Quorum sensing inhibitory compounds from extremophilic microorganisms isolated from a hypersaline cyanobacterial mat

TL;DR

This study isolated extremophilic microorganisms from hypersaline mats that produce compounds inhibiting quorum sensing and microbial growth, revealing potential for biotechnological applications such as antifouling agents.

Contribution

First identification of quorum sensing inhibitory compounds from extremophilic microbes in hypersaline environments, including novel diketopiperazines with anti-QS activity.

Findings

Isolated halophilic strains produce QS inhibitors.

Purified diketopiperazines inhibit QS in reporter assays.

Strains produce compounds active against pathogens and microalgae.

Abstract

In this study extremely halophilic and moderately thermophilic microorganisms from a hypersaline microbial mat were screened for their ability to produce antibacterial, antidiatom, antialgal and quorum sensing (QS) inhibitory compounds. Five bacterial strains belonging to the genera Marinobacter and Halomonas and one archaeal strain belonging to the genus Haloterrigena were isolated from a microbial mat. The strains were able to grow at a maximum salinity of 22-25% and a maximum temperature of 45-60{\deg}C. Hexanes, dichloromethane and butanol extracts from the strains inhibited the growth of at least one out of nine human pathogens. Only butanol extracts of supernatants of Halomonas sp. SK-1 inhibited growth of the microalga Dunaliella salina. Most extracts from isolates inhibited QS of the acyl homoserine lactone producer and reporter Chromobacterium violaceum CV017. Purification of QS inhibitory dichloromethane extracts of Marinobacter sp. SK-3 resulted in isolation of four related diketopiperazines (DKPs): cyclo(L-Pro-L-Phe), cyclo(L-Pro-L-Leu), cyclo(L-Pro-L-isoLeu) and cyclo(L-Pro-D-Phe). QS inhibitory properties of these DKPs were tested using C. violaceum CV017 and Escherichia coli-based QS reporters (pSB401 and pSB1075) deficient in AHL production. Cyclo(L-Pro-L-Phe) and cyclo(L-Pro-L-isoLeu) inhibited QS dependent production of violacein by C. violaceum CV017. Cyclo(L-Pro-L-Phe), cyclo(L-Pro-L-Leu), and cyclo(L-Pro-L-isoLeu) reduced QS dependent luminescence of the reporter E. coli pSB401 induced by 3-oxo-C6-HSL. Our study demonstrated the ability of halophilic and moderately thermophilic strains from a hypersaline microbial mat produce biotechnologically-relevant compounds that could be used as antifouling agents