title: Found and Lost: The Fates of Horizontally Acquired Genes in Arthropod-Symbiotic Spiroplasma.
abstract: Horizontal gene transfer (HGT) is an important mechanism that contributed to biological diversity, particularly in bacteria. Through acquisition of novel genes, the recipient cell may change its ecological preference and the process could promote speciation. In this study, we determined the complete genome sequence of two Spiroplasma species for comparative analyses and inferred the putative gene gains and losses. Although most Spiroplasma species are symbionts of terrestrial insects, Spiroplasma eriocheiris has evolved to be a lethal pathogen of freshwater crustaceans. We found that approximately 7% of the genes in this genome may have originated from HGT and these genes expanded the metabolic capacity of this organism. Through comparison with the closely related Spiroplasma atrichopogonis, as well as other more divergent lineages, our results indicated that these HGT events could be traced back to the most recent common ancestor of these two species. However, most of these horizontally acquired genes have been pseudogenized in S. atrichopogonis, suggesting that they did not contribute to the fitness of this lineage that maintained the association with terrestrial insects. Thus, accumulation of small deletions that disrupted these foreign genes was not countered by natural selection. On the other hand, the long-term survival of these horizontally acquired genes in the S. eriocheiris genome hinted that they might play a role in the ecological shift of this species. Finally, the implications of these findings and the conflicts among gene content, 16S rRNA gene sequencing, and serological typing, are discussed in light of defining bacterial species.
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, NationalChung Hsing University and Academia Sinica, Taipei, Taiwan Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan.
authors.forename: Wen-Sui
authors.initials: WS
authors.lastname: Lo
authors.affiliation: Department of Biological Sciences, Towson University.
authors.forename: Gail E
authors.initials: GE
authors.lastname: Gasparich
authors.affiliation: Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, NationalChung Hsing University and Academia Sinica, Taipei, Taiwan Biotechnology Center, National Chung Hsing University, Taichung, Taiwan chk@gate.sinica.edu.tw.
authors.forename: Chih-Horng
authors.initials: CH
authors.lastname: Kuo
mesh_terms: D000818:Animals; D001181:Arthropods / Q000382:microbiology; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D020071:Interspersed Repetitive Sequences; D010802:Phylogeny; D013149:Spiroplasma / Q000145:classification / Q000235:genetics*; D013559:Symbiosis
keywords: Mollicutes; Spiroplasma; genome degradation; horizontal gene transfer (HGT); mobile genetic element (MGE); pseudogene