THE ENDOGENEITY OF THE STEADY-STATE GROWTH RATE

This study aims to estimate the steady-state growth rate or the natural growth rate and to determine whether the steady-state growth rate is endogenous to demand conditions or not. In order to achieve these aims, this study makes an econometric analysis using ordinary least squares method based on the data of Turkey covering the period 1969-2006. The present study estimates the natural growth rate and analyzes whether the natural growth rate is endogenous or not. But, different from the previous studies, the present study makes estimations in the conditions that capital-output ratio remains constant. According to the results of the study, the steady-state or natural growth rate is 5.71% in Turkey for the period 1969-2006. Moreover, the natural growth rate becomes 9.51% in the boom periods. This result shows that the steady-state or natural growth rate is endogenous to demand conditions in Turkey. Thus, the present study provides evidence for the Thirlwall’s (1969) theory in a different manner. Keywords: Natural growth rate, endogeneity, steady-state, capital-output ratio, economic history of Turkey

Pleiotropic mutations can rapidly evolve to directly benefit self and cooperative partner despite unfavorable conditions

Cooperation, paying a cost to benefit others, is widespread. Cooperation can be promoted by pleiotropic 'win-win' mutations which directly benefit self ('self-serving') and partner ('partner-serving'). Previously, we showed that partner-serving should be defined as increased benefit supply rate per intake benefit (Hart & Pineda et al., 2019). Here, we report that win-win mutations can rapidly evolve even under conditions unfavorable for cooperation. Specifically, in a well-mixed environment we evolved engineered yeast cooperative communities where two strains exchanged costly metabolites lysine and hypoxanthine. Among cells that consumed lysine and released hypoxanthine, ecm21 mutations repeatedly arose. ecm21 is self-serving, improving self's growth rate in limiting lysine. ecm21 is also partner-serving, increasing hypoxanthine release rate per lysine consumption and the steady state growth rate of partner. ecm21 also arose in monocultures evolving in lysine-limited chemostats. Thus, even without any history of cooperation or pressure to maintain cooperation, pleiotropic win-win mutations may readily evolve.

EFFECTS OF R&D SUBSIDIES IN A HYBRID MODEL OF ENDOGENOUS GROWTH AND SEMI-ENDOGENOUS GROWTH

We explore R&D subsidies in a hybrid growth model which may exhibit semi-endogenous growth or fully endogenous growth. We consider two types of subsidies on variety-expanding innovation and quality-improving innovation. R&D subsidies on quality-improving innovation only have effects in the fully endogenous-growth regime, in which more subsidies cause an earlier activation of quality-improving innovation and increase the transitional/steady-state growth rate. R&D subsidies on variety-expanding innovation have contrasting effects in the two regimes. In the semi-endogenous-growth regime, more subsidies on variety-expanding innovation increase transitional growth but have no effect on steady-state growth. In the fully endogenous-growth regime, more subsidies on variety-expanding innovation continue to increase short-run growth but delay the activation of quality-improving innovation and reduce long-run growth. Increasing subsidies on variety-expanding (quality-improving) innovation makes the semi-endogenous-growth (fully endogenous-growth) regime more likely to emerge. Finally, we calibrate the model and find that under reasonable parameter values, the fully endogenous-growth regime is more likely to emerge.

Posttranslational Control of PlsB Is Sufficient To Coordinate Membrane Synthesis with Growth in Escherichia coli

ABSTRACT Every cell must produce enough membrane to contain itself. However, the mechanisms by which the rate of membrane synthesis is coupled with the rate of cell growth remain unresolved. By comparing substrate and enzyme concentrations of the fatty acid and phospholipid synthesis pathways of Escherichia coli across a 3-fold range of carbon-limited growth rates, we show that the rate of membrane phospholipid synthesis during steady-state growth is determined principally through allosteric control of a single enzyme, PlsB. Due to feedback regulation of the fatty acid pathway, PlsB activity also indirectly controls synthesis of lipopolysaccharide, a major component of the outer membrane synthesized from a fatty acid synthesis intermediate. Surprisingly, concentrations of the enzyme that catalyzes the committed step of lipopolysaccharide synthesis (LpxC) do not differ across steady-state growth conditions, suggesting that steady-state lipopolysaccharide synthesis is modulated primarily via indirect control by PlsB. In contrast to steady-state regulation, we found that responses to environmental perturbations are triggered directly via changes in acetyl coenzyme A (acetyl-CoA) concentrations, which enable rapid adaptation. Adaptations are further modulated by ppGpp, which regulates PlsB activity during slow growth and growth arrest. The strong reliance of the membrane synthesis pathway upon posttranslational regulation ensures both the reliability and the responsiveness of membrane synthesis. IMPORTANCE How do bacterial cells grow without breaking their membranes? Although the biochemistry of fatty acid and membrane synthesis is well known, how membrane synthesis is balanced with growth and metabolism has remained unclear. This is partly due to the many control points that have been discovered within the membrane synthesis pathways. By precisely establishing the contributions of individual pathway enzymes, our results simplify the model of membrane biogenesis in the model bacterial species Escherichia coli. Specifically, we found that allosteric control of a single enzyme, PlsB, is sufficient to balance growth with membrane synthesis and to ensure that growing E. coli cells produce sufficient membrane. Identifying the signals that activate and deactivate PlsB will resolve the issue of how membrane synthesis is synchronized with growth.

Pleiotropic win-win mutations can rapidly evolve in a nascent cooperative community despite unfavorable conditions

Cooperation, paying a cost to benefit other individuals, is widespread. Cooperation can be promoted by pleiotropic “win-win” mutations which directly benefit self and partner. Previously, we showed that “partner-serving” should be defined as increased benefit supply rate per intake benefit (Hart & Pineda et al., 2019). Here, we report that “win-win” mutations can rapidly evolve even in nascent cooperation under conditions unfavorable for cooperation. Specifically, in a well-mixed environment we evolved engineered yeast cooperative communities where two strains exchanged costly metabolites lysine and hypoxanthine. Among cells that consumed lysine and released hypoxanthine, ecm21 mutations repeatedly arose. ecm21 is “self-serving”, improving self’s growth rate in limiting lysine. ecm21 is also “partner-serving”, increasing hypoxanthine release rate per lysine consumption and the steady state growth rate of partner. ecm21 also arose in monocultures evolving in lysine-limited chemostats. Thus, even without any pressure to maintain cooperation, pleiotropic win-win mutations may readily evolve.