Structure and expression of a cyanobacterial ilvC gene encoding acetohydroxyacid isomeroreductase

Study on the estradiol degradation gene expression and resistance mechanism of Rhodococcus R-001 under low-temperature stress

Estradiol (E2), an endocrine disruptor, acts by mimicking or interfering with the normal physiological functions of natural hormones within organisms, leading to issues such as endocrine system disruption. Notably, seasonal fluctuations in environmental temperature may influence the degradation speed of estradiol (E2) in the natural environment, intensifying its potential health and ecological risks. Therefore, this study aims to explore how bacteria can degrade E2 under low-temperature conditions, unveiling their resistance mechanisms, with the goal of developing new strategies to mitigate the threat of E2 to health and ecological safety. In this paper, we found that Rhodococcus equi DSSKP-R-001 (R-001) can efficiently degrade E2 at 30 °C and 10 °C. Six genes in R-001 were shown to be involved in E2 degradation by heterologous expression at 30 °C. Among them, 17β-HSD, KstD2, and KstD3, were also involved in E2 degradation at 10 °C; KstD was not previously known to degrade E2. RNA-seq was used to characterize differentially expressed genes (DEGs) to explore the stress response of R-001 to low-temperature environments to elucidate the strain's adaptation mechanism. At the low temperature, R-001 cells changed from a round spherical shape to a long rod or irregular shape with elevated unsaturated fatty acids and were consistent with the corresponding genetic changes. Many differentially expressed genes linked to the cold stress response were observed. R-001 was found to upregulate genes encoding cold shock proteins, fatty acid metabolism proteins, the ABC transport system, DNA damage repair, energy metabolism and transcriptional regulators. In this study, we demonstrated six E2 degradation genes in R-001 and found for the first time that E2 degradation genes have different expression characteristics at 30 °C and 10 °C. Linking R-001 to cold acclimation provides new insights and a mechanistic basis for the simultaneous degradation of E2 under cold stress in Rhodococcus adaptation.

Efficient L-valine production using systematically metabolic engineered Klebsiella oxytoca

L-Valine, a branched-chain amino acid with diversified applications, is biosynthesized with α-acetolactate as the key precursor. In this study, the metabolic flux in Klebsiella oxytoca PDL-K5, a Risk Group 1 organism producing 2,3-butanediol as the major fermentation product, was rearranged to L-valine production by introducing exogenous L-valine biosynthesis pathway and blocking endogenous 2,3-butanediol generation at the metabolic branch point α-acetolactate. After further enhancing L-valine efflux, strengthening pyruvate polymerization and selecting of key enzymes for L-valine synthesis, a plasmid-free K. oxytoca strain VKO-9 was obtained. Fed-batch fermentation with K. oxytoca VKO-9 in a 7.5 L fermenter generated 122 g/L L-valine with a yield of 0.587 g/g in 56 h. In addition, repeated fed-batch fermentation was conducted to prevent precipitation of L-valine due to oversaturation. The average concentration, yield, and productivity of produced L-valine in three cycles of repeated fed-batch fermentation were 81.3 g/L, 0.599 g/g, and 3.39 g/L/h, respectively.

Plasma branched-chain and aromatic amino acids correlate with the gut microbiota and severity of Parkinson's disease

Disturbances of circulating amino acids have been demonstrated in patients with Parkinson’s disease (PD). However, there have been no consistent results for branched-chain amino acids (BCAAs) and aromatic amino acids (AAAs), and related factors have not been explored. We aimed to explore plasma BCAA and AAA profiles in PD patients, and identify their correlations with clinical characteristics and the gut microbiota. Plasma BCAA (leucine, isoleucine, and valine) and AAA (tyrosine and phenylalanine) levels were measured in 106 PD patients and 114 controls. Fecal samples were collected from PD patients for microbiota sequencing and functional analysis. We found that plasma BCAAs and tyrosine were decreased in PD patients. BCAAs and AAAs were correlated with clinical characteristics and microbial taxa, and, in particular, they were negatively correlated with the Hoehn and Yahr stage. Compared with early PD patients, BCAA and AAA levels were even lower, and microbial composition was altered in advanced PD patients. Predictive functional analysis indicated that predicted genes numbers involved in BCAA biosynthesis were lower in advanced PD patients. What’s more, the fecal abundances of critical genes (ilvB, ilvC, ilvD, and ilvN) involved in BCAA biosynthesis were reduced and fecal BCAA concentrations were lower in advanced PD patients. In conclusion, the disturbances of plasma BCAAs and AAAs in PD patients may be related to the gut microbiota and exacerbated with PD severity. The microbial amino acid metabolism may serve as a potential mechanistic link.

Integrated biomarker for type 2 diabetes mellitus and impaired fasting glucose based on metabolomics analysis using ultra-high performance liquid chromatography quadrupole-Orbitrap high-resolution accurate mass spectrometry

RATIONALE

The prevalence of type 2 diabetes mellitus (T2DM) is increasing but its early diagnosis in high risk populations remains challenging using only fasting blood glucose (FBG) or hemoglobin A1c measurements. It is, therefore, important to search for an integrated biomarker for early diagnosis by determining metabolites associated with the progression of the disease.

METHODS

We recruited 149 participants (51 T2DM patients, 50 individuals with impaired fasting glucose (IFG) and 48 normal glucose tolerance subjects). Their serum samples were analyzed based on a metabolomics approach using ultra-high-performance liquid chromatography quadrupole-Orbitrap high-resolution accurate mass spectrometry (UHPLC/Q-Orbitrap HRMS). The changes in metabolites were profiled and evaluated using univariate and multivariate analyses. Furthermore, a biomarker model was established and the potential biomarkers were evaluated using binary logistic regression analysis and receiver operating characteristic analysis with AUC (area under the curve). Pathway analysis of differential metabolites was performed to reveal the important biological information.

