The production of secondary metabolites (including compounds with antimicrobial activity) is associated with the transition of bacteria to the stationary phase. Suboptimal/ stressogenic culture conditions induce the transition of microorganisms to the stationary phase, and thus can stimulate the production of secondary metabolites. No wonder that the optimal temperature for the production of secondary metabolites is different from the temperature of optimal growth (under such conditions, microbes are maintained in the logarithmic phase of growth and there is relatively low production of antimicrobial substances).

Your organism may not be a psychrophile, it may be a psychrotroph.

Hi Tariq,

If your organism give heavy growth at 25c, so I think it is mesophilic organism and can tolerate at lower temperatures such as 15c°. Also consider the time of complete growth of the organism at both temperatures. Also; it is a good results and you can record it that the optimum temperature for growth differs from that of secretion of antimecrobial compounds. good luck

Phychrophiles have their optimun growth at 15ºC, but the strains you describe can survive at 25ºC, this temperature is perfect for mesophilic microorganisms and the phsychrophiles produce antimicrobials to survive when they reach the stationary phase.

I support Pawel's point. For instance, phosphorus starvation/limitation (stress) leads to the increase of toxins productions by some marine cyanobacteria. Tariq may test Pawel's point by the plotting of an antimicrobial production versus the density of a psychrophilic culture or [protein]/mL at two temperatures. My prediction is that an antimicrobial production at 25oC will not be accompanied by cultural density increase. IB