Description
The production of fermented food is an expanding industry and a better understanding of the microorganisms used as starters in the fermentation processes is required to improve the final quality of the fermented food and to reduce its spoilage. The lactic acid bacteria (LAB) are currently of general use for elaboration of fermented products. The main beneficial activity of these bacteria is the fermentation of sugars present in the substrates, producing lactic acid by homo- or hetero-fermentative pathways. Some of these LAB can also metabolise other substrates such as citrate. This compound is present in juices, milk and vegetables and can be added as preservative to the food. Moreover, some LAB like Lactococcus lactis biovar diacetylactis (L. diacetylactis) y Weisella paramesenteroides metabolise citrate producing aroma compounds, such as the diacetyl, which is used by the dairy industry to improve the organoleptic properties of cheese, butter and butter cheese.
Our group has previously shown that in L. diacetylactis the citrate transport system is activated at the transcriptional level as an adaptive response to the acidic stress. Currently, we are studying the correlation between the citrate metabolism and the acidic stress by transcriptional and proteomic analysis as well as observing the impact of these processes in the metabolic fluxes of this bacteria by nuclear magnetic resonance analysis in collaboration with the group of Prof. Helena Santos (Instituto de Tecnología Química y Biológica, Oeiras, Portugal). In parallel, we are using DNA-protein interactions and in vitro transcription analysis to study the Weisella paramesenteroides CitI transcriptional regulator, which controls the transport and conversion of citrate into pyruvate in collaboration with the group of Dr. Christian Magni (Instituto de Biología Celular y Molecualr de Rosario, Rosario, Argentina).
This line of research has the backing, since 2003, of the multinational projects funded by the European Union (QLKI-2002-02388 in which the CIB was the coordinator http://decarboxylate.cib.csic.es. and KBBE-CT-2007-211441 coordinated by Dr. Juke Lolkema, University of Groningen, The Netherland)
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