Members of the amylovora group of Erwinia are cellulolytic and possess genes homologous to the type II secretion pathway

A cellulase-producing clone was isolated from a genomic library of the Erwi nia rhapontici (Millard) Burkholder strain NCPPB2989. The corresponding gen e, named celA, encodes an endoglucanase (EC 3.2.1.4) with the extremely low pH optimum of 3.4 and a temperature optimum between 40 and 50 degrees C. A single ORF of 999 nt was found to be responsible for the Cel activity. The corresponding protein, named CelA, showed 67% identity to the endoglucanas e Y of E. chrysanthemi and 51.5% identity to the endoglucanase of Cellulomo nas mda, and thus belongs to the glycosyl hydrolase family 8. The celA gene , or its homologue, was found to be present in all E. rhapontici isolates a nalysed, in E. chrysanthemi, and in E. amylovora. The presence of plant cel l wall-degrading enzymes in the amylovora group of Erwinia spp. had not pre viously been established. Furthermore, the DNA of both E. rhapontici and E. amylovora was found to exhibit homology to genes encoding the type II (GSP ) secretion pathway, which is known to be responsible for extracellular tar geting of cellulases and pectinases in Erwinia spp. that cause soft rotting , such as E. carotovora and E. chrysanthemi. Secretion of the CelA protein by E. rhapontici could not be verified. However, the CelA protein itself wa s found to include the information necessary for heterologous secretion by E. chrysanthemi.