Serratia marcescens grown at different temperatures showed color differences due to temperature-dependent pigment production. E. coli was killed at 4ยฐC through inhibition of metabolic processes at low temperatures. Bacillus subtilis was more heat resistant than E. coli in the lethal effects experiment due to its endospore formation providing protection against heat. A follow up experiment to determine E. coli's thermal death point could involve exposing it to increasing temperatures over time and measuring survival.