File:Figure 2 - Examples of social behavior in microbes.pdf

English: Example microbial interactions. A. Division of labor in Cyanobacteria. Some cells within clonal filaments differentiate into heterocysts (large, round cell, right). Heterocysts abandon oxygen-producing photosynthesis in order to fix nitrogen with the oxygen-sensitive enzyme nitrogenase. Vegetative and heterocyst cells divide labor by exchanging sugars and nitrogen. B. Bacterial quorum sensing. Quorum sensing cells constitutively secrete autoinducer (yellow triangles). At low cell densities, autoinducer concentration remains low and autoinducer-activated transcription factors (orange circles) are inactive. At high cell densities, autoinducer binds to and activates transcription factors, which in turn bind to and activate gene expression. C. Social development in Dictyostelium discoideum. Upon starving, vegetative amoebae aggregate into a mobile, multicellular slug, which moves through the soil. Fruiting body formation follows, during which a minority of the cells (blue) sacrifice themselves to develop into a stalk to hold the remainder of the aggregate (red) as it develops into durable spores. D. Biofilm development in Pseudomonas aeruginosa. Cells adhere to and colonize a surface through a combination of active migration and division. Secreted extracellular matrix components (dark green) accumulate into a complex structure. Cells detach and disperse from the biofilm’s upper layer via autolysis of cells in the lower layer. E. Symbiont exploitation in Candidatus Hodgkinia cicadicola. Hodgkinia cells live within specialized cells in the abdomens of 17-year cicadas (Magicicada tredecim) and produce amino acids (yellow and orange triangles) required by their hosts. Competition between strains within a single host favors fast growth rates, selecting for loss of amino acid production. In time, strains fragment into multiple complementary lineages, each producing only a fraction of the necessary amino acids. The host must accommodate increasingly large symbiont populations to maintain sufficient amino acid production.