The discovery of Wolbachia in arthropods and nematodes - A historical perspective

Collaborative studies between Marshall Hertig, an entomologist, and Samuel Wolbach, a pathologist, on the presence and identification of microorganisms in arthropods, resulted in the discovery of Wolbachia in Culex pipientis in 1924, although the complete description of Wolbachia pipientis was not published until 1936. It has been subsequently demonstrated that Wolbachia is widespread in arthropods, infecting about 25-70% of species of insects, and is now known to be a remarkable genetic manipulator of the infected arthropod hosts. Application of electron microscopy to elucidate the structure of nematodes revealed that many filariae (17 species reported to date, including most of the species pathogenic to humans) harbored transovarially transmitted bacterial endosymbionts, subsequently determined as belonging to the Wolbachia, clades C, D, and F. The Wolbachia are apparently mutualistic endosymbionts required for survival of their hosts and embryogenesis of microfilariae, are present in all larval stages during the life cycle of filarial, and contribute to some of the inflammatory responses and pathological manifestations of filarial infections in the vertebrate hosts. Susceptibility of Wolbachia of filariae to certain antibiotics offers an attractive possibility of treatment and control of filarial infections in humans and animals. Recently sequenced genomes of W. pipientis (Sanger Institute, UK, and The Institute for Genomic Research, USA) and Wolbachia from Brugia malayi (New England Biolabs, USA) have opened a new chapter in the studies on Wolbachia. The detailed comparisons and the ongoing Wolbachia genome sequencing studies in other filarial nematodes and insects could provide the means to fully characterize the structure, composition and the nature of these organisms that play a significant role in mutualism and parasitism.