Lyngbyoic acid, a “tagged” fatty acid from a marine cyanobacterium, disrupts quorum sensing in Pseudomonas aeruginosa

Abstract

Quorum sensing (QS) is a mechanism of bacterial gene regulation in response to increases in population density. Perhaps most studied are QS pathways mediated by acylhomoserine lactones (AHLs) in Gram-negative bacteria. Production of small molecule QS signals, their accumulation within a diffusion-limited environment and their binding to a LuxR-type receptor trigger QS-controlled gene regulatory cascades. In Pseudomonas aeruginosa, for example, binding of AHLs to their cognate receptors (LasR, RhlR) controls production of virulence factors, pigments, antibiotics and other behaviors important for its interactions with eukaryotic hosts and other bacteria. We have previously shown that marine cyanobacteria produce QS-inhibitory molecules, including 8-epi-malyngamide C (1), malyngamide C (2) and malyngolide (3). Here we isolated a new small cyclopropane-containing fatty acid, lyngbyoic acid (4), as a major metabolite of the marine cyanobacterium, Lyngbya cf. majuscula, collected at various sites in Florida. We screened 4 against four reporters based on different AHL receptors (LuxR, AhyR, TraR and LasR) and found that 4 most strongly affected LasR. We also show that 4 reduces pyocyanin and elastase (LasB) both on the protein and transcript level in wild-type P. aeruginosa, and that 4 directly inhibits LasB enzymatic activity. Conversely, dodecanoic acid (9) increased pyocyanin and LasB, demonstrating that the fused cyclopropane “tag” is functionally relevant and potentially confers resistance to β-oxidation. Global transcriptional effects of 4 in some ways replicate the gene expression changes of P. aeruginosa during chronic lung infections of cystic fibrosis patients, with reduced lasR signaling, increased biofilm and expression of the virulence locus HSI-I. Compound 4 may therefore prove to be a useful tool in the study of P. aeruginosa adaption during such chronic infections.

Mini-review: Inhibition of biofouling by marine microorganisms

“…Cyanobacteria produce chemicals in order to facilitate aggregation to form biofilms and to compete with other organisms for space and nutrients. Therefore, marine cyanobacteria have been recognised as a rich source of secondary metabolites with AF properties (Burja et al 2001;Pulz & Gross 2004;Abed et al 2009;Dobretsov et al 2010;Kwan et al 2011). Although there are more than 300 nitrogencontaining secondary metabolites with different biological activities reported from marine cyanobacteria, only a few compounds are known for their AF properties (Tan & Goh 2009).…”

“…Such screens led to the identification of dozens of compounds with presumed QS-inhibitory activities. However, further work with 1 of the reporters (based on the lasRI QS system of P. aeruginosa) revealed that a number of small molecules produced by marine organisms can interfere with the activity of the reporter, although not only through interference with the receptor-AHL interactions Kwan et al 2011).…”

Multifaceted Interfaces of Bacterial Competition

“…For example, some marine bacteria produce SMs that interfere with quorum sensing and thus disrupt subsequent downstream processes reliant on communication between competitor cells (32,33). One challenge is to understand the fitness benefits of such modulatory activities in competitive interactions between bacteria.…”

Modular Strategies for Structure and Function Employed by Marine Cyanobacteria: Characterization and Synthesis of Pitinoic Acids

“…This was shown in several previous reports, [17][18][19][20] including by our group where we reported the anti-quorum sensing activity of lyngbyoic acid. 21 In Pseudomonas aeruginosa, quorum sensing (QS) system integrates two chemically distinct classes of signal molecules which act on differnet QS pathways, the Nacylhomoserine lactones which act on the LasR-LasI pathway, and the 4-quinolones which act on the Pseudomonas quinolone signaling pathway. 22,23 Lyngbyoic acid was found to inhibit QS through the LasR pathway, where the cyclopropyl ring appeared to be essential for this activity.…”

“…22,23 Lyngbyoic acid was found to inhibit QS through the LasR pathway, where the cyclopropyl ring appeared to be essential for this activity. 21 Based on structural similarity, 1 could also possess QS inhibitory activity similar to lyngbyoic acid, where the exo-methylene group might also be influential for this biological activity. Accordingly, we tested 1 for its ability to interfere with quorum sensing in P. aeruginosa by monitoring its effect on the transcription and the production of two virulence factors, the elastase LasB enzyme and the pigment pyocyanin.…”