Genomics of Lactic Acid Bacteria for Glycerol Dissimilation

From waste management to circular economy: Leveraging thermophiles for sustainable growth and global resource optimization

Waste of any origin is one of the most serious global and man-made concerns of our day. It causes climate change, environmental degradation, and human health problems. Proper waste management practices, including waste reduction, safe handling, and appropriate treatment, are essential to mitigate these consequences. It is thus essential to implement effective waste management strategies that reduce waste at the source, promote recycling and reuse, and safely dispose of waste. Transitioning to a circular economy with policies involving governments, industries, and individuals is essential for sustainable growth and waste management. The review focuses on diverse kinds of environmental waste sources around the world, such as residential, industrial, commercial, municipal services, electronic wastes, wastewater sewerage, and agricultural wastes, and their challenges in efficiently valorizing them into useful products. It highlights the need for rational waste management, circularity, and sustainable growth, and the potential of a circular economy to address these challenges. The article has explored the role of thermophilic microbes in the bioremediation of waste. Thermophiles known for their thermostability and thermostable enzymes, have emerged to have diverse applications in biotechnology and various industrial processes. Several approaches have been explored to unlock the potential of thermophiles in achieving the objective of establishing a zero-carbon sustainable bio-economy and minimizing waste generation. Various thermophiles have demonstrated substantial potential in addressing different waste challenges. The review findings affirm that thermophilic microbes have emerged as pivotal and indispensable candidates for harnessing and valorizing a range of environmental wastes into valuable products, thereby fostering the bio-circular economy.

High-Yield Production of Propionate from 1,2-Propanediol by Engineered Pseudomonas putida KT2440, a Robust Strain with Highly Oxidative Capacity

Bio-based propionate attracts increasing attention owing to its green nature and specific food additive market. To date, the time-consuming and costly fermentation process by strict anaerobes makes propionate production not ideal. In this study, we designed a new route for propionate production, in which 1,2-propanediol was first dehydrated to propionaldehyde and then to propionate by taking advantage of the robust oxidization capacity of the Pseudomonas putida KT2440 strain. The high atom economy (0.97 g/g) in this proposed pathway is more advantageous than the previous l-threonine-derived route (0.62 g/g). The molecular mechanism of the extraordinary oxidation capacity of P. putida KT2440 was first deciphered. The propionate production was realized in P. putida KT2440 by screening suitable glycerol dehydratases and optimizing the expression to eliminate the formation of 1-propanol and the accumulation of the intermediate propionaldehyde. The engineered strain produced propionate with a molar conversion rate of >99% from 1,2-propanediol. A high titer of 46.5 g/L pure propionic acid with a productivity of 1.55 g/L/h and a mass yield of 0.96 g/g was achieved in fed-batch biotransformation. Thus, this study provides another idea for the production of high-purity bio-based propionate from renewable materials with high atom economy.

Glycerol Utilization as a Sole Carbon Source Disrupts the Membrane Architecture and Solventogenesis in Clostridium beijerinckii NCIMB 8052

