|Liao, Ching Hsing|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: December 26, 2003
Publication Date: January 5, 2005
Citation: Liao, C., Ukuku, D.O. 2005. Role of fluorescent pseudomonads and their pectolytic enzymes in spoilage of fresh and fresh-cut produce. Book Chapter. CRC Press. 483-504. Technical Abstract: Pectolytic fluorescent (PF) pseudomonads consisting of P. fluorescens and P. viridiflava are the cause of a large proportion of postharvest rot of fresh fruits and vegetables. They are commonly found on the surfaces of fresh produce and constitute a major component of resident microflora on potato tubers and leafy vegetables. The ability of these pseudomonads to cause spoilage (often in the form of soft-rot) results from their ability to produce a variety of depolymerases including pectinases [primarily pectate lyase (PL)], proteases (Prt), cellulases, and lipases. Unlike multiple PL isozymes produced by Erwinia, a single alkaline PL is produced by most if not all PL pseudomonads. The conclusion that a single alkaline PL is the sole or principal pectinase required for induction of soft rot is based on the results from a series of experiments including enzyme purification, isoelectric-focusing electrophoresis, transposon mutagenesis, gene cloning, and complementation studies. Two genes regulating the production and/or secretion of PL, Prt, the exopolysaccharides (alginate and levan), and fluorescent iron-chelating siderophores have been identified. These two genes, designated gacS and gacA, are members of the two-component regulatory gene family. Presence of calcium is absolutely required by P. fluorescens and P. viridiflava to produce and excrete PL and Prt and is also required for catalytic activity of both enzymes. Application of ion chelators such as EDTA and organic acids such as acetic acid and citric acid, therefore, becomes a possible approach for reducing the soft-rot caused by PF pseudomonads.