SURVIVAL OF POTENTIALLY PATHOGENIC HUMAN-ASSOCIATED BACTERIA IN THE RHIZOSPHERE OF HYDROPONICALLY GROWN WHEAT

Plants may serve as reservoirs for human-associated bacteria (H-AB) in long-term space missions containing bioregenerative life support syst ems, The current study examined the abilities of five human-associated potential pathogens, Pseudomonas aeruginosa, Pseudomonas cepacia, Sta phylococcus aureus, Streptococcus pyogenes and Escherichia coli, to co lonize and grow in the rhizosphere of hydroponically grown wheat, a ca ndidate crop for life support. All of these bacteria have been recover ed from past NASA missions and present potential problems for future m issions. The abilities of these organisms to adhere to the roots of ax enic five-day-old wheat (Triticum aestivum L. cv. Yecora rojo) were ev aluated by enumeration of the attached organisms after a one hour incu bation of roots in a suspension (approximately 10(8) cfu ml(-1)) of th e H-AB. Results showed that a greater percentage of P. aeruginosa cell s adhered to the wheat roots than the other four H-AB, Similarly incub ated seedlings were also grown under attempted axenic conditions for s even days to examine the potential of each organism to proliferate in the rhizosphere (root colonization capacity), P. cepacia and P. aerugi nosa showed considerable growth, E. coli and S. aureus showed no signi ficant growth, and S. pyogenes died off in the wheat rhizosphere. Stud ies examining the effects of competition on the survival of these micr oorganisms indicated that P. aeruginosa was the only organism that sur vived in the rhizosphere of hydroponically grown wheat in the presence of different levels of microbial competition.