C-signal: a cell surface-associated morphogen that induces and co-ordinates multicellular fruiting body morphogenesis and sporulation in Myxococcus xanthos

In Myxococcus xanthus, morphogenesis of multicellular fruiting bodies end s porulation are coordinated temporally and spatially, csgA mutants fail to s ynthesize the cell surface-associated C-signal and are unable to aggregate and sporulate, We report that csgA encodes two proteins, a 25 kDa species c orresponding to full-length CsgA protein and a 17 kDa species similar in si ze to C-factor protein, which has been shown previously to have C-signal ac tivity. By systematically varying the accumulation of the csgA proteins, we show that overproduction of the csgA proteins results in premature aggrega tion and sporulation, uncoupling of the two events and the formation of sma ll fruiting bodies, whereas reduced synthesis of the csgA proteins causes d elayed aggregation, reduced sporulation and the formation of large fruiting bodies, These results show that C-signal induces aggregation as well as sp orulation, and that an ordered increase in the level of C-signalling during development is essential for the spatial co-ordination of these events. Th e results support a quantitative model, in which aggregation and sporulatio n are induced at distinct threshold levels of C-signalling. In this model, the two events are temporally co-ordinated by the regulated increase in C-s ignalling levels during development, The contact-dependent C-signal transmi ssion mechanism allows the spatial co-ordination of aggregation and sporula tion by coupling cell position and signalling levels.