First description of the microbial diversity in the Amarillo River (La Rioja, Argentina); a natural extreme environment where the whole microbial community paints the landscape yellow

Abstract

Abstract Background. The Amarillo River is an acidic river located in the mining district of Famatina, La Rioja, Argentina, named after the vast yellow-ochreous iron precipitates deposited all through its course. Even though the area has been exploited for metals extraction, the waters of the river are naturally acidic due to environmental factors beyond mineralogy, where microbial species have a crucial role. Iron-oxidizing bacteria have been identified, however a comprehensive analysis of the entire microbial community in this extreme environment has not been conducted. In this work we explore, for the first time using high-throughput sequencing, the bacterial as well as the so long neglected fungal diversity in the Amarillo River and the Cueva de Pérez terraces, considered the prehistoric analogues of the current river basin. Furthermore, we attempt to untangle the ecological relations between bacteria and fungi using co-occurrence and network analysis. Fe(II)-enrichment cultures at different temperature and nutritional conditions, mimicking different environmental settings of the river, were also analysed to better understand the roles of prokaryotes and fungi in iron oxidation processes.Results. The findings highlight the presence of a diverse bacterial community in the river as well as the terraces, with a marked presence of uncultured Acidimicrobiia also found in other acidic environments and apparently part of a yet uncharacterised universal microbial acidic diversity. Acidophiles and iron-oxidising species, despite being in low abundances in the environmental samples, constitute the core of the microbial community, showing significant involvement in intraspecies interactions. Moreover, both environmental samples and enrichment cultures exhibit a wide diversity of fungi, highly connected with bacteria according to network analysis.Conclusions. Through the utilization of 16S-amplicon sequencing, Venn diagrams and co-occurrence networks, this work has shaded light into the intricate connections between bacterial and fungal communities of the Amarillo River. The occurrence of certain acidophiles within both the river and the ancient terraces indicates their enduring significance in the environment’s iron cycle as well as the flexibility of the system. These findings reinforce the importance of the microbial community as fundamental geological agents in the Amarillo River where their collaborative work in the precipitation of iron minerals paint the landscape yellow.