Role of the receptor for bacteriophage lambda in the functioning of the maltose chemoreceptor of Escherichia coli.

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RESUMO

Chemotaxis towards maltose is specifically defective in many strains of Escherichia coli carrying mutations affecting lamB, the gene coding for the outer membrane receptor for bacteriophage lambda. However, with one exception, the most extreme effect of lamB mutants on the maltose response as determined in the capillary assay is a shift to higher sugar concentrations and a reduction in the number of bacteria accumulated to about 25% of the wild-type level. The severity of the taxis defect is strongly correlated with reduced ability of the cells to take up the maltose present at 1 and 10 muM. Evidence presented here and in the accompanying paper indicates that the lambda receptor is involved in the transport of maltose at these concentrations. The effects of lamB mutations on maltose taxis can be explained by postulating that the high-affinity maltose transport system in which the lambda receptor participates transfers maltose from the surrounding medium across the outer membrane and into the periplasmic space. If the maltose chemoreceptor detects sugar present in the periplasmic space, and not molecules external to the outer membrane, then defective transport of low concentrations of maltose into the periplasm would result in the observed apparent reduction in the sensitivity of the maltose receptor. Thus, the lambda receptor protein would participate in maltose chemorecepton only indirectly through its role in maltose transport.

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