Primary metabolites from overproducing microbial system using sustainable substrates

Poly-γ-glutamic acid overproduction of Bacillus licheniformis ATCC 9945a by developing a novel optimum culture medium and glutamate pulse feeding using different experimental design approaches

The commercial production of multifunctional, biocompatible, and biodegradable biopolymers such as poly-γ-glutamic acid via microbial fermentation requires the development of simple and cheap methods for mass production. This study optimized the poly-γ-glutamic acid production of Bacillus licheniformis ATCC 9945a in several steps. At first, the most critical components of the culture medium, including l-glutamic acid, citric acid, and glycerol, were selected by screening nine factors through the Plackett-Burman experimental design and then were optimized using the response surface method and the central composite design algorithm. Under optimal conditions, the production of poly-γ-glutamic acid increased by more than 4.2 times from 11.2 to 47.2 g/L. This is one of the highest production rates of this strain in submerged batch fermentation reported so far using the optimized medium compared to the conventional base medium. A novel and efficient sudden pulse feeding strategy (achieved by a novel one-factorial statistical technique) of l-glutamic acid to the optimized medium increased biopolymer production from 47.2 to 66.1 g/L, the highest value reported in published literature with this strain. This simple, reproducible, and cheap fermentation process can considerably enhance the commercial applications of the poly-γ-glutamic acid synthesized by B. licheniformis ATCC 9945a.

Effective hydrolysis for waste plant biomass impacts sustainable fuel and reduced air pollution generation: A comprehensive review

Among various natural biowastes availability in the environment, agricultural residues showed great impacts. It is due to huge availability and cheap carbon source, creating big challenges for their utility and systematic reduction. Objective of this review is to address the waste biomass availability and huge quantities issues and also put effort to minimize this nutrient load via biotransforming into value-added products. Different wastes (organic/inorganic) generation with their negative issues are due to numbers of developmental and social activities, reported. Currently, various efforts are found for these wastes minimization via generation of different types of value-added products (biogas, bioH₂, alcoholic fuel, organic acids and others products) and these wastes in municipal cities are also reported with production of advanced biofuels as promising outcomes. For hydrolysis of complex organic resources including lignocellulosic biomasses, physicochemical, structural or compositional changes are needed that aid in conversion into sugar and organic compounds such as biofuels. So, efficient and effective pretreatment processes selection (physical, biological, chemical or combined one) is critical to achieve these hydrolysis goals and resultant cellulose or hemicellulose components can be accessible by biological catalysis. These can achieve final hydrolysis and fermentative or monomer sugars. And later, synthesis of fuels or value-added products during microbial fermentation or biotransformation processes can be achieved. This review discusses pretreatment techniques for improved hydrolysis for fermentative sugar with emphasis on reduced quantities of toxic compounds (furfural compound) in hydrolyzed biomasses. Minimum deterioration fuel economy also reported with production of different bioproducts including biofuels. Additionally, impacts of toxic products and gasses emission are also discussed with their minimization.

Increasing Lovastatin Production by Re-routing the Precursors Flow of Aspergillus terreus via Metabolic Engineering

Lovastatin is an anti-cholesterol medicine that is commonly prescribed to manage cholesterol levels, and minimise the risk of suffering from heart-related diseases. Aspergillus terreus (ATCC 20542) supplied with carbohydrates or sugar alcohols can produce lovastatin. The present work explored the application of metabolic engineering in A. terreus to re-route the precursor flow towards the lovastatin biosynthetic pathway by simultaneously overexpressing the gene for acetyl-CoA carboxylase (acc) to increase the precursor flux, and eliminate ( +)-geodin biosynthesis (a competing secondary metabolite) by removing the gene for emodin anthrone polyketide synthase (gedC). Alterations to metabolic flux in the double mutant (gedCΔ*acc^ox) strain and the effects of using two different substrate formulations were examined. The gedCΔ*acc^ox strain, when cultivated with a mixture of glycerol and lactose, significantly (p < 0.05) increased the levels of metabolic precursors malonyl-CoA (48%) and acetyl-CoA (420%), completely inhibited the (+)-geodin biosynthesis, and increased the level of lovastatin [152 mg/L; 143% higher than the wild-type (WT) strain]. The present work demonstrated how the manipulation of A. terreus metabolic pathways could increase the efficiency of carbon flux towards lovastatin, thus elevating its overall production and enabling the use of glycerol as a substrate source. As such, the present work also provides a framework model for other medically or industrially important fungi to synthesise valuable compounds using sustainable carbon sources.