Growth, survival, and root colonization of plant growth beneficial Pseudomonas fluorescens ANP15 and Pseudomonas aeruginosa 7NSK2 at different temperatures

The plant growth-promoting rhizopseudomonad (PGPR) strains 7NSK2 and ANP15 have different optimum temperature ranges for growth and siderophore production. Maximum cell yield of the mesophilic Pseudomonas aeruginosa 7NSK2, under iron limiting conditions, is at 28°C and maximum pyoverdin production at 19°C. The minimum and maximum temperatures that permit growth are 12 and 42°C. The psychrotrophic Pseudomonas fluorescens ANP15 grows at temperatures between ca 4 and 32°C. Maximum cell yield is obtained at 19°C and maximum pyoverdin production at 12°C. The survival of the two strains was compared in a non-sterile soil at different temperatures. Both strains survived temperatures of 4 and 20°C equally well. P. fluorescens ANP15, however, survived better at subzero temperatures while P.aeruginosa 7NSK2 survived better at 28°C. Root colonization studies at different temperatures revealed that at 30°C, P. aeruginosa 7NSK2 colonized maize roots more effectively than P. fluorcscens ANP15. while at 18°C P. fluorescens ANP15 was the better root colonizer. Pyoverdin production seems to play a role in plant growth stimulation by ANP15 and 7NSK2.