Rational synthetic combination genetic devices boosting high temperature ethanol fermentation

Application of microbial resources in biorefineries: Current trend and future prospects

The recent growing interest in sustainable and alternative sources of energy and bio-based products has driven the paradigm shift to an integrated model termed "biorefinery." Biorefinery framework implements the concepts of novel eco-technologies and eco-efficient processes for the sustainable production of energy and value-added biomolecules. The utilization of microbial resources for the production of various value-added products has been documented in the literatures. However, the appointment of these microbial resources in integrated resource management requires a better understanding of their status. The main of aim of this review is to provide an overview on the defined positioning and overall contribution of the microbial resources, i.e., algae, fungi and bacteria, for various bioprocesses and generation of multiple products from a single biorefinery. By utilizing waste material as a feedstock, biofuels can be generated by microalgae while sequestering environmental carbon and producing value added compounds as by-products. In parallel, fungal biorefineries are prolific producers of lignocellulose degrading enzymes along with pharmaceutically important novel products. Conversely, bacterial biorefineries emerge as a preferred platform for the transformation of standard cells into proficient bio-factories, developing chassis and turbo cells for enhanced target compound production. This comprehensive review is poised to offer an intricate exploration of the current trends, obstacles, and prospective pathways of microbial biorefineries, for the development of future biorefineries.

A cold shock protein promotes high-temperature microbial growth through binding to diverse RNA species

Endowing mesophilic microorganisms with high-temperature resistance is highly desirable for industrial microbial fermentation. Here, we report a cold-shock protein (CspL) that is an RNA chaperone protein from a lactate producing thermophile strain (Bacillus coagulans 2–6), which is able to recombinantly confer strong high-temperature resistance to other microorganisms. Transgenic cspL expression massively enhanced high-temperature growth of Escherichia coli (a 2.4-fold biomass increase at 45 °C) and eukaryote Saccharomyces cerevisiae (a 2.6-fold biomass increase at 36 °C). Importantly, we also found that CspL promotes growth rates at normal temperatures. Mechanistically, bio-layer interferometry characterized CspL’s nucleotide-binding functions in vitro, while in vivo we used RNA-Seq and RIP-Seq to reveal CspL’s global effects on mRNA accumulation and CspL’s direct RNA binding targets, respectively. Thus, beyond establishing how a cold-shock protein chaperone provides high-temperature resistance, our study introduces a strategy that may facilitate industrial thermal fermentation.

Turning the Screw: Engineering Extreme pH Resistance in Escherichia coli through Combinatorial Synthetic Operons

Adoption of microorganisms as platforms for sustainable biobased production requires host cells to be able to withstand harsh conditions, usually very distant from those in which these organisms are naturally adapted to thrive. However, novel survival mechanisms unearthed by the study of microbiomes from extreme habitats may be exploited to enhance microbial robustness under the strict conditions needed for different industrial appplications. In this work, synthetic biology approaches were used to engineer enhanced acidic resistance in Escherichia coli through the characterization of a collection of unique operons composed of combinatorial assemblies of three novel genes from an extreme environment and three synthetic ribosome binding sites. The results here presented illustrate the efficacy of combining different metagenomic genes for resistance in synthetic operons, as expression of these gene clusters increased hundred-fold the survival percentage of cells exposed to an acidic shock in minimal media at pH 1.9 under aerobic conditions.

Recent Development of Extremophilic Bacteria and Their Application in Biorefinery

The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.

Enhancing 5-aminolevulinic acid tolerance and production by engineering the antioxidant defense system of Escherichia coli

5-Aminolevulinic acid (ALA) is a value-added compound with potential applications in the fields of agriculture and medicine. Although massive efforts have recently been devoted to building microbial producers of ALA through metabolic engineering, few studies focused on the cellular response and tolerance to ALA. In this study, we demonstrated that ALA caused severe cell damage and morphology change of Escherichia coli via generating reactive oxygen species (ROS), which were further determined to be mainly hydrogen peroxide and superoxide anion radical. ALA treatment activated the native antioxidant defense system by upregulating catalase (CAT) and superoxide dismutase (SOD) expression to combat ROS. Further overexpressing CAT (encoded by katG and katE) and SOD (encoded by sodA, sodB, and sodC) not only improved ALA tolerance but also its production level. Notably, coexpression of katE and sodB in an ALA synthase expressing strain enhanced the biomass and final ALA titer by 81% and 117% (11.5 g/L) in a 5 L bioreactor, respectively. This study demonstrates the importance of tolerance engineering in strain development. Reinforcing the antioxidant defense system holds promise to improve the bioproduction of chemicals that cause oxidative stress.

Resistance mechanisms and reprogramming of microorganisms for efficient biorefinery under multiple environmental stresses

In the fermentation process of biorefinery, industrial strains are normally subjected to adverse environmental stresses, which leads to their slow growth, yield decline, a substantial increase in energy consumption, and other negative consequences, which ultimately seriously hamper the development of biorefinery. How to minimize the impact of stress on microorganisms is of great significance. This review not only reveals the damaging effects of different environmental stresses on microbial strains but also introduces commonly used strategies to improve microbial tolerance, including adaptive evolution, reprogramming of the industrial host based on genetic circuits, global transcription machinery engineering (gTME) and bioprocess integration. Furthermore, by integrating the advantages of these strategies and reducing the cost of system operation, the tolerance of industrial strains, combined with production efficiency and process stability, will be greatly improved, and the development prospects of biorefinery will be more widespread.