A MAP4 kinase related to Ste20 is a nutrient-sensitive regulator of mTOR signalling

The mTOR (mammalian target of rapamycin) signalling pathway is a key regulator of cell growth and is controlled by growth factors and nutrients such as amino acids. Although signalling pathways from growth factor receptors to mTOR have been elucidated, the pathways mediating signalling by nutrients are poorly characterized. Through a screen for protein kinases active in the mTOR signalling pathway in Drosophila we have identified a Ste20 family member (MAP4K3) that is required for maximal S6K (S6 kinase)/4E-BP1 [eIF4E (eukaryotic initiation factor 4E)-binding protein 1] phosphorylation and regulates cell growth. Importantly, MAP4K3 activity is regulated by amino acids, but not the growth factor insulin and is not regulated by the mTORC1 inhibitor rapamycin. Our results therefore suggest a model whereby nutrients signal to mTORC1 via activation of MAP4K3.     

Dual nutrient limited growth: models, experimental observations, and applications

Dual nutrient limited growth, the control of the cell growth rate (kinetic aspect) or the restriction of the amount of biomass (stoichiometric aspect) by two nutrients at the same time, is a relatively unknown ability of the microorganisms and consequently, still not mentioned in textbooks to date. Nevertheless, multiple nutrient limited or controlled growth has been reported for different systems; e.g. ecosystems, batch, fed-batch, and chemostat cultures. Generally, dual nutrient limited growth has been observed when the microorganism of interest: (a) showed a variation of the cellular composition, (b) was able to accumulate a storage compound, (c) changed the cell metabolism, or (d) excreted metabolic intermediates. Consequently, stoichiometric models have been developed to estimate the growth conditions leading to dual nutrient limited growth. A general problem of the kinetic aspect is the accurate measurement of the growth controlling nutrients in the culture broth (microg l(-1) range), as the cells may consume residual nutrients during sampling. Nevertheless, most models of dual limited growth deal with the kinetic aspect although the control experiments are difficult to carry out. The aim of this survey is to introduce this special growth feature with respect to basic models, experimental data, and potential applications in bioprocesses.     

The use of growth and ingestion rates of Capitella sp. I as the bioassay approaches to determine the sediment quality of coastal wetlands of Taiwan

Food is a limiting factor for the deposit feeders. The availability of sediment nutrients thus has a tight relationship with the growth, survival and development of the animal. There are two purposes of this study: (1) to determine if the ingestion and growth rates can be used as a bioassay approach to assess the sediment nutrients; and (2) use the combination of bioassay approaches and chemical analyses to determine which chemical parameter is the better predicator of the sediment nutrients to the animals. In the preliminary study, the optimal growth length and average ingestion rate of Capitella sp. I were obtained from the laboratory. The standardized relationships of the growth and ingestion rates in response to different nutrients were prepared. Then, the sediments collected from different coastal wetlands in Western Taiwan were used in the feeding, growth experiments and chemical analyses. The comparisons were made between the field and laboratory experiments to determine the sediment nutrients in the wetland of Taiwan. In the growth rate standardized relationship, Capitella sp. I increased its growth rate with the total organic nitrogen (TON) concentration between 0 to 2.8 mgN·g sediment⁻¹, total organic carbon (TOC) concentration between 0 and 22.4 mgC·g sediment⁻¹, and enzymatically hydrolyzable amino acid (EHAA) concentration between 0 and 4.48 mg protein·g sediment⁻¹. After the nutrient concentrations exceed these values, the growth rates decreased gradually. In the ingestion rate standardized relationship, the animal increased its ingestion rate with the total organic nitrogen (TON) concentration between 0 and 2 mgN·g sediment⁻¹, total organic carbon (TOC) concentration between 0 and 14.1 mgC·g sediment⁻¹, and EHAA concentration between 0 and 3.2 mg protein·g sediment⁻¹. After the nutrient concentrations exceed these values, the ingestion rates also decreased. To determine which nutrient parameter is the best predictor for the sediment nutrient in the field, we first analyzed whether the data obtained from the laboratory fell within 99% confidence interval of the regression obtained from the field data. Then, to determine which parameter had the shortest perpendicular distance between the field and the laboratory regression curves. Both the growth and ingestion rates comparisons showed that the EHAA is the best candidate of the sediment nutrient of deposit feeders in the field. The results of this study proved tentatively that the growth and ingestion rates of Capitella sp. I can be used as the bioassay approaches to estimate the sediment nutrients. The combination of the bioassay approaches and the relevant chemical analyses allows us to determine the bioavailability fraction of sediment to the deposit feeders.     

