Studies directed to the optimization of fermentation of <i>Rhodococcus</i> sp. DAP 96253 and <i>Rhodococcus rhodochrous</i> DAP 96622
Bench- and pilot plant scale fed-batch fermentations were performed in stirred-tank bioreactors (STBR) with Rhodococcus sp. DAP 96253 and R. rhodochrous DAP 96622 in an attempt to elucidate parameters that may affect the optimization of a fermentation process for high biomass production and high inducible expression of cobalt-high-molecular-mass nitrile hydratase (Co-H-NHase). The effects of these factors on amidase (AMDase) activity were also investigated. Biomass and NHase production were inhibited by a total addition of acetonitrile and acrylonitrile (AC/AN) at 500 ppm during a 48 h run. Biomass and enzyme activity were uncoupled when the inoculum mass was increased from 4 g (wet weight) to ≥ 19 g. Other factors that allowed for the uncoupling of biomass production from enzyme activity were the reduction of the AC/AN feed rate from a step-addition at 2500 μl/min to a continuous addition at 80–120 μl/min, and the delay to 18 h post-inoculation the time of initial inducer addition. The inhibition of both biomass production and NHase activity was relieved when both the total concentration of AC/AN was reduced to ≤ 350 ppm and the AC/AN feedrate was reduced.
The factors with the greatest influence were shown to be the inducer, the inducer concentration, inoculum mass and source as well as the major carbohydrate and nitrogen source. In addition, this lab is the first to report high AN-specific NHase induction by asparagine (1300 ppm) in a fed-batch fermentation system. Prior to this program, 250 mg of cells (wet weight) per liter could be provided in 4–10 days with an activity of 1 U NHase per mg of cells (dry weight). Current production is > 50 g/L in 48 h with an NHase activity > 150 U/mg of dry cell weight.
INDEX WORDS: Amidase, Asparagine, Biodetoxification, Fermentation, Nitrile, Nitrile Hydratase, Rhodococcus