The Pta-AckA Pathway Regulates LrgAB-Mediated Pyruvate Uptake in Streptococcus mutans

Abstract

Pyruvate forms the central node of carbon metabolism and promotes growth as an alternative carbon source during starvation. We recently revealed that LrgAB functions as a stationary phase pyruvate uptake system in Streptococcus mutans, the primary causative agent of human dental caries, but its underlying regulatory mechanisms are still not clearly understood. This study was aimed at further characterizing the regulation of LrgAB from a metabolomic perspective. We utilized a series of GFP quantification, growth kinetics, and biochemical assays. We disclosed that LrgAB is critical for pyruvate uptake especially during growth under low-glucose stress. Inactivation of the Pta-Ack pathway, responsible for the conversion of acetyl-CoA to acetate, completely inhibits stationary phase lrgAB induction and pyruvate uptake, and renders cells insensitive to external pyruvate as a signal. Inactivation of Pfl, responsible for the conversion of pyruvate to acetyl-CoA under anaerobic conditions, also affected stationary phase pyruvate uptake. This study explores the metabolic components of pyruvate uptake regulation through LrgAB, and highlights its potential as a metabolic stimulator, contributing to the resuscitation and survival of S. mutans cells during nutritional stress.

Understanding LrgAB Regulation of Streptococcus mutans Metabolism

“…In line with this supposition, either lack or overexpression of lrgAB promoted pyruvate excretion during S. mutans growth. Intimate linkage between LrgAB and pyruvate catabolism was anticipated from our previous results (Ahn et al, 2020b) in which stationary-phase lrgAB induction and pyruvate uptake were also completely inhibited by disruption of the Pta-AckA pathway, responsible for the conversion of acetyl-CoA to acetate with the production of one molecule of ATP. Collectively, these findings suggest the catabolic rate of pyruvate is an important trigger to take up external pyruvate through LrgAB, and vice versa.…”

“…We recently reported that stationary phase P lrgA activation was further increased in both the Δ lrgAB and SAB163 strains, relative to wildtype ( Ahn et al, 2020a , b ; Ishkov et al, 2020 ). For measurement of P lrgA activity in SAB161 during growth, the P lrgA-gfp construct was introduced into SAB161 and P lrgA activity compared between the wildtype, Δ lrgAB , SAB161 and SAB163 backgrounds.…”

“…As a control strain, the empty pDL278 plasmid was also transformed in this mutant. The GFP reporter and control constructs in wildtype, Δ lrgAB , and SAB163 backgrounds were previously generated ( Kim et al, 2019 ; Ahn et al, 2020b ; Ishkov et al, 2020 ). For a dual-species competition assay with S. mutans , S. gordonii wildtype DL1 (generating H 2 O 2 in a SpxB-dependent manner) and Δ spxB ( spxB -deficient) strains ( Huang et al, 2016 ) were used.…”

The Staphylococcus aureus CidA and LrgA Proteins Are Functional Holins Involved in the Transport of By-Products of Carbohydrate Metabolism

“…Consistent with this was the finding that plant homologs of the cidAB and lrgAB genes (the Arabidopsis thaliana PLGG1 gene, also referred to as At LrgB ) are required for the transport of glycerate and glycolate, two small carbohydrate intermediates important in the Calvin cycle of photosynthesis ( 22 ). In addition, it has been shown that the lrgAB operons of Bacillus subtilis and Streptococcus mutans are required for pyruvate transport ( 23 – 26 ). The B. subtilis lrgAB operon is induced as the amount of extracellular pyruvate increases and mutations within the operon exhibit growth defects when grown on media with pyruvate as primary carbon source.…”