ABSTRACT
A brief account of size, shape, and arrangement of bacterial cells is given. The structures and functions of different cell parts and metabolic activities of a bacterial cell are given. The knowledge of metabolic activities of bacterial cells helps in understanding the mechanisms, which the plant pathogenic bacteria use to cause plant diseases. The role of spores/endospores is highlighted in the survival of bacteria. A brief account of plasmids and their occurrence in phytopathogenic bacteria is given. Most genera of plant pathogenic bacteria harbor one or more plasmids containing genes that encode traits of importance to ecological fitness and/or virulence. Plasmids contribute significantly to host evolution in a multi-faceted manner and tend to encode determinants of virulence and ecological fitness that can enhance adaptation to a specific niche or can influence niche expansion. The acquisition and expression of novel sequences may confer pathogenicity on a saprophytic strain. A classical example of the transformation of Pantoea agglomerans, a widespread epiphytic and commensal bacterium into a host specific tumorigenic pathogen, namely, P. agglomerans pv. gypsophilae by acquiring a plasmid called pPATH containing pathogenicity island is dealt.
