Concerning the minimal size, we observed that liposomes with radius ca.

100 nm were still capable of protein expression; furthermore, surprisingly enough, the efficiency was higher than in bulk water. In order to express the protein, the liposomes should contain all hundred or so molecular components. This proves to be a riddle, as classic statistical analysis would give zero or negligible probability to the simultaneous entrapment of so many different molecular components (Souza et al, submitted). The possible raisons of this challenging puzzle, possibly important for the origin of life scenario, are discussed. Financial Support T.P. Souza was supported by the CNPq Post-doctoral fellowship 210295/2006-6 (Brazil). Luisi, P. L. (2006) Epigenetics inhibitor The emergence of life: from chemical origins to synthetic biology. Cambridge University Press. Luisi, P. L., Ferri, F., and Stano, P. (2006) Approaches to semi-synthetic

minimal cells: a review. Naturwissenschaften, 93, 1–13. Souza, T. P., Stano, P., and Luisi, P. L. (submitted) The minimal size of cells: an experimental approach based on liposomes. E-mail: terezapsouza@yahoo.​com.​br A Genomic Approach to the Evolution of Metabolism: Convergence and Complementation in Insect Endosymbionts J. Peretó, M.J. López-Sánchez, A. Lamelas, M.J. Gosálbez, A. Neef, R. Gil, A. Moya, A. Latorre Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de Valencia Comparative studies of insect-endosymbiont LDE225 cost genomes have illuminated the metabolic adaptation to intracellular lifestyle (Moya et al. 2008). A high number of insect species have established a symbiotic relationship with bacteria. In general, such insects feed on unbalanced diets, which are supplemented by bacterial endosymbionts. Aphids and cockroaches are model systems to study the dependence of the metabolic

evolution of endosymbiotic bacteria on the chemical composition of their diet. Aphids are plant-sap feeding insects, a diet rich in carbohydrates but deficient in essential amino acids and vitamins that are supplied by the endosymbionts. In particular, Buchnera aphidicola BCc (a gamma-proteobacteria associated with the aphid Cinara cedri) possesses the smallest Phosphoribosylglycinamide formyltransferase Buchnera genome, with only 422 kb. Its functional analysis indicates that tryptophan and riboflavin should be supplied by another source. Thus, the secondary endosymbiont Candidatus Serratia symbiotica has been proposed to carry out this role (Pérez-Brocal et al., 2006). We have sequenced the genome of S. symbiotica using 454 technology, and the results indicate that there is a metabolic complementation between both bacterial endosymbionts. Cockroaches are omnivorous insects that harbour Blattabacterium sp. (Flavobacteria, Bacteroidetes). Although the function of these endosymbionts is still unknown, it has been proposed that the blattabacteria might have a beneficial role for the host via an involvement in nitrogen waste recycling.