The multifactorial influences of RpoS, Mlc and cAMP on ptsG expression under glucose-limited and anaerobic conditions.
The ptsG gene encodes the high-affinity glucose receptor component of the PEP:glucose phosphotransferase system. PtsG is the major glucose transporter in Escherichia coli under glucose-excess conditions but its regulation under glucose limitation or anaerobiosis is poorly defined. Using a ptsG-lacZ transcriptional fusion, ptsG expression was found to peak with low (micromolar) external glucose levels in glucose-limited chemostats, so PtsG is primed to contribute to glucose scavenging under hunger response conditions. This regulatory pattern was confirmed using methyl- alpha-glucoside transport assays of PtsG-dependent transport. The regulation of ptsG by cAMP contributed to the optimal expression with micromolar glucose but ptsG was actually repressed to levels below that in glucose-excess batch cultures at very slow growth rates and submicromolar glucose concentrations. RpoS contributed to repression of ptsG in slow-growing bacteria but not under glucose-excess conditions. Also, Mlc increasingly contributed to the repression of ptsG at residual glucose concentrations too low to saturate PtsG. A similar pattern of ptsG regulation was observed in anaerobic cultures with either glucose-excess or glucose-limiting situations.
Seeto
Shona
S
School of Molecular and Microbial Biosciences, G08, University of Sydney, Sydney, NSW 2006, Australia.
Notley-McRobb
Lucinda
L
Ferenci
Thomas
T
D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000378:metabolism*; D001692:Biological Transport; D019149:Bioreactors; D000242:Cyclic AMP / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D005947:Glucose / Q000378:metabolism; D008757:Methylglucosides / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System / Q000096:biosynthesis* / Q000235:genetics; D012097:Repressor Proteins / Q000378:metabolism*; D012808:Sigma Factor / Q000378:metabolism*
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008757:Methylglucosides; C111065:Mlc protein, E coli; D009004:Monosaccharide Transport Proteins; D012097:Repressor Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; C027020:methylglucoside; D000242:Cyclic AMP; D010731:Phosphoenolpyruvate Sugar Phosphotransferase System; C031629:phosphoenolpyruvate-glucose phosphotransferase; D005947:Glucose