The concept of multiple-nutrient-limited growth of microorganisms and its application in biotechnological processes

The "law of the minimum" (Liebig's law) states that usually one nutrient restricts the maximum quantity of biomass that can be produced within a system, whereas all other nutrients are in excess. This general rule has been applied also to the growth of microorganisms, e.g., by adjusting the relative concentrations of the individual nutrients in growth media such that one of them, in the case of heterotrophic microbes, usually the carbon source, determines the maximum cell density that can be obtained in a culture. However, experimental data demonstrated that growth of microbial cultures can be limited simultaneously by two or more nutrients. These authors reported that during growth of bacteria and yeasts at a constant dilution rate in the chemostat, three distinct growth regimes were recognised as a function of the C:N ratio in the inflowing medium: (1) a clearly carbon-limited regime with the nitrogen source in excess, (2) a transition ("double-nutrient-limited") growth regime where both the carbon and the nitrogen source were below the detection limit, and (3) a clearly nitrogen-limited growth regime with the carbon source in excess. Subsequent calculations suggested that the extension and position of this double-nutrient-limited zone should be strongly dependent on the imposed growth rate: Whereas it is very narrow at high growth rates it should become very broad during slow growth. This pattern as a function of growth rate has now been confirmed for a number of different organisms. In industrial processes, microbial growth is always in some way controlled by the limited availability of nutrients, and limitation of specific nutrients is frequently used to force microbial cultures into a productive physiological state. This article will discuss what the consequences of multiple-nutrient-limited growth are for industrial processes and how the concept might be applied. Specific examples will be given that demonstrate the advantages and the potential of multiple nutrient-limited growth conditions for industrial production processes.     

Defined media optimization for growth of recombinant Escherichia coli X90

An optimized, defined minimal medium was developed to support balanced growth of Escherichia coli X90 harboring a recombinant plasmid. Foreign protein expression was repressed in these studies. A pulse injection technique was used to identify the growth responses to nutrients in a chemostat. Once the nutrients essential for growth had been identified, the yield coefficients for individual medium components. These yield coefficients were used to develop an optimized, glucose-limited defined minimal medium that supports balanced cell growth in chemostat culture. The biomass and substrate concentrations follow the Monod chemostat model. The maximum specific growth rate determined in a washout experiment is 0.87 h(-1) for this strain in the optimized medium. the glucose yield factor is 0.42 g DCW/g glucose and the maintenance coefficient is zero in the glucose-limited chemostat culture. (c) 1993 John Wiley & Sons, Inc.     

水曲柳幼苗根系对土壤养分和水分空间异质性的反应

通过沙培试验方法,研究了温室条件下水曲柳幼苗在施肥和浇水区,非施肥和非浇水区中根系生长,生物量分布,地下部分与地上部分关系,细根直径等特征。结果表明,土壤养分和水分的空间异质性对水曲柳幼苗根系生长和分布有明显影响。在施肥区和浇水区根系生长快,密度大,生物量高,而在非施肥和非浇水区根系生长受到抑制,根系密度小,生物量低,与非施肥区相比,施肥区细根直径下降,有利于根系对养分和水分的运输,但是在非浇水区     

