Salt stress perception and metabolic regulation network analysis of a marine probiotic Meyerozyma guilliermondii GXDK6

Deciphering the ammonia transformation mechanism of a novel marine multi-stress-tolerant yeast, Pichia kudriavzevii HJ2, as revealed by integrated omics analysis

Ammonia nitrogen posed a significant threat to aquatic animals in aquaculture environments, and the substantial potential of microorganisms in removing ammonia nitrogen had garnered considerable attention. This study identified a marine yeast, Pichia kudriavzevii HJ2, which effectively removed ammonia nitrogen. By combining transcriptomics and metabolomics, the ammonia nitrogen transformation mechanism of HJ2 was elucidated. HJ2 achieved 100% ammonia nitrogen removal efficiency within 1 day of fermentation at 35°C with 300 mg/L ammonia nitrogen and 73.56% removal efficiency within 36 h with 600 mg/L ammonia nitrogen. Transcriptomics revealed that exposure to 600 mg/L ammonia nitrogen resulted in 541 up-regulated genes and 567 down-regulated genes in the HJ2 strain. Differentially expressed genes (DEGs) were primarily involved in the tricarboxylic acid (TCA) cycle and amino acid metabolism. Metabolomics revealed that HJ2 facilitated the production of 383 up-regulated metabolites and suppressed 137 down-regulated metabolites when exposed to 600 mg/L ammonia nitrogen. Integrating transcriptomics and metabolomics analyses showed that HJ2 removed ammonia nitrogen by sensing its presence in the extracellular environment, activating the TCA cycle, enhancing amino acid metabolism and nucleotide metabolism, and promoting its robust growth and reproduction. Amino acid metabolism played an important role in the ammonia transformation mechanism of HJ2. The result was confirmed by the increased activity of glutamate dehydrogenase (GDH) and aspartate aminotransferase (GOT). Up-regulated nitrogen metabolites such as L-glutamate, L-aspartic acid, spermidine, and trigonelline were produced. The results of enzyme activity tests, construction of overexpressing strains, and adding exogenous amino acid experiments demonstrated that HJ2 could utilize GDH and GOT ammonia assimilation pathways.IMPORTANCEAmmonia nitrogen removal ability was a universal characteristic among the ammonia-oxidizing bacteria or archaea. Recently, yeast strains from the genus Pichia were found to have ammonia nitrogen removal ability. However, the mechanism of ammonia nitrogen removal in Pichia had not been reported. In the study, the ammonia nitrogen removal efficiency of Pichia kudriavzevii HJ2 was identified, and the mechanisms by which HJ2 transformed ammonia nitrogen into non-toxic organic nitrogen were elucidated, offering potential solutions to pollution challenges in aquaculture and helping minimize resource waste. The study offered new insights into the transformation mechanism of microbial ammonia nitrogen removal and its environmentally friendly application.

Discovery and interaction of four key biosynthetic enzymes under co-regulation for dopamine biosynthesis with marine Meyerozyma guilliermondii GXDK6 and Bacillus aryabhattai NM1-A2

Dopamine has proven effective in treating conditions such as depression and myocardial infarction. The marine Meyerozyma guilliermondii GXDK6 and Bacillus aryabhattai NM1-A2, both known for their robust nitrogen conversion capabilities, were selected for co-fermentation to synthesize dopamine. The metabolic co-regulation mechanism was further elucidated, demonstrating that the synergistic interaction between GXDK6 and NM1-A2 significantly enhanced dopamine synthesis. Under optimized conditions, dopamine production reached 2019.22 mg/L in a bioreactor. Genome-wide analysis revealed that co-fermentation enriched proteins involved in the conversion of tyrosine to dopamine, including polyphenol oxidase (encoded by gene PPO) and tyrosine decarboxylase (encoded by gene BamfnA) from NM1-A2, as well as cytochrome P450 76AD1 (encoded by gene CYP76AD1) and tyrosine decarboxylase (encoded by gene MgmfnA) from GXDK6. These proteins strengthen the dopamine metabolic pathway, facilitating efficient dopamine expression. Heterologous expression of biosynthetic enzymes indicated that dual-gene expression was more effective in dopamine biosynthesis than individual gene expression, for which the synthesized L-dopa was used to catalyze the synthesis of dopamine. In vitro catalysis with purified PPO showed that 5 mM of tyrosine could be converted to 0.21 mM of L-dopa. This co-fermentation strategy provides a novel theoretical framework for the de novo microbial synthesis of dopamine.

