pH stress can cause cell elongation in Bacillus and Clostridium species: a research note

Spoilage of low pH products by a wide range of sporeformers is often observed. Work was done to isolate these organisms and establish the minimum pH allowing growth. At low pH values (below 4.3), a haziness or slight turbidity was noted in the broths which did not correspond to an increase in cell numbers determined by plate count. Microscopic investigations revealed the presence of elongated cells or chains of rods in the lower pH broths which were not present in the higher pH broths. The elongated cell morphology disappeared when cells were returned to optimum pH conditions. Phillips, L. E., Humphrey, T. J., & Lappin-Scott, H. M. (1998). [Journal of Applied Microbiology, 84 (5), 820–826] illustrated this with Salmonella when chilled. It is concluded that cell elongation is a stress response to sub-optimal pH conditions, which can revert and give a rapid apparent increase in cell numbers when conditions become more favourable.