Global control in Pseudomonas fluorescens mediating antibiotic synthesis and suppression of black root rot of tobacco.

Abstract

Pseudomonas fluorescens CHA0 colonizes plant roots, produces several secondary metabolites in stationary growth phase, and suppresses a number of plant diseases, including Thielaviopsis basicola-induced black root rot of tobacco. We discovered that mutations in a P. fluorescens gene named gacA (for global antibiotic and cyanide control) pleiotropically block the production of the secondary metabolites 2,4-diacetylphloroglucinol (Phl), HCN, and pyoluteorin. The gacA mutants of strain CHA0 have a drastically reduced ability to suppress black root rot under gnotobiotic conditions, supporting the previous observations that the antibiotic Phl and HCN individually contribute to the suppression of black root rot. The gacA gene is directly followed by a uvrC gene. Double gacA-uvrC mutations render P. fluorescens sensitive to UV irradiation. The gacA-uvrC cluster is homologous to the orf-2 (= uvrY)-uvrC operon of Escherichia coli. The gacA gene specifies a trans-active 24-kDa protein. Sequence data indicate that the GacA protein is a response regulator in the FixJ/DegU family of two-component regulatory systems. Expression of the gacA gene itself was increased in stationary phase. We propose that GacA, perhaps activated by conditions of restricted growth, functions as a global regulator of secondary metabolism in P. fluorescens.

Effect of sorghum seedlings, and previous crop, on soil fluorescent Pseudomonas spp.

“…After cycling seedlings in previously cropped soils (cycles 5 through 8), two trends were noticed in the characteristics of populations of fluorescent Pseudomonas spp. Firstly, there appeared to be an overall increase in HCN producers (Table 1); although HCN may be involved in suppression of plant diseases (Laville et al 1992), production by rhizobacteria also can have a detrimental effect on some plants (Bakker and Schippers 1987). Secondly, throughout the course of these cycling experiments, there appeared to be an overall decline in the number of Phl isolates (Table 1), especially noticeable in cycles 5 through 8.…”

The global regulator GacA of Pseudomonas fluorescens CHA0 is required for suppression of root diseases in dicotyledons but not in Gramineae

“…For construction of a GacA ¹ Pvd ¹ double mutant of CHA0 from the Pvd ¹ strain CHA400, a gacA'::' lacZ fusion was used instead of the kanamycinresistance cartridge previously proposed by Laville et al (1992), since strain CHA400 already carries a kanamycin-resistance determinant (on Tn1733). Triparental matings were performed in two steps, as described previously (Voisard et al, 1988.…”

The resistance-nodulation-division efflux pump EmhABC influences the production of 2,4-diacetylphloroglucinol in Pseudomonas fluorescens 2P24

“…Recent reports revealed that besides environmental factors and its autoregulation (Abbas et al, 2002;Duffy & Defago, 1999;Schnider-Keel et al, 2000), the production of 2,4-DAPG is regulated by a series of transcriptional and translational factors, including the repressor PhlF (Delany et al, 2000;Haas et al, 2000), the two-component regulatory system GacS/GacA (Haas & Défago, 2005;Laville et al, 1992), regulatory PrrB (Aarons et al, 2000) and RsmY (Valverde et al, 2003) RNA, global regulator proteins MvaT and MvaV (Baehler et al, 2006) and disulfide interchange protein DsbA (Mavrodi et al, 2006).…”