engleski

Beneath the Oxia: Insight into the prokariotes of marine meromictic Rogoznica lake (Croatia) and their potential in elemental cycling

Earth's oxygen-depleted zones are expanding areas that are the site of, and are implicating in, changing biogechemical cycles. This fact broaden the importance of understanding the functioning, mirobiology and elemental cycling in hypoxic environments and the role of these environments into the future. Under these conditions, microbial populations are essential mediators of elemental cycling and energy transfer. In the present study, we explored active bacterial and archaeal community in the chemocline, monimolimnion and sediment of marine meromictic Rogoznica Lake (Croatia). A long-term (1996-2015) sampling campaign was undertaken to comprehenisvely characterise, and monitor, the biogeocehemistry of the lake. We also employed high-throughput 16S rRNA gene sequencing of cDNA along with quantitive PCR assays targeting phylogenetic markers to describe the ecophysiological interactions underpinning the biogeochemistry and elemental cycling of carbon, sulfur and nitrogen in the lake. The results revealed clear vertical stucture of microbial community with Gammaproteobacteria dominating the chemocline, Deltaproteobacteria dominating the monimolimnion and significantly higher archaeal abundance in the sediment. Futrhermore, in contrast to findings in similar environments, diversity in Rogoznica Lake was found to be very low in both, DNA and RNA gene pools. This is likely the result of development of highly specialized taxa under relatively conserved region from the chemocline beneath. Thus, a biogeochemical cycling of carbon, nitrogen and sulfur is distributed amog limited number of taxa. No evidences of potential nitrifiers and denitrifiers and a very weak potential for methane oxidation and anammox reaction was found in this sulfur-dominated environment. Long-term data showed that the temperature, ammonium and sulfide concentration in the lake are increasing. That can lead to further weakening of these metabolic pathways and extinction of some taxa which could have deletoriuos concenquences on functioning of the lake. Overall, this study identified threats to this vournable environment and offer a detailed insight into the microbial ecology of meromictic lake which can serve as a valuable proxies to study microbial ecology across a wide range of euxinc environments.

Prokaryotes, 16S rRNA, euxinia, MiSeq, Rogoznica Lake

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