The symbiotic, nitrogen-fixing bacterium Sinorhizobium meliloti favors succinate and related dicarboxylic acids as carbon sources. As a preferred carbon source, succinate can exert catabolite repression upon genes needed for the utilization of many secondary carbon sources, including the alpha-galactosides raffinose and stachyose. We isolated lacR mutants in a genetic screen designed to find S. meliloti mutants that had abnormal succinate-mediated catabolite repression of the melA-agp genes, which are required for the utilization of raffinose and other alpha-galactosides. The loss of catabolite repression in lacR mutants was seen in cells grown in minimal medium containing succinate and raffinose and grown in succinate and lactose. For succinate and lactose, the loss of catabolite repression could be attributed to the constitutive expression of beta-galactoside utilization genes in lacR mutants. However, the inactivation of lacR did not cause the constitutive expression of alpha-galactoside utilization genes but caused the aberrant expression of these genes only when succinate was present. To explain the loss of diauxie in succinate and raffinose, we propose a model in which lacR mutants overproduce beta-galactoside transporters, thereby overwhelming the inducer exclusion mechanisms of succinate-mediated catabolite repression. Thus, some raffinose could be transported by the overproduced beta-galactoside transporters and cause the induction of alpha-galactoside utilization genes in the presence of both succinate and raffinose. This model is supported by the restoration of diauxie in a lacF lacR double mutant (lacF encodes a beta-galactoside transport protein) grown in medium containing succinate and raffinose. Biochemical support for the idea that succinate-mediated repression operates by preventing inducer accumulation also comes from uptake assays, which showed that cells grown in raffinose and exposed to succinate have a decreased rate of raffinose transport compared to control cells not exposed to succinate.
Download full-text PDF |
Source |
|---|---|
| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC135350 | PMC |
| http://dx.doi.org/10.1128/JB.184.19.5385-5392.2002 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Advances in fungal sugar transporters: unlocking the potential of second-generation bioethanol production.
Appl Microbiol Biotechnol
January 2025
Department of Biochemistry and Immunology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, 14049-900, Brazil.
Second-generation (2G) bioethanol production, derived from lignocellulosic biomass, has emerged as a sustainable alternative to fossil fuels by addressing growing energy demands and environmental concerns. Fungal sugar transporters (STs) play a critical role in this process, enabling the uptake of monosaccharides such as glucose and xylose, which are released during the enzymatic hydrolysis of biomass. This mini-review explores recent advances in the structural and functional characterization of STs in filamentous fungi and yeasts, highlighting their roles in processes such as cellulase induction, carbon catabolite repression, and sugar signaling pathways.
View Article and Find Full Text PDFResistant for Biodegradation of Diesel Fuel at High Concentration and Low Temperature.
Microorganisms
December 2024
Department of Civil and Environmental Engineering, University of Strathclyde, James Weir Building, Level 5, 75 Montrose Street, Glasgow G11XJ, UK.
The resistance of 16 strains to diesel fuel was studied. The minimal inhibitory concentrations of diesel fuel against were 4.0-64.
View Article and Find Full Text PDFUpregulation of the gluconeogenesis pathway was observed by KDH1, mitigating glucose catabolite repression.
Food Sci Biotechnol
January 2025
Department of Bioengineering and Technology, Kangwon National University, Chuncheon, Republic of Korea.
Unlabelled: was engineered to mitigate carbon catabolite repression to efficient co-fermenting mixed sugars, which are primary components of cellulosic biomass. KDH1 produced ethanol with 0.42 ± 0.
View Article and Find Full Text PDFTransforming waste wood into pure L-(+)-lactic acid: Efficient use of mixed sugar media through cell-recycled continuous fermentation.
Bioresour Technol
December 2024
Leibniz Institute for Agricultural Engineering and Bioeconomy e. V. (ATB), Department Microbiome Biotechnology, Max-Eyth-Allee 100, Potsdam 14469, Germany. Electronic address:
Lignocellulosic media, containing diverse sugars and growth inhibitor compounds, pose great challenges to fermentation processes. This study tested thermophile Heyndrickxia coagulans strains for the production of L-(+)-lactic acid from waste wood hydrolysate. H.
View Article and Find Full Text PDFThe GATA factor AreB regulates nitrogen metabolism, fungal development, and aflatoxin production in Aspergillus flavus.
FEMS Microbiol Lett
January 2025
School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China.
Article Synopsis
- Nitrogen is crucial for the growth and development of fungi, and while the GATA transcription factor AreA is well-studied, AreB’s role in Aspergillus flavus is less understood.
- Researchers characterized the areB gene in A. flavus, finding that its deletion negatively affects fungal growth, reduces spore production, and increases aflatoxin production, especially under poor nitrogen conditions.
- The study highlights areB's role as a negative regulator of nitrogen catabolite repression, affecting not only nitrogen utilization but also development and secondary metabolism, which could aid in managing aflatoxin contamination.
Want AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!