Dear Kokila,

One possibility is a morphology change of the cells, we had similar observations with Corynebacterium. This inpacts the light transmission, the cell dry biomass remains the same, but the OD value goes down. Measure the dry cell mass in parallel, then you know.

Second possibility is phase infection, we had this once with E. coli. WIthin 1 hour, OD went down from 150 (high cell density culture) to practically zero, while all cells lysed.

Best,

Christoph

First of all Bacillus spp are rod shaped and they show an uneven movement along their axes of rotation and that is why you get a drop in OD. Secondly, as the fermentation proceeds, some cell tends to sporulate. More the number of spores more will be the drop in OD as Bacillus spores are more refractile than the vegetative cells which leads to drop in OD values.