Abstract

Seasonal upwelling in Concepción Bay supplies the surface water with large amounts of nutrients and creates low oxygen conditions. Reduced sulfur compounds from sediments are advected to the water column where they are oxidized in the oxycline. This suggests that the sulfide-oxidizing metabolism may be an important process present in this zone. The maximum level of chlorophyll is located several meters below the surface, indicating light penetration, which drives primary production at intermediate depths. Water samples were analyzed with flow cytometry in order to quantify and identify bacterioplankton populations. We found two bacterial populations at 5m depth, but only one at depths below. Additionally, we used CARD-FISH and PCR to study the presence of functional genes. Sulfide-oxidation could be identified by both techniques, with a higher relative abundance at the oxycline. This suggests the presence of bacteria capable of oxidizing reduced sulfur compounds with nitrate or nitrite as electron acceptors. The presence of protorhodopsin genes, which were identified by PCR, in the upper layers is suggesting that photoorganoheterotrophic bacteria able to use a light-driven energy conversion mechanisms are contributing to the productivity in these upwelling zones.