Fed-batch process for the psychrotolerant marine bacterium <it>Pseudoalteromonas haloplanktis</it>

<p>Abstract</p> <p>Background</p> <p><it>Pseudoalteromonas haloplanktis </it>is a cold-adapted γ-proteobacterium isolated from Antarctic sea ice. It is characterized by remarkably high growth rates at low temperatures. <it>P. haloplanktis </it>is one of the model organisms of cold-adapted bacteria and has been suggested as an alternative host for the soluble overproduction of heterologous proteins which tend to form inclusion bodies in established expression hosts. Despite the progress in establishing <it>P. haloplanktis </it>as an alternative expression host the cell densities obtained with this organism, which is unable to use glucose as a carbon source, are still low. Here we present the first fed-batch cultivation strategy for this auspicious alternative expression host.</p> <p>Results</p> <p>The key for the fed-batch cultivation of <it>P. haloplanktis </it>was the replacement of peptone by casamino acids, which have a much higher solubility and allow a better growth control. In contrast to the peptone medium, on which <it>P. haloplanktis </it>showed different growth phases, on a casamino acids-containing, phosphate-buffered medium <it>P. haloplanktis </it>grew exponentially with a constant growth rate until the stationary phase. A fed-batch process was established by feeding of casamino acids with a constant rate resulting in a cell dry weight of about 11 g l^-1(OD₅₄₀= 28) which is a twofold increase of the highest densities which have been obtained with <it>P. haloplanktis </it>so far and an eightfold increase of the density obtained in standard shake flask cultures.</p> <p>The cell density was limited in the fed-batch cultivation by the relatively low solubility of casamino acids (about 100 g l^-1), which was proven by pulse addition of casamino acid powder which increased the cell density to about 20 g l^-1(OD₅₄₀= 55).</p> <p>Conclusion</p> <p>The growth of <it>P. haloplanktis </it>to higher cell densities on complex medium is possible. A first fed-batch fermentation strategy could be established which is feasible to be used in lab-scale or for industrial purposes. The substrate concentration of the feeding solution was found to influence the maximal biomass yield considerably. The bottleneck for growing <it>P. haloplanktis </it>to high cell densities still remains the availability of a highly concentrated substrate and the reduction of the substrate complexity. However, our results indicate glutamic acid as a major carbon source, which provides a good basis for further improvement of the fed-batch process.</p>