A novel application of gene arrays: Escherichia coli array provides insight into the biology of the obligate endosymbiont of tsetse flies

Abstract

Symbiotic associations with microorganisms are pivotal in many insects. Yet, the functional roles of obligate symbionts have been difficult to study because it has not been possible to cultivate these organisms in vitro. The medically important tsetse fly (Diptera: Glossinidae) relies on its obligate endosymbiont, Wigglesworthia glossinidia, a member of the Enterobacteriaceae, closely related to Escherichia coli, for fertility and possibly nutrition. We show here that the intracellular Wigglesworthia has a reduced genome size smaller than 770 kb. In an attempt to understand the composition of its genome, we used the gene arrays developed for E. coli. We were able to identify 650 orthologous genes in Wigglesworthia corresponding to Ϸ85% of its genome. The arrays were also applied for expression analysis using Wigglesworthia cDNA and 61 gene products were detected, presumably coding for some of its most abundant products. Overall, genes involved in cell processes, DNA replication, transcription, and translation were found largely retained in the small genome of Wigglesworthia. In addition, genes coding for transport proteins, chaperones, biosynthesis of cofactors, and some amino acids were found to comprise a significant portion, suggesting an important role for these proteins in its symbiotic life. Based on its expression profile, we predict that Wigglesworthia may be a facultative anaerobic organism that utilizes ammonia as its major source of nitrogen. We present an application of E. coli gene arrays to obtain broad genome information for a closely related organism in the absence of complete genome sequence data.insect ͉ Glossina ͉ symbiosis ͉ Wigglesworthia ͉ expression profile

Genome sequence of the endocellular obligate symbiont of tsetse flies, Wigglesworthia glossinidia

“…In a previous study, where we hybridized DNA of W. pallidipes (a relative of W. brevipalpis studied here) to heterologous Escherichia coli gene arrays, we detected 457 orthologs, 197 of which were present in the genome of W. brevipalpis 8 . The additional homologous genes detected on the E. coli array may have been an artifact resulting from the extremely high AT content of the W. glossinidia genome.…”

“…The genome size of W. glossinidia has been estimated as 740-770 kilobases 8 (kb), and that of Buchnera sp., the obligate symbiont of the pea aphid (Homoptera:Aphidoidea), as 640,681 bp 9,10 . Both genomes approach the size of the smallest genome reported thus far, that of Mycoplasma genitalium (580 kb) 11 .…”

Production of ammonia by Tritrichomonas foetus and Trichomonas vaginalis

“…brucei brucei since this insect form grows in a medium that lacks carbohydrate other than what is present in the serum. Production of ammonia by trypanosomes was of further interest since it has been suggested that the tsetse fly (Diptera: Glossinidae) relies on an endosymbiotic bacterium for its fertility and nutrition (Akman & Aksoy, 2001). Based upon Escherichia coli gene array analysis, one of the endosymbionts (Wigglesworthia) was suggested to utilize ammonia in the absence of trypanosomes.…”

The Diversity of Insect-bacteria Interactions and its Applications for Disease Control

“…Sequencing of W. glossinidia genome revealed the presence of several cofactor biosynthetic pathways, including over 60 genes involved in the synthesis of vitamins and nutrients that are necesssay for fly fertility (Akman et al, 2002). The expression profile of these genetic pathways has also been confirmed using microarrays (Akman et al, 2001a). Moreover, a clear reduction in the number of bacterial genes related to the typical free-living state has been reported.…”

“…Among the most important genes lost is the DNA replication initiation protein, DnaA, which may reflect the dependency of W. glossinidia on host genome functions and may be one mechanism by which the host controls symbiont numbers (Akman et al, 2002). Studies of the gene expression in Wigglesworthia have been conducted using E. coli gene arrays, which have suggested that Wigglesworthia could be a facultative anaerobic organism that utilises ammonia as its major source of nitrogen (Akman et al, 2001a). The secondary symbiont of the tsetse fly is the S-symbiont Sodalis glossinidius (Akman et al, 2001b).…”