Effects of glucose availability in Lactobacillus sakei; metabolic change and regulation of the proteome and transcriptome.

Anette Mcleod,Ida Rud,Lars Axelsson,Lars Snipen,Ellen F Mosleth,Filipe Branco Dos Santos,Kristian Hovde Liland,Luca Cocolin

doi:10.1371/journal.pone.0187542

Anette Mcleod, Ida Rud + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0187542

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Abstract

Effects of glucose availability were investigated in Lactobacillus sakei strains 23K and LS25 cultivated in anaerobic, glucose-limited chemostats set at high (D = 0.357 h-1) and low (D = 0.045 h-1) dilution rates. We observed for both strains a shift from homolactic towards more mixed acid fermentation when comparing high to low growth rates. However, this change was more pronounced for LS25 than for 23K, where dominating products were lactate>formate>acetate≥ethanol at both conditions. A multivariate approach was used for analyzing proteome and transcriptome data from the bacterial cultures, where the predictive power of the omics data was used for identifying features that can explain the differences in the end-product profiles. We show that the different degree of response to the same energy restriction revealed interesting strain specific regulation. An elevated formate production level during slow growth, more for LS25 than for 23K, was clearly reflected in correlating pyruvate formate lyase expression. With stronger effect for LS25, differential expression of the Rex transcriptional regulator and NADH oxidase, a target of Rex, indicated that maintainance of the cell redox balance, in terms of the NADH/NAD+ ratio, may be a key process during the metabolic change. The results provide a better understanding of different strategies that cells may deploy in response to changes in substrate availability.

Highlights

A superior performance of the lactic acid bacterium (LAB) Lactobacillus sakei in meat fermentation has been explained by its genomic and physiological adaptions to the raw-meat environment [1]
For the two strains of L. sakei, 23K and LS25, cultivated under anaerobic conditions in glucose-limited chemostat cultures set at high (D = 0.357 h-1) and low (D = 0.045 h-1) dilution rates, glucose was completely consumed throughout cultivation
We have investigated the effect of glucose availability in L. sakei strains 23K and LS25 on the metabolite, proteome and transcriptome levels, where different degrees of response to the same energy restriction revealed strain specific regulation

Summary

Introduction

A superior performance of the lactic acid bacterium (LAB) Lactobacillus sakei in meat fermentation has been explained by its genomic and physiological adaptions to the raw-meat environment [1]. The bacterium is useful in industrial meat fermentation, where important attributes for starter cultures are effective growth and high acidification activity. L. sakei is strictly fermentative, completely devoid of a respiratory chain, still aerotolerant [1, 2]. Depending on the growth condition, the bacterium can shift between a pathway leading to nearly exclusively lactate production versus a pathway leading to the production of mixed acids.

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