Genome size determination and coding capacity of Sodalis glossinidius, an enteric symbiont of tsetse flies, as revealed by hybridization to Escherichia coli gene arrays

Recent molecular characterization of various microbial genomes has revealed differences in genome size and coding capacity between obligate symbionts and intracellular pathogens versus free-living organisms. Multiple symbioti c microorganisms have evolved with tsetse By, the vector of African trypano somes, over Long evolutionary times. Although these symbionts are indispens able for tsetse fecundity, the biochemical and molecular basis of their fun ctional significance is unknown. Here, we report on the genomic aspects of the secondary symbiont Sodalis glossinidius. The genome size of Sodalis is approximately 2 Mb. Its DNA is subject to extensive methylation and based o n some of its conserved gene sequences has an A+T content of only 45%, comp ared to the typically AT-rich genomes of endosymbionts. Sodalis also harbor s an extrachromosomal plasmid about 134 kb in size, We used a novel approac h to gain insight into Sodalis genomic contents, i.e., hybridizing its DNA to macroarrays developed for Escherichia coli, a closely related enteric ba cterium, In this analysis we detected 1,800 orthologous genes, correspondin g to about 85% of the Sodalis genome. The Sodalis genome has apparently ret ained its genes for DNA replication, transcription, translation, transport, and the biosynthesis of amino acids, nucleic acids, vitamins, and cofactor s, However, many genes involved in energy metabolism and carbon compound as similation are apparently missing, which may indicate an adaptation to the energy sources available in the only nutrient of the tsetse host, blood, We present gene arrays as a rapid tool for comparative genomics in the absenc e of whole genome sequence to advance our understanding of closely related bacteria.