Submerged monoxenic culture of the entomopathogenic nematode Steinernema carpocapsae in an internal‐loop airlift bioreactor using two configurations of the inner tube

This article reports the submerged culture of the entomopathogenic nematode Steinernema carpocapsae and its symbiotic bacterium, Xenorhabdus nematophila , within an internal‐loop airlift bioreactor. Two configurations of the inner cylinder were tested: a standard draft tube (SDT) and a static mixer (SM), as well as two production media: MP1 (500 mL/L whey, among other ingredients) and MP2 (82 mL/L agave‐juice from Agave spp., among other ingredients). Three fermentations were carried out: F1 → SDT‐MP1, F2 → SM‐MP1 and F3 → SM‐MP2. The operating conditions were expressed on the basis of dimensionless Reynolds number (Re) and volumetric oxygen transfer coefficient ( k L a), both of them determined on riser and downcomer sections within the bioreactor. The experiments began with fewer than 1,000 infective juvenile nematode stages (IJ) per mL and at t  = 20 d, they achieved (nematodes/mL‐%IJ) 222,000‐87%, 62,200‐23% and 114,600‐80%, within F1, F2 and F3 experiments, respectively. Nonetheless, the achieved maximum nematode biomass concentrations (g/L) were F1 → 408, F2 → 557 and F3 → 613, and occurred at t  = 16, 10 and 12 d, respectively. The fermentation operating conditions involved 0.042 (−) < Re < 647 (−) and 2.8× 10 −4 s −1  <  k L a < 0.0447 s −1 , as functions of 0.004 m/s < superficial gas velocity (within the riser) < 0.079 m/s, 0.001 m/s < mean downcomer velocity < 0.014 m/s, and culture broth rheological properties which evolved from nearly the Newtonian behaviour to the pseudoplastic one. The maximum IJ concentration was achieved within F1 experiment (193,406 IJ/mL). Also, fermentation conditions involving higher riser‐Re and lower downcomer‐Re as well as higher nutriment concentrations in culture medium, promote higher nematode biomass concentrations but lower %IJ, maybe as a result of better conditions for the nematode population development. Biotechnol. Bioeng. 2007; 98: 167–176. © 2007 Wiley Periodicals, Inc.