Abstract
Abstract. Endolithic microbial communities are prominent features of intertidal marine habitats, where they colonize a variety of substrates, contributing to their erosion. Almost 2 centuries worth of naturalistic studies focused on a few true-boring (euendolithic) phototrophs, but substrate preference has received little attention. The Isla de Mona (Puerto Rico) intertidal zone offers a unique setting to investigate substrate specificity of endolithic communities since various phosphate rock, limestone and dolostone outcrops occur there. High-throughput 16S rDNA genetic sampling, enhanced by targeted cultivation, revealed that, while euendolithic cyanobacteria were dominant operational taxonomic units (OTUs), the communities were invariably of high diversity, well beyond that reported in traditional studies and implying an unexpected metabolic complexity potentially contributed by secondary colonizers. While the overall community composition did not show differences traceable to the nature of the mineral substrate, we detected specialization among particular euendolithic cyanobacterial clades towards the type of substrate they excavate but only at the OTU phylogenetic level, implying that close relatives have specialized recurrently into particular substrates. The cationic mineral component was determinant in this preference, suggesting the existence in nature of alternatives to the boring mechanism described in culture that is based exclusively on transcellular calcium transport.
Highlights
In shallow and intertidal marine habitats, endolithic microbes colonize a variety of carbonaceous and phosphatic substrates, such as bone, shell, coraline carbonate, ooliths, limestones, dolostone and phosphorite outcrops (Campbell, 1983)
During laboratory studies with the cultivated strain of Mastigocoleus testarum strain BC008, used as a model to understand the physiology of cyanobacterial boring (Garcia-Pichel et al, 2010; Guida and Garcia-Pichel, 2016; Ramírez-Reinat and Garcia-Pichel, 2012b), we found that, among the carbonates, this strain excavated most rapidly into various types of calcite and aragonite minerals (CaCO3)
When comparing operational taxonomic units (OTUs) detected in samples which were mineralogically dominated by Ca carbonates with those that were dolomitic in nature (CaMg carbonate, n = 14), we found 31 OTUs to be significantly enriched in Ca-carbonate substrates (p < 0.05; corresponding to log2 fold difference > |2.83|), while 22 preferred dolomite with p < 0.05, out of 1039 cyanobacterial OTUs considered
Summary
In shallow and intertidal marine habitats, endolithic microbes colonize a variety of carbonaceous and phosphatic substrates, such as bone, shell, coraline carbonate, ooliths, limestones, dolostone and phosphorite outcrops (Campbell, 1983). Some of these microbes take advantage of the natural pores or crevices in the solids, but some have the ability to actively bore their way into the substrate. Long-term rates of microborer-driven carbonate dissolution, the “bioerosion” process, range between 20 and 930 g CaCO3 m−2 d−1, of clear geologic significance (Grange et al, 2015; Peyrot-Clausade et al, 1995; Tudhope and Risk, 1985; Vogel et al, 2000) and may increase under future scenarios of increased atmospheric CO2 and ocean acidification (Tribollet et al, 2009)
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