Effects of different bacterial isolates on the hatching of Aedes aegypti eggs

Previous work has showed that eggs of Aedes aegypti will hatch when the water in which they are submerged contains microbes.  Laboratory studies showed that bacteria stimulate egg hatch through a decline in dissolved oxygen (DO) concentration during microbial growth.  We recently showed that a mix of 14 bacteria species or their metabolites, not just low DO concentration, stimulate hatching of Ae. aegypti eggs.  We hypothesize that the bacterial species isolates constituting the mix would not be equally effective in stimulating egg hatch.  To test this hypothesis we exposed eggs of Ae. aegypti to purified bacterial cells or bacteria-free metabolies excreted by bacteria into the culture medium and assessed subsequent hatch rates.  Out of 10 isolates tested with bacterial cells, six isolates stimulated 86-96% hatch within 4-h.  The DO concentration ranged from 5.8 to 7.6 ppm over the 4-h period of experimentation and only 2% of eggs hatched in the control saline solution. Out of 10 isolates tested with metabolic by-products excreted by bacteria, six isolates stimulated 86-96% hatch within 4-h.  Two bacterial isolates effectively stimulated egg hatch in both assays.  The results provide evidence that some bacterial isolates and/or water-soluble compounds secreted by bacteria stimulated hatching of Ae. aegypti eggs.