No abstract

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 x 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.

The production of infective juvenile stages (IJ) of the entomopathogenic nematode Steinernema carpocapsae in the presence of its symbiotic bacterium Xenorhabdus nematophilus was carried out in orbitally agitated bottles. Four complex culture media (M1-M4) were used, containing from 8% to 28% (by vol.) agave juice (aguamiel) from Mexican maguey-pulquero (Agave spp) as the main carbohydrate source. After 20 days of fermentation, a maximum viable IJ concentration of 249,000 IJ/ml and an initial nematode population multiplication factor of x620 were achieved when medium M4 was used (aguamiel concentration in this medium was 28% by vol.). M4 medium contained (w/v): 0.3% total nitrogen, 3.2% total carbohydrates and 3.0% total fat. According to the results obtained, total carbohydrates concentration appeared to be of great importance in obtaining high IJ concentrations.

It is well known that helical ribbon (HR) impellers exhibit poor bottom pumping properties. Three different HR impeller geometries, varying in their bottom design, are compared in terms of their mixing performance. Particular emphasis is given to the improvement of pumping capabilities. The selected bottom geometries were a standard bottom termination, an anchor-type termination and a paddle-type termination. The investigation was based on the use of 3D finite-element simulation to assess the hydrodynamics and mixing performance using various distributive and dispersive criteria. Analysis of Poincaré maps showed that an HR with a paddle-type termination operating in a down-pumping mode offered the best performance. 