Glutarate is a five carbon platform chemical produced during the catabolism of l-lysine. It is known that it can be catabolized through the glutaryl-CoA dehydrogenation pathway. Here, we discover that Pseudomonas putida KT2440 has an additional glutarate catabolic pathway involving l-2-hydroxyglutarate (l-2-HG), an abnormal metabolite produced from 2-ketoglutarate (2-KG). In this pathway, CsiD, a Fe2+/2-KG-dependent glutarate hydroxylase, is capable of converting glutarate into l-2-HG, and LhgO, an l-2-HG oxidase, can catalyze l-2-HG into 2-KG. We construct a recombinant strain that lacks both glutarate catabolic pathways. It can produce glutarate from l-lysine with a yield of 0.85 mol glutarate/mol l-lysine. Thus, l-2-HG anabolism and catabolism is a metabolic alternative to the glutaryl-CoA dehydrogenation pathway in P. putida KT2440; l-lysine can be both ketogenic and glucogenic.

l-Serine biosynthesis, a crucial metabolic process in most domains of life, is initiated by d-3-phosphoglycerate (d-3-PG) dehydrogenation, a thermodynamically unfavorable reaction catalyzed by d-3-PG dehydrogenase (SerA). d-2-Hydroxyglutarate (d-2-HG) is traditionally viewed as an abnormal metabolite associated with cancer and neurometabolic disorders. Here, we reveal that bacterial anabolism and catabolism of d-2-HG are involved in l-serine biosynthesis in A1501 and PAO1. SerA catalyzes the stereospecific reduction of 2-ketoglutarate (2-KG) to d-2-HG, responsible for the major production of d-2-HG in vivo. SerA combines the energetically favorable reaction of d-2-HG production to overcome the thermodynamic barrier of d-3-PG dehydrogenation. We identified a bacterial d-2-HG dehydrogenase (D2HGDH), a flavin adenine dinucleotide (FAD)-dependent enzyme, that converts d-2-HG back to 2-KG. Electron transfer flavoprotein (ETF) and ETF-ubiquinone oxidoreductase (ETFQO) are also essential in d-2-HG metabolism through their capacity to transfer electrons from D2HGDH. Furthermore, while the mutant with D2HGDH deletion displayed decreased growth, the defect was rescued by adding l-serine, suggesting that the D2HGDH is functionally tied to l-serine synthesis. Substantial flux flows through d-2-HG, being produced by SerA and removed by D2HGDH, ETF, and ETFQO, maintaining d-2-HG homeostasis. Overall, our results uncover that d-2-HG-mediated coupling between SerA and D2HGDH drives bacterial l-serine synthesis.

Corn cob is the secondary agricultural residue that can be easily hydrolyzed into hydrolysate with abundant d-xylose. Besides d-xylose, d-glucose, and l-arabinose are also utilizable sugars in corn cob hydrolysate. Here, we established a coutilization system through which recombinant Escherichia coli can use d-glucose and l-arabinose supporting its growth and convert d-xylose in corn cob hydrolysate into d-xylonate. First, biosynthetic pathway of d-xylonate was overexpressed and two xylonate dehydratases were knocked out in E. coli W3110 to enhance d-xylonate production from d-xylose. Then, the genes responsible for acetate, ethanol, and lactate synthesis were knocked out to decrease these byproducts production during the growth of the recombinant strain. Three successive strategies were employed to enhance the d-xylonate productionusing lactose as the inducer, eliminating carbon catabolite repression, and inactivating the lactose degradation. Finally, 108.2 g/L d-xylonate was produced with a yield of 1.09 g of d-xylonate/g of d-xylose using d-xylose as the substrate and d-glucose as the carbon source through fed-batch fermentation. When corn cob hydrolysate was used, 91.2 g/L d-xylonate was produced with a specific productivity of 1.52 g/[L·h]. This study is valuable not only for producing d-xylonate but also for providing a coutilization system to obtain other important chemicals from corn cob hydrolysate.

Glutarate, a metabolic intermediate in the catabolism of several amino acids and aromatic compounds, can be catabolized through both the glutarate hydroxylation pathway and the glutaryl-coenzyme A (glutaryl-CoA) dehydrogenation pathway in Pseudomonas putida KT2440. The elucidation of the regulatory mechanism could greatly aid in the design of biotechnological alternatives for glutarate production. In this study, it was found that a GntR family protein, CsiR, and a LysR family protein, GcdR, regulate the catabolism of glutarate by repressing the transcription of csiD and lhgO, two key genes in the glutarate hydroxylation pathway, and by activating the transcription of gcdH and gcoT, two key genes in the glutaryl-CoA dehydrogenation pathway, respectively. Our data suggest that CsiR and GcdR are independent and that there is no cross-regulation between the two pathways. l-2-Hydroxyglutarate (l-2-HG), a metabolic intermediate in the glutarate catabolism with various physiological functions, has never been elucidated in terms of its metabolic regulation. Here, we reveal that two molecules, glutarate and l-2-HG, act as effectors of CsiR and that P. putida KT2440 uses CsiR to sense glutarate and l-2-HG and to utilize them effectively. This report broadens our understanding of the bacterial regulatory mechanisms of glutarate and l-2-HG catabolism and may help to identify regulators of l-2-HG catabolism in other species. IMPORTANCE Glutarate is an attractive dicarboxylate with various applications. Clarification of the regulatory mechanism of glutarate catabolism could help to block the glutarate catabolic pathways, thereby improving glutarate production through biotechnological routes. Glutarate is a toxic metabolite in humans, and its accumulation leads to a hereditary metabolic disorder, glutaric aciduria type I. The elucidation of the functions of CsiR and GcdR as regulators that respond to glutarate could help in the design of glutarate biosensors for the rapid detection of glutarate in patients with glutaric aciduria type I. In addition, CsiR was identified as a regulator that also regulates l-2-HG metabolism. The identification of CsiR as a regulator that responds to l-2-HG could help in the discovery and investigation of other regulatory proteins involved in l-2-HG catabolism.

All-inorganic halide perovskite crystals are considered excellent optical host lattices for various dopants to obtain wavelength-tunable emissions with ultra-broad bands even over a wide spectral range. Here, a series of Mn2+-doped bulk ligand-free CsCdCl3 (CCC) perovskite crystals with a hexagonal shape and size of about 1 millimeter (mm) have been prepared by a facile hydrothermal method. These CCC:Mn2+ (CCC:Mn) crystals emit the representative orange-red photoluminescence (PL) of Mn2+ (4T1(G)-6A1(S)) in the centers of hexagonal octahedrons coordinated with six Cl– ions. A fine-tuning of the Mn2+ concentration from 1 to 50 mol % Cd2+ induces a substantial red shift of emission spectra from 570 to 630 nm due to the shrinkage of the crystalline host lattice, and the maximum intensity of emission is achieved at 20 mol % Mn2+ doping. A further increase in the Mn2+ concentration causes a decrease of the PL intensity due to the phase transition from CCC to CsMnCl3·2H2O (CMCH). The strong excitation bands at 360, 370, 420, and 440 nm can make the excitation of the emissive CCC:Mn crystals possible with ultraviolet (UV) and blue chips for application in white light-emitting diodes (WLEDs). The similarity of the Mn2+-concentration-dependent emission spectra excited by various wavelengths indicates that there is only one type of site for Mn2+ occupation in CCC.