First evidence of quorum sensing activity in bacteria associated with Antarctic sponges

Abstract

Porifera dominate vast areas of the Antarctic shelves and are successfully colonized by bacteria. Quorum sensing (QS) is a cell-to-cell communication system based on bacterial population density that, enabling the coordination of group-based behaviour, plays a critical role in the successful colonization of higher organisms, also driving the formation of biofilm for adhesion to surfaces. In this study, the production of N-Acyl homoserine lactones (AHLs), signal molecules involved in the QS mechanism, was examined for 211 Antarctic sponge-associated Gram-negative bacteria. AHL production was screened by using three different AHL biodetection systems, i.e. Agrobacterium tumefaciens pZLR4, Chromobacterium violaceum CV026 and Pseudomonas putida pKR-C12 with optimal sensitivity to moderate-chain (C8–C12), short-chain (C4–C8) and long-chain (≥ C14) AHLs, respectively. 57.8% of tested isolates activated at least one of the monitor systems used and belonged mainly to bacterial genera that are known to be involved in surface colonization by biofilm production. A thin-layer chromatographic assay based on the A. tumefaciens reporter system was utilized to determine the AHL profiles of five selected positive isolates. Visible spots on thin-layer chromatography (TLC) plates were produced by Roseobacter sp. TB60 and Psychrobacter sp. TB67 (both from the sponge, Anoxycalyx joubini). The former probably produced N-(3-oxohexanoyl)-L-homoserine lactone (similar to the standard 3-oxo-C6-HSL), whereas the isolate TB67 produced molecules that were similar to the standard N-butanoyl-homoserine lactone (C4-HSL). The obtained results demonstrated that AHL-based signalling may play a key role in sponge–bacteria interactions also in the Antarctic environment.