Temperature Exerts Control of Bacillus cereus Emetic Toxin Production on Post-transcriptional Levels

Abstract

In recent years, the emetic toxin cereulide, produced by Bacillus cereus, has gained high relevance in food production and food safety. Cereulide is synthesized non-ribosomal by the multi-enzyme complex Ces-NRPS, which is encoded on a megaplasmid that shares its backbone with the Bacillus anthracis pX01 toxin plasmid. Due to its resistance against heat, proteolysis and extreme pH conditions, the formation of this highly potent depsipeptide toxin is of serious concern in food processing procedures including slow cooling procedures and/or storage of intermediate products at ambient temperatures. So far, systematic data on the effect of extrinsic factors on cereulide synthesis has been lacking. Thus, we investigated the influence of temperature, a central extrinsic parameter in food processing, on the regulation of cereulide synthesis on transcriptional, translational and post-translational levels over the growth temperature range of emetic B. cereus. Bacteria were grown in 3°C interval steps from 12 to 46°C and cereulide synthesis was followed from ces gene transcription to cereulide toxin production. This systematic study revealed that temperature is a cardinal parameter, which primarily impacts cereulide synthesis on post-transcriptional levels, thereby altering the composition of cereulide isoforms. Our work also highlights that the risk of cereulide production could not be predicted from growth parameters or sole cell numbers. Furthermore, for the first time we could show that the formation of the recently identified cereulide isoforms is highly temperature dependent, which may have great importance in terms of food safety and predictive microbiology. Notably the production of isocereulide A, which is about 10-fold more cytotoxic than cereulide, was specifically supported at low temperatures.

Oxygen Consumption Rate Analysis of Mitochondrial Dysfunction Caused by Bacillus cereus Cereulide in Caco-2 and HepG2 Cells

“…Relatively lower prevalence of cer + B. cereus and the fact that CER is not produced at refrigeration temperatures (t min for CER is considered to be 10–12 °C) contribute to the relatively low prevalence of CER in food. In addition, amounts of CER produced at 12° (are much smaller than at 30–37 °C (2–8 μg/g in bacterial wet weight and 31–194 μg/g bacterial wet weight, respectively) [ 31 ].…”

Identification of cereulide producingBacillus cereusby MALDI-TOF MS

“…If a strain has the ability to produce cereulide but does not produce cereulide on an agar plate, the result of the MALDI-TOF MS measurement would be false negative. In principle, like previously described for many other bacterial toxins, cereulide production depends strongly on the growth and enrichment conditions applied (12, 36). For the evaluation of the toxin productivity of emetic B. cereus strains, in earlier studies the bacteria were grown on tryptic soy agar (TSA) plates for up to ten days at 28 °C and then the biomass was extracted by organic solvents (37).…”

Bacillus cereus group: genetic aspects related to food safety and dairy processing

“…The isocereulides A and C show the highest and lowest cytotoxic action, respectively (MARXEN et al, 2015). KRANZLER et al (2016) have proven that cereulide production depends on temperature. These authors highlighted that the risk for emetic syndrome cannot be established using the counting of microorganisms or multiplication, because the toxin production was interrupted on temperatures that allow the highest bacterial multiplication and Isocereulide A (the most cytotoxic) production was higher on low temperatures.…”