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Title: EFFECTS OF MICROBIAL COMMUNITY DIVERSITY ON THE SURVIVAL OF PSEUDOMONAS AERUGINOSA IN THE WHEAT RHIZOBACTERIA

Author
item MATOS, ANABELLE
item GARLAND, JAY - DYNAMAC CORPORATION
item KERKOF, LEE - RUTGERS UNIVERSITY
item GRAY, KENDALL - UNIV. OF SOUTH FLORIDA

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2004
Publication Date: N/A
Citation: N/A

Interpretive Summary: In plant-based life support systems designed for long duration space missions, the transfer of microorganisms between humans, plants, bioreactors, and the environment occurs within a backdrop of a closed system insulated from invasion by new microorganisms. Therefore, the types of microorganisms that are initially introduced into the system may play an nimportant role in controlling the growth of deleterious microorganisms. Th need for biological control strategies is reinforced by the difficulty in using chemical control in a closed system where any potential toxin can have immediate, undesirable effects. In this study, we examined groups of microorganisms, including natural and artificially constructed assemblages, to determine their ability to resist invasion by an opportunistic infection-causing bacterium. We found that resistance to colonization of wheat roots by an opportunistic infection-causing bacterium was best conferred by inoculation with a naturally diverse assemblage of microorganisms. Our results lend support to the ecological view that the presence of more diverse microbial assemblages can make it more difficult for an invader to survive. Our results can be used as the basis for the selection of an effective inoculum to be used in future studies evaluating biological control approaches to inhibit the growth of deleterious microorganisms.

Technical Abstract: Ecological theory suggests that hydroponic ecosystems with greater microbial diversity would be less susceptible to invasion by Pseudomonas aeruginosa. We investigated whether the survival of P. aeruginosa in the wheat rhizosphere would be affected by the presence of natural and constructed microbial communities of various diversity levels. Three levels sof microbial community diversity were derived from wheat roots by a dilution/extinction approach. These wheat rhizosphere inocula, as well as a gnotobiotic microbial community consisting of seven culturable wheat rhizobacterial isolates, were introduced into the nutrient solution of hydroponically-grown wheat plants on the day of planting. Phenotypic characterization of the culturable microbial communities on R2A medium, Shannon microbial diversity index, community-level physiological profiles, and terminal restriction fragment length polymorphisms were used to assess the varying microbial diversity levels. At day seven, the roots were invaded with P. aeruginosa and the number of P. aeruginosa colony forming units per root were measured at day 14. The average number of surviving P. aeruginosa cells was 3.52, 4.90, 7.18, 6.65 log10 cfu/root in the high, medium, low, and gnotobiotic microbial community diversity level treatments, respectively. The gnotobiotic community did not confer protection against P. aeruginosa invasion, even though it consisted of the dominant microbial types found in the natural high diversity community. These data suggest that the unculturable portion of the wheat rhizobacterial community may play a role in protection against invasion.