Abstract
Marine sponges, a well-documented prolific source of natural products, harbor highly diverse microbial communities. Their extracts were previously shown to contain quorum sensing (QS) signal molecules of the N-acyl homoserine lactone (AHL) type, known to orchestrate bacterial gene regulation. Some bacteria and eukaryotic organisms are known to produce molecules that can interfere with QS signaling, thus affecting microbial genetic regulation and function. In the present study, we established the production of both QS signal molecules as well as QS inhibitory (QSI) molecules in the sponge species Sarcotragus spinosulus. A total of eighteen saturated acyl chain AHLs were identified along with six unsaturated acyl chain AHLs. Bioassay-guided purification led to the isolation of two brominated metabolites with QSI activity. The structures of these compounds were elucidated by comparative spectral analysis of 1HNMR and HR-MS data and were identified as 3-bromo-4-methoxyphenethylamine (1) and 5,6-dibromo-N,N-dimethyltryptamine (2). The QSI activity of compounds 1 and 2 was evaluated using reporter gene assays for long- and short-chain AHL signals (Escherichia coli pSB1075 and E. coli pSB401, respectively). QSI activity was further confirmed by measuring dose-dependent inhibition of proteolytic activity and pyocyanin production in Pseudomonas aeruginosa PAO1. The obtained results show the coexistence of QS and QSI in S. spinosulus, a complex signal network that may mediate the orchestrated function of the microbiome within the sponge holobiont.
Highlights
Overuse of antibiotics is one of the factors involved in the emergence of drug-resistant pathogens.The discovery of alternative novel strategy to tackle these infections is required to solve this emergent problem
It has been theorized that, if the signal communication was blocked by different inhibitory mechanisms including enzymatic inactivation of the signal molecule [5,6], inhibition of signal biosynthesis [7], and inhibition of signal detection [8,9], bacteria would lose their ability to form organized community structures that confers antibiotic resistance [10]
We report data showing the presence of acyl homoserine lactone (AHL) as well as QS inhibitory (QSI) molecules in the sponge species Sarcotargus spinosulus; two brominated metabolites: 3-bromo-4-methoxyphenethylamine
Summary
Overuse of antibiotics is one of the factors involved in the emergence of drug-resistant pathogens. Sponges (phylum Porifera) are an important component of aquatic benthic communities Their arsenal of chemicals has been investigated in terms of chemical ecology (e.g., [11]), drug discovery [12], and for biotechnological purpose (e.g., [13]). Few studies have reported the presence of QSI compounds in the sponges and their isolates. The concept that such molecules could provide alternatives for antimicrobials [25,26,27,28,29] has been recently discussed.
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