Initial experiments employing fed-batch fermentation of Rhodococcus rhodochrous DAP 96253 with activity against selected fungi

Rhodococcus rhodochrous is a non-pathogenic Gram-positive bacterium commonly used as a biocatalyst for industrial applications such as wastewater treatment or in the biotransformation of harmful environmental pollutants. Recently the contact-independent antagonism of induced R. rhodochrous DAP 96253 towards selected pathogenic fungi has been demonstrated. Accordingly, R. rhodochrous is being developed as a biocontrol agent of plant and animal pathogenic fungi. In a 30L bioreactor, pilot-scale fed-batch fermentations, for the production of whole-cell catalyst, were carried out with induction conditions as described in US patents 7,531,343 and 7,531,344. In the production of R. rhodochrous, conditions in the bioreactor were improved in order to enhance the production, performance, and stability of the biological catalyst. Factors analyzed included the state and size of the inoculum, inducer concentration, fermentation time, and storage of the cell paste. Biological catalyst was produced that showed contact-independent inhibition against both B. cineria and P. destructans in vitro and in vivo. In response to the catalyst, B. cineria and P. destructans showed a decrease in mycelial growth and reduced or slowed spore production in co-cultures. Additionally R. rhodochrous inhibited fungal growth of B.cinerea on grapes and tomatoes and in an initial trial, improved survivorship of white-nose positive bats treated in a contact-independent manner.