RESULTS

Thirty-eight differential metabolites were identified as significantly associated with T2DM patients and 23 differential metabolites with IFG individuals, mainly amino acids, carnitines, and phospholipids. By evaluating 17 potential biomarkers, we defined a novel integrated biomarker consisting of 2-acetolactate, 2-hydroxy-2,4-pentadienoate, L-arabinose and L-glutamine. The AUCs of the integrated biomarker with IFG and T2DM patients were 0.874 and 0.994, respectively, which showed a superior diagnostic performance. The levels of 2-acetolactate and 2-hydroxy-2,4-pentadienoate were strongly positively correlated with FBG, while L-glutamine and L-arabinose were strongly negatively associated with FBG. After pathway analysis, it was suggested that the majority of the influenced metabolic pathways associated with diabetes referred to amino acid metabolism.

CONCLUSIONS

The integrated biomarker could diagnose IFG and T2DM with a superior diagnostic performance. This finding provides support for novel biomarkers in the diagnosis and treatment of diabetes.

Regulation by external pH and stationary growth phase of the acetolactate synthase from Synechocystis PCC6803

Several characteristics identify the protein encoded by the alsS gene [sll1981 in Cyanobase (http://www.kazusa.or.jp/cyano/cyano. html)] of Synechocystis PCC6803 as an acetolactate synthase. The AlsS protein is about 60% homologous to the AlsS from Bacillus subtilis or other bacteria. These enzymes condense two pyruvates to form acetolactate, implicated in pH homeostasis via the acetoin-2, 3-butanediol pathway or in valine biosynthesis. Transcriptional fusions revealed that alsS was induced at the onset of stationary phase, as in B. subtilis, a situation leading to an increase in the pHout to above 11 in Synechocystis. This is the first cyanobacterial gene showing a dependence on pH for its expression. Induction was also obtained by the presence of > 100 mM Na+, the effect being prevented by amiloride, in agreement with Na+/H+ exchange in the pH homeostasis process. Homology of the Synechocystis AlsS protein to the close family of acetohydroxy acid synthases (including one in Synechocystis) is around 30%. These enzymes are involved in the parallel routes for valine/leucine and isoleucine biosynthesis. No phenotype of auxotrophy for any of these amino acids was associated with a null mutation in the Synechocystis alsS gene. The AlsS enzyme did not complement the isoleucine deficiency of an acetohydroxy acid synthase-deficient Escherichia coli mutant.

Cloning and molecular analysis of two different ILV5 genes from a brewing strain of Saccharomyces cerevisiae

Two different ILV5 genes encoding acetohydroxy-acid isomeroreductases, and named ILV5G and ILV5X, were cloned and sequenced from a Saccharomyces cerevisiae brewing strain. The coding sequence of ILV5X shows a single nucleotide change with respect to that from the ILV5 gene of a S. cerevisiae laboratory strain. In addition, all promoter motifs which are, or are presumed to be, implicated in transcription regulatory functions are identical in ILV5 and ILV5X. In contrast, the coding sequence of ILV5G differs in 5.6% of its nucleotides from that of ILV5 and most of its promoter regulatory motifs show a single nucleotide change with respect to those from ILV5.

Branched-chain-amino-acid biosynthesis in plants: molecular cloning and characterization of the gene encoding acetohydroxy acid isomeroreductase (ketol-acid reductoisomerase) from Arabidopsis thaliana (thale cress)

Towards the goal of gaining a better understanding of the molecular mechanisms controlling branched-chain-amino-acid biosynthesis in plants, we have isolated, sequenced and characterized a gene encoding acetohydroxy acid isomero-reductase (ketol-acid reductoisomerase) from Arabidopsis thaliana (thale cress). Comparison between the acetohydroxy acid isomeroreductase cDNA and the genomic sequence has allowed us to determine the exon structure of the coding region. The isolated acetohydroxy acid isomeroreductase gene is distributed over approx. 4.5 kbp and contains nine introns (79-347 bp). The transcriptional start site was found to be 52 bp upstream of the translational initiation site. Southern-blot analysis of A. thaliana genomic DNA shows that the acetohydroxy acid isomeroreductase is encoded by a single-copy gene.

Identification and sequence determination of the acetohydroxy acid isomeroreductase gene from Brevibacterium flavum MJ233

The enzyme acetohydroxy acid isomeroreductase (AHAIR) is the second enzyme in the parallel isoleucine-valine biosynthetic pathway. We previously reported the cloning and sequencing of the acetohydroxy acid synthase (AHAS) genes from Brevibacterium flavum MJ233. Analysis of the sequence downstream of the AHAS genes identified another open reading frame highly homologous at the amino acid level to the AHAIR gene from Escherichia coli (ilvC). We subcloned the B. flavum AHAIR gene on a 2.1 kb Bg/II-EcoRI fragment by complementation of an E. coli ilvC mutant. The nucleotide sequence of the B. flavum AHAIR gene consists of 338 codons (molecular weight of 36158). Comparison of the deduced protein sequence revealed a high degree of identity with the sequences of ilvC genes from other organisms. Disruption of the B. flavum ilvC gene by a kanamycin resistance cassette resulted in L-isoleucine and L-valine auxotrophy.