Bioelectrochemical systems are revolutionary new bioengineering technologies which integrate microorganisms or enzymes with the electrochemical method to improve the reducing or oxidizing metabolism. Generally, the bioelectrochemical systems show the processes referring to electrical power generation or achieving the reducing reaction with a certain potential poised by means of electron transfer between the electron acceptor and electron donor. Researchers have focused on the selection and optimization of the electrode materials, design of electrochemical device, and screening of electrochemically active or inactive model microorganisms. Notably, all these means and studies are related to electron transfer: efflux and consumption. Thus, here we introduce the basic concepts of bioelectrochemical systems, and elaborate on the extracellular and intracellular electron transfer, and the hypothetical electron transfer mechanism. Also, intracellular energy generation and coenzyme metabolism along with electron transfer are analyzed. Finally, the applications of bioelectrochemical systems and the prospect of microbial electrochemical technologies are discussed.

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.

Consolidated bioprocessing (CBP) has attracted increasing attention since it can accomplish hydrolytic enzymes production, lignocellulose degradation and microbial fermentation in one single step. Currently, biobutanol is mainly produced by mesophilic and solventogenic clostridia, such as Clostridium beijerinckii and C. acetobutylicum, which cannot directly utilize lignocellulose, an abundant, renewable and economic feedstock. Hence, metabolic construction or isolation of novel cellulolytic/hemicellulolytic and solventogenic bacteria to achieve direct butanol production from lignocellulose offers a promising alternative. In this study, a newly isolated Thermoanaerobacterium sp. M5 could directly produce butanol from xylan through CBP at 55 °C via the butanol–ethanol pathway. Further genomic and proteomic analysis showed that the capabilities of efficient xylan degradation and butanol synthesis were attributed to the efficient expression of xylanase, β-xylosidase and the bifunctional alcohol/aldehyde dehydrogenase (AdhE). Process optimization based on the characteristic of AdhE could further improve the final butanol titer to 1.17 g/L from xylan through CBP. Furthermore, a new co-cultivation system consisting of Thermoanaerobacterium sp. M5 which could release xylose from xylan efficiently and C. acetobutylicum NJ4 which possesses the capacity of high butanol production was established. This microbial co-cultivation system could improve the butanol titer to 8.34 g/L, representing the highest butanol titer from xylan through CBP. A newly thermophilic and butanogenic bacterium Thermoanaerobacterium sp. M5 was isolated and key enzymes responsible for butanol production were characterized in this study. High butanol titer was obtained from xylan through process optimization. In addition, the newly set up microbial co-cultivation system, consisting of Thermoanaerobacterium sp. M5 and C. acetobutylicum NJ4, achieved the highest butanol production from xylan compared with the reported co-cultivation systems.

Microbial communities are ubiquitous in nature and exhibit several attractive features, such as sophisticated metabolic capabilities and strong environment robustness. Inspired by the advantages of natural microbial consortia, diverse artificial co-cultivation systems have been metabolically constructed for biofuels, chemicals and natural products production. In these co-cultivation systems, especially genetic engineering ones can reduce the metabolic burden caused by the complex of metabolic pathway through labor division, and improve the target product production significantly. This review summarized the most up-to-dated co-cultivation systems used for biofuels, chemicals and nature products production. In addition, major challenges associated with co-cultivation systems are also presented and discussed for meeting further industrial demands.