Efficient bioconversion of abundant waste glycerol to value-added chemicals calls for a wider range of fermentative workhorses that can catabolize glycerol. In this study, we used quantitative gene expression and solvent profiling, qualitative metabolite analysis, and enzyme activity assays to investigate the factors that limit glycerol utilization as a sole carbon source by Clostridium beijerinckii NCIMB 8052. C. beijerinckii NCIMB 8052 did not produce acetate, acetone and butanol on glycerol. Congruently, the genes encoding the coenzyme A transferase subunits (ctfAB) and bifunctional acetaldehyde-CoA/alcohol dehydrogenase (adhE) were down-regulated up to 135- and 21-fold, respectively, at 12 h in glycerol-grown cells compared to glucose-grown cells. Conversely, NADH-dependent butanol dehydrogenase A (bdhA) was upregulated 2-fold. Glycerol dehydrogenase (gldA) and dihydroxyacetone kinase (subunit dhaK) were upregulated up to 5- and 881-fold, respectively. Glyceraldehyde-3-phosphate dehydrogenase (gapdh) showed mostly similar expression profiles at 12 h on glucose and glycerol. At 24 h, gapdh was downregulated 1.5-fold, while NADP+-dependent gapdh was upregulated up to 1.9-fold. Glycerol-grown cells showed higher or similar activity profiles for all solventogenic enzymes studied, compared to glucose-grown cells. Butyraldehyde (3 g/L) supplementation led to the production of ~0.1 g/L butanol, whilst butyrate (3.5 g/L) supplementation produced 0.7 and 0.5 g/L acetone and butanol, respectively, with glycerol. Further, the long chain saturated fatty acids cyclopentaneundecanoic acid, methyl ester and hexadecanoic acid, butyl ester were detected in glucose- but not in glycerol-grown cells. Collectively, growth on glycerol appears to disrupt synthesis of saturated long chain fatty acids, as well as solventogenesis in C. beijerinckii NCIMB 8052.

R, Maitra S, Tarafdar A, Alphy MP, Kumar AN, Madhavan A, Sirohi R, Awasthi MK, Sindhu R, Varjani S, Binod P. Waste-Derived Fuels and Renewable Chemicals for Bioeconomy Promotion: A Sustainable Approach

Bio-based fuels and chemicals through the biorefinery approach has gained significant interest as an alternative platform for the petroleum-derived processes as these biobased processes are noticed to have positive environmental and societal impacts. Decades of research was involved in understanding the diversity of microorganisms in different habitats that could synthesize various secondary metabolites that have functional potential as fuels, chemicals, nutraceuticals, food ingredients, and many more. Later, due to the substrate-related process economics, the diverse low-value, high-carbon feedstocks like lignocellulosic biomass, industrial byproducts, and waste streams were investigated to have greater potential. Among them, municipal solid wastes can be used as the source of substrates for the production of commercially viable gaseous and liquid fuels, as well as short-chain fattyacids and carboxylic acids. In this work, technologies and processes demanding the production of value-added products were explained in detail to understand and inculcate the value of municipal solid wastes and the economy, and it can provide to the biorefinery aspect.

Recent advances in microbial biosynthesis of C3 - C5 diols: Genetics and process engineering approaches

Diols derived from renewable feedstocks have significant commercial interest in polymer, pharmaceutical, cosmetics, flavors and fragrances, food and feed industries. In C3-C5 diols biological processes of 1,3-propanediol, 1,2-propanediol and 2,3-butanediol have been commercialized as other isomers are non-natural metabolites and lack natural biosynthetic pathways. However, the developments in the field of systems and synthetic biology paved a new path to learn, build, construct, and test for efficient chassis strains. The current review addresses the recent advancements in metabolic engineering, construction of novel pathways, process developments aimed at enhancing in production of C3-C5 diols. The requisites on developing an efficient and sustainable commercial bioprocess for C3-C5 diols were also discussed.

Recent update on lactic acid bacteria producing riboflavin and folates: application for food fortification and treatment of intestinal inflammation

Lactic acid bacteria (LAB), widely used as starter cultures for the fermentation of a large variety of food, can improve the safety, shelf life, nutritional value and overall quality of the fermented products. In this regard, the selection of strains delivering health-promoting compounds is now the main objective of many researchers. Although most LAB are auxotrophic for several vitamins, it is known that certain strains have the capability to synthesize B-group vitamins. This is an important property since humans cannot synthesize most vitamins, and these could be obtained by consuming LAB fermented foods. This review discusses the use of LAB as an alternative to fortification by the chemical synthesis to increase riboflavin and folate concentrations in food. Moreover, it provides an overview of the recent applications of vitamin-producing LAB with anti-inflammatory/antioxidant activities against gastrointestinal tract inflammation. This review shows the potential uses of riboflavin and folates producing LAB for the biofortification of food, as therapeutics against intestinal pathologies and to complement anti-inflammatory/anti-neoplastic treatments.