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Direct utilization of palm oil for the simultaneous production of polyhydroxyalkanoates (PHAs) and rhamnolipids was demonstrated using Pseudomonas aeruginosa IFO3924. By secreted lipase, palm oil was hydrolyzed into glycerol and fatty acids. Fatty acids became favorable carbon sources for cell growth and PHA production via beta-oxidation and glycerol for rhamnolipid production via de novo fatty acid synthesis. Both PHA and rhamnolipid syntheses started after the nitrogen source was exhausted and cell growth ceased. PHA synthesis continued until all fatty acids were exhausted, and at that time, PHA content in the cells reached a maximum, but stopped despite the remaining glycerol (<2g/l). In contrast, rhamnolipid synthesis continued until glycerol was exhausted.

The feasibility of the simultaneous production of polyhydroxyalkanoates (PHAs) and rhamnolipids, as a novel approach to reduce their production costs, was demonstrated by the cultivation of Pseudomonas aeruginosa IFO3924. Fairly large amounts of PHAs and rhamnolipids were obtained from the bacterial cells and the culture supernatant, respectively. Decanoate was a more suitable carbon source than ethanol and glucose for the simultaneous production, although glucose was suitable for cell growth without an induction period under pH control. The kind of carbon source affected PHA monomer composition markedly and PHA molecular weight slightly. Monorhamnolipids and dirhamnolipids were included in the rhamnolipids extracted from the culture supernatant using decanoate, glucose, or ethanol as the carbon source. Both PHAs and rhamnolipids were synthesized after the growth phase. PHA content in the cell reached a maximum when the carbon source was exhausted. After exhaustion of the carbon source, PHA content decreased rapidly, but rhamnolipid synthesis, which followed PHA synthesis, continued. This resulted in a time lag for the attainment of maximum levels of PHAs and rhamnolipids. The reusability of the cells used in rhamnolipid production was evaluated in the repeated batch culture of P. aeruginosa IFO3924 for the simultaneous production of PHAs and rhamnolipids. High concentrations of rhamnolipids in the culture supernatant were attained at the end of both the first and second batch cultures. High PHA content was achieved in the resting cells that were finally harvested after the second batch. Simultaneous production of PHAs and rhamnolipids will enhance the availability of valuable biocatalysts of bacterial cells, and dispel the common belief that the production cost of PHAs accumulated intracellularly is almost impossible to become lower than that of cells themselves., (Copyright 2002 Wiley Periodicals, Inc.)

Abstract: Medium-chain-length polyhydroxyalkanoates (mcl-PHAs) and rhamnolipids produced by Pseudomonas aeruginosa share 3-hydroxyalkanoates (3HAs) as common structural units. Previously, we demonstrated their simultaneous production to share the cultivation cost for the intracellular products, PHAs, with the extracellular products, rhamnolipids. Here, we investigated the effects of temperature and carbon length of fatty acid substrates on the simultaneous production by P. aeruginosa IFO3924. The optimum temperatures for PHA and rhamnolipid syntheses were 30°C and 28°C, respectively, suggesting that the product ratio between these two products can be controlled by changing temperature. After the induction periods, both PHAs and rhamnolipids were produced at constant rates by resting cells. The apparent activation energies were determined as 45kJ/mol for PHA synthesis and 40kJ/mol for rhamnolipid synthesis from Arrhenius plots. These values in a similar level suggest that a common reaction such as β-oxidation before the synthesis of 3HA units is the rate-determining step. PHAs and rhamnolipids synthesized from fatty acids of even-number carbon length (Ceven) consisted of only Ceven-3HAs. By contrast, PHAs and rhamnolipids synthesized from fatty acids of odd-number carbon length (Codd) consisted of not only Codd-3HAs but also Ceven-3HAs. This is the first report to show the incorporation of Codd-3HAs into rhamnolipids. [ABSTRACT FROM AUTHOR]