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

GEREA, M.; SOTO CARDENAS, C; GARCIA, PE; QUIROGA, MV; QUEIMALIÑOS, C

Congreso; ISME Virtual Microbial Ecology Summit; 2020

In aquatic systems, dissolved organic matter (DOM) is the main carbon source for bacterioplankton. DOM qualityand concentration impact on the bacterial community structure. In this study weanalyzed the biolability of DOM in southern temperate lakes along a naturalgradient of dissolved organic carbon (DOC) concentration and quality, inrelation to bacterial community structure. The investigation included three oligotrophic lakes (two shallow lakesand the three thermal strata of one deep lake) during two contrasting seasonswhich present different allochthonous influence. We performed two series of biodegradationexperiments (dry and wet season) using lake water and their naturalbacterioplankton, estimating changes in DOM features through spectrophotometricand spectrofluorometric techniques, and the variation in the bacterialcommunity through flow cytometry. The percentage of biodegradable DOC (%BDOC) washigher during dry season in all lakes, mainly in the upper strata of the deeplake. Higher values of %BDOC were associated with DOM of low molecular size, loweraromaticity and lignin content. The DOM fluorescent components determinedthrough PARAFAC analysis were dominated by the microbial humic C1 (peaks A+M;>50% in all lakes), followed by the terrestrial humic C2 (peaks A+C), and thenon-humic C3 (peak T). The bacterial communities were always dominated by thelow nucleic acid (LNA)-content group. Nevertheless, an increase of the abundanceand percentage of high nucleic acid (HNA)-content bacteria was observed duringthe experiments in all lakes and seasons, which may indicate an association ofthis cytometric group with the biodegradation processes detected. The cytometricfingerprint of bacterioplankton showed a significant relationship with some DOMfeatures. We observed that DOC concentration, DOM molecular weight/size, aswell as C1:DOC and C3:DOC are key features/components shaping bacterioplanktoncommunity structure in these aquatic ecosystems.