Oleic acid can be a product of lipase activity so one might expect it to cause catabolite repression.

Yes, oleic acid (beside being a product and thus in elevated concentration causes inhibition as said above by Stephen) is inhibitory for many microorganisms, especially in the absence of suitable and required concentrations of calcium. In our hands (not Bacillus) the best inductions is with lipid emulsions ----done by ultra sonic treatment of the medium before inoculation. Lipid hydrolysis occurs in the interface (see reviews). (Olive oil or similar oils are a cheap substrate.

Thanks for both of you, Stephen and Jurgen, ....I suppose that the presence of calcium is for emulsion stability...is 'n it? or is it for enzyme activation?

sorry for the late answer. There is ample literature on it, it is to take care of the inhibitory effect of the free fatty acids. Many anaerobic and a few aerobic lipolytic bacteria only use the glycerol for growth and do not use the fatty acides, Here is one of our reviews M. Salameh and J. Wiegel. 2007 Lipases from extremophiles and potential for industrial applications Chapter 7. in Advances in Applied Microbiology 61: 253-283

Thanks Pr. Wiegel

Calcium anions often stimulate the reaction by removing, as calcium soaps, fatty acids which are inhibitory.