Determination of specific oxygen uptake rate of Photorhabdus luminescens during submerged culture in lab scale bioreactor

Photorhabdus luminescens, a bacterial symbiont of entomoparasitic nematodes, was cultured in a 10 L bioreactor. Cellular density and bioluminescence were recorded and volumetric oxygen transfer coefficient (k(L)a) and specific oxygen transfer rates were determined during the batch process. Exponential phase of the bacterium lasted for 20 h, showing a maximum specific growth rate of 0.339 h(-1) in a defined medium. Bioluminescence peaked within 21h, and was maintained until the end of the batch process (48 h). The specific oxygen uptake rate (SOUR) was high during both lag and early exponential phase, and eventually reached a stable value of 0.33 mmol g(-1) h(-1) during stationary phase. Maintenance of 200 rpm agitation and 1.4 volume of air per volume of medium per minute (vvm) aeration, gave rise to a k(L)a value of 39.5 h(-1). This k(L)a value was sufficient to meet the oxygen demand of 14.4 g L-1 (DCW) biomass. This research is particularly relevant since there are no reports available on SOURs of symbiotic bacteria or their nematode partners. The insight gained through this study will be useful during the development of a submerged monoxenic culture of Heterorhabditis bacteriophora and its symbiotic bacterium P. luminescens in bioreactors.