Extended Data Fig. 8: Different evolutionary trajectories of Legionella in the environment result in the convergent evolution of distinct but compensatory virulence mechanisms.

In the environment, a common ancestor of Legionella encounters distinct, possibly overlapping, sets of diverse amoebal hosts. Amoebal heterogeneity in different environmental niches provides the selective pressure driving the diversification of individual Legionella species through the assembly of both common and distinct sets of virulence genes. The resulting virulence gene repertoires collectively determined fitness in the environment and human macrophages. In some cases, the evolutionary trajectory of the bacterium results in a set of virulence factors that is not sufficient to support replication in macrophages (a). In other cases, different evolutionary trajectories lead to distinct sets of virulence factors that each promote replication in macrophages (b, c) and thus distinct but compensatory virulence mechanisms. Conversely, some bacteria accumulate virulence factors that while important for growth in amoebae restrict replication in macrophages (d).