Environmental Triggers oflrgAExpression inStreptococcus mutans

Abstract

20The lrgAB and cidAB operons of Streptococcus mutans encode proteins that are 21 structurally similar to the bacteriophage lambda family of holin-antiholin proteins, which 22 are believed to facilitate cell death in other bacterial species. Although their precise 23 function is not known, cidAB and lrgAB are linked to multiple virulence traits of S. mutans, 24 including oxidative stress tolerance, biofilm formation, and autolysis. The regulation of 25 cidAB and lrgAB is still not understood, as these operons show opposite patterns of 26 expression as well as a complex dependence on growth conditions. We have used a 27 microfluidic approach, together with single-cell imaging of a fluorescent gene reporter, to 28 identify with greater precision the cues that trigger lrgA expression and characterize cell- 29 to-cell heterogeneity in lrgA activity. lrgA activates very abruptly at stationary phase, with 30 a high degree of synchrony across the population. We find this activation is controlled by 31 a small number of inputs that are sensitive to growth phase: Extracellular pyruvate, 32 glucose, and molecular oxygen. Further, activation of lrgA appears to be self-limiting, so 33 that lrgA is strongly expressed only for a very short interval of time. Consequently, lrgA is 34 programmed to switch on briefly at the end of exponential growth, as glucose and 35 molecular oxygen are exhausted and extracellular pyruvate is available. Our findings are 36 consistent with studies showing that homologs of lrgAB are linked, together with lytST, to 37 the reimport of pyruvate for anaerobic fermentative growth. 38 39 40 41 42 3 Importance 43The function and regulation of cidAB and lrgAB in Streptococcus mutans is not 44 understood, although these operons have been clearly linked to stress responses and 45 they show a complex dependence on environmental inputs and growth phase. Identifying 46 specific environmental cues that trigger activation of lrgAB has been difficult owing to the 47 cells' own modification of key inputs such as glucose and oxygen: In S. mutans the lrgAB 48 operon is strongly upregulated at the end of exponential phase, where growth conditions 49 in a bulk culture become poorly defined. Here we have used microfluidics to apply precise 50 control of environmental inputs to S. mutans and identify specific chemical cues that 51 activate lrgAB. We find that rigorously anaerobic conditions and the presence of 52 extracellular pyruvate are sufficient to induce lrgAB expression, suggesting that lrgAB is 53 timed to activate just as pyruvate fermentation becomes favorable. 55The oral pathogen Streptococcus mutans (1) possesses two operons designated 56 cidAB (SMU.1701/1700) and lrgAB (SMU.575/574) (2), which are closely homologous to 57 the lrgAB and cidAB operons that have been extensively studied in organisms such as 58 Bacillus subtilis and Staphylococcus aureus (3-10). Sequence homology indicates that 59 cidAB and lrgAB encode membrane proteins that are similar to holin-antiholin membrane 60 prote...

Metabolic adaption to extracellular pyruvate triggers biofilm formation inClostridioides difficile

“…Recently, it was demonstrated that Staphylococcus aureus requires the presence of extracellular pyruvate to form and maintain a biofilm (Goodwine et al, 2019). In Streptococcus mutans , pyruvate improves stationary phase survival and protects against microbiota-generated oxidative stresses in a density- and CcpA-dependent fashion (Ahn et al, 2019; Ishkov et al, 2020; Redanz et al, 2020). Furthermore, pyruvate fermentation is important for Pseudomonas aeruginosa microcolony formation and long-term survival in anaerobic environments (Eschbach et al, 2004; Petrova et al 2012).…”