2.2. Photomultiplier tube assay

Observations of biophoton emissions were made by placing the bacterial cultures on the 3‐cm² aperture of a Sens‐Tech, Ltd. Model DM0090C Digital Photomultiplier Tube (PMT). Measurements consisted of 3,000 samples at a rate of one sample per 20 msec (50 Hz). According to specifications, the PMT is sensitive to photons of wavelengths between 280 and 850 nm. The subject bacterial culture within the 5 cm dish was placed upon the PMT aperture, and the whole apparatus (PMT +bacteria) was placed within a 15 x 15 x 15 cm dark box with an open top to permit access. The open top was later sealed with a number of heavy black towels. The same process was conducted for the bacterial species receiving H₂O₂ injections, to be described shortly. Experiments were conducted in an “8 + 1” design, where prior to placing the bacterial culture upon the PMT an environmental baseline recording was made, where baseline is defined as a background photon emission recording. The culture was then placed on the PMT and a run, consisting of eight observational recordings, began.

The bacteria were observed for UPE during the eight recordings, four of which were baseline and four of which coincided with injections of hydrogen peroxide (H₂O₂) in a γ‐A‐γ‐A‐γ‐B‐γ‐B design. In this design, A represents an injection volume of 0.1 cc, B represents an injection volume of 0.2 cc, and γ denotes a baseline recording. By virtue of this design, only the first γ is a “true” baseline, which we accounted for in our statistical analyses, as well as potential cumulative effects of the H₂O₂. The injections were made via 1 mm diameter serological tubing suspended over the injection culture within the second dark box, into which the H₂O₂ was sent using a 5 ml laboratory syringe.

To summarize, the standard experimental run consisted of a bacterial culture being placed upon the PMT inside one dark box, a second bacterial culture was placed in a separate dark box ~5 m away and received H₂O₂ injections via a syringe. Injections occurred approximately 5 s into each injection run. For each run, a new plate of bacteria was used at both the PMT recording and injection sites, were again a run refers to the “8 + 1” design.