PARENT SESSION
Poster Session 24: Agro-Ecology
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Phenazine antibiotics derived from environmental organisms: role in rhizosphere ecology and pathogen suppression.

Vukomanovic, Dragic^*,1, Cutler, Joshua², Dinon, Sarah², Rasch, Jennifer², Rajaniemi, Tara², Scarano, Frank³, ¹ Department of Chemistry and Biochemistry, North Dartmouth, Massachusetts, U.S.A.² Department of Biology, North Dartmouth, Massachusetts, U.S.A.³ Department of Medical Lab. Science, North Dartmouth, Massachusetts, U.S.A

ABSTRACT- Soil-borne root-colonizing bacteria can profoundly influence plant health by suppressing diseases caused by pathogenic plant bacteria, fungi and viruses. The biocontrol ability of some Pseudomonas strains depends mostly on root colonization and the production of diffusible phenazine antibiotics. Phenazine production is the primary mechanism responsible for the survival and ecological fitness of Pseudomonas in the rhizosphere. In order to enhance the competitive fitness of rhizo-Pseudomonas we have designed 12 novel and very potent derivatives of the natural antibiotics. The most-widely studied natural phenazine antibiotic, pyocyanin, demonstrated the MIC₉₀ to a variety of bacterial pathogens (Escherichia coli 35218 and 29212, Enterococcus faecalis 29212 and 51299, Staphylococcus aureus 29213, MRSA 43300, Streptococcus pneumoniae 49616 and Klebsiella pneumoniae 7002), from 12.0 to 150 g/mL while our novel derivatives, 1-R₁, 2-hydroxy, 7,8 di-(R₂) phenazine N,N dioxide, showed a dramatic decrease in the MIC₉₀ which is in the range of 0.8 to 3.1 g/mL. Susceptibility testing with pathogenic plant fungi and bacteria important in New England agricultural systems (Pythium, Rhizoctoni, Plectosporiu, Xanthomona and Erwinia) is ongoing. Acute toxicity studies in mice showed that our phenazine compounds are not toxic up to 100 mg/kg when administered both intraperitoneally and orally. The antimicrobial mode of action for these novel phenazines has not yet been fully elucidated, however our computational studies indicated that most of them have a planar geometry and may intercalate with DNA while our electrochemical studies showed that they are prolific producers of toxic oxy-radicals. Mutualism in a variety of plants with some beneficial environmental Pseudomonas may be enhanced by the phenazine treatment that would increase survival and ecological fitness of Pseudomonas and cause only a transient disturbance on microbial community. Biological control of soil borne plant pathogens may offer a practical supplement or attractive alternative to currently used management strategies that depend heavily on chemical pesticides.

Key words: rhizosphere ecology, environmental organisms, pathogen suppression, phenazine antibiotics