Effects of cyanogenic Pseudomonas aeruginosa on the growth of vegetable crops and tomato bacterial wilt caused by Ralstonia solanacearum

• Main Authors: Yi-Hsien Lin, 林宜賢
• Other Authors: Kuo-Ching Tzeng
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/05738396767042501221

博士 === 國立中興大學 === 植物病理學系 === 92 === Pseudomonas aeruginosa is a gram-negative fluorescent bacterium that can be isolated from various habitats. Many P. aeruginosa strains isolated from leaf surface were cyanogenic, although cyanide did not appear to play an important role in their survival in our test conditions. Cyanide is known to inhibit aerobic respiration in many organisms. However, the viability of other pseudomonads in soil was not affected by the presence of cyanogenic P. aeruginosa. The cyanide toxicity on seed germination and seedling growth of lettuce was tested in this research, and the results showed the inhibition of seed germination was correlated with the cyanide produced by P. aeruginosa. The hcnABC genes coding for amino acid dehydrogenase and oxidase were cloned from cyanogenic P. aeruginosa strain WFP11r and transformed into a non-cyanogenic P. putida YLFP44 by electroporation. The P. putida derivative Y44H1, produced high quantities of cyanide could strongly inhibit seed germination and seedling growth of lettuce, cabbage, Chinese cabbage, and tomato. Among these, tomato was the most sensitive vegetable to cyanide, which might be due to its low activity of b-cyanoalanine synthase (b-CAS) that is responsible for cyanide detoxification. We also found the growth of many plant pathogenic bacteria was inhibited by cyanogenic P. aeruginosa strains in the paired-plate system. The more cyanide P. aeruginosa produced, or the longer it incubated with other organisms, the fewer viable cells were recovered from the paired-plates. For example, prolonged incubation (5 days) with Y44H1 led to the death of R. solanacearum and altered the colony and cell morphology of the bacterium. However, when tomato plants were co-inoculated with R. solanacearum and cyanogenic P. aeruginosa or Y44H1, the disease severity was greater than that of plants treated with R. solanacearum only. It was likely the effect of cyanide on tomato plants was greater than that on bacterial wilt pathogen R. solanacearum in the experimental conditions; the question as to how cyanide increases bacterial wilt disease remains elusive. In addition to cyanide, hemolytic phospholipase C (PLC-H), which is encoded by plcS gene, also plays an important role in the virulence of P. aeruginosa on animals and plants. We applied PCR technique and found plcS gene in all strains of P. aeruginosa and one strain of P. fluorescens (YLFP8) in Taiwan. Moreover, all the plcS-harboring pseudomonads were hemolytic. Both P. aeruginosa WFP11r and P. fluorescens YLFP8 caused brownish water-soaking symptoms on garlic, but the other non-hemolytic pseudomonads did not. To elucidate the role of plcSR genes in bacterial pathogenicity on plants, plcSR genes from P. aeruginosa WFP11r were cloned and transformed into non-hemolytic P. putida YLFP44. The resulting transformant, Y44P1, showed hemolytic activity and caused brownish water-soaking symptoms on garlic, which was comparable to the parental strain YLFP8. The results presented in this research indicate that cyanide and PLC-H were important virulence factors in P. aeruginosa pathogenecity on plants.