Development of a novel paratransgenic symbiotic-based control strategy for vector-borne infectious diseases

Introduction Paratransgenesis for the control of vector-borne infectious diseases is based on reintroduction into the host insect of genetically modified symbiotic bacteria expressing effector molecules that interfere with pathogen transmission. Key features for the success of a paratransgenic system are the ability of engineered bacteria to display or excrete the effector molecule and the fitness of the recombinant symbionts in insect physiological conditions. Objective of the present study is the development of a paratransgenic strategy to control vector-borne human diseases stimulating insect immunity against invading pathogens. Materials and Methods The stable dominant insect-associated bacterium Asaia platycodi wild-type (wt) strain SF2.1, was transformed with a plasmid bearing the gene of the potent insect immunomodulating surface protein of Wolbachia (WSP). To prejudicially verify the feasibility of the approach, the expression of the recombinant WSP by A. platycodi was evaluated. In addition, the fitness of the recombinant and wt isolates were compared in vitro by maximal growth rate (MGR) analysis in different culture conditions and by pairwise competition assays. Results Expression studies showed that recombinant A. platycodi displayed WSP on bacterial surface. MGR analysis showed that the transformation might differently affect the fitness of the bacterial host, in relation to the increase of the pH value of growth medium. Competition experiments carried out at A. platycodi pH optimal growth showed a slight reduction in vitality of the recombinant strain. Conclusions A recombinant insect-associated symbiotic bacterium displaying WSP on its surface was produced. We expect that paratransgenic immune activation of insects induced by WSP could hamper their infection by pathogens. Fitness studies indicated that the suggested symbiotic approach can be assumed in case of compatible pH values of colonized organs of the insect vectors and that possible problems of competitiveness of the transformed strain relatively to the wt should be considered. To increase the fitness of recombinant symbionts, bacteria may be engineered to stably include the WSP gene in the bacterial chromosome.