Abstract
BackgroundEnterocin AS-48 is produced by Enterococcus faecalis S48 to compete with other bacteria in their environment. Due to its activity against various Gram positive and some Gram negative bacteria it has clear potential for use as a food preservative. Here, we studied the effect of enterocin AS-48 challenges on vegetative cells of Bacillus cereus ATCC 14579 by use of transcriptome analysis.ResultsOf the 5200 genes analysed, expression of 24 genes was found to change significantly after a 30 min treatment with a subinhibitory bacteriocin concentration of 0.5 μg/ml. Most of up-regulated genes encode membrane-associated or secreted proteins with putative transmembrane segments or signal sequences, respectively. One operon involved in arginine metabolism was significantly downregulated. The BC4206-BC4207 operon was found to be the most upregulated target in our experiments. BC4206 codes for a PadR type transcriptional regulator, while BC4207 codes for a hypothetical membrane protein. The operon structure and genes are conserved in B. cereus and B. thuringiensis species, but are not present in B. anthracis and B. subtilis. Using real-time qPCR, we show that these genes are upregulated when we treated the cells with AS-48, but not upon nisin treatment. Upon overexpression of BC4207 in B. cereus, we observed an increased resistance against AS-48. Expression of BC4207 in B. subtilis 168, which lacks this operon also showed increased resistance against AS-48.ConclusionBC4207 membrane protein is involved in the resistance mechanism of B. cereus cells against AS-48.
Highlights
Enterocin AS-48 is produced by Enterococcus faecalis S48 to compete with other bacteria in their environment
Effect of enterocin AS-48 on global gene expression in B. cereus ATCC14579 Enterocin AS-48 was shown to inhibit growth of vegetative cells and spore outgrowth of B. cereus [12] and it can be an effective bioagent against B. cereus in various food related media, e.g. hard cheese, rice based foods, fruit and vegetable juices [13,14,15]
Two regulators belonging to the PadR family were significantly upregulated, both located upstream of, and in one operon with, genes coding for membrane proteins that are enhanced during our experiments
Summary
Enterocin AS-48 is produced by Enterococcus faecalis S48 to compete with other bacteria in their environment. Strains of B. cereus are widely distributed in the environment, mainly in soil, from where they spread to many types of foods, especially of vegetable origin, as well as meat, eggs, milk, and dairy products. This bacterium is one of the leading causes of food poisoning in the developed world. The second type is manifested primarily by abdominal cramps and diarrhea with an incubation period of 8 to 16 hours This type is referred to as the "long-incubation" or diarrheal form of the disease [1,2]
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