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3 Publications visible to you, out of a total of 3
Growth rate dependent control in Enterococcus faecalis: effects on the transcriptome, proteome and strong regulation of lactate dehydrogenase

Abstract (Expand)

Enterococcus faecalis V583 was grown in a glucose-limited chemostat at three different (0.05 h(-1), 0.15 h(-1) and 0.4 h(-1)) growth rates. The fermentation pattern changed with growth rate, from a … mostly homolactic profile at high growth rate to a fermentation dominated by formate, acetate and ethanol production at low growth rate. A number of amino acids were consumed at the lower growth rates but not by fast growing cells. The change in metabolic profile was mainly caused by decreased flux through lactate dehydrogenase. Transcription of ldh-1, encoding the principal lactate dehydrogenase, showed very strong growth rate dependence and differed by three orders of magnitude between the highest and the lowest growth rates. Despite the increase in ldh-1 transcript, the content of the Ldh-1 protein was the same under all conditions. Using microarrays and qPCR the levels of 227 gene transcript were found to be affected by the growth rate, and 56 differentially expressed proteins were found by proteomic analyses. Few genes or proteins showed a growth rate-dependent increase or decrease in expression over the whole range of conditions, and many showed at maximum or minimum at the middle growth rate (D=0.15h(-1)). For many gene products a discrepancy between transcriptomic and proteomic data were seen, indicating post-transcriptional regulation of expression.

Authors: , Ellen M Faergestad, , Lars Snipen, ,

Date Published: 1st Nov 2011

Publication Type: Not specified

Transcriptome, proteome and metabolite analysis of a lactate dehydrogenase negative mutant of Enterococcus faecalis V583

Abstract (Expand)

A constructed lactate dehydrogenase-negative mutant of Enterococcus faecalis V583 grows at the same rate as the wild type, but ferments glucose to ethanol, formate, and acetoin. Microrray analysis … showed that LDH deficiency had profound transcriptional effects, 43 genes in the mutant were found to be upregulated and 45 to be downregulated. Most of the upregulated genes encode enzymes of energy metabolism or transport. By 2D gel analysis 45 differentially expressed proteins were identified. A comparison of transcriptomic and proteomic data suggests that for several proteins the level of expression is regulated beyond the level of transcription. Pyruvate catabolic genes, including the truncated ldh, showed highly increased transcription in the mutant. These genes, along with a number of other differentially expressed genes, are preceded by sequences with homology to binding sites for the global redox-sensing repressor, Rex, of Staphylococcus aureus. The data indicate that the genes are transcriptionally regulated by the NADH/NAD ratio and that this ratio plays an important role in the regulatory network controlling energy metabolism in E. faecalis.

Authors: , , Ellen M Fergestad, Geir Mathiesen, ,

Date Published: 8th Feb 2011

Publication Type: Not specified

Physiological characterization of three lactic acid bacteria and their isogenic ldh deletion mutants shows that these organisms are optimized for Yatp and not ATP formation rates at their physiological pH

Abstract (Expand)

Several lactic acid bacteria use homolactic fermentation for generation of ATP. Here we studied the role of the lactate dehydrogenase enzyme on the general physiology of the three homolactic acid … bacteria Lactococcus lactis, Enterococcus faecalis and Streptococcus pyogenes. Of note, deletion of the ldh genes hardly affected the growth rate in chemically defined medium in microaerophilic conditions. However, growth rate was affected in rich medium. Furthermore, deletion of ldh affected the ability for utilization of various substrates as a carbon source. A switch to mixed acid fermentation was observed in glucose-limited continuous growth and was dependent on the growth rate for S. pyogenes and dependent on the pH for E. faecalis. In S. pyogenes and L. lactis a change in pH resulted in a clear change in Yatp. The pH that showed the highest Yatp corresponded to the pH of the natural habitat of the organisms.

Authors: , , , , Anja Pritzschke, Nikolai Siemens, , ,

Date Published: 25th Nov 2010

Publication Type: Not specified

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