Relevance of NADH Dehydrogenase and Alternative Two-Enzyme Systems for Growth of Corynebacterium glutamicum With Glucose, Lactate, and Acetate.

Tomoya Maeda,Abigail Koch-Koerfges,Michael Bott

doi:10.3389/fbioe.2020.621213

Tomoya Maeda, Abigail Koch-Koerfges + Show 1 more

Open Access

https://doi.org/10.3389/fbioe.2020.621213

Copy DOI

Abstract

The oxidation of NADH with the concomitant reduction of a quinone is a crucial step in the metabolism of respiring cells. In this study, we analyzed the relevance of three different NADH oxidation systems in the actinobacterial model organism Corynebacterium glutamicum by characterizing defined mutants lacking the non-proton-pumping NADH dehydrogenase Ndh (Δndh) and/or one of the alternative NADH-oxidizing enzymes, L-lactate dehydrogenase LdhA (ΔldhA) and malate dehydrogenase Mdh (Δmdh). Together with the menaquinone-dependent L-lactate dehydrogenase LldD and malate:quinone oxidoreductase Mqo, the LdhA-LldD and Mdh-Mqo couples can functionally replace Ndh activity. In glucose minimal medium the Δndh mutant, but not the ΔldhA and Δmdh strains, showed reduced growth and a lowered NAD+/NADH ratio, in line with Ndh being the major enzyme for NADH oxidation. Growth of the double mutants ΔndhΔmdh and ΔndhΔldhA, but not of strain ΔmdhΔldhA, in glucose medium was stronger impaired than that of the Δndh mutant, supporting an active role of the alternative Mdh-Mqo and LdhA-LldD systems in NADH oxidation and menaquinone reduction. In L-lactate minimal medium the Δndh mutant grew better than the wild type, probably due to a higher activity of the menaquinone-dependent L-lactate dehydrogenase LldD. The ΔndhΔmdh mutant failed to grow in L-lactate medium and acetate medium. Growth with L-lactate could be restored by additional deletion of sugR, suggesting that ldhA repression by the transcriptional regulator SugR prevented growth on L-lactate medium. Attempts to construct a ΔndhΔmdhΔldhA triple mutant were not successful, suggesting that Ndh, Mdh and LdhA cannot be replaced by other NADH-oxidizing enzymes in C. glutamicum.

Highlights

Corynebacterium glutamicum is a Gram-positive, non-pathogenic soil bacterium that was isolated in a screen for microorganisms which excrete the flavor enhancer L-glutamate (Kinoshita et al, 1957)
For the analysis of growth, organic acid production, carbon source consumption, oxygen consumption, enzyme activities, and NAD+/NADH ratios, a 5 ml preculture in brain-heart infusion (BHI) medium was inoculated with colonies from a fresh agar plate (BHI agar) and incubated for 8 h at 30◦C and 170 rpm
In order to determine the relevance of NADH dehydrogenase Ndh, malate dehydrogenase Mdh and L-lactate dehydrogenase LdhA for aerobic growth of C. glutamicum, we characterized the deletion mutants ndh, mdh, and ldhA during cultivation in shake flasks with glucose, L-lactate, or acetate, as carbon source

Summary

Introduction

Corynebacterium glutamicum is a Gram-positive, non-pathogenic soil bacterium that was isolated in a screen for microorganisms which excrete the flavor enhancer L-glutamate (Kinoshita et al, 1957) It is used in industry for the biotechnological production of amino acids and proteins (Eggeling and Bott, 2015; Freudl, 2017). The majority of the corresponding production processes are performed under aerobic conditions and require a functional respiratory chain (Bott and Niebisch, 2003; Matsushita, 2013). Several dehydrogenases oxidize their substrates with concomitant reduction of menaquinone, the only respiratory quinone in corynebacteria. Electron transfer from menaquinol to oxygen is catalyzed either by a cytochrome bc1-aa supercomplex (Niebisch and Bott, 2003; Graf et al, 2016; Kao et al, 2016) or by cytochrome bd oxidase (Kusumoto et al, 2000; Kabus et al, 2007)

Methods

Results

Conclusion