title: Protein turnover forms one of the highest maintenance costs in Lactococcus lactis.
abstract: Protein turnover plays an important role in cell metabolism by regulating metabolic fluxes. Furthermore, the energy costs for protein turnover have been estimated to account for up to a third of the total energy production during cell replication and hence may represent a major limiting factor in achieving either higher biomass or production yields. This work aimed to measure the specific growth rate (μ)-dependent abundance and turnover rate of individual proteins, estimate the ATP cost for protein production and turnover, and compare this with the total energy balance and other maintenance costs. The lactic acid bacteria model organism Lactococcus lactis was used to measure protein turnover rates at μ = 0.1 and 0.5 h(-1) in chemostat experiments. Individual turnover rates were measured for ~75% of the total proteome. On average, protein turnover increased by sevenfold with a fivefold increase in growth rate, whilst biomass yield increased by 35%. The median turnover rates found were higher than the specific growth rate of the bacterium, which suggests relatively high energy consumption for protein turnover. We found that protein turnover costs alone account for 38 and 47% of the total energy produced at μ = 0.1 and 0.5 h(-1), respectively, and gene ontology groups Energy metabolism and Translation dominated synthesis costs at both growth rates studied. These results reflect the complexity of metabolic changes that occur in response to changes in environmental conditions, and signify the trade-off between biomass yield and the need to produce ATP for maintenance processes.
authors.affiliation: Competence Centre of Food and Fermentation Technologies, Akadeemia tee 15a, 12618 Tallinn, Estonia.|Department of Chemistry, Tallinn University of Technology, Akadeemia tee 15, 12618 Tallinn, Estonia.
authors.forename: Petri-Jaan
authors.initials: PJ
authors.lastname: Lahtvee
authors.affiliation: Competence Centre of Food and Fermentation Technologies, Akadeemia tee 15a, 12618 Tallinn, Estonia.
authors.forename: Andrus
authors.initials: A
authors.lastname: Seiman
authors.affiliation: Competence Centre of Food and Fermentation Technologies, Akadeemia tee 15a, 12618 Tallinn, Estonia.|Department of Food Processing, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.
authors.forename: Liisa
authors.initials: L
authors.lastname: Arike
authors.affiliation: Department of Food Processing, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia.|Competence Centre of Food and Fermentation Technologies, Akadeemia tee 15a, 12618 Tallinn, Estonia.|Department of Chemistry, Tallinn University of Technology, Akadeemia tee 15, 12618 Tallinn, Estonia.
authors.forename: Kaarel
authors.initials: K
authors.lastname: Adamberg
authors.affiliation: Competence Centre of Food and Fermentation Technologies, Akadeemia tee 15a, 12618 Tallinn, Estonia.|Department of Chemistry, Tallinn University of Technology, Akadeemia tee 15, 12618 Tallinn, Estonia.
authors.forename: Raivo
authors.initials: R
authors.lastname: Vilu
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D004777:Environment; D013294:Lactococcus lactis / Q000254:growth & development / Q000502:physiology*; D059748:Proteolysis; D020543:Proteome
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D020543:Proteome; D002244:Carbon; D000255:Adenosine Triphosphate