Nutritional Stress Conditions Research Articles

New insights into transport capability of sugars and its impact on growth from novel mutants of Escherichia coli.

The fast-growing capability of Escherichia coli strains used to produce industrially relevant metabolites relies on their capability to transport efficiently glucose or potential industrial feedstocks such as sucrose or xylose as carbon sources. E. coli imports extracellular glucose into the periplasmic space across the outer membrane porins: OmpC, OmpF, and LamB. As the internal membrane is an impermeable barrier for sugars, the cell employs several primary and secondary active transport systems, and the phosphoenolpyruvate (PEP)-sugar phosphotransferase (PTS) system for glucose transport. PTS:glucose is the preferred system by E. coli to transport and phosphorylate the periplasmic glucose; nevertheless, PTS imposes a strict metabolic control mechanism on the preferential consumption of glucose over other carbon sources in sugar mixtures such as glucose and xylose resulting from the hydrolysis of lignocellulosic biomass, by the carbon catabolite repression. In this contribution, we summarize the major sugar transport systems for glucose and disaccharide transport, the exhibited substrate plasticity, and their impact on the growth of E. coli, highlighting the relevance of PTS in the control of the expression of genes for the transport and catabolism of other sugars as xylose. We discuss the strategies developed by evolved mutants of E. coli during adaptive laboratory evolution experiments to overcome the nutritional stress condition imposed by inactivation of PTS as a strategy for the selection of fast-growing derivatives in glucose, xylose, or mixtures of glucose:xylose. This approach results in the recruitment of other primary and secondary active transporters, demonstrating relevant sugar plasticity in derivative-evolved mutants. Elucidation of the molecular and biochemical basis of sugar-transport substrate plasticity represents a consistent approach for sugar-transport system engineering for the design of efficient E. coli derivative strains with improved substrate assimilation for biotechnological purposes.

Trypanosoma cruzi RNA-binding protein ALBA30 aggregates into cytoplasmic foci under nutritional stress.

Trypanosoma cruzi, the causative agent of Chagas disease, has a complex life cycle that requires the adaptation to different environments. In the absence of traditional mechanisms for regulation of gene expression, this parasite relies on posttranscriptional control events, which allow the progression of its life cycle in different hosts and stress conditions. In this context, different stress conditions trigger the aggregation of RNA-binding proteins and their target mRNAs into cytoplasmic foci known as RNA granules, which act as RNA-sorting centers. In this study, we have characterized the T. cruzi RNA-binding protein ALBA30 during nutritional stress conditions. Using a recombinant form of TcALBA30 to facilitate its detection (rTcALBA30), we showed that this protein resides in the cytoplasm in normal growth conditions but is recruited into cytoplasmic foci after starvation. Moreover, evaluation of rTcALBA30 in parasites that reached the stationary phase of growth also showed the recruitment of this protein into cytoplasmic foci. Our results indicate that, similar to TbALBA3, TcALBA30 aggregates into stress granules in parasites submitted to nutritional stress.

Regulation and Roles of Autophagy in the Brain.

Autophagy is crucial for neuronal integrity. Loss of key autophagic components leads to progressive neurodegeneration and structural defects in neuronal synapses. However, the molecular mechanisms regulating autophagy in the brain remain elusive. Similarly, while it is widely accepted that protein turnover is required for synaptic plasticity, the contribution of autophagy to the degradation of synaptic proteins is unknown. We find that BDNF signaling via the tropomyosin receptor kinase B (TrkB) and the phosphatidylinositol 3-kinase (PI3K)/Akt pathway suppresses autophagy in vivo. Autophagy is differentially regulated by fasting, in different brain regions. Suppression of autophagy is required for BDNF-induced synaptic plasticity and for memory enhancement, under conditions of nutritional stress. BDNF signaling suppresses autophagy in the forebrain of adult mice. Indeed, BDNF ablation in the neural lineage causes uncontrolled increase in autophagy. In turn, increased autophagy mediates the synaptic defects caused by BDNF deficiency. Thus, fasting suppresses autophagy in regions of the mouse forebrain, thereby promoting synaptic remodeling and memory through a BDNF-regulated mechanism. We identify three key remodelers of postsynaptic densities as cargo of autophagy. Our results establish autophagy as a pivotal component of BDNF signaling, which is essential for BDNF-induced synaptic plasticity. This molecular mechanism underlies behavioral adaptations that increase fitness in times of scarcity.

Biorefinery Approach from Nannochloropsis oceanica CCALA 978: Neutral Lipid and Carotenoid Co-Production Under Nitrate or Phosphate Deprivation

The large-scale culture of microalgae has become a focus of interest for the biorefinery industry, combining the production of biofuels with that of other value-added bioproducts and thus increasing the profitability of the process. In order to evaluate its potential as biodiesel feedstock under a biorefinery approach, the biomass, pigment, nutrient, total lipid and lipid fraction kinetics of the Argentinian Nannochloropsis oceanica CCALA 978 strain were analysed. The species was first cultivated under optimal conditions (f/2 medium) and then transferred to nutritional stress conditions (N-deprivation or P-deprivation media). Under complete f/2 medium, N. oceanica presented maximum growth rate (μ) and chlorophyll-a values and minimum values for lipid and carotenoid content. The high nutrient consumption rate (N or P) in this exponential phase was associated with increasing cell density. Under both nitrate and phosphate deprivation, μ was drastically reduced but biomass production reached its highest values, indicating a phase of metabolite accumulation. Maximum values of total lipids (ca. 39% dw) and carotenoids (1100 × 10−3 ± 15 μg mL−1) were obtained under nitrate deprivation. In addition, total lipid composition was characterized by 92% neutral lipids, 0.7% phospholipids, a high percentage of C16:1 (ca. 37% of total fatty acids) and minimum values of PUFA (5.9% of total fatty acids). Biodiesel properties inferred from the fatty acid methyl ester profile of neutral lipids meet the standards established by EN 14214 and ASTMD 6751-08. Although N and P deficiency both produced an increase in neutral lipids in the studied strain, under a biorefinery approach, nitrate deprivation is considered to be a better method of stress induction than phosphate deprivation for the purpose of co-producing neutral lipids for biodiesel and value-added pigments.

