Sponge microbiome stability during environmental acquisition of highly specific photosymbionts.

In this study, we used in situ transplantations to provide the first evidence of horizontal acquisition of cyanobacterial symbionts by a marine sponge. The acquisition of the symbionts by the host sponge Petrosia ficiformis, which was observed in distinct visible patches, appeared several months after transplantation and at different times on different sponge specimens. We further used 16S rRNA gene amplicon sequencing of genomic DNA (gDNA) and complementary DNA (cDNA) and metatranscriptomics to investigate how the acquisition of the symbiotic cyanobacterium Candidatus Synechococcus feldmannii perturbed the diverse microbiota associated with the host P. ficiformis. To our surprise, the microbiota remained relatively stable during cyanobacterial symbiont acquisition at both structural (gDNA content) and activity (cDNA expression) levels. At the transcriptomic level, photosynthesis was the primary function gained following the acquisition of cyanobacteria. Genes involved in carotene production and oxidative stress tolerance were among those highly expressed by Ca. S. feldmannii, suggesting that this symbiont may protect itself and its host from damaging light radiation.

Identification of Quorum Sensing Activators and Inhibitors in The Marine Sponge Sarcotragus spinosulus.

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.

A New N-Acyl Homoserine Lactone Synthase in an Uncultured Symbiont of the Red Sea Sponge Theonella swinhoei.

Sponges harbor a remarkable diversity of microbial symbionts in which signal molecules can accumulate and enable cell-cell communication, such as quorum sensing (QS). Bacteria capable of QS were isolated from marine sponges; however, an extremely small fraction of the sponge microbiome is amenable to cultivation. We took advantage of community genome assembly and binning to investigate the uncultured majority of sponge symbionts. We identified a complete N-acyl-homoserine lactone (AHL)-QS system (designated TswIR) and seven partial luxI homologues in the microbiome of Theonella swinhoei. The TswIR system was novel and shown to be associated with an alphaproteobacterium of the order Rhodobacterales, here termed Rhodobacterales bacterium TS309. The tswI gene, when expressed in Escherichia coli, produced three AHLs, two of which were also identified in a T. swinhoei sponge extract. The taxonomic affiliation of the 16S rRNA of Rhodobacterales bacterium TS309 to a sponge-coral specific clade, its enrichment in sponge versus seawater and marine sediment samples, and the presence of sponge-specific features, such as ankyrin-like domains and tetratricopeptide repeats, indicate a likely symbiotic nature of this bacterium.

Identification and chemical characterization of N-acyl-homoserine lactone quorum sensing signals across sponge species and time.

Marine sponges form symbiotic relationships with complex microbial communities, yet little is known about the mechanisms by which these microbes regulate their behavior through gene expression. Many bacterial communities regulate gene expression using chemical signaling termed quorum sensing. While a few previous studies have shown presence of N-acyl-homoserine lactone (AHL)-based quorum sensing in marine sponges, the chemical identity of AHL signals has been published for only two sponge species. In this study, we screened for AHLs in extracts from 15 sponge species (109 specimens in total) from the Mediterranean and Red Sea, using a wide-range AHL biosensor. This is the first time that AHL presence was examined over time in sponges. We detected the presence of AHL in 46% of the sponge species and found that AHL signals differ for certain sponge species in time and across sponge individuals. Furthermore, for the Mediterranean sponge species Sarcotragus fasciculatus, we identified 14 different AHLs. The constant presence of specific AHL molecules in all specimens, together with varying signaling molecules between the different specimens, makes Sa. fasciculatus a good model to further investigate the function of quorum sensing in sponge-associated bacteria. This study extends the knowledge of AHL-based quorum sensing in marine sponges.