Abstract
Despite the discovery of the first N-acyl homoserine lactone (AHL) based quorum sensing (QS) in the marine environment, relatively little is known about the abundance, nature and diversity of AHL QS systems in this diverse ecosystem. Establishing the prevalence and diversity of AHL QS systems and how they may influence population dynamics within the marine ecosystem, may give a greater insight into the evolution of AHLs as signaling molecules in this important and largely unexplored niche. Microbiome profiling of Stelletta normani and BD1268 sponge samples identified several potential QS active genera. Subsequent biosensor-based screening of a library of 650 marine sponge bacterial isolates identified 10 isolates that could activate at least one of three AHL biosensor strains. Each was further validated and profiled by Ultra-High Performance Liquid Chromatography Mass Spectrometry, with AHLs being detected in 8 out of 10 isolate extracts. Co-culture of QS active isolates with S. normani marine sponge samples led to the isolation of genera such as Pseudomonas and Paenibacillus, both of which were low abundance in the S. normani microbiome. Surprisingly however, addition of AHLs to isolates harvested following co-culture did not measurably affect either growth or biofilm of these strains. Addition of supernatants from QS active strains did however impact significantly on biofilm formation of the marine Bacillus sp. CH8a sporeforming strain suggesting a role for QS systems in moderating the microbe-microbe interaction in marine sponges. Genome sequencing and phylogenetic analysis of a QS positive Psychrobacter isolate identified several QS associated systems, although no classical QS synthase gene was identified. The stark contrast between the biodiverse sponge microbiome and the relatively limited diversity that was observed on standard culture media, even in the presence of QS active compounds, serves to underscore the extent of diversity that remains to be brought into culture.
Highlights
The marine ecosystem is considered to be an underexplored resource for the study of bacterial interactions within eukaryotic hosts
The individual profiles remained relatively consistent from the perspective of the dominant phyla and families, there were differences in relative abundances between the microbiome profiles from the distinct sponge samples suggesting that heterogeneity of the population may exist within the sponge (Figure 2A)
Genera known to encode quorum sensing (QS) signaling systems (e.g., Pseudomonas, Halomonas, Psychrobacter) were present in the microbiomes of both sponges, it was interesting to note that they were low in abundance when compared to the principal colonizers of the sponges
Summary
The marine ecosystem is considered to be an underexplored resource for the study of bacterial interactions within eukaryotic hosts. Despite a number of well-studied examples of bacterial interactions within marine hosts such as the density dependent production of luminescence by Aliivibrio fischeri within the light organ of Euprymna scolopes, relatively little is known about the interactions that occur within marine microbial communities (Hmelo, 2017). This is true in the case of the ancient invertebrate, the marine sponge. Given the difficulties faced in bringing marine sponge biodiversity into culture, it is intriguing to speculate that these signals may play a role in moderating the dynamics of the microbial communities within which they operate
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