Growth of Mixed Cultures of Bacteria on Methanol

Abstract

225The bacterium Pseudomonas C was grown in a chemostat on methanol as sole source of carbon and energy. At a dilution rate of 0.1 h-I, other methanol-utilizing bacteria (Pseudomonas 1 and Pseudomonas 135), when added separately at a steady state, became dominant in the fermenter and Pseudomonas C was excluded. At a dilution rate of 0.3 h-l, however, Pseudomonas C dominated and the other bacteria were excluded. When various bacteria unable to utilize methanol were added to the chemostat during a steady state growth of Pseudomonas C , they remained in the fermenter independent of the dilution rate, but as a very low percentage of the total population (about 1%). When pathogenic bacteria (Staphylococcus aureus and SalmoneEEa typhimurium), which are unable to utilize methanol as a sole carbon source, were added separately to a pure culture of Pseudomonas C in a chemostat, they too remained in the fermenter independent of the dilution rate. However, they constituted less than 1 yo of the population in the culture broth but a high percentage of the population on the fermenter wall. When added to a mixture of Pseudomonas C and bacteria unable to utilize methanol, the pathogenic bacteria could not be found in the fermenter after a few medium changes.The results suggest that operation of a continuous culture of Pseudomonas C at high dilution rates serves to prevent contamination with other methylotrophs that may have lower yields. A mixture of Pseudornonas C and heterotrophs from soil is relatively resistant to invasion by pathogens.

Mixed microbial culture technology

“…(g) Protection against contamination due to the fact that potential niches for contaminant organisms are occupied already by members of the mixed community. This advantage has been demonstrated with respect to microbial protein production (Rokem et al, 1980). (h) Resistance to environmental perturbations.…”

New dimensions in microbiology: an introduction

“…The incentive to develop a mixed-culture process for single cell protein from methane and natural gas was largely prompted by the finding that monospecies cultures of methylotrophs grew erratically on such substrates, produced low biomass yields or failed to utilize the mixture of w-alkanes in natural gas. Indeed, Mateles and his colleagues have dis cussed the proposition that mixed cultures may be desirable for single cell protein processes because of their greater ability than pure cultures to withstand accidental contamination (Mateles 1979;Rokem et al 1980). Thus, when Pseudomonas strain C was grown on methanol in continuous culture, together with a mixture of heterotrophic soil bacteria ( .…”