Many organisms rely on bacteria to provide them with nutrients that are lacking from their diet. We, as humans, contain ~ 800 species of bacteria within our guts (Bäckhed et al 2005) – many of which are thought to prevent invasion and colonization by pathogenetic strains.

Primary (PS) and secondary (SS) symbiotic bacteria have been identified in numerous insect species, in particular within those insects feeding on an imbalanced diet, such as xylem, phloem or blood.  Many belong to the alpha-Proteobacteria and are closely related to free-living members of the Enterobacteriacea. Primary insect endosymbionts such as Buchnera (found in aphids) are vital to their insect hosts, often providing nutrients that would otherwise be lacking from the diet. The function of most SS endosymbionts, such as the tsetse symbiont Sodalis glossinidius, is still unclear although they do seem to be facultative. Many other insect-bacterial symbioses have now been characterized, several on the genomic level.

My research focuses on symbiotic bacteria isolated from chewing lice of the genus Columbicola, which contains 88 species, all of which parasitize pigeons and doves (Adams et al. 2005). Much of the work coming out of our lab has concentrated on reconstructing the coevolutionary history of birds and their ectoparasitic lice. Columbicola has been the main focus of much of this work. Interestingly, symbiotic bacteria were observed within Columbicola 75 years ago (Ries 1931, see Figure 1 below); however, up until our study no further work had been published regarding the nature of these bacteria, nor their evolutionary history. The overriding goal of my project is to add a third (microbial) tier to the bird-Columbicola system. Importantly, robust bird and Columbicola phylogenies already exist (see list of Clayton Lab Publications).

Figure 1	Figure 2
Figure 1. Micrograph of female C. columbae showing transovarial stages of symbiotic bacteria penetrating the egg follicle Ries 1931. Figure 2. General localization of the symbiont in nymphs and adults of C. columbae. Red and green signals indicate symbiont cells and host nuclei, respectively, while cuticles often exhibit red signals due to autofluorescence. Arrowheads, hybridization signals of bacteriocytes in the body cavity; arrows, hybridization signals associated with lateral oviducts, ovarial ampullae, and/or oocytes.

Through sequencing and phylogenetic analysis of 1.4 kb of 16s rDNA, along with the protein coding genes fusA and groEL we have demonstrated that the bacterial endosymbiont of Columbicola columbae belongs to the Gammaproteobacteria (Fukatsu et al. 2007).  Many insect symbionts belong to this class, including symbionts of body lice (Sasaki-Fukatsu et al. 2006), aphids (Unterman et al. 1989), whitefly (Thao and Baumann 2004), tsetse fly (Aksoy et al. 1997), weevils (Heddi et al. 1998) and sharpshooters (Moran et al. 2003). Remarkably, the endosymbionts found within C. columbae are more closely related to symbionts of tsetse flies and grain eating weevils than they are to symbionts found in other lice.

In collaboration with the Fukatsu lab (AIST, Japan) we have used our 16s rDNA sequences to design fluorescent probes specific to C. columbae (Fukatsu et al. 2007).  We then performed whole mount fluorescent in situ hybridization (wFISH) on C. columbae to visualize the morphology and distribution of symbionts within this louse. Their localization confirms the original findings of Ries in which he observed bacteria along either side of the internal abdomen of C. columbae.  In female lice we observed the bacteria migrating to the oviducts of third instar nymphs, from where they form ovarial ampullae  - specialized tissue formations used for symbiont transmission (Fukatsu et al. 2007).  In adult females, bacteria then migrated once more, from the ovarial ampullae to the posterior pole of the oocytes. Critically, this confirms the vertical transmission of these symbionts from mother to offspring.

In an attempt to establish the nature of the Columbicola-bacteria symbiosis, we are performing a series of antibiotic experiments in which lice are fed on feathers coated with antibiotic.  By treating lice with antibiotics we hoped to reduce the symbiont populations, while at the same time monitoring the lice for fitness effects­ - in this case survival, numbers of eggs laid and numbers of nymphs hatched, over a 10 day period.

Wendy Smith Publications

Pontes MH, Smith K, Smith WA and Dale C.  2008.  Insect Facultative Symbionts: Biology, culture and manipulation.  In K Bourtzis and TA Miller (eds).  Insect Symbiosis Volume 3. CRC Press, Taylor and Francis.

Fukatsu T, Koga R, Smith WA, Tanaka K, Nikoh N, Sasaki-Fukatsu K, Yoshizawa K, Dale C and Clayton DH.  2007.  Bacterial endosymbiont of the slender pigeon louse Columbicola columbae, allied to endosymbionts of grain weevils and tsetse flies.  App. Env. Micro.  73: 6660.

Kaliszewska ZA, Seger J, Rowntree VJ, Barco SG, Benegas R, Best PB, Brown MW, Brownell RL Jr, Carribero A, Harcourt R, Knowlton AR, Marshall-Tilas K, Patenaude NJ, Rivarola M, Schaeff CM, Sironi M, Smith WA, Yamada TK. 2005.  Population histories of right whales (Cetacea: Eubalaena) inferred from mitochondrial sequence diversities and divergences of their whale lice (Amphipoda: Cyamus).  Mol Ecol. Oct; 14(11): 3439-56.

Hutchinson OC, Smith W, Jones NG, Chattopadhyay A, Welburn SC, Carrington M. 2003.  VSG structure: similar N-terminal domains can form functional VSGs with different types of C-terminal domain.  Mol Biochem Parasitol.  31; 130(2):127-31.

Moran NA, Dale C, Dunbar H, Smith WA, Ochman H.  2003.  Intracellular symbionts of sharpshooters (Insecta: Hemiptera: Cicadellinae) form a distinct clade with a small genome.  Environ Microbiol.  5(2): 116-26.

Dale C, Smith WA, Ochman H.   2003.  Physical Analysis of chromosome size variation.  In, Prokaryotic Genomics (Methods and Tools in Biosciences and Medicine), Michel Blot (Ed), Birkhauser, ISBN: 376436596X.

Ashford DA, Smith WA, Douglas AE.  2000.  Living on a high sugar diet: the fate of sucrose ingested by a phloem-feeding insect, the pea aphid Acyrthosiphon pisum.  J Insect Physiol. 46(3):335-341.