Physiochemical changes mediated by Candidatus Liberibacter asiaticus in Asian citrus psyllids

Plant pathogenic bacteria interact with their insect host(s)/vector(s) at the cellular and molecular levels. This interaction may alter the physiology of their insect vector, which may also promote the growth and transmission of the bacterium. Here we studied the effect of Candidatus Liberibacter asiaticus (Ca. L. asiaticus) on physiochemical conditions within its insect vector, the Asian citrus psyllid (ACP), and whether these changes were beneficial for the pathogen. The local microenvironments inside ACPs were quantified using microelectrodes. The average hemolymph pH was significantly higher in infected ACPs (8.13 +/- 0.21) than in Ca. L. asiaticus-free ACPs (7.29 +/- 0.15). The average hemolymph oxygen tension was higher in Ca. L. asiaticus-free ACPs than in infected ACPs (67.13% +/- 2.11% vs. 35.61% +/- 1.26%). Oxygen tension reduction and pH increase were accompanied by Ca. L. asiaticus infection. Thus, oxygen tension of the hemolymph is an indicator of infection status, with pH affected by the severity of the infection.