SUMMARY: A freshwater sp., which apparently belongs to a niche of low nutritional status (Matin & Veldkamp, 1978), accumulated poly-β-hydroxybutyric acid (PHB) during lactate-limited growth in continuous culture. The PHB content varied in a complex manner with the dilution rate (), but was greatest at the lowest value examined: about 18% (w/w) at = 0.025 h. It is not known what mechanism accounted for PHB accumulation during carbon-limited growth. The resistance of cultures of sp. to starvation after growth at various values was compared with that of a sp. which appears to belong to relatively richer environments (Matin & Veldkamp, 1978) and does not accumulate PHB. In sp., resistance correlated directly with the PHB content of the culture subjected to starvation, whereas in sp. it increased with RNA content. Further, after growth at = 0·03 to 0·05 h, the sp. was much more resistant to starvation than was the sp. Since the microflora of oligotrophic environments are probably often subjected to starvation conditions, PHB accumulation by sp. during growth in such environments may assist survival. PHB in sp. was rapidly degraded during starvation but it had no sparing effect on RNA degradation. It is not known how PHB enhanced resistance to starvation.


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