Kin discrimination between sympatric Bacillus subtilis isolates

Abstract

Kin discrimination, broadly defined as differential treatment of conspecifics according to their relatedness, could help biological systems direct cooperative behavior toward their relatives. Here we investigated the ability of the soil bacterium Bacillus subtilis to discriminate kin from nonkin in the context of swarming, a cooperative multicellular behavior. We tested a collection of sympatric conspecifics from soil in pairwise combinations and found that despite their history of coexistence, the vast majority formed distinct boundaries when the swarms met. Some swarms did merge, and most interestingly, this behavior was only seen in the most highly related strain pairs. Overall the swarm interaction phenotype strongly correlated with phylogenetic relatedness, indicative of kin discrimination. Using a subset of strains, we examined cocolonization patterns on plant roots. Pairs of kin strains were able to cocolonize roots and formed a mixed-strain biofilm. In contrast, inoculating roots with pairs of nonkin strains resulted in biofilms consisting primarily of one strain, suggestive of an antagonistic interaction among nonkin strains. This study firmly establishes kin discrimination in a bacterial multicellular setting and suggests its potential effect on ecological interactions.swarming | biofilm | social evolution | kin recognition | antagonism

Multifaceted Interfaces of Bacterial Competition

“…Thus, entry into the swarm promotes competitive fitness of bacteria by excluding unrelated cells and by enhancing defense against antibiotics. Similar boundary formation has also been reported for M. xanthus (121) and B. subtilis (122). The observation of discrimination in B. subtilis demonstrates that CDI and T6SS are not the only mechanisms that bacteria use for kin discrimination, as B. subtilis does not produce CDI or T6SS.…”

Facultative cheating supports the coexistence of diverse quorum-sensing alleles

“…39-41). Notably, it has been suggested that variability in several bacterial traits, such as the production of bacteriocins (42), contact-dependent inhibition toxins (43), or colony segregation (44,45), is maintained through kin-recognition mechanisms. Typically, kin-recognition tags are considered to direct cooperative behavior only among organisms with the same tag or to direct aggressive behavior only toward organisms with a different tag.…”

Microscale kin discrimination in a famous soil bacterium

“…In total, 12 recognition groups were found, suggesting that unrelated clones were unlikely to share the recognition type by chance. Moreover, discrimination was shown to prevent cellular movement between neighboring swarms on an agar substrate (6). The data also showed that most clones found Slovenia.…”

“…Using an approach to studying microbial social evolution that stays faithful to the natural context, Stefanic et al (6) examine the kin discrimination ability of 39 B. subtilis clones found as spores in two small soil samples (Fig. 1).…”