Bacterial and fungal diversity and interactions in Rio Amarillo, a natural acidic river in the Famatina hill, La Rioja, Argentina

BERNARDELLI C.; COLMAN D.; DONATI E.R.; URBIETA M.S.

Quilmes

Congreso; III Congreso ISME Lat 2023; 2023

Universidad Nacional de Quilmes

The Rio Amarillo runs for 35 Km along the eastern slope of the Famatina hill (La Rioja, Argentina). It is naturally acidic (pH≈3 in all its course) and naturally concentrated in heavy metals, especially Fe, and metalloids due to the geology of the area dominated by sulphur minerals. The river gets its name from the highly abundant iron ochre-yellow deposits that cover its margins. The landscape of the river is completed by terraced deposits called Cueva de Perez formation, that could be considered as fossil analogues of the basin of the river.The original models that explained the yellow precipitates were purely geochemical; however in recent work based on cultivation we unveiled the role of a variety of iron-oxidising bacteria, such as Acidithiobacillus ferridurans, Leptospirillum ferrooxidans, Ferrimicrobium acidophilum, Alicyclobacillus, that catalysed the otherwise very slow Fe(II) oxidation to Fe(III) at the river´s temperature and pH. In this work we present a complete assessment of the bacterial and fungal microbial diversity of the Rio Amarillo and its terraces using high throughput sequencing (16S rRNA V3-V4 region and ITS1 region, respectively). The river was sampled at three points (water and sediments); one near the origin and two others downstream, after receiving neutral tributary courses. The terraces were sampled also at three points (solid material) near the origin of the river at different heights. The interactions in the community were evaluated in a network analysis of the two domains. Bacteria and Fungi were highly diverse in all samples. In the bacteria domain the most abundant species were associated with Acidimicrobiia, a class commonly found in natural acidic environments but with very few isolated or sequenced species, which made Rio Amarillo an extraordinary niche for their study. Regarding fungi, the river was vastly dominated by different species of the order Heliotales, mainly Acidea, a hyaline, acidophilic fungi reported in other acidic environments. The network analysis shows a highly connected community, with much of the species with many neighbours and others that connect different clusters. The iron oxidising bacteria presented surprisingly low abundance; however, they seem to be important players in the community structure as they are in a very well-connected separated cluster together with many Acidimicrobiia, Acidea and the most abundant fungal species.