Heat shock and prolonged heat stress attenuate neurotoxin and sporulation gene expression in group I Clostridium botulinum strain ATCC 3502

Abstract

Foodborne pathogenic bacteria are exposed to a number of environmental stresses during food processing, storage, and preparation, and in the human body. In order to improve the safety of food, the understanding of molecular stress response mechanisms foodborne pathogens employ is essential. Many response mechanisms that are activated during heat shock may cross-protect bacteria against other environmental stresses. To better understand the molecular mechanisms Clostridium botulinum, the causative agent of botulism, utilizes during acute heat stress and during adaptation to stressfully high temperature, the C. botulinum Group I strain ATCC 3502 was grown in continuous culture at 39°C and exposed to heat shock at 45°C, followed by prolonged heat stress at 45°C to allow adaptation of the culture to the high temperature. Growth in continuous culture was performed to exclude secondary growth phase effects or other environmental impacts on bacterial gene transcription. Changes in global gene expression profiles were studied using DNA microarray hybridization. During acute heat stress, Class I and III heat shock genes as well as members of the SOS regulon were activated. The neurotoxin gene botA and genes encoding the neurotoxin-associated proteins were suppressed throughout the study. Prolonged heat stress led to suppression of the sporulation machinery whereas genes related to chemotaxis and motility were activated. Induced expression of a large proportion of prophage genes was detected, suggesting an important role of acquired genes in the stress resistance of C. botulinum. Finally, changes in the expression of a large number of genes related to carbohydrate and amino acid metabolism indicated remodeling of the cellular metabolism.

Comparative Genomic Analysis of the DUF34 Protein Family Suggests Role as a Metal Ion Chaperone or Insertase

“…Links to virulence and environmental stress responses dominated the studies of bacterial and fungal DUF34 homologs [ 32 , 74 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 ]. In addition, links to the regulation of central carbon metabolism were made in Geobacillus stearothermophilus [ 128 ] and Bacillus subtilis [ 129 ].…”

Sporulation Strategies and Potential Role of the Exosporium in Survival and Persistence of Clostridium botulinum

“…These layers determine the spore properties, resistance, and how it interacts with its environment [ 16 ]. Earlier spore research in C. botulinum focused on the regulation and activation of sporulation [ 17 , 18 , 19 , 20 ], spore heat resistance [ 9 , 21 , 22 ], and germination [ 23 ]. Sporulation triggers, the proportion of sporulating cells, and the timeline of spore maturation and release can vary depending on the strain or species and the environmental conditions.…”

Neurotoxin synthesis is positively regulated by the sporulation transcription factor Spo0A in Clostridium botulinum type E

“…The only known negative regulator of BoNT synthesis, CBO0787/CBO0786, is a TCS whose regulator component CBO0786 binds specifically to the promoter of ntnh-botA and inhibits transcription of this operon by blocking the binding of the RNA polymerase-BotR complex to its target promoter DNA (Zhang et al, 2013b). The nature of the environmental signals activating the neurotoxinregulating TCSs is scarcely known, but availability of certain carbohydrates (Bonventre and Kempe, 1959) and amino acids (Patterson-Curtis and Johnson, 1989;Leyer and Johnson, 1990;Fredrick et al, 2017) and temperature (Selby et al, 2017), influence neurotoxin production and provide interesting hypotheses for further TCS studies. Not only the extracellular environment but also the intracellular state, such as the metabolic status of C. botulinum cells, affects BoNT production via the transition-state central regulator CodY .…”