Bacteria play an important role in nutrients uptake and remineralization and work as nutrient sources for other trophic levels. The strength of stoichiometric homeostasis for C, N, and P differs among major phylogenetic groups, furthermore they can change your stoichiometry in function of the environmental conditions (for example, nutrient limitation). These particularities can greatly affect local to global carbon balance estimates. However, bacterial biomass in aquatic systems is commonly estimated using fixed conversion factors from bacterial density or biomass into carbon. As a consequence, as these factors do not take into account the great environmental heterogeneity, the mass balances may be greatly biased. Considering that the elemental composition of bacterial biomass is poorly investigated in natural assemblages, during the first µSudaqua meeting, we proposed the group “Chemical composition of bacterial biomass in South America aquatic systems” to address: (I) How does the carbon composition in bacterial biomass varies in the aquatic ecosystems in South America? (II) How the environmental parameters (e.g. trophic state, latitudinal gradients) would affect the C, N and P composition and stoichiometry in bacterial biomass from South America aquatic bacterial communities? As a result, we elaborated a standardized and detailed protocol to be employed in several aquatic ecosystems across the continent in the next months and a table to be completed by the collaborating researchers. Each collaborator in this project will contribute with samples from at least 4 systems or 1 system in the seasonal approach with at least 4 samplings over time. For the next meeting, we plan to write one methodological paper that aims to reveal equations based on environmental parameters to achieve more adequate conversion factors to carbon into biomass to each ecosystem.