Fertilizer-dependent efficiency of Pseudomonads for improving growth,yield, and nutrient use efficiency of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Acquisition of nutrients by plants is primarily dependent on root growth and bioavailability of nutrients in the rooting medium. Most of the beneficial bacteria enhance root growth, but their effectiveness could be influenced by the nutrient status around the roots. In this study, two 1-aminocyclopropane-1-carboxylate (ACC)-deaminase containing plant-growth-promoting rhizobacteria (PGPR), Pseudomonas fluorescens and P. fluorescens biotype F were tested for their effect on growth, yield, and nutrient use efficiency of wheat under simultaneously varying levels of all the three major nutrients N, P, and K (at 0%, 25%, 50%, 75%, and 100% of recommended doses). Results of pot and field trials revealed that the efficacy of these strains for improving growth and yield of wheat reduced with the increasing rates of NPK added to the soil. In most of the cases, significant negative linear correlations were recorded between percentage increases in growth and yield parameters of wheat caused by inoculation and increasing levels of applied NPK fertilizers. It is highly likely that under low fertilizer application, the ACC-deaminase activity of PGPR might have caused reduction in the synthesis of stress (nutrient)-induced inhibitory levels of ethylene in the roots through ACC hydrolysis into NH₃ and α-ketobutyrate. The results of this study imply that these Pseudomonads could be employed in combination with appropriate doses of fertilizers for better plant growth and savings of fertilizers.     

mTORC1 signaling and regulation of pancreatic β-cell mass

The capacity of β cells to expand in response to insulin resistance is a critical factor in the development of type 2 diabetes. Proliferation of β cells is a major component for these adaptive responses in animal models. The extracellular signals responsible for β-cell expansion include growth factors, such as insulin, and nutrients, such as glucose and amino acids. AKT activation is one of the important components linking growth signals to the regulation of β-cell expansion. Downstream of AKT, tuberous sclerosis complex 1 and 2 (TSC1/2) and mechanistic target of rapamycin complex 1 (mTORC1) signaling have emerged as prime candidates in this process, because they integrate signals from growth factors and nutrients. Recent studies demonstrate the importance of mTORC1 signaling in β cells. This review will discuss recent advances in the understanding of how this pathway regulates β-cell mass and present data on the role of TSC1 in modulation of β-cell mass. Herein, we also demonstrate that deletion of Tsc1 in pancreatic β cells results in improved glucose tolerance, hyperinsulinemia and expansion of β-cell mass that persists with aging.     

Sugar-induced apoptosis in yeast cells

Sugars induce death of Saccharomyces cerevisiae within a few hours in the absence of additional nutrients to support growth; by contrast, cells incubated in water or in the presence of other nutrients without sugar remain viable for weeks. Here we show that this sugar-induced cell death (SICD) is characterized by rapid production of reactive oxygen species (ROS), RNA and DNA degradation, membrane damage, nucleus fragmentation and cell shrinkage. Addition of ascorbic acid to sugar-incubated cells prevents SICD, indicating that SICD is initiated by ROS. The lack of a protection mechanism against SICD suggests that sugars use to be the limiting nutrients for yeast and are probably depleted before all other nutrients. Being the limiting nutrient, sugars became the growth-stimulating agent, signaling the presence of sufficient nutrients for growth, but in the absence of the complementing nutrients they induce apoptotic death.     

Effects of micro-nutrients and major nutrients on natural phytoplankton populations

Six experiments were carried out with natural phytoplanktonpopulations grown under simulated natural conditions, in anattempt to assess the gross effects of major nutrient and micronutrientperturbations upon the growth and species composition of thesepopulations. Water was collected from Yaquina Bay, Oregon, andfiltered into twenty-litre growth containers. Some of this waterwas treated with activated carbon to remove a portion of thetrace metals and trace organics. Various combinations of majornutrients, micro-nutrients, and chelators were added to thesecultures. Inoculation was with unfiltered bay water, at a ratioof 1:1000. Incubation was in outdoor tanks of water circulatingfrom the bay, under natural sunlight. The major nutrients andmicro-nutrients appeared to have fundamentally different effectson the growth and species composition of phytoplankton. Themicro-nutrients had marked effects on the species compositionof the phytoplankton populations, while major nutrients hadminimal effects on species composition. The micro-nutrientsalso had substantial effects on population growth rates, lagperiods, and final yields. The major nutrients had a substantialeffect only on final yields.     

