title: Molecular Mechanisms Contributing to the Growth and Physiology of an Extremophile Cultured with Dielectric Heating.
abstract: The effect of microwave frequency electromagnetic fields on living microorganisms is an active and highly contested area of research. One of the major drawbacks to using mesophilic organisms to study microwave radiation effects is the unavoidable heating of the organism, which has limited the scale (<5 ml) and duration (<1 h) of experiments. However, the negative effects of heating a mesophile can be mitigated by employing thermophiles (organisms able to grow at temperatures of >60°C). This study identified changes in global gene expression profiles during the growth of Thermus scotoductus SA-01 at 65°C using dielectric (2.45 GHz, i.e., microwave) heating. RNA sequencing was performed on cultures at 8, 14, and 24 h after inoculation to determine the molecular mechanisms contributing to long-term cellular growth and survival under microwave heating conditions. Over the course of growth, genes associated with amino acid metabolism, carbohydrate metabolism, and defense mechanisms were upregulated; the number of repressed genes with unknown function increased; and at all time points, transposases were upregulated. Genes involved in cell wall biogenesis and elongation were also upregulated, consistent with the distinct elongated cell morphology observed after 24 h using microwave heating. Analysis of the global differential gene expression data enabled the identification of molecular processes specific to the response of T. scotoductus SA-01 to dielectric heating during growth.
  
  
  
  The residual heating of living organisms in the microwave region of the electromagnetic spectrum has complicated the identification of radiation-only effects using microorganisms for 50 years. A majority of the previous experiments used either mature cells or short exposure times with low-energy high-frequency radiation. Using global differential gene expression data, we identified molecular processes unique to dielectric heating using Thermus scotoductus SA-01 cultured over 30 h in a commercial microwave digestor. Genes associated with amino acid metabolism, carbohydrate metabolism, and defense mechanisms were upregulated; the number of repressed genes with unknown function increased; and at all time points, transposases were upregulated. These findings serve as a platform for future studies with mesophiles in order to better understand the response of microorganisms to microwave radiation.
authors: National Research Council Research Associate Programs, U.S. Naval Research Laboratory (Chemistry Division), Washington, DC, USA.
authors: Kathleen D
authors: KD
authors: Cusick
authors: Center for Bio/Molecular Science and Engineering, U.S. Naval Research Laboratory, Washington, DC, USA.
authors: Baochuan
authors: B
authors: Lin
authors: Center for Bio/Molecular Science and Engineering, U.S. Naval Research Laboratory, Washington, DC, USA.
authors: Anthony P
authors: AP
authors: Malanoski
authors: Center for Bio/Molecular Science and Engineering, U.S. Naval Research Laboratory, Washington, DC, USA.
authors: Sarah M
authors: SM
authors: Strycharz-Glaven
authors: National Research Council Research Associate Programs, U.S. Naval Research Laboratory (Chemistry Division), Washington, DC, USA.
authors: Allison
authors: A
authors: Cockrell-Zugell
authors: Chemistry Division, U.S. Naval Research Laboratory, Washington, DC, USA.
authors: Lisa A
authors: LA
authors: Fitzgerald
authors: Chemistry Division, U.S. Naval Research Laboratory, Washington, DC, USA.
authors: Jeffrey A
authors: JA
authors: Cramer
authors: Chemistry Division, U.S. Naval Research Laboratory, Washington, DC, USA.
authors: Daniel E
authors: DE
authors: Barlow
authors: Chemistry Division, U.S. Naval Research Laboratory, Washington, DC, USA.
authors: Thomas J
authors: TJ
authors: Boyd
authors: Chemistry Division, U.S. Naval Research Laboratory, Washington, DC, USA Justin.biffinger@nrl.navy.mil.
authors: Justin C
authors: JC
authors: Biffinger
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D000071825:Extremophiles / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects*; D006358:Hot Temperature; D008872:Microwaves; D013824:Thermus / Q000235:genetics / Q000254:growth & development* / Q000528:radiation effects*
chemical_list: D001426:Bacterial Proteins