Temporal, genome-scale analysis of Myxococcus xanthus developmental fate in a mixed population

Myxococcus xanthus bacteria create aggregates when deprived of nutrients on solid surfaces, with some cells transforming into spores. Researchers have studied this multi-cellular developmental process using mutants in monoculture, but a comprehensive understanding of the genetic factors remains elusive. To delve into the genetic determinants at a genome-wide level, scientists generated a collection of barcoded transposon insertion mutants, exposed them to starvation, and subsequently separated the samples into non-aggregated cells, aggregated cells, and spores.

Additionally, the researchers subjected the mutant pool to chemically-induced sporulation in a unicellular state.

By analyzing the changes in mutant abundance in the samples, the team identified 200 genes in which insertions consistently led to distinct patterns of depletion or accumulation over time. Many of these genes are well-known for their roles in development, confirming the effectiveness of this approach, while several others have not been previously linked to development.

Among the genes discovered, those involved in type IV pili (T4P)-dependent motility were found to be crucial for both aggregation and sporulation in the mixed population, surpassing the importance of gliding motility genes. Contrary to the requirement of exopolysaccharide (EPS) synthesis genes for aggregation in monoculture, most of these genes were found to be dispensable for aggregation in the mutant pool, suggesting that EPS can be shared among cells. However, these genes became essential for efficient sporulation when performed cell-autonomously.

Furthermore, genes encoding positive regulators of EPS synthesis proved to be vital for both aggregation and sporulation, indicating functions beyond mere EPS production. Insertions in several previously unknown genes disrupted both starvation- and chemically-induced sporulation. Many genes enhanced the efficiency of starvation-induced sporulation, some of which the researchers dubbed "developmental winners."

Notably, these mutants also exhibit cheater behavior. The study demonstrates the potential of utilizing the newly-established mutant library to unravel the intricacies of Myxococcus xanthus biology.