Identification of TogMNAB, an ABC transporter which mediates the uptake ofpectic oligomers in Erwinia chrysanthemi 3937

The bacterium Erwinia chrysanthemi, which causes soft rot disease on variou s plants, is able to use pectin as a carbon source for growth. Knowledge of the critical step in pectin catabolism which allows the entry of pectic ol igomers into the cells is scarce. We report here the first example of a tra nsport system involved in the uptake of pectic oligomers. The TogMNAB trans porter of E. chrysanthemi is a member of the ATP-binding cassette (ABC) sup erfamily. TogM and TogN are homologous to the inner membrane components, To gA exhibits the signature of ABC ATPases and TogB shows similarity with per iplasmic ligand-binding proteins. The TogMNAB transporter is a new member o f the carbohydrate uptake transporter-1 family (CUT1, TC no. 3.1.1), which is specialized in the transport of complex sugars. The four genes, togM, to gN, togA and togB, are apparently co-transcribed in a large operon which al so includes the pectate lyase gene pelW. The transcription of the tog opero n is induced in the presence of pectic derivatives and is affected by catab olite repression. It is controlled by the KdgR repressor and the CRP activa tor. The TogMNAB system is able to provide Escherichia coli with the abilit y to transport oligogalacturonides. In E. chrysanthemi, the TogMNAB system seems to play a major role in switching on the induction of pectin cataboli sm. TogB also acts as a specific receptor for chemotaxis towards oligogalac turonides. The decreased capacity of maceration of a togM mutant indicates the importance of transport and/or attraction of oligogalacturonides for E. chrysanthemi pathogenicity.