Differential biolability of dissolved organic matter in southern temperate lakes in relation to bacterioplankton structure

GEREA M.; QUIROGA M.V.; GARCÍA, P.E.; SOTO CÁRDENAS, C.; QUEIMALIÑOS, C.

Congreso; ISME Virtual Microbial Ecology Summit; 2020

International Society for Microbial Ecology (ISME)

In aquatic systems, dissolved organic matter (DOM) is the main carbon source for bacterioplankton. DOM quality and concentration impact on the bacterial community structure. In this study we analyzed the biolability of DOM in southern temperate lakes along a natural gradient of dissolved organic carbon (DOC) concentration and quality, in relation to bacterial community structure. The investigation included three oligotrophic lakes (two shallow lakes and the three thermal strata of one deep lake) during two contrasting seasons which present different allochthonous influence. We performed two series of biodegradation experiments (dry and wet season) using lake water and their natural bacterioplankton, estimating changes in DOM features through spectrophotometric and spectrofluorometric techniques, and the variation in the bacterial community through flow cytometry. The percentage of biodegradable DOC (%BDOC) was higher during dry season in all lakes, mainly in the upper strata of the deep lake. Higher values of %BDOC were associated with DOM of low molecular size, lower aromaticity and lignin content. The DOM fluorescent components determined through PARAFAC analysis were dominated by the microbial humic C1 (peaks A+M), followed by the terrestrial humic C2 (peaks A+C), and the non-humic C3 (peak T). The bacterial communities were always dominated by the low nucleic acid (LNA)-content group. Nevertheless, an increase of the abundance and percentage of high nucleic acid (HNA)-content bacteria was observed during the experiments in all lakes and seasons, which may indicate an association of this cytometric group with the biodegradation processes detected. The cytometric fingerprint of bacterioplankton showed a significant relationship with some DOM features. We observed that DOC concentration, DOM molecular weight/size, as well as C1:DOC and C3:DOC are key features/components shaping bacterioplankton community structure in these aquatic ecosystems.