Efficient Production of 9,22-Dihydroxy-23,24-bisnorchol-4-ene-3-one from Phytosterols by Modifying Multiple Genes in Mycobacterium fortuitum.

C19 steroids and C22 steroids are vital intermediates for the synthesis of steroid drugs. Compared with C19 steroids, C22 steroids are more suitable for synthesizing progesterone and adrenocortical hormones, albeit less developed. 9,22-dihydroxy-23,24-bisnorchol-4-ene-3-one(9-OHBA), due to its substituents at positions C-9 and C-22, is a beneficial and innovative steroid derivative for synthesizing corticosteroids. We focused on the C22 pathway in Mycobacterium fortuitum ATCC 35855, aiming to develop a productive strain that produces 9-OHBA. We used a mutant strain, MFΔkstD, that knocked out kstds from Mycobacterium fortuitum ATCC 35855 named MFKD in this study as the original strain. Hsd4A and FadA5 are key enzymes in controlling the C19 metabolic pathway of steroids in Mycobacterium fortuitum ATCC 35855. After knocking out hsd4A, MFKDΔhsd4A accumulated 81.47% 9-OHBA compared with 4.13% 9-OHBA in the strain MFKD. The double mutant MFKDΔhsd4AΔfadA5 further improved the selectivity of 9-OHBA to 95.13%, and 9α-hydroxy-4-androstenedione (9-OHAD) decreased to 0.90% from 4.19%. In the end, we obtained 6.81 g/L 9-OHBA from 10 g/L phytosterols with a molar yield of 80.33%, which showed the best performance compared with formerly reported strains.

Phytosterol conversion into C9 non-hydroxylated derivatives through gene regulation in Mycobacterium fortuitum.

Androst-4-ene-3,17-dione (AD) and 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) are important drug intermediates that can be biosynthesized from phytosterols. However, the C9 hydroxylation of steroids via 3-ketosteroid 9α-hydroxylase (KSH) limits AD and 4-HBC accumulation. Five active KshAs, the oxidation component of KSH, were identified in Mycobacterium fortuitum ATCC 35855 for the first time. The deletion of kshAs indicated that the five KshA genes were jointly responsible for C9 hydroxylation during phytosterol biotransformation. MFKDΔkshA, the five KshAs deficient strain, blocked C9 hydroxylation and produced 5.37 g/L AD and 0.55 g/L 4-HBC. The dual function reductase Opccr knockout and 17ß-hydroxysteroid dehydrogenase Hsd4A enhancement reduced 4-HBC content from 8.75 to 1.72% and increased AD content from 84.13 to 91.34%, with 8.24 g/L AD being accumulated from 15 g/L phytosterol. In contrast, hsd4A and thioesterase fadA5 knockout resulted in the accumulation of 5.36 g/L 4-HBC from 10 g/L phytosterol. We constructed efficient AD (MFKDΔkshAΔopccr_hsd4A) and 4-HBC (MFKDΔkshAΔhsd4AΔfadA5) producers and provided insights for further metabolic engineering of the M. fortuitum ATCC 35855 strain for steroid productions. KEY POINTS: • Five active KshAs were first identified in M. fortuitum ATCC 35855. • Deactivation of all five KshAs blocks the steroid C9 hydroxylation reaction. • AD or 4-HBC production was improved by Hsd4A, FadA5, and Opccr modification.

Functional analysis of acyl-CoA dehydrogenases and their application to C22 steroid production.

Acyl-CoA dehydrogenase (ChsE) is involved in the steroid side-chain degradation process. However, their function in vivo remains unclear. In this study, three ChsE, ChsE1-ChsE2, ChsE3, and ChsE4-ChsE5, were identified in Mycolicibacterium neoaurum, and their functions in vivo are studied and compared with those from Mycobacterium tuberculosis in vitro. By gene knockout, complementation, and the bioconversion of phytosterols, the function of ChsE was elucidated that ChsE4-ChsE5 could utilize C27, C24, and C22 steroids in vivo. ChsE3 could utilize C27 and C24 steroids in vivo. ChsE1-ChsE2 could utilize C27, C24, and C22 steroids in vivo. What is more, the production strain of a C22 steroid, 3-oxo-4,17-pregadiene-20-carboxylic acid methyl ester (PDCE), is constructed with ChsE overexpression. This study improved the understanding of the steroid bioconversion pathway and proposed a method of the production of a new C22 steroid. KEY POINTS: • Three ChsE paralogs from M. neoaurum are identified and studied. • The function of ChsE is overlapped in vivo. • A C22 steroid (PDCE) producer was constructed with ChsE overexpression.

Improving the production of 9α-hydroxy-4-androstene-3,17-dione from phytosterols by 3-ketosteroid-Δ1-dehydrogenase deletions and multiple genetic modifications in Mycobacterium fortuitum.

