Unprecedented loss of ammonia assimilation capability in a urease-encoding bacterial mutualist.
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BACKGROUND: Blochmannia are obligately intracellular bacterial mutualists of ants of the tribe Camponotini. Blochmannia perform key nutritional functions for the host, including synthesis of several essential amino acids. We used Illumina technology to sequence the genome of Blochmannia associated with Camponotus vafer. RESULTS: Although Blochmannia vafer retains many nutritional functions, it is missing glutamine synthetase (glnA), a component of the nitrogen recycling pathway encoded by the previously sequenced B. floridanus and B. pennsylvanicus. With the exception of Ureaplasma, B. vafer is the only sequenced bacterium to date that encodes urease but lacks the ability to assimilate ammonia into glutamine or glutamate. Loss of glnA occurred in a deletion hotspot near the putative replication origin. Overall, compared to the likely gene set of their common ancestor, 31 genes are missing or eroded in B. vafer, compared to 28 in B. floridanus and four in B. pennsylvanicus. Three genes (queA, visC and yggS) show convergent loss or erosion, suggesting relaxed selection for their functions. Eight B. vafer genes contain frameshifts in homopolymeric tracts that may be corrected by transcriptional slippage. Two of these encode DNA replication proteins: dnaX, which we infer is also frameshifted in B. floridanus, and dnaG. CONCLUSIONS: Comparing the B. vafer genome with B. pennsylvanicus and B. floridanus refines the core genes shared within the mutualist group, thereby clarifying functions required across ant host species. This third genome also allows us to track gene loss and erosion in a phylogenetic context to more fully understand processes of genome reduction.
Published Version (Please cite this version)
Williams, Laura E, and Jennifer J Wernegreen (2010). Unprecedented loss of ammonia assimilation capability in a urease-encoding bacterial mutualist. BMC Genomics, 11. p. 687. 10.1186/1471-2164-11-687 Retrieved from https://hdl.handle.net/10161/4350.
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Research in our lab centers on environmental and evolutionary genomics, primarily in bacteria. Broadly, our group explores mechanisms shaping genetic and functional variation in microbes that play important roles in the natural environment. Much of our work integrates evolutionary, population genetic, computational, and molecular approaches to clarify how bacterial genomes change over time. Among these studies, we are exploring how ecological interactions – such as symbiosis - influence genome content and architecture of the species involved. Conversely, we also explore how genomic alterations can impact microbial functions and interactions. As models to link genomics and environmental biology, we largely focus on mutualistic microbes, including bacteria that supply essential nutrients to invertebrate hosts.
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