Slower Growth Recovery Research Articles

The nucleotide pGpp acts as a third alarmone in Bacillus, with functions distinct from those of (p)ppGpp

The alarmone nucleotides guanosine tetraphosphate and pentaphosphate, commonly referred to as (p)ppGpp, regulate bacterial responses to nutritional and other stresses. There is evidence for potential existence of a third alarmone, guanosine-5′-monophosphate-3′-diphosphate (pGpp), with less-clear functions. Here, we demonstrate the presence of pGpp in bacterial cells, and perform a comprehensive screening to identify proteins that interact respectively with pGpp, ppGpp and pppGpp in Bacillus species. Both ppGpp and pppGpp interact with proteins involved in inhibition of purine nucleotide biosynthesis and with GTPases that control ribosome assembly or activity. By contrast, pGpp interacts with purine biosynthesis proteins but not with the GTPases. In addition, we show that hydrolase NahA (also known as YvcI) efficiently produces pGpp by hydrolyzing (p)ppGpp, thus modulating alarmone composition and function. Deletion of nahA leads to reduction of pGpp levels, increased (p)ppGpp levels, slower growth recovery from nutrient downshift, and loss of competitive fitness. Our results support the existence and physiological relevance of pGpp as a third alarmone, with functions that can be distinct from those of (p)ppGpp.

Differences in Near Isohydric and Anisohydric Behavior of Contrasting Poplar Hybrids (I-101 (Populus alba L.) × 84K (Populus alba L. × Populus glandulosa Uyeki)) under Drought-Rehydration Treatments

Carbon starvation and hydraulic failure are considered important factors in determining the mechanisms associated with tree mortality. In this study, iso/anisohydric classification was used to assess drought resistance and mortality mechanisms in two contrasting poplar species, as it is generally believed that isohydric species are more susceptible to carbon starvation, while anisohydric species are more susceptible to hydraulic failure. However, these assumptions are rarely tested in poplar genotypes with contrasting growth strategies. Thus, we subjected potted poplar genotypes (I-101 (Populus alba L.) × 84K (Populus alba L. × Populus glandulosa Uyeki)) with fast and slow growth rates to drought–rehydration treatments. The slow-growing genotype maintained higher stomatal conductance and lower predawn leaf water potential than the fast-growing genotype, thus exhibiting a near-anisohydric stomatal behavior throughout the treatment period. The nonstructural carbohydrate (NSC) content indicated that the two genotypes had the same trend of carbon change (e.g., the NSC content in the leaves increased with drought and then decreased). However, when NSC content data were combined with the growth and photosynthetic data, it was observed that the slow-growing genotype mobilized carbon to maintain hydraulic safety, while the NSC content of the fast-growing genotype among tissues was static. The percent loss of hydraulic conductivity in the branches during treatments indicated that the fast-growing genotype could recover more quickly from xylem embolism than the slow-growing genotype. The slow-growing genotype with a slow growth recovery after rehydration showed a significant increase in carbon consumption, combined with a significant increase in the hydraulic safety threshold value, indicating that there may be drought tolerance. In comparison, the fast-growing genotype showed a faster hydraulic recovery ability that had no effect on the NSC content in the leaves and roots. Our findings demonstrate intraspecific isohydric behavior in poplar; however, the trade-off between carbon distribution and stomatal regulation should be considered separately within genotypes of the same species. In addition, NSC plays an important role in water–carbon balance in the drought–rehydration cycle.

Springing into Action: Reg2 Negatively Regulates Snf1 Protein Kinase and Facilitates Recovery from Prolonged Glucose Starvation in Saccharomyces cerevisiae.

Glucose is the preferred carbon source for the yeast Saccharomyces cerevisiae Glucose limitation activates Snf1 protein kinase, a key regulator of energy homeostasis that promotes utilization of alternative carbon sources and enforces energy conservation. Snf1 activation requires phosphorylation of its T-loop threonine (Thr210) by upstream kinases. When glucose is abundant, Snf1 is inhibited by Thr210 dephosphorylation. This involves the function of the type 1 protein phosphatase Glc7, which is targeted to Snf1 by a regulatory subunit, Reg1. The reg1 mutation causes increased Snf1 activity and mimics various aspects of glucose limitation, including slower growth. Reg2 is another Glc7 regulatory subunit encoded by a paralogous gene, REG2 Previous evidence indicated that the reg2 mutation exacerbates the Snf1-dependent slow-growth phenotype caused by reg1, suggesting a link between Reg2 and Snf1. Here, we explore this link in more detail and present evidence that Reg2 contributes to Snf1 Thr210 dephosphorylation. Consistent with this role, Reg2 interacts with wild-type Snf1 but not with nonphosphorylatable Snf1-T210A. Reg2 accumulation increases in a Snf1-dependent manner during prolonged glucose deprivation, and glucose-starved cells lacking Reg2 exhibit delayed Snf1 Thr210 dephosphorylation and slower growth recovery upon glucose replenishment. Accordingly, cells lacking Reg2 are outcompeted by wild-type cells in the course of several glucose starvation/replenishment cycles. Collectively, our results support a model in which Reg2-Glc7 contributes to the negative control of Snf1 in response to glucose refeeding after prolonged starvation. The competitive growth advantage provided by Reg2 underscores the evolutionary significance of this paralog for S. cerevisiae The ability of microorganisms to respond to stress is essential for their survival. However, rapid recovery from stress could be equally crucial in competitive environments. Therefore, a wise stress response program should prepare cells for quick recovery upon reexposure to favorable conditions. Glucose is the preferred carbon source for the yeast S. cerevisiae Glucose depletion activates the stress response protein kinase Snf1, which functions to limit energy-consuming processes, such as growth. We show that prolonged glucose deprivation also leads to Snf1-dependent accumulation of Reg2 and that this protein helps to inhibit Snf1 and to accelerate growth recovery upon glucose replenishment. Cells lacking Reg2 are readily outcompeted by wild-type cells during glucose depletion/replenishment cycles. Thus, while prolonged glucose deprivation might seem to put yeast cells "on their knees," concomitant accumulation of Reg2 helps configure the cells into a "sprinter's crouch start position" to spring into action once glucose becomes available.

