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

CECILIA BERNARDELLI; DEBORAH COLMAN; EDGARDO DONATI; MARIA SOFIA URBIETA

Bernal

Congreso; ISME-LAT; 2023

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 heavymetals, especially Fe, and metalloids due to the geology of the area dominated by sulphurminerals. The river gets its name from the highly abundant iron ochre-yellow deposits that coverits margins. The landscape of the river is completed by terraced deposits called Cueva de Perezformation, 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 inrecent work based on cultivation we unveiled the role of a variety of iron-oxidising bacteria, suchas Acidithiobacillus ferridurans, Leptospirillum ferrooxidans, Ferrimicrobium acidophilum,Alicyclobacillus, that catalysed the otherwise very slow Fe(II) oxidation to Fe(III) at the river ́stemperature and pH.In this work we present a complete assessment of the bacterial and fungal microbial diversity ofthe Rio Amarillo and its terraces using high throughput sequencing (16S rRNA V3-V4 region andITS1 region, respectively). The river was sampled at three points (water and sediments); onenear the origin and two others downstream, after receiving neutral tributary courses. Theterraces were sampled also at three points (solid material) near the origin of the river at differentheights. The interactions in the community were evaluated in a network analysis of the twodomains.Bacteria and Fungi were highly diverse in all samples. In the bacteria domain the mostabundant species were associated with Acidimicrobiia, a class commonly found in natural acidicenvironments but with very few isolated or sequenced species, which made Rio Amarillo anextraordinary niche for their study. Regarding fungi, the river was vastly dominated by differentspecies of the order Heliotales, mainly Acidea, a hyaline, acidophilic fungi reported in otheracidic environments. The network analysis shows a highly connected community, with much ofthe species with many neighbours and others that connect different clusters. The iron oxidisingbacteria presented surprisingly low abundance; however, they seem to be important players inthe community structure as they are in a very well-connected separated cluster together withmany Acidimicrobiia, Acidea and the most abundant fungal species.