Some molecular aspects of the heat inactivation of C. freundii

Verrips, Th.; Brevoort, H.

doi:10.1007/bf00403661

Cited by 3 publications

(1 citation statement)

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“…Several workers have reported that the 30s ribosomal subunit is more heat-labile than the 50s subunit and Verrips & Brevoort (1979) proposed an inactivation scheme based on denaturation of the 30s subunit followed by hydrolysis of 16s RNA. Exposure of cells of Salmonella typhimurium to mild heat (48 "C) in phosphate buffer results in selective destruction of the 30s ribosomal subunit (Tomlins & Ordal, 1976).…”

Section: Direrential Scanning Calorimetry Of E Coli 237mentioning

confidence: 99%

Thermal denaturation of whole cells and cell components of Escherichia coli examined by differential scanning calorimetry

Mackey¹,

Miles²,

Parsons³

et al. 1991

Journal of General Microbiology

135

126

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Thermograms of whole cells of Escherichia coli obtained by differential Scanning calorimetry contained ten main peaks (denoted& l, m, , m2, m3, n,p, q, r and s) occurring at temperatures of approximately 25,54,61,71,76,81, 95, 105, 118 and 124 "C, respectively. After cooling to 5 "C and reheating, peaks denoted fr, m, and p r were observed at 23,73 and 94 "C, respectively. By examining thermograms of different cell fractions we have identified the following thermal denaturation events. During primary heating there is a broad endotherm ( f ) beginning below 20 "C and extending to just above 40 "C that is caused by melting of membrane lipids. Superimposed on'this is an exothermic process associated with a change of state of the peptidoglycan. The first irreversible denaturation event occurs just above 47 "C, associated with the onset of denaturation of the 30s ribosomal subunit and soluble cytoplasmic proteins. Ribosome melting is a complex process occurring between 47 and 85 "C and is characterized by peaks m, , m2 and n. Peak m3 at 75-76 "C is of unknown identity but may possibly represent melting of tRNA.Peak p at 95 "C results from melting of a portion of the cellular DNA combined with denaturation of a cell wall component. Peak q at 105 "C is multicomponent and may be caused by melting of a different region of DNA together with denaturation of another cell wall component. The complex events denoted r and s at 118 and 125 "C, respectively, are associated with denaturation of a component of the cell envelope, and possibly also of DNA.Following cooling and reheating there is a broad endotherm with a maximum at 23 "C caused by remelting of membrane lipid and a very broad endotherm extending between 40 and lo0 "C caused by the remelting of ribosomal RNA. Peak p , at 94 "C is caused by the melting of reannealed DNA. Additional features not appearing in whole cells were evident in some cell fractions. These observations should allow us to distinguish events that may lead to loss of viability from those that do not. IntroductionThe inactivation of micro-organisms by heat forms the basis of large sections of the food and pharmaceutical industries. Not surprisingly, the factors affecting microbial heat-resistance and the nature of heat damage are of continuing practical and scientific concern.The mechanisms of thermal inactivation of microorganism have commonly been investigated by using biochemical methods to examine the effect of heat on particular cell structures or processes. Membranes, nucleic acids and certain enzymes have all been identified as cellular sites of heat injury and, in some cases, information is available on the molecular nature of heat damage (Tomlins & Ordal, 1976 Gould, 1989). However, despite this large body of information, we still do not understand precisely how micro-organisms are killed by heat. 1984;Differential scanning calorimetry (DSC) enables denaturation and other thermal processes that occur when samples are heated to be detected and recorded as a time-temperature sequence. The techn...

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Section: Direrential Scanning Calorimetry Of E Coli 237mentioning

confidence: 99%