Genome Size Determination and Coding Capacity of Sodalis glossinidius , an Enteric Symbiont of Tsetse Flies, as Revealed by Hybridization to Escherichia coli Gene Arrays

Abstract

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 symbiotic microorganisms have evolved with tsetse fly, the vector of African trypanosomes, over long evolutionary times. Although these symbionts are indispensable for tsetse fecundity, the biochemical and molecular basis of their functional 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 on some of its conserved gene sequences has an A؉T content of only 45%, compared to the typically AT-rich genomes of endosymbionts. Sodalis also harbors an extrachromosomal plasmid about 134 kb in size. We used a novel approach to gain insight into Sodalis genomic contents, i.e., hybridizing its DNA to macroarrays developed for Escherichia coli, a closely related enteric bacterium. In this analysis we detected 1,800 orthologous genes, corresponding to about 85% of the Sodalis genome. The Sodalis genome has apparently retained its genes for DNA replication, transcription, translation, transport, and the biosynthesis of amino acids, nucleic acids, vitamins, and cofactors. However, many genes involved in energy metabolism and carbon compound assimilation 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 absence of whole genome sequence to advance our understanding of closely related bacteria.

Comparative Genomics of Insect-Symbiotic Bacteria: Influence of Host Environment on Microbial Genome Composition

“…; Diptera, Glossinidae), and Sitophilus oryzae primary endosymbiont (SOPE), a symbiont with the rice weevil (Sitophilus oryzae; Coleoptera, Dryophthoridae). Both of these recently established symbionts (4,24) show no AϩT bias in several of their sequenced genes (2,24). Although their genomes, 2.0 Mb for Sodalis (2) and 3.0 Mb for SOPE (11), have been reduced in size in comparison to free-living relatives, they are significantly larger than those of obligates.…”

DNA Microarray-Based Typing of an Atypical Monophasic Salmonella enterica Serovar

“…Microarrays have been shown to be helpful for quick detection of antibiotic resistance (24), determination of virulence and pathogenicity (5,16,17), species determination (6), genome comparison (1,2,8,18), and molecular epidemiological typing of strains (3,9). In addition, the microarray procedure was used successfully to analyze the deletions and amplification mutations commonly found in Salmonella mutagenicity assay strains (Ames test) (21).…”

Transposon Insertion Reveals pRM, a Plasmid ofRickettsia monacensis

“…Among nonpathogenic arthropod endosymbionts, some but not all species of Buchnera carry plasmids encoding proteins involved in the biosynthesis of amino acids that are deficient in the phloemsap diet of the host aphid (50). Genome sequencing of an obligate endosymbiont, Wigglesworthia glossinidia (2), and a secondary symbiont, Sodalis glossinidius (1,14), of blood-feeding tsetse flies (Diptera: Glossinidae) revealed the presence of plasmids of undefined biological significance. Within the Rickettsiales, a plasmid has been described only for R. felis isolate California 2, a rickettsial endosymbiont of fleas (32).…”