Baseline and in vivo Total Photoluminescence of Endospore Material Using the Parasitoid Wasp C. Congregata

Abstract

In a laboratory test, total luminescence spectroscopy was used to detect and measure the in vivo presence of a biohazard surrogate, endospores of Bacillus megaterium, within the parasitoid wasp C. congregata (Say) (Hymenoptera:Braconidae). Upon emergence, exposed wasps were allowed to feed on five different concentrations of endospores suspended in 5 mL of honey solution. After 12 h insects were chilled at −80 °C for 5 min to permit capture. Aqueous suspensions were prepared by homogenizing the wasps in 3 mL of deionized water. The total excitation-emission matrix (EEM) was measured for each suspension by using an SLM Series 2 luminescence spectrometer. For wasps exposed to spore concentrations of 3.0 × 10² to 3.0 × 10⁶ colony forming units (CFU)/mL, two intensity maxima were observed. The emission for tryptophan was identified at excitation (Ex) 300 nm and emission (Em) 350 nm. A second emission that resulted from other biological materials including nitroheterocyclic compounds and endospores occurred at Ex 350 nm and Em 420 nm. Changes in the ratio of intensity between the tryptophan and second emission were found to be related to endospore material present in the suspensions at original feeding concentrations of 15 000 to 15 million spores. Intensity ratios for the positive samples equaled 0.9, while the intensity ratios for the control equaled 1.9. One notable difference recorded for the emission spectra was an apparent, but minor, red shift of approximately 5 nm of the second emission when compared against a signature library of pure cultures. Diagnostic information such as this should contribute to methods for the detection and potential identification of biohazard materials with the use of photoluminescence.