[The Correlation between Pathogenicity and Cellulolytic Enzymes Secretion in some Phytopathogenic Bacterial Isolates]

Cell Wall Degrading Enzymes (CWDE) are very important factors of pathogenicity in plant pathogenic bacteria, especially those causing soft rot diseases. Current researches are focusing on the role of these enzymes in the bacterial virulence and symptoms severity on the host plant. As the studies about the cellulolytic enzymes are few in this field, our study aimed to detect the secretion of cellulolytic enzymes by some bacterial isolates from different genera and species, then to assess the role of these enzymes in their pathogenicity. Fifty one plant pathogenic bacterial isolates were tested during 2009_]2011, including 15 isolates of Erwinia, 12 isolates of Xanthomonas, 11 isolates of Bacillus, 8 isolates of Agrobacterium tumefaciens and 5 isolates of Pseudomonas savastanoi pv. savastanoi. Significant differences between bacterial genera were found in carboxy methyl cellulose (CMC) degrading efficiency. Erwinia isolates were the most efficient, followed by Xanthomonas isolates and finally the Bacillus isolates. On the other hand no CMC degrading efficiency was found in Xanthomonas translucens, Agrobacterium tumefaciens, and Pseudomonas savastanoi pv. savastanoi isolates. Isolates of Erwinia carotovora subsp. carotovora (Ecc) were the most efficient in CMC degradation compared with the isolates of Erwinia carotovora subsp. atroseptica (Eca) and Erwinia chrysanthemi (Ech). The isolate A10.1 (Ecc) was signi icantly superior in CMC degradation (the efficiency mean = 3.85), and in Endoglucanase activity (CMCase)(0.52 IU/mg protein), and in _À_]Glucosidase activity (BGase) (0.26 IU/mg protein). CMCase and BGase accumulated in the late exponential phase and the stationary phase of bacterial growth, also the accumulation of these enzymes was negatively affected by the increased concentration of glucose in the supernatant. The Pathogenicity of Erwinia isolates was tested on potato tuber slices. Results showed a significant increase in virulence at higher concentrations of bacterial inoculums.The largest diameter of maceration was at 107 CFU/ml after 24 hours of incubation. Isolates of Ech were the most virulent compared with Ecc and Eca, and the isolate Ech_]D (Ech) was significantly superior by mean of maceration diameter (26.8 mm). Statistical analysis showed a significant positive correlation between pathogenicity and cellulolytic activity. This indicates the role CMCase and BGase enzymes in the pathogenicity of Ecc and Eca isolates, while this role was secondary in the Ech isolates. All Bacillus isolates showed high CMC degradation efficiency. The isolate O127_]2_]2 was the most efficient (mean 3.24), and showed the highest CMCase and BGase level mean of activity 0.48, 0.28 IU/mg protein respectively compared with the other isolates of the same genus. On the contrast of the other isolates, the Bacillus isolates showed a progressively increasing cellulolytic activity by the time, and this activity increased as the glucose concentration increased. Pathogenicity test on tomato fruit showed that the diameter of maceration increased by the higher concentration of inoculum until 107 CFU/ml. The isolate O127_]2_]2 was the most virulent on tomato compared with other Bacillus isolates (mean of soft rot zone diameter 50.23 mm), a strong and significant positive correlation was found between the pathogenicity and the Cellulolytic activity, and this indicates the important role of CMCase and BGase in Bacillus Pathogenicity. All Xcm isolates gave close efficiency values in the CMC degradation test, except the isolate RG1_]1 which was less efficient. The isolate RG3_]1 showed the highest efficiency value (2.55). On the other hand results showed a significant differences between isolates in the cellulolytic activity of CMCase and BGase, and the isolate RG2 was superior. But the role of cellulolytic enzymes was secondary in the pathogenicity of Xcm, out of which isolates A79 and RG1_]1 gave typical symptoms on cotton plants in spite of the low cellulolytic effectivity compared with the isolate RG2 which didn't give the typical leaf spot symptoms on cotton plants.