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Open Access Research

Fed-batch process for the psychrotolerant marine bacterium Pseudoalteromonas haloplanktis

Boris Wilmes123, Angelika Hartung234, Michael Lalk5, Manuel Liebeke56, Thomas Schweder125* and Peter Neubauer37*

Author Affiliations

1 Institute of Marine Biotechnology, W.-Rathenau-Str. 49, D-17489 Greifswald, Germany

2 Pharmaceutical Biotechnology, Institute of Pharmacy, Ernst-Moritz-Arndt-University, F.-L.-Jahn-Str. 17, D-17487 Greifswald, Germany

3 Bioprocess Engineering Laboratory, University of Oulu, P.O.Box 4300, FI-90014 Oulu, Finland

4 Department of Internal Medicine IV, University of Tübingen, Otfried-Müller Str.10, D-72076 Tübingen, Germany

5 Competence Center - Functional Genomics, Institute of Pharmacy, Ernst-Moritz-Arndt-University, F.-L.-Jahn-Str. 17, D-17487 Greifswald, Germany

6 Biomolecular Medicine, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, UK SW7 2AZ, UK

7 Laboratory of Bioprocess Engineering, Department of Biotechnology, Technical University Berlin, Ackerstr. 71-76, D-13355 Berlin, Germany

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Microbial Cell Factories 2010, 9:72  doi:10.1186/1475-2859-9-72

Published: 21 September 2010

Abstract

Background

Pseudoalteromonas haloplanktis is a cold-adapted γ-proteobacterium isolated from Antarctic sea ice. It is characterized by remarkably high growth rates at low temperatures. P. haloplanktis 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 P. haloplanktis 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.

Results

The key for the fed-batch cultivation of P. haloplanktis 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 P. haloplanktis showed different growth phases, on a casamino acids-containing, phosphate-buffered medium P. haloplanktis 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 P. haloplanktis so far and an eightfold increase of the density obtained in standard shake flask cultures.

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).

Conclusion

The growth of P. haloplanktis 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 P. haloplanktis 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.