What is cyanobacterial mats

However, in mature mats net growth of cyanobaceria appears to be of minor importance. Most of the organic matter produced from photosynthetic CO 2 fixation is liberated in the sediment by oneof the following: fermentation, photorespiration, pouring out of solutes or secretion of mucus.

This organic matter is degraded by chemotrophic microorganisms, among which sulfate-reducing bacteria are particularly important. The combined activities of the cyanobacteria and sulfate-reducing bacteria result in steep and fluctuating gradients of sulfide and oxygen. Cyanobacteria may thus have to cope with high concentrationsof sulfide and oxygen but also with anoxic conditions.

The physicochemicalgradients force different functional groups of microorganisms to particular vertical stratified positions in the mat. This, and the fact that accretion of sediment fluctuates, gives rise to one of the most conspicuous properties of microbial mats,namely their laminated structure.

Modern microbial mats have this laminated structure in common with Precambrian stromatolites. However, the great majority of modern mats do not lithify. Only a few examples of recent calcifying stromatolithic microbial matsare known. A hypothesis has been developed which conceives a role for extracellular polysaccharides in calcification.

These moleculesmayserve as inhibitors of calcification. Extracellular polysaccharides in cyanobacterial mats are probably produced as a result of unbalanced growth caused by nitrogen limitation. Although nitrogen fixation is an important process in many marine microbial mats, in only a few cases the specialized nitrogen-fixing hetero cystouscyanobacteria are present. Non-heterocystous diazotrophic cyanobacteria are less efficient in nitrogen fixation.

The possible reasons for the exclusion of heterocystous species in many mats are discussed. Unable to display preview. Download preview PDF. Skip to main content. This service is more advanced with JavaScript available.

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Keywords: cyanobacteria, microbial mats, hypersaline, diversity, morphological characterization, 16S rRNA gene, phylogeny, next-generation sequencing. Introduction Photosynthetic microbial mats are complex, micro-scale ecosystems that can be found globally in a wide range of environments and are a major driving force in the formation of some modern microbialites, i. Open in a separate window. Figure 1. Field sampling, sample processing, and study design Mat samples from each site were collected from an area of 1 m 2 Supplementary Image S1D , in February during the rainy season Supplementary Images S1D—F.

Within parentheses are average values for the 13 months prior to sampling. Figure 2. Schematic overview of the experimental design. See text for methodological details. Isolation, culturing, and morphological-based characterization of cyanobacteria For the isolation of cyanobacteria, subsamples were subjected to liquid culture enrichment, streaking in agar plates or micromanipulation Rippka, ; Waterbury, ; see also Brito et al.

Survey of cyanobacterial taxa from previous publications A primary literature search was performed to assess the cyanobacterial species richness previously recorded in the Araruama's complex. Denaturing gradient gel electrophoresis, and cloning After gel visualization, PCR products from the same mat sample were pooled. Sanger sequencing Purified plasmids and PCR products obtained from isolates purified with the same spin columns mentioned above were sent for sequencing at Macrogen Amsterdam, Netherlands.

Table 2 Number of cyanobacterial 16S rRNA gene sequences used in or discarded from phylogeny, by sample. Results Characterization of microbial mats Morphologically, the cyanobacterial mats found at the sampling sites belonged to the smooth EB1 or polygonal EB2 and EB3 types, while structurally they were layered Supplementary Table S1 and Supplementary Image S1.

Table 3 Species composition and morphological-based characterization of cyanobacteria observed in the upper layer of the microbial mats collected at Araruama EB1 , Pitanguinha EB2 , and Pernambuco EB3 lagoons. Black circles or squares denote first reported observations of a species for that water body. White circles or squares indicate that the species was also observed in previous studies see also the full checklist available in Supplementary Table S1. Squares mean that the taxon was found to dominate or was abundant in samples from this study.

Figure 3. Table 4 List of cyanobacterial strains isolated from hypersaline microbial mats collected at the Araruama lagoon system RJ, Brazil. Strain Order Sampling site Figure Leptolyngbya aff. Figure 4. Molecular and phylogenetic characterization The pyrosequencing generated 10, high quality reads in total, for the three mat samples. Figure 5. Figure 6. Table 5 Taxon richness comparison, by taxonomic order, of morphospecies and phylotypes identified in this study and morphospecies previously reported for lagoons from the Araruama's entire complex, as retrieved from the literature survey see Supplementary Table S1 for the full checklist.

Number of genera shown in parentheses. Some OTUs belonging to this lineage were previously detected by Clementino et al. Moreover, the genus Halothece may actually contain some species of Aphanothece order Synechococcales , including A. Discussion In this work, we have attempted to uncover the cyanobacterial diversity present in hypersaline mats from three lagoons of the Araruama system, while exploring the impact of different classification methods or procedures to evaluate such diversity.

Culture-dependent approach Five of the nine isolates corresponded to a single species, Geitlerinema cf. Comparison between molecular- and morphological-based approaches For the first time, a molecular study was performed in order to characterize and classify the cyanobacterial diversity present in microbial mats from the Araruama's lagoons. Classification and identification issues The assignment of taxa to sequences is often a challenge in molecular-based classification methods, chiefly in the analysis of metagenomic data directly retrieved from environmental samples Mobberley et al.

Conflict of interest statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Footnotes Funding.

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