Cyanobacterial mats from hot springs produce antimicrobial compounds and quorum-sensing inhibitors under natural conditions

Abstract

Polar (water) and non-polar (ethyl acetate) extracts from the cyanobacterial layer (top 1-3 mm) of four hot spring microbial mats in the Sultanate of Oman were tested for their antibacterial, antidiatom and quorumsensing inhibitory activities under natural conditions. The chemical composition of the active extracts was analysed using gas chromatography-mass spectrometry (GC-MS). Cyanobacteria within these mats were identified by direct microscopy while the total bacterial community composition was compared using automated ribosomal intergenic spacer analysis (ARISA). Only the extracts from Bowshar and Nakhl mats showed antibacterial properties against Bacillus sp., Micrococcus luteus, Shigella sonnei, Salmonella enterica and Klebsiella pneumoniae. All tested extracts inhibited the growth of the benthic diatom Amphora coffeaeformis. Extracts from Bowshar, Rustaq and Nakhl inhibited quorum-sensing of the reporter strains Chromobacterium violaceum CV017 and Agrobacterium tumefaciens NTL4.The highest bioactivity was recorded for ethyl acetate extracts from Nakhl mats, which had the lowest number of operational taxonomic units (OTUs). Using GC-MS, 74 chemical compounds were obtained, however with different distribution among the four mat extracts (similarity<43%). Various cyanobacteria, belonging mainly to Chroococcus, Phormidium, Leptolyngbya, Spirulina and Lyngbya were detected in the different mats, and each mat had its unique bacterial community, as confirmed by ARISA profiles. We conclude that antimicrobial and quorum-sensing inhibitory compounds can be produced by hot spring mat microorganisms under natural conditions and the differences in these compounds could be attributed to the differences in the mats' bacterial composition as well as the physical-chemical conditions of the springs.

Phototrophic marine benthic microbiomes: the ecophysiology of these biological entities

“…Signalling may not always be required and cells in a colony or biofilm may organize themselves without it (Cho et al, 2007). The discovery of compounds that inhibited quorum sensing in extracts of cyanobacterial mats may even hint to a detrimental effect of signalling (Dobretsov et al, 2011;Abed et al, 2013).…”

Cave Cyanobacteria showing antibacterial activity

“…This widespread distribution reflects the tolerance of Cyanobacteria towards environmental stress due, inter alia, to a broad spectrum of specific properties in physiology (Uzair et al, 2012). Generally, microorganisms forming microbial mats in extreme environments have been recently identified as a good source of bioactive compounds for different biotechnological applications (Harvey, 2000;Dobretsov et al, 2011).…”

Anticancer compounds from cyanobacterium Lyngbya species: a review

“…This group has diverse forms, unicellular and branched/un-branched filaments/trichomes; sometimes the latter are with/ without heterocysts (Galhano et al 2011), and can survive throughout the biosphere, ranging from Antarctic ice fields to thermal springs. In addition, cyanobacteria possess unique secondary metabolites (Dobretsov et al 2011), and those of several bloomforming species growing in stagnant fresh waters are most often toxic to biota, helping domination on other cyanobacteria, algae and hydrophytes (Jaiswal et al 2005(Jaiswal et al , 2008Rodríguez-Meizoso et al 2008;Cheung et al 2013). Furthermore, cyanobacterial secondary metabolites of bloom-forming species in extracellular secretions eliminate zooplankton and aquatic fauna, during bloom formation.…”