INTERSPECIES COMPETITION IN COLONIZED POROUS PELLETS

Packed-bed bioreactors filled with diatomaceous earth (D.E.) pellets were used to evaluate the effects of competition between inoculated and invading microbial species on the spatial and temporal distribution of microorganisms within an individual pellet. The (D.E.) pellets were cylinders 6 mm in diameter and 5-10 mm long with a mean pore diameter of 20 mu m. Bench-scale experiments evaluated competition between two distinct microbial species: Pseudomonas aeruginosa, a motile, obligate aerobe (mu(max) = 0.4 h(-1)) and Klebsiella pneumoniae, a non-motile, facultative organism (mu(max) = 2.0 h(-1)). Organism growth rate appeared to be more important than motility or order of introduction in determining organism spatial and temporal distribution within the pellets. Pilot-scale experiments used pellets colonized with a pseudomonad growing on chlorobenzene as the sole carbon and energy source. Organic-rich ground water containing benzene, chlorobenzene and a population of indigenous microorganisms was used as feed. Pellet concentrations of the inoculated pseudomonad dropped from 10(9) to 10(6) colony forming units (cfu) ml(-1) pellet volume over 15 days. These experiments demonstrate that inoculated organisms within porous packing media may undergo significant loss in colonization numbers when faced with competition from faster growing organisms.