Exploration of the advantages of targeted isolation of deep-sea microorganisms and genetically engineered strains

Oil, mineral processing and environmental restoration can be dangerous processes. Attempts are often made to apply microorganisms to reduce the risks, but the adaptability of terrestrial organisms is often weak. Although genetically engineered strains can improve their environmental adaptability through targeted modification, there are problems such as metabolite accumulation, poor plasmid stability and potential pathogenicity. Screening of extremophiles from the natural environment has become an inevitable choice. The special environment in the deep sea (high pressure, low temperature, low nutrition, high salinity) is a natural place for extremophiles to grow and survive, thus screening of extremophiles from the deep sea is conducive to the green and sustainable development of industry. In this paper, the application status and problems of genetically engineered strains are reviewed based on the microorganisms needed for extreme industry. This paper focuses on the application status and advantages of deep-sea microorganisms. It is found that their advantages are strong adaptability, stable gene, friendly environment, simple and convenient technology (compared with genetic engineering), which has a broad industry processes application prospect. This review broadens the scope of microbial applications.

Response Mechanisms of Zelkova schneideriana Leaves to Varying Levels of Calcium Stress

Calcium stress can negatively impact plant growth, prompting plants to respond by mitigating this effect. However, the specific mechanisms underlying this response remain unclear. In this study, we used non-targeted metabolomics and transcriptomics to investigate the response mechanisms of Zelkova schneideriana leaves under varying degrees of calcium stress. Results revealed that calcium stress led to wilt in young leaves. When calcium stress exceeds the tolerance threshold of the leaf, it results in wilting of mature leaves, rupture of chloroplasts in palisade tissue, and extensive wrinkling and breakage of leaf cells. Transcriptomic analysis indicated that calcium stress inhibited photosynthesis by suppressing the expression of genes related to photosynthetic system II and electron transport. Leaf cells activate phenylpropanoid biosynthesis, flavonoid biosynthesis, and Vitamin B6 metabolism to resist calcium stress. When calcium accumulation gradually surpassed the tolerance threshold of the cells, this results in failure of conventional anti-calcium stress mechanisms, leading to cell death. Furthermore, excessive calcium stress inhibits the expression of CNGC and anti-pathogen genes. The results of the metabolomics study showed that five key metabolites increased in response to calcium stress, which may play an important role in countering calcium stress. This study provides insights into the response of Z. schneideriana leaves to different levels of calcium stress, which could provide a theoretical basis for cultivating Z. schneideriana in karst areas and enhance our understanding of plant responses to calcium stress.

Regulatory mechanisms of dopamine metabolism in a marine Meyerozyma guilliermondii GXDK6 under NaCl stress as revealed by integrative multi-omics analysis

Dopamine can be used to treat depression, myocardial infarction, and other diseases. However, few reports are available on the de novo microbial synthesis of dopamine from low-cost substrate. In this study, integrated omics technology was used to explore the dopamine metabolism of a novel marine multi-stress-tolerant aromatic yeast Meyerozyma guilliermondii GXDK6. GXDK6 was found to have the ability to biosynthesize dopamine when using glucose as the substrate. 14 key genes for the biosynthesis of dopamine were identified by whole genome-wide analysis. Transcriptomic and proteomic data showed that the expression levels of gene AAT2 encoding aspartate aminotransferase (regulating dopamine anabolism) were upregulated, while gene AO-I encoding copper amine oxidase (involved in dopamine catabolism) were downregulated under 10 % NaCl stress compared with non-NaCl stress, thereby contributing to biosynthesis of dopamine. Further, the amount of dopamine under 10 % NaCl stress was 2.51-fold higher than that of zero NaCl, which was consistent with the multi-omics results. Real-time fluorescence quantitative PCR (RT-qPCR) and high-performance liquid chromatography (HPLC) results confirmed the metabolic model of dopamine. Furthermore, by overexpressing AAT2, AST enzyme activity was increased by 24.89 %, the expression of genes related to dopamine metabolism was enhanced, and dopamine production was increased by 56.36 % in recombinant GXDK6AAT2. In conclusion, Meyerozyma guilliermondii GXDK6 could utilize low-cost carbon source to synthesize dopamine, and NaCl stress promoted the biosynthesis of dopamine.