Identification of bacteria associated with postharvest diseases of fruits and vegetables by cellular fatty acid composition: an expert system for personal computers

• Published in: Phytopathology 1993-01, Vol.83 (4), p.445-455
• Main Authors: Wells, J.M, Butterfield, J.E, Revear, L.G
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; bacteria; Bacterial plant pathogens; Biological and medical sciences; chemical composition; chemotaxonomy; computer techniques; expert systems; fatty acids; Food industries; fruit; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; Generalities. Techniques. Transmission, epidemiology, ecology. Antibacterial substances, control; identification; numerical taxonomy; Phytopathology. Animal pests. Plant and forest protection; postharvest diseases; strain differences; vegetables
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/Phyto-83-445

The cellular fatty acid composition of 190 bacterial strains representing six genera associated with postharvest diseases of fruits and vegetables was statistically analyzed and was used as the basis of an expert system of identification. The expert system was built with off-the-shelf hardware and software, i.e., a commercially available, database management program and personal computer. The database included fatty acid profiles of Bacillus, Clostridium, Cytophaga, Xanthomonas, and the species: Erwinia amylovora, E. ananas, E. herbicola, E. carotovora subsp. carotovora and E. carotovora subsp. atroseptica, E. chrysanthemi, E. rhapontici, Pseudomonas cepacia, P. gladioli, P. aeruginosa, P. cichorii, P. fluorescens, P. putida, P. syringae, and P. viridiflava. A total of 78 fatty acids were detected by gas-liquid chromatography, and mean percentages (of the total) were analyzed statistically for each fatty acid and chemical class. Genera were differentiated by a class analysis. Clostridium had the highest mean percentage (63.90%) of saturated, straight-chain, even-carbon fatty acids (class A), significantly different from all genera except Erwinia (40.89%). Cytophaga was unique, with a high mean percentage (9.44%) of saturated, straight-chain, odd-carbon fatty acids (class B). Mean percentages for class C, saturated, straight-chain fatty acids, were significantly higher for Erwinia (42.11%) and Pseudomonas (fluorescent, 53.10%, and nonfluorescent, 35.33%) than for Bacillus (8.91%), Clostridium (16.31%), and Cytophaga (19.98%). In class D, hydroxy-substituted acids, mean percentages for Bacillus (1.06%) and Clostridium (2.28%) were significantly lower than for Cytophaga (11.00%) and the nonfluorescent pseudomonads (13.97%). In class E, saturated, branched-chain fatty acids, mean percentages for Erwinia and Pseudomonas were less than 1.5% compared to over 11% in other genera. In class F, unsaturated, branched-chain fatty acids, mean percentages for the pseudomonads were less than 0.2%, significantly lower than in any other genus. The ratio of class C to class D was useful in differentiating over 90% of the fluorescent pseudomonads (< 3.5) from the nonfluorescent pseudomonads (> 3.5). Of 61 fatty acids identified in Erwinia and Pseudomonas, the mean percentages of nine differed significantly in Erwinia species, and 23 differed significantly in the pseudomonads. "Rules" based on a profile of percentage ranges for each fatty acid and each class total differentiat