Microwave radiation induces a heat-shock response and enhances growth in the nematode Caenorhabditis elegans

This paper shows that prolonged (overnight) exposure to continuous microwav e fields (750 MHz, 0.5 W) can induce both a heat-shuck response and enhance d growth in the nematode worm Caenorhabditis elegans. Exposures were conduc ted in a TEM cell with matched load, producing an E-field of approximately 45 V m(-1) at the center (where test worms are placed). Biomonitoring of he at-shock responses has been simplified by using two transgenic strains (PC7 2 and PC161), which both carry stress-inducible reporter constructs, respec tively, placing lacZ (beta -galactosidase) and lacZ plus green fluorescent protein expression under the control of C. elegans hsp16-1 promoters. In si tu localization of reporter expression reveals a minority of test worms, wh ich respond strongly to microwave exposure. Enzyme activity measurements av erage these reporter responses across many thousands of individual worms, g iving a reliable indication of the overall stress imposed on a population. The temperature profile of reporter responses induced by microwave exposure parallels that induced in controls by heat alone, but is displaced down th e temperature scale by some 3 degreesC. Length measurements were conducted at intervals in synchronized C. elegans cultures seeded with L1 larvae. Usi ng pooled data from nine separate runs, growth was stimulated by 8.5% after overnight microwave exposure (relative to controls), and this disparity in creased to 11% after 24 h of further growth without irradiation. Both heat- shock responses and increased growth would be consistent with a modest incr ease in temperature, raising the possibility that microwave exposure might cause limited heating in this system. However, there is no detectable rise in the temperature of either medium or worms during overnight exposure unde r these conditions, discounting both generalized and localized (worm-specif ic) heating effects, We conclude that both growth and heat-shock responses are induced by microwave exposure through one or more nonthermal routes.