Heinemann, M. | bioRxiv Science

bioRxiv2018

Saccharomyces cerevisiae goes through distinct metabolic phases during its replicative lifespan

A comprehensive description of the phenotypic changes during cellular aging is key towards unraveling its causal forces. Using recently developed experimental tools, which previously had enabled us to map age related changes in proteome and transcriptome (Janssens et al., 2015), and model-based inference methods, here, we generated a comprehensive account of the metabolic changes during the entire replicative life of Saecharomyces cerevisiae. With age, we found decreasing metabolite levels, decreasing growth and substrate uptake rates accompanied by a switch from aerobic fermentation to a respiratory metabolism, with increased glycerol and acetate production. The identification of intracellular metabolic fluxes revealed an increase in redox cofactor turnover, likely to combat the increased production of reactive oxygen species. The identified metabolic changes possibly reflect a dynamic adaptation to the age-associated, non- homeostatic increase in volume. With metabolism being an important factor of the cellular phenotype, this work complements our recent mapping of the transcriptomic and proteomic changes towards a holistic description of the cellular processes during aging.

cell biology↗

bioRxiv2017

The Escherichia coli CpxAR system does not sense surface contact

For proper biofilm formation, bacteria must have mechanisms in place to sense adhesion to surfaces. In Escherichia coli, the CpxAR and RcsCDB systems have been reported to sense surfaces. The CpxAR system is widely considered to be responsible for sensing attachment, to specifically hydrophobic surfaces. Here, using both single-cell and population-level analyses, we confirm RcsCDB activation upon surface contact, but find that the CpxAR system is not activated, in contrast to what had earlier been reported. Thus, the role of CpxAR in surface sensing and initiation of biofilm formation needs to be reconsidered.\n\nSignificance statementE. coli is capable of forming medically problematic biofilms, which are surface-associated microbial communities, protected by an exopolymeric matrix and with increased antibiotic tolerance. How these bacteria sense physical contact with a surface, which may lead to initiation of the biofilm formation process, is largely elusive. The signal transduction systems CpxAR and RcsCDB have previously been found to activate upon surface contact. Here, we confirm that RcsCDB is a surface sensing system, immediately responding to attachment. In contrast, using two different experimental approaches, we found that the CpxAR system does not perceive surface contact. Thus, contrary to the current view, the CpxAR system does not play a signaling role in the first step of biofilm initiation.

microbiology↗