The “Subpar” Recovery: A Long-standing Misunderstanding

Is the slow growth recovery and expansion a break from past patterns? These two economists argue that it is consistent with a long-term trend toward slower growth that started in the 1970s. It is not likely that rapid economic growth will return anytime soon.

What Now? Addressing the Burden of Canada's Slow-Growth Recovery

The Canadian economy faces serious short-term macroeconomic challenges, the most important of which is addressing the burden of our slow-growth recovery. The sources and consequences of this slow growth are the focus of this Commentary. Canadian monetary policy has little ability to further stimulate Canadian growth. Given the large amount of uncertainty now faced by Canadian firms, further reductions in the policy interest rate are unlikely to be effective in stimulating aggregate demand. In addition, the ongoing problems associated with very low interest rates cannot be ignored and may soon present the Bank of Canada with a compelling case for rate increases. Canadian fiscal authorities have more room to manoeuvre than their counterparts in many other developed countries. Yet there remain solid arguments for budgets to be brought back to balance in the next few years. One is that discretionary fiscal policy is an ineffective pro-growth policy when the economy is not experiencing a sudden collapse of aggregate demand. Another is the longer-term budgetary challenges that Canadian governments will face over the next few decades as a result of population aging. Neither fiscal nor monetary policy is therefore likely to stimulate Canada’s economic growth over the next few years. This lack of stimulus from traditional macroeconomic policy suggests that any pick-up in Canadian growth will rely on a recovery of private demand. Given the lingering uncertainty and the continued slow pace of the global economic recovery, however, a significant rebound in Canadian private demand is unlikely in the near future. High household debt suggests that consumption is an improbable source of near-term growth. An investment revival will require a return of corporate confidence, while a rally in Canadian exports will depend on a strong and sustained foreign recovery. A central conclusion of this Commentary is therefore that Canadian policymakers should accept the continuation of Canada’s slow-growth recovery for the next few years. Slow growth has undesirable consequences, however, including longer unemployment spells, more part-time employment, and a greater incidence of long-term unemployment. Policymakers should focus on addressing the associated burden by enhancing income support for the unemployed, increasing the mobility of workers and improving incentives for labour-market training.

Interspecies variation in survival and growth of filamentous heterotrophic bacteria in response to UVC radiation

Ultraviolet radiation is an important environmental constraint on the evolution of life. In addition to its harmful effects, ultraviolet radiation plays an important role in generating genetic polymorphisms and acting as a selective agent. Understanding how prokaryotes cope with high radiation can give insights on the evolution of life on Earth. Four representative filamentous bacteria from the family Cytophagaceae with different pigmentation were selected and exposed to different doses of UVC radiation (15–32,400 J m −2). The effect of UVC radiation on bacterial survival, growth and morphology were investigated. Results showed high survival in response to UVC for Rudanella lutea and Fibrisoma limi, whereas low survival was observed for Fibrella aestuarina and Spirosoma linguale. S. linguale showed slow growth recovery after ultraviolet exposure, R. lutea and F. limi showed intermediate growth recovery, while F. aestuarina had the fastest recovery among the four tested bacteria. In terms of survival, S. linguale was the most sensitive bacterium whereas R. lutea and F. limi were better at coping with UVC stress. The latter two resumed growth even after 2 h exposure (∼10,800 J m −2). Additionally, the ability to form multicellular filaments after exposure was tested using two bacteria: one representative of the high ( R. lutea) and one of the low ( F. aestuarina) survival rates. The ability to elongate filaments due to cell division was preserved but modified. In R. lutea 10 min exposure reduced the average filament length. The opposite was observed in F. aestuarina, where the 5 and 10 min exposures increased the average filament length. R. lutea and F. limi are potential candidates for further research into survival and resistance to ultraviolet radiation stress.

The choice of an exchange rate regime: Outcomes and constraints

An inappropriate exchange rate policy is likely to undermine overall efforts to transform the economy. Namely, it is now well accepted either at the theoretical or policy level that situations of real exchange rate misalignment could be translated into important welfare costs. This country study highlights "irrelevancy" of the stability criteria when slow growth recovery threatens to endanger even social roots of determination for reform. We discuss foreign exchange policy and other related policy measures that are likely to align economic and political goals inside a trade-off between stability and growth.