Mid-infrared versus far-infrared (THz) relative intensities of room-temperature Bacillus spores

We have simultaneously recorded the mid-IR and far-IR (a.k.a. terahertz, THz) spectra of the sporulated form of five Bacillus bacteria: Bacillus subtilis ATCC 49760, B. subtilis ATCC 6051, Bacillus thuringiensis subsp. kurstaki ATCC 35866, Bacillus globigii 01, and Bacillus atrophaeus 49337. The 295 K spectra were recorded from ∼8 to 6000 cm−1 using spore counts on the order of 109 deposited onto windows transparent in both the mid- and far-infrared. The results indicate that any room-temperature THz absorption features due to the spores are at least 28 times weaker (based on p–p noise) than the corresponding mid-IR amide I band.