![]() ![]() Here we provide a detailed examination of the evolutionary fate of these specialized cells and provide evidence that they represent a terminally differentiated putatively altruistic cell type within these multicellular microbes. However, the fitness of the mutant subpopulation is significantly reduced. The ability to generate this subpopulation of cells appears to benefit the whole colony, by virtue of their increased antibiotic production, without causing a decline in overall colony spore production. In addition, we have recently shown that colonies are further divided into a subpopulation of cells that hyperproduces antibiotics 13. These bacteria have a well-characterized reproductive division of labor due to a developmental program that leads to the formation of durable spores following a period of vegetative growth and the elongation of spore-bearing aerial hyphae 11, 12. High relatedness during multicellular growth or development is even further guaranteed if the cells within colonies remain physically connected to each other, as observed in filamentous streptomycetes 9, 10. In microbes, the requirement of high relatedness is most easily met if colonies are initiated from a single cell or spore. ![]() Thus, in analogy with sterile castes of workers within colonies of social insects that are morphologically differentiated to perform specialized tasks, the extreme altruism needed for reproductive sterility is facilitated by high relatedness 8. By contrast, groups with aggregative multicellularity like dictyostelid social amoebae or myxobacteria, which potentially have lower relatedness between cells if unrelated genotypes coaggregate during development, tend to show reduced specialization 5– 7. Clonal groups, where relatedness among cells is high, show more cellular specialization and an increased likelihood of expressing the reproductive division of labor between somatic and germ cells 1– 4. Despite their differences, a recent study showed that a central factor determining organismal complexity is the way in which multicellular organisms are formed 1. Multicellular organisms show enormous variation in size and complexity, ranging from multicellular microbes to sequoias and whales, and from transient undifferentiated cellular clusters to stable individuals with highly specialized cell types. coelicolor division of labor are analogous to altruistic reproductively sterile castes of social insects. Taken together, these results suggest the cells arising in the S. Ecological damage, caused by reduced sporulation, coupled with DNA damage due to point mutations and deletions, leads to an inevitable and irreversible type of mutational meltdown in these cells. In addition, the base-substitution rate in mutants increases roughly 10-fold, possibly due to mutations in genes for DNA replication and repair. We show that in contrast to wild-type cells, putatively altruistic mutant cells continue to decline in fitness during transfer while they lose more fragments from their chromosome ends. ![]() To understand these mutant cells’ reproductive and genomic fate after their emergence, we use experimental evolution by serially transferring populations via spore-to-spore transfer for 25 cycles, reflective of the natural mode of bottlenecked transmission for these spore-forming bacteria. Because these cells contain large genomic deletions that cause massive reductions to individual fitness, their behavior is similar to altruistic worker castes in social insects or somatic cells in multicellular organisms. In colonies of the filamentous multicellular bacterium Streptomyces coelicolor, a subpopulation of cells arises that hyperproduces metabolically costly antibiotics, resulting in a division of labor that increases colony fitness. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |