La vía del glioxilato como una estrategia metabólica de bacterias del tipo Pelagibacter en respuesta a la disponibilidad natural de hierro en el Océano Austral.

Abstract

The effect of iron on cell biology is important, in part because it is a cofactor of several metalloproteins involved in respiration, photosynthesis and nutrient assimilation. The absence of iron may therefore induce metabolic changes in organisms. The SAR11 clade is a marine heterotrophic bacterial group recognized as the most abundant and therefore a successful microorganism, inhabiting surface and deep waters worldwide. The tricarboxylic acid cycle (TCA) is a metabolic pathway in which the oxidation of organic molecules generates energy for the cell in autotrophic and heterotrophic organisms. Several enzymes involved in the TCA require metal cofactors for structural or catalytic roles. The glyoxylate shunt is a metabolic bypass of the TCA which allows cells to use simple carbon molecules as carbon source when complex sources are not available by by-passing the decarboxylation steps present in the TCA. SAR11 contains the genes involved in the glyoxylate shunt allowing them to use this metabolism under environmental stress. During this study, the response of natural assemblages of Pelagibacter-like bacteria to environmental iron availability was investigated. Samples were taken from a naturally iron fertilized area and an iron depleted area in the Southern Ocean during the KEOPS2 project. Up to a 16.5-fold up-regulation in the transcription of isocitrate lyase enzyme, a functional marker of the glyoxylate cycle, was found under iron depleted compared to iron enriched conditions. However, since iron fertilization in the Southern Ocean induces a phytoplankton bloom, it was not possible to determine if the low transcription levels of isocitrate lyase in iron enriched stations was caused by iron or labile dissolved organic matter availability in the environment or by both parameters simultaneously. The finding of this study suggests a metabolic strategy of Pelagibacter under adverse energetic conditions which contributes to understanding the success of SAR11 in marine environment. On the long term, a switch from the TCA to the glyoxylate cycle may impact the budget of carbon recycled by marine microbial communities. This emphasizes the relevance of future investigations in this research area.