Diazotrophic community structure along the Brazilian coast and adjacent oceanic area

Abstract

Nitrogen is essential to life, accounting for up to 10% of the dry weight of the microbial cells in the oceans. Trichodesmium are widely recognized as one of the most important nitrogen fixers in the oceans. Cyanobacteria may affect the coupling of the carbon-nitrogen-phosphorus cycles, contributing significantly to the atmospheric carbon dioxide sink, through the biologically mediated export of particulate organic matter from the ocean surface. The lack of information about the importance of Trichodesmium colonies in the Brazilian coast represents a considerable loss of an accurate picture on the flow of nutrients like nitrogen and carbon in our coast.This research aims to: a) evaluate temporal and spatial rates of nitrogen fixation of Trichodesmium, as well as the carbon flux associated, covering two transects (southeast and northeast) in the Brazilian continental shelf and adjacent oceanic zone; b) identify environmental factors that could cause changes in the rates of incorporation of carbon and nitrogen fixation presented by Trichodesmium, and c) elaborate algorithms correlating data on remote sensing of Trichodesmium blooms and rates of carbon and nitrogen fixation in the water column. Transects will be sampled in the NE and SE Brazil, as well as in their adjacent ocean areas. The samplings will be carried aboard the N. Oc. Alpha Crucis. Cyanobacteria of the genus Trichodesmium will be collected. Environmental analyzes (Primary Productivity, Dissolved Organic Carbon, Total Organic Carbon, Total Suspended Solids, Total Nitrogen, Total Phosphorus, Dissolved organic matter, chlorophyll a, among others), will be collected simultaneously. After collection and in situ analysis, the organisms will be transported to experimental boxes, where the rates of incorporation of carbon and nitrogen fixation will be monitored, with variable parameters such as different concentrations of iron, phosphorous, as well as varying degrees of pH. Similarly, the organisms cultivated in the experimental boxes will be monitored for the expression of nitrogenase (nifH).The data regarding the density of Trichodesmium will be correlated with the environmental analysis carried out in situ in order to find significant differences between sampled areas. All the data obtained in situ will be assessed through multiple linear regression and Principal Component Analysis (PCA), with the aim of identifying the major sources of variability in bacterial communities in relation to environmental parameters. The rates of incorporation of carbon and nitrogen fixation obtained through the experimental boxes will be evaluated due to the different treatments using simple linear regression. Thus, algorithms can be traced for correlation of data on the presence and extent of blooms of Trichodesmium obtained through remote sensing and the importance of these for the carbon and nitrogen flows in the water column.The data obtained through molecular biology, will be compared to results obtained by the experimental approach, in order to find correlations between the expression of nitrogenase and the real nitrogen fixation observed.