Pressure, temperature impact inactivation and germination of B. cereus spores.The goal of scientists at the University of Delaware [3] The student body at the University of Delaware is largely an undergraduate population. Delaware students have a great deal of access to work and internship opportunities. was to study the germination germination, in a seed, process by which the plant embryo within the seed resumes growth after a period of dormancy and the seedling emerges. The length of dormancy varies; the seed of some plants (e.g. and inactivation inactivation /in·ac·ti·va·tion/ (in-ak?ti-va´shun) the destruction of biological activity, as of a virus, by the action of heat or other agent. of B. cereus cereus: see cactus. cereus Any of various large cacti (genus Cereus and related genera) of the western U.S. and tropical New World, including the saguaro and the organ-pipe cactus (Lemairocereus thurberi, also L. marginatus or C. thurberi). spores exposed to hydrostatic pressure hydrostatic pressure The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity. Hydrostatic pressure increases in proportion to depth measured from the surface because of the increasing weight of fluid and elevated temperature. Investigators determined the extent of inactivation by the number of survivors plated on nutrient agar Noun 1. nutrient agar - any culture medium that uses agar as the gelling agent agar culture medium, medium - (bacteriology) a nutrient substance (solid or liquid) that is used to cultivate micro-organisms directly after pressure treatment. Germination was determined by viable counts after the pressure-treated spores were exposed to 70 C for 10 minutes. For B. cereus 569, the wild-type strain, 15-minute treatments at 37 C resulted in: a 3.9 [log.sub.10] germination after exposure to 150 MPa; a 3.2 [log.sub.10] germination at 200 MPa exposure; and a 3.0 log[10.sub.10] germination after exposure at 250 MPa using an initial spore count of ~1 x 108 per mL. Spore inactivation from 15 minute treatments at 37 C reached: 3.0 [log.sub.10] at 150 MPa; 1.9 [log.sub.10] at 200 MPa; and 1.3 [log.sub.10] at 250 MPa. Exposure to pressures of 150 MPa resulted in higher levels of germination and inactivation than exposure to pressures ranging from 200 MPa to 250 MPa at 37 C. Exposure to 150 MPa and 30 C for 15 minutes yielded a 2.1 [log.sub.10] germination and a 1.0 [log.sub.10] inactivation. Similar experiments with germination mutants, gerI5 and gerL1, which lacked inosine inosine /in·o·sine/ (I) (in´o-sen) a purine nucleoside containing the base hypoxanthine and the sugar ribose, which occurs in transfer RNAs and as an intermediate in the degradation of purines and purine nucleosides to uric acid and in and L-alanine receptors, respectively, demonstrated: 2.0 [log.sub.10] germination; 1.6 [log.sub.10] inactivation (gerI5); 3.1 [log.sub.10] germination; and 1.7 [log.sub.10] inactivation (gerL1). The treatment conditions were 150 MPa at 37 C for 15 min. These data suggest that low pressures of approximately 150 MPa triggered the germination of B. cereus spores, and germinant receptors--gerI5 and gerL1--played a role in the mechanism of germination induced by high pressure and elevated temperatures. Other germination mutants, such as gerP (which lacked inosine receptors) and gerN (which lacked germinant-transfer proteins), were also deficient in pressure-induced germination. They appeared to possess a similar germination mechanism. Temperature also played an important role in spore inactivation. High pressure and elevated temperatures of 50 C to 65 C increased the rate of germination. Further information. Dallas Hoover, Department of Animal and Food Sciences, University of Delaware, 017 Townsend Hall, 531 S. College Ave., Newark, DE 19716; phone: 302-831-8772; fax: 302-831-2822; email: dgh@udel.edu. |
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