Glucose limitation inLactococcusshapes a single-peaked fitness landscape exposing membrane occupancy as a constraint

Abstract

36A central theme in biology is to understand the molecular basis of fitness: which strategies 37 succeed under which conditions; how are they mechanistically implemented; and which 38 constraints shape trade-offs between alternative strategies. We approached these questions

Proteome constraints reveal targets for improving microbial fitness in nutrient‐rich environments

“…Apparent catabolic and total carbon balances were between 89 and 100% (Dataset EV3). We also found increased mixed acid and decreased lactic acid fermentation for the CcpA mutant compared with wild type (Appendix Fig S6), in agreement with the published data (Price et al, 2019).…”

“…To further test the model, we conjectured that these sensitivities should also point toward targets of growth improvements that selection should favor. We took advantage of a previous study where a CcpA mutant of L. lactis was selected and shown to have higher fitness under glucose-limited chemostats (Price et al, 2019). Here, we cultivated wild type and the evolved mutant again in glucose-limited chemostats at D = 0.5/h, where the model predicted that glucose and arginine uptake were dominant at limiting growth rates, and collected proteomics and flux data.…”

“…For the simulations, we used previously experimentally determined constraints on the uptake of amino acids (Goel et al, 2015), and we predicted that these could be improved under glucose-limited chemostat conditions according to our simulations-with arginine as the prime target (Fig 2). We therefore compared wild-type L. lactis MG1363 with a mutant strain (designated 445C1) that was selected during long-term cultivation in glucose-limited chemostat conditions at D = 0.5/h and that harbors a point mutation in the global carbon catabolite repression regulator (CcpA) (Price et al, 2019). This CcpA mutant shows a twofold increase in mixed acid fermentation at the endpoint of the laboratory evolution experiment, while fermentation toward lactate is decreased (Price et al, 2019).…”

“…We therefore compared wild-type L. lactis MG1363 with a mutant strain (designated 445C1) that was selected during long-term cultivation in glucose-limited chemostat conditions at D = 0.5/h and that harbors a point mutation in the global carbon catabolite repression regulator (CcpA) (Price et al, 2019). This CcpA mutant shows a twofold increase in mixed acid fermentation at the endpoint of the laboratory evolution experiment, while fermentation toward lactate is decreased (Price et al, 2019). This change in metabolism is consistent with the prediction that the total proteome constraint is not yet active at 0.5/h: An active total proteome constraint would provide a driving force toward lactate formation as it has a higher protein efficiency than mixed acid fermentation (Fig 3B).…”

Systems Biology – A Guide for Understanding and Developing Improved Strains of Lactic Acid Bacteria

“…In contrast to traditional ALE with the serial-passage regime, the growth rate can be controlled by limiting specific nutrients in a chemostat ALE setup, which is used to mimic the slow growth and metabolic activity of LAB during cheese ripening (Van Mastrigt et al, 2018). Price et al (2017) performed a glucose-limited ALE for L. lactis in a chemostat setup to study the response to carbohydrate starvation. After a few generations of adaption, fast-growing L. lactis mutants emerged and finally dominated the population.…”