Survival of Human-Associated Bacteria in Prototype Advanced Life Support Systems

Abstract

Dynamac CorporationABSTRACTThe inclusion of bioregenerative life support elements (i.e.,plant growth systems and bioreactors) will significantlyincrease the total abundance of microorganisms inextraterrestrial facilities. If the microbial communitiesassociated with these systems (e.g., biofilms attached to plantroots or hardware surfaces) serve as reservoirs for potentiallypathogenic human-associated bacteria, then bioregenerativesystems may represent a human health risk. Research at theKennedy Space Center during the past several years hasattempted to quantify this risk by assessing the capacity ofdifferent human-associated bacteria to survive in prototypeALS systems. Preliminary, short-term studies indicated thatmany potentially pathogenic human-associated bacterialspecies identified from past space missions ( Pseudomonasaeruginosa , Pseudomonas cepacia , Escherichia coli ,Staphylococcus aureus , and Streptococcus pyogenes ) have thecapacity to grow on the roots of plants, one of the largestpotential sites of microbial activity in bioregenerative lifesupport systems. However, only P. aeruginosa could persist atdetectable levels when competition from typical root-associated bacteria was present. Subsequent long-term plantgrowth experiments have confirmed the greater capacity of P.aeruginosa to persist in plant growth systems, although nohuman-associated bacteria tested to date have proliferated inthe systems. Rather, relative success is measured by the rate atwhich bacterial numbers decrease following introduction.Recent and current studies have focused on the influence ofcommunity richness (i.e., the number of microbial species) onthe ability of introduced human-associated bacteria to persistwithin prototype systems. Richness may be manipulated in abioregenerative system; a stringent decontamination approachcould lead to very low richness, but specific inoculation witheither defined bacterial isolates or undefined mixtures ofmicrobial communities would increase richness.INTRODUCTIONAlthough microbes are capable of growing anywhereeven a small amount of liquid water exists, habitats thatcontain organic carbon that can be used as an energy source bythe microorganisms will support abundant microbialpopulations. The inclusion of bioregenerative life support(BLS) elements (i.e., plant growth systems and bioreactors forwaste processing) will significantly increase the totalabundance of microbes in extraterrestrial facilities. Forexample, bacterial numbers on the roots of plants withinprototype hydroponic systems can be as high as 10