GbetaL,a positive regulator of the rapamycin-sensitive pathway required for the nutrient-sensitive interaction between raptor and mTOR

mTOR and raptor are components of a signaling pathway that regulates mammalian cell growth in response to nutrients and growth factors. Here, we identify a member of this pathway, a protein named GbetaL that binds to the kinase domain of mTOR and stabilizes the interaction of raptor with mTOR. Like mTOR and raptor, GbetaL participates in nutrient- and growth factor-mediated signaling to S6K1, a downstream effector of mTOR, and in the control of cell size. The binding of GbetaL to mTOR strongly stimulates the kinase activity of mTOR toward S6K1 and 4E-BP1, an effect reversed by the stable interaction of raptor with mTOR. Interestingly, nutrients and rapamycin regulate the association between mTOR and raptor only in complexes that also contain GbetaL. Thus, we propose that the opposing effects on mTOR activity of the GbetaL- and raptor-mediated interactions regulate the mTOR pathway.     

Dynamic change of metabolites and nutrients in suspension cells of <Emphasis Type="Italic">Panax Quinquefolium</Emphasis> L. in bioreactor

In order to understand how the nutrient elements were taken up during the cell growth as well as the production of metabolites, it was quite necessary to identify the dynamic change of metabolites and nutrients in suspension cells of Panax quinquefolium in bioreactor. In this study, dynamic accumulation of biomass and ginsenosides Re, Rb1 and polysaccharide as well as major nutrients consumption in cell suspension culture of P. quinquefolium in a 5-L stirred tank bioreactor were investigated. The dry cell weight and the contents of ginsenosides Re, Rb1 and polysaccharide reached the maximum peak simultaneously on about 21 days and the results showed that cell growth and metabolites synthesis related to nutrients consumption. For this reason, we supposed that the contents of metabolites can be increased through added nutrient at the right moment. These results provided theory reference for two-stage or continuous perfusion culture in suspension cells of P. quinquefolium in bioreactor.     

Unified kinetic treatment for growth on dual nutrients

This paper presents a new formulation for the analysis of growth kinetics on multiple nutrients. The baseline for the theory is the concept that a noninteractive growth process occurs among perfectly substitutable nutrients if the locus of points of the substrate concentrations producing equal growth rate is linear. A deviation function is then defined with respect to this base case, and several models for this function are suggested. The underlying theory is taken by analogy with mixture thermodynamics. The proposed formulation is tested against data in the literature on growth under substitutable and complementary substrate mixtures. (c) 1994 John Wiley & Sons, Inc.     

Towards an integrated view of monocarpic plant senescence

After the flowering of an annual plant, the whole plant will senesce and die. For the process to go to completion, this monocarpic senescence must include three coordinated processes, which have not previously been considered as a total syndrome: (1) the arrest of growth and senescence of the shoot apical meristem; (2) senescence of the leaves; and (3) the suppression of axillary bud growth. Concurrently there is a shift in resource allocation from continued vegetative growth to reproductive growth, combined with a withdrawal of nutrients, especially nitrogen compounds, from the leaves and the transfer of these nutrients to the developing seeds. The start of the senescence process is caused by a shift, almost certainly in gene expression, very early in the reproductive phase. Continuation of the resource transfer and senescence of the vegetative plant involves hormonal regulation and continued changes in gene expression. Each of these processes is examined, especially with reference to the transfer of resources from vegetative to reproductive growth.     