BACKGROUND: 9α-hydroxyandrost-4-ene-3,17-dione (9-OHAD) is a significant intermediate for the synthesis of glucocorticoid drugs. However, in the process of phytosterol biotransformation to manufacture 9-OHAD, product degradation, and by-products restrict 9-OHAD output. In this study, to construct a stable and high-yield 9-OHAD producer, we investigated a combined strategy of blocking Δ1­dehydrogenation and regulating metabolic flux. RESULTS: Five 3-Ketosteroid-Δ1-dehydrogenases (KstD) were identified in Mycobacterium fortuitum ATCC 35855. KstD2 showed the highest catalytic activity on 3-ketosteroids, followed by KstD3, KstD1, KstD4, and KstD5, respectively. In particular, KstD2 had a much higher catalytic activity for C9 hydroxylated steroids than for C9 non-hydroxylated steroids, whereas KstD3 showed the opposite characteristics. The deletion of kstDs indicated that KstD2 and KstD3 were the main causes of 9-OHAD degradation. Compared with the wild type M. fortuitum ATCC 35855, MFΔkstD, the five kstDs deficient strain, realized stable accumulation of 9-OHAD, and its yield increased by 42.57%. The knockout of opccr or the overexpression of hsd4A alone could not reduce the metabolic flux of the C22 pathway, while the overexpression of hsd4A based on the knockout of opccr in MFΔkstD could remarkably reduce the contents of 9,21 ­dihydroxy­20­methyl­pregna­4­en­3­one (9-OHHP) by-products. The inactivation of FadE28-29 leads to a large accumulation of incomplete side-chain degradation products. Therefore, hsd4A and fadE28-29 were co-expressed in MFΔkstDΔopccr successfully eliminating the two by-products. Compared with MFΔkstD, the purity of 9-OHAD improved from 80.24 to 90.14%. Ultimately, 9­OHAD production reached 12.21 g/L (83.74% molar yield) and the productivity of 9-OHAD was 0.0927 g/L/h from 20 g/L phytosterol. CONCLUSIONS: KstD2 and KstD3 are the main dehydrogenases that lead to 9-OHAD degradation. Hsd4A and Opccr are key enzymes regulating the metabolic flux of the C19- and C22-pathways. Overexpression of fadE28-29 can reduce the accumulation of incomplete degradation products of the side chains. According to the above findings, the MF-FA5020 transformant was successfully constructed to rapidly and stably accumulate 9-OHAD from phytosterols. These results contribute to the understanding of the diversity and complexity of steroid catabolism regulation in actinobacteria and provide a theoretical basis for further optimizing industrial microbial catalysts.

New-type urbanization ecologically reshaping China.

Addressing critical ecological issues is one of the core objectives of the Chinese National New-type Urbanization Plan (NTU). However, there is not enough research to clearly demonstrate NTU's impact on environmental pollution. There is a need to provide solid empirical evidence from evaluation of the effects of NTU on environmental pollution. This study implements a series of propensity score matching and difference-in-difference analyses based on a comprehensive panel dataset spanning the period 2006-2017. The quantitative results show that NTU is largely conducive to curbing environmental pollution, with PM2.5 concentrations as a proxy, and its robustness is demonstrated by the parallel trend test and placebo test. Further, the ecological effect of NTU is heterogeneous in terms of city level, location, and former pollution level. Small and medium cities benefit more than larger or central cities from NTU, and eastern cities exhibit better air quality improvement than cities in western regions. In addition, through quantile regression, we find that the positive outcomes of NTU are restricted by level of pollution, i.e., heavier pollution adds greatly to the difficulty of abatement.

Production of 21-hydroxy-20-methyl-pregna-1,4-dien-3-one by modifying multiple genes in Mycolicibacterium.

C22 steroid drug intermediates are suitable for corticosteroids synthesis, and the production of C22 steroids is unsatisfactory due to the intricate steroid metabolism. Among the C22 steroids, 21-hydroxy-20-methyl-pregna-1,4-dien-3-one (1,4-HP) could be used for Δ1-steroid drug synthesis, such as prednisolone. Nevertheless, the production of 1,4-HP remains unsatisfactory. In this study, an ideal 1,4-HP producing strain was constructed. By the knockout of 3-ketosteroid-9-hydroxylase (KshA) genes and 17ß-hydroxysteroid dehydrogenase (Hsd4A) gene, the steroid nucleus degradation and the accumulation of C19 steroids in Mycolicibacterium neoaurum were blocked. The mutant strain could transform phytosterols into 1,4-HP as the main product and 21-hydroxy-20-methyl-pregna-4-ene-3-one as a by-product. Subsequently, the purity of 1,4-HP improved to 95.2% by the enhancement of 3-ketosteroid-Δ1-dehydrogenase (KSTD) activity, and the production of 1,4-HP was improved by overexpressing NADH oxidase (NOX) and catalase (KATE) genes. Consequently, the yield of 1,4-HP achieved 10.5 g/L. The molar yield and the purity of 1,4-HP were optimal so far, and the production of 1,4-HP provides a new intermediate for the pharmaceutical steroid industry. KEY POINTS: • A third 3-ketosteroid-9-hydroxylase was identified in Mycolicibacterium neoaurum. • An 1,4-HP producer was constructed by KshA and Hsd4A deficiency. • The production of 1,4-HP was improved by KSTD, NOX, and KATE overexpression.