Browsing by Author "Norrgård, Heidi"

Clostridium botulinum is an anaerobic rod shaped bacterium. It forms endospores that are commonly found in soils and aquatic sediments. C. botulinum produces one of the most potent neurotoxins that causes dangerous neuroparalytic disease called botulism. Food-borne botulism is an intoxication due to ingestion of preformed neurotoxin in foods. When favouring minimally processed food which safety depends almost only on chilled storage the risk of neurotoxin formation increases. It is essential to know the mechanisms of cold tolerance of C. botulinum when improving the safety of high-risk foods. A rapid temperature downshift causes decrease in the synthesis of most of the proteins in the cell. However the synthesis of structurally related cold shock proteins (Csp) reaches the maximum level after cold shock. It is assumed that these proteins are important for bacterial cold shock response. The exact function and meaning of cold shock proteins is not fully understood but they are believed e.g. to inhibit the formation of unwanted secondary structures of nucleic acids and regulate the synthesis of other proteins. The genome of C. botulinum ATCC 3502 strain contains three cold shock protein coding genes: cspA, cspB and cspC. The meaning of the cold shock proteins for the growth of ATCC 3502 was studied by comparing the growth of wild type strain and cspB- and cspC -mutant strains at different temperatures. The alterations in the expression of cspA-, cspB- and cspC -genes after cold shock were also studied. The results confirm that cspB and cspC genes are related to cold tolerance of the C. botulinum ATCC 3502 strain. cspB and cspC mutant strains grew at 20 °C at a reduced rate compared to C. botulinum ATCC 3502 wild type strain. There was no difference in growth rate between the strains grown at 37 °C and 44 °C. With quantitative RT-PCR, a significant twofold increase in the expression of cspA and cspB was detected for C. botulinum ATCC 3502 wild type strain while the expression of cspC stayed at normal level after cold shock. In cspB mutant strain the expression of cspA increased almost fivefold after cold shock. In cspC mutant strain after cold shock the trend of the expression of the other csp-genes was to decrease or stay at normal level. The results of quantitative RT-PCR method indicate some ability of csp genes to compensate for the functions of down regulated csp gene by other csp genes.