Date of Award


Degree Name

MS in Agriculture - Dairy Products Technology


Dairy Science


Rafael Jimenez-Flores


Endospore-forming bacteria of the genus Bacillus are of significant importance to the food industry. Species from this genus exhibit the ability to form metabolically dormant endospores characterized by resistance to heat, UV, and chemical treatment. Spores have undetectable metabolic activity and remain impervious to the harsh conditions of their environment, but they can detect environmental cues signaling favorable growth conditions and begin the process of germination. Once germination and outgrowth are complete, the fully viable cell is capable of reproducing and forming colonies. The resistance of these endospores has been a topic of decades of research, particularly because of their impact on food processing. Only a few species of Bacillus are actually pathogenic, but many others present quality defects, particularly in milk and other dairy products.

This study involved the selection and use of primers specific for GerAC, gpr, and SleB genes to evaluate their relative expression and potential for indicators of lag phase in germination. Gene expression studies with qPCR were carried out during germination in Bacillus subtilis and Bacillus licheniformis spores that were given a heat shock in a tryptic soy broth at 80°C and subsequently incubated for 0, 30, 60, and 120 minutes at their optimal growth temperatures. Expression ratios calculated relative to the samples incubated for 120min (R=1) showed increased expression as germination and outgrowth progressed (GerAC gene on B. licheniformis and B. subtilis; R30min=0.14 and 0.14, R60min=0.76 and 0.51). The different expression levels measured in this preliminary study suggest that the selected genes and methodology merit further optimization to verify the accuracy and significance of the assay as well as its application it to the milk powder process.