Lee SA, et al. Nutr Res Pract. 2015 Jun;9(3):242-248. https://doi.org/10.4162/nrp.2015.9.3.242

C ₄ -dicarboxylates and the C ₄ -dicarboxylic amino acid l -aspartate support aerobic and anaerobic growth of Escherichia coli and related bacteria. In aerobic growth, succinate, fumarate, D - and L -malate, L -aspartate, and L -tartrate are metabolized by the citric acid cycle and associated reactions. Because of the interruption of the citric acid cycle under anaerobic conditions, anaerobic metabolism of C ₄ -dicarboxylates depends on fumarate reduction to succinate (fumarate respiration). In some related bacteria (e.g., Klebsiella ), utilization of C ₄ -dicarboxylates, such as tartrate, is independent of fumarate respiration and uses a Na ⁺ -dependent membrane-bound oxaloacetate decarboxylase. Uptake of the C ₄ -dicarboxylates into the bacteria (and anaerobic export of succinate) is achieved under aerobic and anaerobic conditions by different sets of secondary transporters. Expression of the genes for C ₄ -dicarboxylate metabolism is induced in the presence of external C ₄ -dicarboxylates by the membrane-bound DcuS-DcuR two-component system. Noncommon C ₄ -dicarboxylates like l -tartrate or D -malate are perceived by cytoplasmic one-component sensors/transcriptional regulators. This article describes the pathways of aerobic and anaerobic C ₄ -dicarboxylate metabolism and their regulation. The citric acid cycle, fumarate respiration, and fumarate reductase are covered in other articles and discussed here only in the context of C ₄ -dicarboxylate metabolism. Recent aspects of C ₄ -dicarboxylate metabolism like transport, sensing, and regulation will be treated in more detail. This article is an updated version of an article published in 2004 in EcoSal Plus . The update includes new literature, but, in particular, the sections on the metabolism of noncommon C ₄ -dicarboxylates and their regulation, on the DcuS-DcuR regulatory system, and on succinate production by engineered E. coli are largely revised or new.

The improvement of bacterial tolerance to organic solvents is a main prerequisite for the microbial production of biofuels which are toxic to cells. For targeted genetic engineering of Escherichia coli to increase organic solvent tolerances (OSTs), we selected and investigated a total of 12 genes that participate in relevant mechanisms to tolerance. In a spot assay of 12 knockout mutants with n-hexane and cyclohexane, the genes fadR and marR were finally selected as the two key genes for engineering. Fatty acid degradation regulon (FadR) regulates the biosynthesis and degradation of fatty acids coordinately, and the multiple antibiotic resistance repressor (MarR) is the repressor of the global regulator MarA for multidrug resistance. In the competitive growth assay, the ΔmarR mutant became dominant when the pooled culture of 11 knockout mutants was cultivated successively in the presence of organic solvent. The increased OSTs in the ΔmarR and ΔfadR mutants were confirmed by a growth experiment and a viability test. The even more highly enhanced OSTs in the ΔfadR ΔmarR double mutant were shown compared with the two single mutants. Cellular fatty acid analysis showed that the high ratio of saturated fatty acids to unsaturated fatty acids plays a crucial role in OSTs. Furthermore, the intracellular accumulation of OST strains was significantly decreased compared with the wild-type strain.

Recently, designers have begun to pursue sustainability through the fabrication of materials from living organisms such as bacteria, fungi, and algae in order to address environmental issues. Based on the potential of materials from living organisms, this study has explored a sustainable design application using biocement formed thorough microbially-induced calcite precipitation (MICP), which produces minerals by bacterial metabolic activity. Since most of the studies on MICP thus far have focused on limited fields such as engineering, biotechnology, and geo-technology, this study has focused more on improving the application of biocement in design. We optimized MICP conditions using two parameters (i.e., concentration of urea-CaCl₂ and bacterial cell density) through water percolation testing, compressive strength testing, and X-ray diffraction (XRD) analysis. Then, based on the optimized conditions, material compatibility testing and scalability testing were performed, and design application research was conducted as well. As a result, biocement has been identified as a potential sustainable design material, based on its 40% compressive strength compared to conventional concrete, improved material finish, aesthetic aspects, and environmental impact. This paper contributes to the development of biocement applications in the environmental design field through multidisciplinary research ranging from biological experiments to design applications.

Escherichia coli can hardly grow anaerobically on glycerol without exogenous electron acceptor. The formate-consuming methanogen Methanobacterium formicicum plays a role as a living electron acceptor in glycerol fermentation of E. coli. Wild-type and mutant E. coli strains were screened for succinate production using glycerol in a co-culture with M. formicicum. Subsequently, E. coli was adapted to glycerol fermentation over 39 rounds (273 days) by successive co-culture with M. formicicum. The adapted E. coli (19.9 mM) produced twice as much succinate as non-adapted E. coli (9.7 mM) and 62% more methane. This study demonstrated improved succinate production from waste glycerol using an adapted wild-type strain of E. coli with wild-type M. formicicum, which is more useful than genetically modified strains. Crude glycerol, an economical feedstock, was used for the cultivation. Furthermore, the increase in methane production by M. formicicum during co-culture with adapted E. coli illustrated the possibility of energy-saving effects for the fermentation process.