Co-aggregation properties of trimeric autotransporter adhesins

ABSTRACT

Trimeric autotransporter adhesins (TAAs) comprise a group of virulence-related proteins in Gram-negative bacteria. Members of this family bind to extracellular matrix components such as collagen and fibronectin, but in addition they exhibit several other functions, such as conferring serum resistance and autoggragation. Autoaggregation promoted by TAAs is homotypic and mediated by the sticky, globular head domains of these lollipop-like molecules. However, whether TAAs mediate heterotypic interactions (i.e. co-aggregation) has not been studied. To address this question, we investigated the co-aggregation of two model TAA groups: YadA from the enteropathogenic Yersiniaeand the immunoglobulin-binding Eib proteins from Escherichia coli. To study TAA co-aggregation, we co-expressed a fluorescent label together with a particular TAA and followed the aggregative interactions using fluorescence microscopy and quantified the interactions using a novel script implemented in Fiji. Our results show that there is co-aggregation between some populations expressing different TAAs, which can be explained by relatively high sequence similarity between the interacting TAAs. Generally, the level of co-aggregation correlated with the sequence similarity. However, some TAAs did not interact despite high sequence similarity, showing exclusion of bacteria producing a non-compatible TAA. These data demonstrate that TAAs can mediate bacterial co-aggregation, but in some cases prevent co-aggregation of bacteria with disparate TAAs. Our results have implications for the ecology of TAA-producing bacteria, where co-aggregation may promote co-operation whereas exclusion might be an indication of competition.

The plugin used for quantifying interaction parameters of two co-aggregating populations is Clustering_v3.10.ijm.groovy.