How Microbes Can Achieve Balanced Growth in a Fluctuating Environment

A microbial colony needs several essential nutrients in order to grow. Moreover, the colony requires these nutrients in fixed combinations, which are dictated by the chemical composition of its biomass. Unfortunately, ambient availabilities of the various nutrients vary all the time. This poses the question of how microbes can achieve balanced growth.The present solution to this problem is novel in that the allocation of molecular building blocks among assimilatory machineries within the cell is regarded as dynamic. This paper shows that allocation can be adapted so as to achieve balanced growth, nearly regardless of environmental conditions. Moreover, it is shown that a feedback mechanism, which monitors internal stores, is able to achieve this allocation.     

Phosphatidylinositol 3-kinase-dependent modulation of carnitine palmitoyltransferase 1A expression regulates lipid metabolism during hematopoietic cell growth

An abundant supply of extracellular nutrients is believed to be sufficient to suppress catabolism of cellular macromolecules. Here we show that, despite abundant extracellular nutrients, interleukin-3-deprived hematopoietic cells begin to catabolize intracellular lipids. Constitutive Akt activation blunts the increased beta-oxidation that accompanies growth factor withdrawal, and in growth factor-replete cells, phosphatidylinositol 3-kinase (PI3K) signaling is required to suppress lipid catabolism. Surprisingly, PI3K and Akt exert these effects by suppressing expression of the beta-oxidation enzyme carnitine palmitoyltransferase 1A (CPT1A). Cells expressing a short hairpin RNA against CPT1A fail to induce beta-oxidation in response to growth factor withdrawal and are unable to survive glucose deprivation. When CPT1A is constitutively expressed, growth factor stimulation fails to repress beta-oxidation. As a result, both net lipid synthesis and cell proliferation are diminished. Together, these results demonstrate that modulation of CPT1A expression by PI3K-dependent signaling is the major mechanism by which cells suppress beta-oxidation during anabolic growth.     

Dietary factors and growth and metabolism in experimental tumors

Development of a diet that provides adequate nutrition and effective cancer prevention is an important goal in nutrition and cancer research. A confounding aspect of dietary control of tumor growth is the fact that some nutrients may up-regulate tumor growth, whereas other nutrients and nonnutrients down-regulate growth. Both up- and down-regulators may be present in the same foodstuff. Identification of these substances, determination of their mechanisms of action and potencies, as well as the interactions among the different mechanisms are topics of ongoing research. In this review, we describe results obtained in vivo or during perfusion in situ using solid tissue-isolated rodent tumors and human cancer xenografts in nude rats. Linoleic acid (LA), an essential n-6 polyunsaturated fatty acid (PUFA), was identified as an agent in dietary fat that is responsible for an up-regulation of tumor growth in vivo. Tumor LA uptake, mediated by high intratumor cAMP, stimulated formation of the mitogen, 13-hydroxyoctadecadienoic acid (13-HODE) and also increased ERK1/2 phosphorylation, [(3)H]thymidine incorporation and growth. A mechanism for control of this growth-promoting pathway was revealed during studies of the effects of dietary nutrients and nonnutrients known to inhibit tumor growth. These included four groups of lipophilic agents: n-3 fatty acids, melatonin, conjugated LA isomers and trans fatty acids. Each of these agents activated an inhibitory G protein-coupled receptor-mediated pathway that specifically suppressed tumor uptake of saturated, monounsaturated and n-6 PUFAs, thereby inhibiting an early step in the LA-dependent growth-promoting pathway.     

