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

Symbiotic associations with microorganisms are pivotal in many insects. Yet , the functional roles of obligate symbionts have been difficult to study b ecause it has not been possible to cultivate these organisms in vitro. The medically important tsetse fly (Diptera: Glossinidae) relies on its obligat e endosymbiont, Wigglesworthia glossinidia, a member of the Enterobacteriac eae, closely related to Escherichia coil, for fertility and possibly nutrit ion. We show here that the intracellular Wigglesworthia has a reduced genom e size smaller than 770 kb. In an attempt to understand the composition of its genome, we used the gene arrays developed for E. coil. We were able to identify 650 orthologous genes in Wigglesworthia corresponding to approxima te to 85% of its genome. The arrays were also applied for expression analys is 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 a n important role for these proteins in its symbiotic life. Based on its exp ression profile, we predict that Wigglesworthia may be a facultative anaero bic organism that utilizes ammonia as its major source of nitrogen. We pres ent an application of E. coil gene arrays to obtain broad genome informatio n for a closely related organism in the absence of complete genome sequence data.