Abstract
Cockroaches harbor the obligate flavobacterial endosymbiont Blattabacterium sp., which resides within the host's bacteriocytes and can recycle ammonia and urea nitrogenous wastes into amino acids for the host. We report the complete genome sequence of the Blattabacterium sp. associated with the giant roach Blaberus giganteus.
GENOME ANNOUNCEMENT
Blattabacterium sp., the obligate flavobacterial endosymbiont of cockroaches and the lower termite Mastotermes darwiniensis, is implicated in rescuing nitrogenous wastes and processing them into amino acids for the host (4, 8, 12, 15, 16). The genome of this beneficial insect endosymbiont is highly reduced (∼590 to 640 kb) compared to closely related, free-living genera. Entire biosynthetic pathways involved in various metabolic functions found in free-living relatives are absent, reflecting a substantial reduction of functional capability. Nonetheless, the pathways that recycle nitrogenous waste compounds, like urea and ammonia, to produce various amino acids and vitamins have been selectively retained in all Blattabacterium genomes. Analysis of Blattabacterium genomes from multiple cockroach families will enhance our understanding of the stability and functional nature of this host-microbe relationship from the endosymbiont perspective.
The tropical Blaberus giganteus (Blaberidae:Dictyoptera) grows to up to 6 inches long, making it one of the largest roaches (3), and it is primarily found in Central and South America. Its primary diet includes, but is not limited to, decaying plant material. Given the host's typically nitrogen-poor, plant-based diet, Blattabacterium sp. strain BGIGA is expected to be under selective pressure to maintain key nitrogen recycling and nutrient biosynthesis pathways.
Thirteen micrograms of DNA was prepared from fat bodies dissected from two lab-reared B. giganteus specimens and submitted to the Yale University Keck DNA Sequencing Lab for sequencing with an Illumina Genome Analyzer IIx. A 100-bp paired-end library was constructed from a multiplexed DNA sample that included B. giganteus fat body DNA. A total of 26,305,538 paired reads were quality filtered (adapter sequences removed and sequences of <40 bp excluded) into 17,458,144 paired reads and 205,533 single reads. Most of the gaps between 12,684 Velvet-generated (19) contigs were closed in silico by using ABACAS (2), IMAGE (17), and ICORN (13) in an iterative genome assembly strategy. PCR amplification and Sanger sequencing were used to bridge gaps between the 40 remaining contigs, yielding a circular chromosome and a single, circular plasmid. Artemis (14) and Projector 2 (18) were used to view assemblies. Putative protein-coding regions were identified using Glimmer (5), and functional prediction was done using searches based on Blastp (1) and HMMR (6) against the GenBank nr and Pfam databases, respectively. The Kegg KAAS database was consulted for metabolic reconstructions (11). RNAs were identified through Rfam database (7) searches and by using tRNAscan-SE (10).
The Blaberus giganteus Blattabacterium sp. endosymbiont strain BGIGA has a 629,165-bp chromosome and a 3,423-bp plasmid. The G+C contents of the chromosome and plasmid are 25.7% and 30.9%, respectively. Over 95% of the BGIGA chromosome consists of open reading frames; there are 573 protein-coding genes and 38 RNA-coding genes, including tRNAs specifying all amino acids and a single complete rRNA operon. The BGIGA genome functionally overlaps with other completely sequenced Blattabacterium genomes in that it is capable of reclaiming nitrogen from urea and ammonia and produces all of the essential amino acids as well as various cofactors. Thus, these data provide further evidence that the general functional role of this endosymbiont as a nutrient provider is ubiquitous among cockroaches.
Nucleotide sequence accession numbers.
The complete chromosome and plasmid sequences have been deposited in the NCBI GenBank database under accession numbers CP003535 and CP003536, respectively.
ACKNOWLEDGMENTS
We acknowledge financial support for this work from the U.S. National Science Foundation (award 0626716 to N.A.M.), Yale University, and the Yale Science and Engineering Association (to C.Y.H.).
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