Question

In our initial enrichment for Bacillus from soil, we used a heat treatment step to kill vegetative cells. However, we did not test whether this heat treatment step was actually effective. Describe a control or controls that you could do to test the effectiveness of the heat treatment, and what types of microbes you would use for these controls

Answer 1

One type of control should be untreated sample, that is non-heat treated sample, the diluted soil suspension should be grown on a separate culture plate along with a plate of heat treated soil sample under same conditions.

the colony forming units(CFUs) on heat treated soil sample will arise mainly from heat resistant endospores of Bacillus that will grow in the medium whereas the CFUs on non treated sample plate will be from Bacillus endospores and other vegetative cells. The two type of strains can be distinguished by the morphology of the colonies. If the heat treatment is effective then the heat treated soil sample should contain only one type of CFUs derived from Bacillus endospores.

another type of control should be pure vegetative cells from pure culture such as Streptomyces. pure culture of Streptomyces should be heated treated and plated onto a culture plate along with heat treated soil sample on a separate culture plate. If the heat treatment is effective then their should be no CFUs on heat treated Streptomyces culture due to killing of vegetative cells by heat