The selective advantage of microbial fratricide

Abstract

Selective lysis of siblings appears to be a highly evolved and complex process. Streptococcus pneumoniae , a leading cause of serious infections, including pneumonia, infections of the middle ear, and meningitis (recently reviewed in ref. 1), is an organism of great public health concern. Antibiotic resistance among S. pneumoniae strains is rapidly increasing, complicating treatment (2). S. pneumoniae , previously known as Diplococcus pneumoniae or pneumococcus, played a central role in discovery of DNA as the “transforming principle,” the molecule that contained the encoded information necessary to transform a bacterial cell from an unencapsulated avirulent type to a virulent encapsulated type (3, 4). Since these seminal observations, the mechanism of DNA uptake by S. pneumoniae and its ecological and medical significance have been subjects of great interest. In this issue of PNAS, Jean-Pierre Claverys and coworkers (5) describe a novel mechanism that ties together the development of competence (the ability to take up DNA from the environment) with the fratricide of siblings, leading to the release of a key S. pneumoniae virulence factor, pneumolysin [Ply (6)], in the process. The release of Ply and other cytoplasmic contents, which occurs at the expense of a large portion of the bacterial population, suggests that the survival benefit of being virulent or alerting the host to its presence outweighs the disadvantage of losing many members of the S. pneumoniae population. Proficiency in uptake of DNA from the environment by S. pneumoniae has contributed to the development of multidrug-resistant strains, providing direct evidence for its importance in the continuing evolution of this species. For example, the mosaic penicillin-binding proteins that render S. pneumoniae resistant to β-lactam antibiotics appear to have originated in oral streptococci, such as Streptococcus mitis (7). The ability of S. pneumoniae to take up DNA is transient and regulated by …