Hormonal regulation of fetal growth

Fetal growth is a complex process depending on the genetics of the fetus, the availability of nutrients and oxygen to the fetus, maternal nutrition and various growth factors and hormones of maternal, fetal and placental origin. Hormones play a central role in regulating fetal growth and development. They act as maturational and nutritional signals in utero and control tissue development and differentiation according to the prevailing environmental conditions in the fetus. The insulin-like growth factor (IGF) system, and IGF-I and IGF-II in particular, plays a critical role in fetal and placental growth throughout gestation. Disruption of the IGF1, IGF2 or IGF1R gene retards fetal growth, whereas disruption of IGF2R or overexpression of IGF2 enhances fetal growth. IGF-I stimulates fetal growth when nutrients are available, thereby ensuring that fetal growth is appropriate for the nutrient supply. The production of IGF-I is particularly sensitive to undernutrition. IGF-II plays a key role in placental growth and nutrient transfer. Several key hormone genes involved in embryonic and fetal growth are imprinted. Disruption of this imprinting causes disorders involving growth defects, such as Beckwith-Wiedemann syndrome, which is associated with fetal overgrowth, or Silver-Russell syndrome, which is associated with intrauterine growth retardation. Optimal fetal growth is essential for perinatal survival and has long-term consequences extending into adulthood. Given the high incidence of intrauterine growth retardation and the high risk of metabolic and cardiovascular complications in later life, further clinical and basic research is needed to develop accurate early diagnosis of aberrant fetal growth and novel therapeutic strategies.     

Ehrlichia secretes Etf-1 to induce autophagy and capture nutrients for its growth through RAB5 and class III phosphatidylinositol 3-kinase

Ehrlichia chaffeensis is an obligatory intracellular bacterium that causes a potentially fatal emerging zoonosis, human monocytic ehrlichiosis. E. chaffeensis has a limited capacity for biosynthesis and metabolism and thus depends mostly on host-synthesized nutrients for growth. Although the host cell cytoplasm is rich with these nutrients, as E. chaffeensis is confined within the early endosome-like membrane-bound compartment, only host nutrients that enter the compartment can be used by this bacterium. How this occurs is unknown. We found that ehrlichial replication depended on autophagy induction involving class III phosphatidylinositol 3-kinase (PtdIns3K) activity, BECN1 (Beclin 1), and ATG5 (autophagy-related 5). Ehrlichia acquired host cell preincorporated amino acids in a class III PtdIns3K-dependent manner and ehrlichial growth was enhanced by treatment with rapamycin, an autophagy inducer. Moreover, ATG5 and RAB5A/B/C were routed to ehrlichial inclusions. RAB5A/B/C siRNA knockdown, or overexpression of a RAB5-specific GTPase-activating protein or dominant-negative RAB5A inhibited ehrlichial infection, indicating the critical role of GTP-bound RAB5 during infection. Both native and ectopically expressed ehrlichial type IV secretion effector protein, Etf-1, bound RAB5 and the autophagy-initiating class III PtdIns3K complex, PIK3C3/VPS34, and BECN1, and homed to ehrlichial inclusions. Ectopically expressed Etf-1 activated class III PtdIns3K as in E. chaffeensis infection and induced autophagosome formation, cleared an aggregation-prone mutant huntingtin protein in a class III PtdIns3K-dependent manner, and enhanced ehrlichial proliferation. These data support the notion that E. chaffeensis secretes Etf-1 to induce autophagy to repurpose the host cytoplasm and capture nutrients for its growth through RAB5 and class III PtdIns3K, while avoiding autolysosomal killing.     

Carbon/nitrogen relationships of fungus culture media

Summary and Conclusions Four basic nutrient types are described and discussed in special reference to the ratios between carbon source materials and nitrogen source materials. These include habitat, natural nutrients, semisynthetic nutrients and synthetic nutrients. Special emphasis is placed on the use of such nutrients in agar media for the primary isolation of fungi from various types of habitat materials such as soils and sewage.It is suggested that a basic C:N ratio for such nutrient agars lies at about 9 or 12 to 1, that increasing this ratio tends to overenrich the culture thus encouraging the formation of intracellular or extracellular carbon-carrying compounds, and that decreasing the ratio tends to encourage the formation of nitrogen-carrying storage products. Both conditions tend to produce staling substances more rapidly, tend to decrease discreteness of colonies, tend to produce more diffuse, less easily counted growth, and tend to develop less readily identifiable colonies.It is implied that if a C:N ratio more or less approximating that found in an agar containing plant parts, or limited nutrients plus plant parts, were used in a medium designed for primary isolation of fungi from natural materials, such a medium would have many advantages over currently popular media used for this purpose.