Selective Enrichment of Bacteria Accumulating Polyhydroxyalkanoates in Multistage Continuous Culture 

G. Renner, F. Scheilauf, G. Braunegg

Institute of Biotechnology, Technical University of Graz, Petersgasse 12, A-8010 Graz

Article history:
Received January 20,1998 
Accepted June 17, 1998

Key words:
Ralstonia eutropha, polyhydroxyalkanoates, bacterial storage compounds 

Summary:
The relationship between polyhydroxyalkanoate (PHA) fraction and cell survival under long-term carbon starvation was utilized for developing a method for the selective enrichment of PHA-forming bacteria from environmental samples. The first reactor of a five-stage continuous culture was fed with a carbon-rich and nitrogen poor medium at very low dilution rates. These conditions allowed not only growth but also PHA accumulation by competent organisms. In the following slages the culture zvas kepi under carbon and nitrogen limiting conditions for a total of 100 to 200 hours. Fifteen different bacterial strains were isolated from various environmental samples. Four of them were able to accumulate high amounts of PHA (mass fraction > 10%), 3 accumulated minor amounts (mass fraction 1-10%), 2 strains accumulated trace amounts and 6 showed no PHA production at all. A control experiment was carried out with a mixed population containing one PHA-accumulating bacterium species (Ralstonia eutropha) and one unable to accumulate PHA (Escherichia coli). In this experiment significant enrichment of the slower growing but PHA-accumulating species, R. eutropha, was achieved.

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