engleski

Environmental selection affecting cyanobacterial microbial mat diversity in the karst intermittent spring Krčić

Microbial mats represent vertically stratified benthic communities growing on solid substrate (Bolhuis et al., 2014), playing a pivotal role in biogeochemical processes and being crucial for ecosystem sustainability (van Gemerden, 1993). We conducted an on-site study on the microbial mats in the intermittent karst spring Krčić during different seasons of the 2014/2015. The Spring is characterized by oligotrophic conditions and water regime fluctuations. Extreme conditions include summer drought, strong rains during autumn and freezing ambient temperature during winter. This topic is gaining more attention with the rising number of intermittent rivers in response to climate change and land and water exploitation (Skoulikidis et al., 2017). By using two phylogenetic markers, 16S rRNA (targeting total Bacteria) and ITS region (targeting Cyanobacteria), we aimed to explore how environmental selection affects microbial mat community. Molecular analyses indicated that mat community is facing strong alternations in its structure and diversity relating to the extreme environmental conditions. This diverse community consisted of an array of functional bacterial groups (11 different phyla) with Cyanobacteria making community core (>50%), followed by Alphaproteobacteria. The most abundant cyanobacterial genera included Microcoleus, Phormidium and uncultured Antarctic cyanobacterium. During two time periods characterized by low temperatures (winter 2014) and drought (summer 2015), Cyanobacteria were diminished within community. Populations that survived extreme cold included Plactomycetes and candidate phylum TM6, found specifically in this sample. Members of the phyla Firmicutes were restricted to the drought period followed by Cytophagia-Fibrella, Polymorphobacter, Polaromonas and Massilia. Another type of disturbance was the high water inflow event, in which Cyanobacteria represented 90% of the total bacterial community. Sample from this period (autumn 2015) included desiccant-tolerant cyanobacteria Chroococcidiopsis, Calothrix and Pleurocapsa. Investigations on disturbances that may affect seasonal dynamics within microbial mat communities aim to recognize and predict potentially negative effects of these changes to the whole ecosystem.

cyanobacteria ; microbial mat ; NGS ; ITS ; intermittent spring

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