Laser-induced breakdown spectroscopy (LIBS) as a novel technique for detecting bacterial infection in insects

Abstract

To prevent the spread of diseases in humans, animals or plants, determining whether potential vectors are infected is crucial. For example, early detection of the citrus disease Huanglongbing, which has been a scourge on the citrus industries around the world, is a critical need. This vector-borne disease is transmitted by Diaphorina citri, the Asian citrus psyllid, which carries the putative bacterial phytopathogen, Candidatus Liberibacter asiaticus (CLas). In this investigation, we introduced Laser-Induced Breakdown Spectroscopy (LIBS) to reveal key biochemical differences between CLas-infected and non-infected psyllids. The emission spectra captured from laser ablation of CLas-infected and healthy psyllids were processed through the principal component analysis (PCA) method and compared. Thirteen peaks from seven different elements were detected in D. citri. The t-test showed that CLas-infected D. citri were deficients in zinc, iron, copper, magnesium, calcium, and nitrogen. The PCA showed that LIBS can successfully differentiate between CLas-infected and healthy D. citri by comparing their elemental profile. In this work, we demonstrated a method that allows for a fast and precise compositional microanalysis of an insect vector which can contribute to the early detection of citrus huanglongbing.

Figure 1

Schematic representation of laser-induced breakdown spectroscopy system used in this study. A stereomicroscope was modified and attached to the laser source to point laser beams on the abdomen of Asian citrus psyllid.

Figure 2

Typical spectra of healthy and CLas-infected Asian citrus psyllid (PCR-positive). Yellow spectrum is a subtraction between healthy and CLas-infected psyllids spectra.

Figure 3

Differentiation between healthy and CLas-infected Asian citrus psyllid using elements identified by LIBS. (A) Principal component analysis of all identified elements (n = 22). (B) PCA-loading-plot for all identified elements. (C) Signal intensity of all elements identified by LIBS in healthy and CLas-infected Asian citrus psyllid. (D) Principal component analysis of five significant identified elements (n = 22). (E) PCA-loading-plot for five significant identified elements identified elements. Bars represent standard errors. P-values were calculated using the Student’s t-test.