BACTERIAL COMMUNITIES IN ANDEAN-PATAGONIAN MOUNTAIN LAKES: FROM TAXONOMIC COMPOSITION TO COMMUNITY FUNCTION

BASTIDAS NAVARRO M.; BALSEIRO E.; MODENUTTI B.

Congreso; XVIII Congreso Argentino de Microbiología General, SAMIGE 2023; 2023

One of the most conspicuous environmental discontinuities in mountains is the abrupt transition that exists between the vegetation below and above the tree line. The presence of vegetation in the drainage area constitutes an important input of nutrients, and dissolved organic carbon (DOC) of terrestrial origin, thus, the location of the lakes with respect to the treeline can be critical in the development of their communities. In the North Patagonian Andes, (41°S), the treeline (~1650 m a.s.l.) is constituted by Nothofagus pumilio deciduous forest, with krummholz forms towards the upper limit. A large number of shallow lakes are located both below (subalpine lakes) and above this line (alpine lakes). Our main objective was to determine differences in the bacterial community composition and to analyze experimentally how different sources of DOC modify the rates of respiration and C-consumption of bacterial communities. Bacterial community composition was studied by Next Generation Sequencing of the V3-V4 region of 16S rRNA gene, with the Illumina Miseq platform. Our results indicated differences in the bacterial communities located in the altitudinal gradient, both in the taxonomic composition and in the processing of organic matter. We observed a nutrient gradient (C, N, and P), with a decrease in towards the highest altitudes, which is related to the differential presence of vegetation. Interestingly, community structure varied among lakes located above and below the tree line, and in the ecotonal zone. DOC concentration was one of the main structuring variables of the communities, and it was also related with Shannon diversity index. The high levels of light intensity recorded in alpine lakes favor bacterial groups with strategies to deal with these conditions or that take advantage of light as a resource, such as Actinobacteria of the hgcl clade, Sandarakinorhabdus, Rhodovarius, among others. Regarding the community metabolism, we observed that the input of leachates from senescent leaves of N. pumilio constitutes an important supply not only of C, but also of P, which accelerates the respiratory rates and C-consumption by the bacterial communities. Our investigations contribute to understand the response of the bacterial communities to future changes in DOC concentration caused by variation in treeline location. Likewise, we highlight the heterogeneity and uniqueness of the bacterial communities and the dominant taxa in mountain lakes, even those located very close to each other