Journal
GEOBIOLOGY
Volume 20, Issue 4, Pages 546-559Publisher
WILEY
DOI: 10.1111/gbi.12489
Keywords
16S rRNA gene amplicon sequencing; bacterial biodiversity; cyanobacteria; microbial mats; microbialites; saline and hypersaline lakes
Funding
- Australian Research Council [DP1093106, FF0883440]
- University International Postgraduate Award from UNSW
- Australian Research Council [FF0883440, DP1093106] Funding Source: Australian Research Council
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This study investigates the bacterial communities in microbialite-forming mats in five South Australian lakes, revealing the important role of Cyanobacteria in carbonate precipitation. Although the mat communities differ across lakes, the metabolic pathways involved in carbonate precipitation are highly conserved. Additionally, stress response, quorum sensing, and circadian clock pathways are predicted to play important roles.
Microbialites are sedimentary rocks created in association with benthic microorganisms. While they harbour complex microbial communities, Cyanobacteria perform critical roles in sediment stabilisation and accretion. Microbialites have been described from permanent and ephemeral saline lakes in South Australia; however, the microbial communities that generate and inhabit these biogeological structures have not been studied in detail. To address this knowledge gap, we investigated the composition, diversity and metabolic potential of bacterial communities from different microbialite-forming mats and surrounding sediments in five South Australian saline coastal lakes using 16S rRNA gene sequencing and predictive metagenome analyses. While Proteobacteria and Bacteroidetes were the dominant phyla recovered from the mats and sediments, Cyanobacteria were significantly more abundant in the mat samples. Interestingly, at lower taxonomic levels, the mat communities were vastly different across the five lakes. Comparative analysis of putative mat and sediment metagenomes via PICRUSt2 revealed important metabolic pathways driving the process of carbonate precipitation, including cyanobacterial oxygenic photosynthesis, ureolysis and nitrogen fixation. These pathways were highly conserved across the five examined lakes, although they appeared to be performed by distinct groups of bacterial taxa found in each lake. Stress response, quorum sensing and circadian clock were other important pathways predicted by the in silico metagenome analysis. The enrichment of CRISPR/Cas and phage shock associated genes in these cyanobacteria-rich communities suggests that they may be under selective pressure from viral infection. Together, these results highlight that a very stable ecosystem function is maintained by distinctly different communities in microbialite-forming mats in the five South Australian lakes and reinforce the concept that 'who' is in the community is not as critical as their net metabolic capacity.
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