeting value-added bioproducts such as—H2, butanediols; polyhydroxyalkanoates, citric acid, vitamins, enzymes, etc from biowastes/lignocellulosic substrates have been planned to flourish in a multi-step process or as a “Biorefinery” Electro-fermentation (EF) is one such technology that has attracted much interest due to its ability to boost the microbial metabolism through extracellular electron transfer during fermentation It has been studied on various acetogens and methanogens, where the enhancement in the biogas yield reached up to 2-fold EF holds the potential to be used with complex organic materials, leading to the biosynthesis of value-added products at an industrial scale

Abstract: Methanol has become an attractive substrate for biotechnological applications due to its abundance and low-price. Chemicals production from methanol could alleviate the environmental concerns, costs, and foreign dependency associated with the use of petroleum feedstock. Recently, a growing fraction of research has focused on metabolites production using methanol as sole carbon and energy source or as co-substrate with carbohydrates by native or synthetic methylotrophs. In this review, we summarized the recent significant progress in native and synthetic methylotrophs and their application for methanol bioconversion into various products. Moreover, strategies for improvement of methanol metabolism and new perspectives on the generation of desired products from methanol were also discussed, which will benefit for the development of a methanol-based economy.

Abstract: Methane, a potent greenhouse gas, and methanol, commonly called wood alcohol, are common by-products of modern industrial processes. They can, however, be consumed as a feedstock by bacteria known as methanotrophs, which can serve as useful vectors for biotransformation and bioproduction. Successful implementation in industrial settings relies upon efficient growth and bioconversion, and the optimization of culturing conditions for these bacteria remains an ongoing effort, complicated by the wide variety of characteristics present in the methanotroph culture collection. Here, we demonstrate the variable growth outcomes of five diverse methanotrophic strains - Methylocystis sp. Rockwell, Methylocystis sp. WRRC1, Methylosinus trichosporium OB3b, Methylomicrobium album BG8, and Methylomonas denitrificans FJG1 - grown on either methane or methanol, at three different concentrations, with either ammonium or nitrate provided as nitrogen source. Maximum optical density (OD), growth rate, and biomass yield were assessed for each condition. Further metabolite and fatty acid methyl ester (FAME) analyses were completed for Methylocystis sp. Rockwell and M. album BG8. The results indicate differential response to these growth conditions, with a general preference for ammonium-based growth over nitrate, except for M. denitrificans FJG1. Methane is also preferred by most strains, with methanol resulting in unreliable or inhibited growth in all but M. album BG8. Metabolite analysis points to monitoring of excreted formic acid as a potential indicator of adverse growth conditions, while the magnitude of FAME variation between conditions may point to strains with broader substrate tolerance. These findings suggest that methanotroph strains must be carefully evaluated before use in industry, both to identify optimal conditions and to ensure the strain selected is appropriate for the process of interest. Much work remains in addressing the optimization of growth strategies for these promising microorganisms since disregarding these important steps in process development could ultimately lead to inefficient or failed bioprocesses.

Abstract: Methane is a promising next-generation carbon feedstock for industrial biotechnology due to its low price and huge availability. Biological conversion of methane to valuable products can mitigate methane-induced global warming as greenhouse gas. There have been challenges for the conversion of methane into various chemicals and fuels using engineered non-native hosts with synthetic methanotrophy or methanotrophs with the reconstruction of synthetic pathways for target products. Herein, we analyze the technical challenges and issues of potent methane bioconversion technology. Pros and cons of metabolic engineering of methanotrophs for methane bioconversion, and perspectives on the bioconversion of methane to chemicals and liquid fuels are discussed.

Abstract: Dairy industry effluents were usually characterized by their high organic matter content. Cheese whey is the most wide studied dairy reject. Though, the high polluting dairy wastewater including product losses and process effluents are also problematic and they need to be treated separately. Despite the quite efficiency of physico-chemical processes, polluting load removal is typically insufficient and the treatment should be completed by a biological process. Lactose bioconversion to single cell proteins; lactic acid; citric acid; biopolymer, bioethanol or even hydrogen seem to be promoting alternatives, not only for the treatment but also for the recovery of valuable products. Anaerobic digestion using dark and/or photofermentation and microbial fuel cells exhibited several advantageous comparing to the conventional dairy wastewater processing pathways. Then, the microbial material role for the bioconversion is crucial and it should be done according to the treatment purposes. Saccharomyces, Klyveromyces and Candida strains are widely used for dairy wastewaters polluting load removal. Lactic acid bacteria are used for their biotechnological proprieties. Some mixed cultures proved to result in more efficient treatment results with valuable products.

