(PI is Nancy Moran)
Many invertebrates contain specialized intracellular bacteria that are transmitted from mother to offspring in eggs and that persist in host lineages for millions of years. Typically, animal hosts and bacteria are unable to live apart, a situation that has slowed genetic characterization of symbiotic bacteria. The current project extends a previous collaboration, between an insect biologist and a bacteriologist, which has exploited modern molecular methods to characterize individual genes in symbionts of aphids. These bacteria have undergone genetic modifications that improve their ability to provide hosts with amino acids that are required for growth and reproduction. The new research is designed to address the question of how symbionts differ from related nonsymbiotic bacteria in overall genome characteristics. The dynamics of genome structure in aphid symbionts will be analyzed using newly developed molecular methods for determining sizes of large chromosomal fragments and for determining chromosomal locations of specific genes in symbionts from several aphid hosts of known relationships. In addition, rates of evolution of specific genes will be determined for pairs of symbionts with known dates of divergence. These results will be compared to corresponding information, from genetic databases, for closely related nonsymbiotic bacteria.
The symbionts of aphids possess some distinctive genetic traits that appear to represent a general syndrome in intracellular bacteria, including both beneficial symbionts of agricultural pests and pathogenic bacteria infecting humans, other animals, and plants. These characteristics include a reduced number of genes and reduced genome size, faster rates of genetic change over time, and biased composition of DNA molecules. Thus, the proposed investigations will increase understanding of a genetic syndrome that encompasses a variety of agriculturally and medically important bacteria. The additional knowledge of the basic biology of these organisms could contribute to new methods of controlling both agricultural pests and/or agents of disease.