Efeito da qualidade e complexidade da matéria orgânica dissolvida de origem fitoplanctônica na diversidade e atividade de comunidades bacterianas

Abstract

Bacteria are the world’s most abundant organisms and the foremost drivers of carbon and nutrient cycles in aquatic environments. Changes in the metabolic activity and composition of heterotrophic bacterial communities in response to interactions with dissolved organic matter (DOM) can potentially alter global biogeochemical cycles. In a context of global environmental changes, effects of the quantity and quality of DOM on the composition and activity of bacterial communities were investigated in experimental microcosms. Although such experiments allow a less descriptive analysis of these communities, they have limitations. Initial experimental communities need to be the same, limiting the number of manipulations that can be performed. Furthermore, microcosm cultivation usually results in drastic compositional changes in the communities. Thus, we also evaluated a cryopreservation method for whole natural communities which allows experiments with a unique initial community to be performed separately, as well as the effects of varying DOMs to keep the diversity of the cryopreserved communities. The results showed that both DOM quantity and quality were related to changes in the communities, with quality exerting an early response effect driven by competition and the intensity and duration of the effect modulated by quantity. Moreover, diversity and community composition of the bacterial communities were generally maintained after cryopreservation, although part of the diversity was lost, something more evident for communities from more stable and oligotrophic environments. In a global warming context, increase in the temperature oceans and freshwater bodies are expected, which could cause changes in the quantity and quality of the available DOM within these environments. This outcome could alter composition and metabolism of heterotrophic bacterial communities, causing not fully understood impacts on the carbon and nutrients global cycles.