Abstract: Efficient bioconversion of lignocellulosic biomass to bioethanol is one of key challenges in the situation of increasing bioethanol demand. The ethanologenic microbes for such conversion are required to possess abilities of utilization of various sugars including xylose and arabinose in lignocellulosic biomass. As required additional characteristics, there are a weak or no glucose repression that allows cells to simultaneously utilize various sugars together with glucose and thermotolerance for fermentation at high temperatures, which has several advantages including reduction of cooling cost. Spathaspora passalidarum ATCC MYA-4345, a type strains, isolated previously have mainly of these abilities or characteristics but its thermotolerance is not so strong and its glucose repression on xylose utilization is revealed. Newly isolated S. passalidarum CMUWF1–2 was found to have a high ability to produce ethanol from various sugars included in lignocellulosic biomass at high temperatures. The strain achieved ethanol yields of 0.43 g, 0.40 g and 0.20 g ethanol/g xylose at 30 °C, 37 °C and 40 °C, respectively. Interestingly, no significant glucose repression was observed in experiments with mixed sugars, being consistent with the strong resistance to 2-deoxyglucose, and antimycin A showed no effect on its growth in xylose medium. Moreover, the strain was tolerant to glucose and ethanol at concentrations up to 35.0% (w/v) and 8.0% (v/v), respectively. S. passalidarum CMUWF1–2 was shown to achieve efficient production of ethanol from various sugars and a high ethanol yield from xylose with little accumulation of xylitol. The strain also exhibited stress-resistance including thermotolerance and no detectable glucose repression as beneficial characteristics. Therefore, S. passalidarum CMUWF1–2 has remarkable potential for conversion of lignocellulosic biomass to bioethanol.

Abstract: Bio-catalysis is an attractive alternative to replace chemical methods due to its high selectivity and mild reaction conditions Furfural is an important bio-based platform compound generated from biomass Herein, the bio-catalytic reduction of furfural (FAL) to furfuryl alcohol (FOL) was performed by using a furfural tolerant strain, Bacillus coagulans NL01 An efficient co-substrate was explored and a high conversion and selectivity of FAL to FOL was reported over this bio-catalytic system using glucose as co-substrate As the bioconversion occurred over 42 mM FAL, 20 g L−1 glucose and 9 mg mL−1 at 50 °C, a high conversion and selectivity was obtained by 3 h reaction This transformation rate of FAL was the highest compared with other reactions Furthermore, about 98 mM FOL was produced from FAL within 24 h by a fed-batch strategy with a conversion of 92% and selectivity of 96% These results indicate that this bio-catalytic reduction of FAL has high potential for application to upgrading of FAL and B coagulans NL01 is a promising biocatalyst for the synthesis of FOL In addition, this bio-catalytic reduction shows a high potential application for catalytic upgrading of FAL from biomass

Abstract: Due to the success of shale gas development in the US, the production cost of natural gas has been reduced significantly, which in turn has made methane (CH4), the major component of natural gas, a potential alternative substrate for bioconversion processes compared with other high-price raw material sources or edible feedstocks. Therefore, exploring effective ways to use CH4 for the production of biofuels is attractive. Biological fixation of CH4 by methanotrophic bacteria capable of using CH4 as their sole carbon and energy source has obtained great attention for biofuel production from this resource. In this study, a fast-growing and lipid-rich methanotroph, Methylomicrobium buryatense 5GB1 and its glycogen-knock-out mutant (AP18) were investigated for the production of lipids derived from intracellular membranes, which are key precursors for the production of green diesel. The effects of culture conditions on cell growth and lipid production were investigated in high cell density cultivation with continuous feeding of CH4 and O2. The highest dry cell weight observed was 21.4 g/L and the maximum lipid productivity observed was 45.4 mg/L/h obtained in batch cultures, which corresponds to a 2-fold enhancement in cell density and 3-fold improvement in lipid production, compared with previous reported data from cultures of 5GB1. A 90% enhancement of lipid content was achieved by limiting the biosynthesis of glycogen in strain AP18. Increased CH4/O2 uptake and CO2 evaluation rates were observed in AP18 cultures suggesting that more carbon substrate and energy are needed for AP18 growth while producing lipids. The lipid produced by M. buryatense was estimated to have a cetane number of 75, which is 50% higher than biofuel standards requested by US and EU. Cell growth and lipid production were significantly influenced by culture conditions for both 5GB1 and AP18. Enhanced lipid production in terms of titer, productivity, and content was achieved under high cell density culture conditions by blocking glycogen accumulation as a carbon sink in the strain AP18. Differences observed in CH4/O2 gas uptake and CO2 evolution rates as well as cell growth and glycogen accumulation between 5GB1 and AP18 suggest changes in the metabolic network between these strains. This bioconversion process provides a promising opportunity to transform CH4 into biofuel molecules and encourages further investigation to elucidate the remarkable CH4 biofixation mechanism used by these bacteria.