PMID:20190045

Citation	Zeng, L, Das, S and Burne, RA (2010) Utilization of lactose and galactose by Streptococcus mutans: transport, toxicity, and carbon catabolite repression. J. Bacteriol. 192:2434-44
Abstract	Abundant in milk and other dairy products, lactose is considered to have an important role in oral microbial ecology and can contribute to caries development in both adults and young children. To better understand the metabolism of lactose and galactose by Streptococcus mutans, the major etiological agent of human tooth decay, a genetic analysis of the tagatose-6-phosphate (lac) and Leloir (gal) pathways was performed in strain UA159. Deletion of each gene in the lac operon caused various alterations in expression of a P(lacA)-cat promoter fusion and defects in growth on either lactose (lacA, lacB, lacF, lacE, and lacG), galactose (lacA, lacB, lacD, and lacG) or both sugars (lacA, lacB, and lacG). Failure to grow in the presence of galactose or lactose by certain lac mutants appeared to arise from the accumulation of intermediates of galactose metabolism, particularly galatose-6-phosphate. The glucose- and lactose-PTS permeases, EII(Man) and EII(Lac), respectively, were shown to be the only effective transporters of galactose in S. mutans. Furthermore, disruption of manL, encoding EIIAB(Man), led to increased resistance to glucose-mediated CCR when lactose was used to induce the lac operon, but resulted in reduced lac gene expression in cells growing on galactose. Collectively, the results reveal a remarkably high degree of complexity in the regulation of lactose/galactose catabolism.
Links	PubMed PMC2863486 Online version:10.1128/JB.01624-09
Keywords	Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Biological Transport/genetics; Biological Transport/physiology; Carbon/metabolism; Galactose/metabolism; Galactosephosphates/metabolism; Lac Operon/genetics; Lactose/metabolism; Models, Biological; Mutagenesis, Site-Directed; Mutation; Phosphoenolpyruvate Sugar Phosphotransferase System/genetics; Phosphoenolpyruvate Sugar Phosphotransferase System/metabolism; Promoter Regions, Genetic/genetics; Reverse Transcriptase Polymerase Chain Reaction; Streptococcus mutans/genetics; Streptococcus mutans/growth & development; Streptococcus mutans/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
STRPS:LACA	Contributes to	GO:0050044: galactose-6-phosphate isomerase activity	ECO:0000315:		F		States that the Streptococcus could not grow after an accumulation of the metabolic intermediates from galactose, particularly the galactose-6-phosphate, with a mutation in the lac genes. Therefore, the isomerase activity is a crucial function for preventing this mode of action.	complete
STRMU:LACG		GO:0005975: carbohydrate metabolic process	ECO:0000315:		P		As seen in table 2, when the lacG gene was disrupted, the bacteria Streptococcus mutans was unable to grow on TV media containing either galactose or lactose. Also, as seen in table 1, when the lacG gene was disrupted, there was a large reduction of the induction of the lacA promoter by lactose.	complete CACAO 3926
STRMU:LACG	involved_in	GO:0005975: carbohydrate metabolic process	ECO:0000315: mutant phenotype evidence used in manual assertion		P		Seeded From UniProt	complete

References

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