Biochemical changes and pregnancy toxemia in pregnant and lactating Harri ewes under arid lands conditions

This study was conducted to evaluate serum biochemical constituents and antioxidant enzymes activities in non-pregnant (open), pregnant and lactating ewes exposed to nutritional climatic stress conditions. Forty pure Harri ewes at 3-6 years of age and weighing 49.6 ± 1.22 kg were synchronized for estrus and bred to pregnancy. Ewes were kept indoors in a semi open shelter and were given concentrate mix as the only daily ration during pregnancy and lactation. Pregnant ewes had higher (P<0.05) total protein than lactating that had higher albumin and lower globulin concentrations than open and pregnant ewes. Pregnant ewes had lower glucose, triglycerides and cholesterol than open and lactating ewes. Pregnant ewes had higher Na and lower K than open and lactating ewes. During last 3 months of pregnancy antioxidant enzymes glutathione peroxidase, nitric oxide and malondialdehyde rose to maximum and declined after parturition. It can be concluded that pregnant ewes often endure dramatic alteration in their metabolism due to heightened fetal development demanding more nutritional intervention to avoid pregnancy toxemia and improve productivity.

Influence of Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) Infection on Mortality of the Sylvatic Triatomine Vector, Mepraia spinolai (Heteroptera: Reuviidae), Under Fasting.

The etiologic agent of Chagas disease, Trypanosoma cruzi, is transmitted by hematophagous insect vectors that subsist on repeated blood meals over their lives separated by periods of fasting. Using naturally infected Mepraia spinolai, we measured the influence of parasite infection on this host vector's mortality during regular feeding and after fasting. After their capture, the insects were fed twice with uninfected mice to evaluate parasitic infection in their fecal samples by microscopic observation and PCR. Then the insects were subjected to a fasting period, followed by a third (final) feeding. After each feeding, a fecal sample was obtained to evaluate T. cruzi infection. To determine its progress through ontogeny, mortality and ecdysis of the infected and uninfected nymphs and adults were recorded on three occasions, over 140 d, and analyzed. Detections of infection by T. cruzi between the two first feedings increased, but this detection level was generally reduced after final feeding unless reinfected. For nymphs (stages III-V), their mortality was highest when infected after the fasting period, whereas adults were equally resistant to death after fasting when infected with T. cruzi. Metacyclic trypomastigotes were principally excreted in the fecal samples. Our results confirm that T. cruzi is pathogenic to its invertebrate hosts under nutritional stress conditions, when nymphs' mortality is higher while infected than uninfected when they were hungry. These results are epidemiologically important because T. cruzi harms the fasting vector M. spinolai, reducing its lifespan and competence as a disease vector, and thereby its rates of parasite transmission.

SWATH-MS quantitative proteomic investigation of intrauterine growth restriction in a porcine model reveals sex differences in hippocampus development

Intrauterine growth restriction (IUGR) is characterized by reduced growth and weight of the foetus, mainly due to the lack of nutrients and oxygen. Animals affected by IUGR show changes in specific brain areas and several neuronal processes. Female offspring affected by IUGR show increased survival and development compared to males. The objective of this study was to analyse changes in the hippocampus proteome in male and female piglets affected by IUGR. Seven pregnant Iberian sows were fed from Day 35 of pregnancy onwards at 50% of their requirements. At Day 100 of pregnancy, foetuses were obtained and classified by sex and weight, as mild IUGR (Normal Body Weight) versus severe IUGR (Low Body Weight). Hippocampi were dissected and the proteomes analysed by SWATH-MS DIA. In this study, 1497 proteins were identified of which 260 were quantitatively analysed. All differential proteins were more abundant in females versus males and were involved in protein synthesis, neuronal development, metabolism, antiapoptotic signalling and vesicular transport. Our findings support that female foetuses tolerate nutrient limitation better than males, especially under mild IUGR. Under severe IUGR, females still seems to maintain normal lipid metabolism and antiapoptotic signalling, which may be related to the increased female survival. SignificanceIn the last years, proteomics have been used to evidence differences related to sex in non-reproductive organs. Intrauterine Growth Restriction (IUGR) can affect female and male offspring differently. Female offspring has stronger protective strategies compared to males, enhancing growth and postnatal survival. Most studies regarding this issue have focused on metabolic organs (i.e. liver). However, the predominance of neurodevelopmental disorders in males suggests that the central nervous system in female offspring adapt better to nutritional stress conditions than that of males. Based on the differential protein expression in hippocampal samples, our work demonstrates that female foetuses indeed adapt better to IUGR than males, especially under mild IUGR conditions. In severe IUGR conditions, differences between males and females were not so evident, but even in this case, the remaining differences suggest increased survival in females than in males.

Autophagosomes accumulation in the vacuoles of the fungus Ustilago maydis and the role of proteases in their digestion.

In the present study we determined whether Ustilago maydis accumulates autophagosomes within vacuoles when the cells are exposed to nutritional stress conditions. We investigated whether proteinase B and proteinase A are involved in their degradation. To this effect, wild type and Δpep4 mutant were incubated in minimal medium lacking a carbon source. It was observed that after incubation in nutrient-deficient media, spherical bodies appeared within the Δpep4 mutant strains vacuoles. In addition, autophagosomes were accumulated in U. maydis WT cells incubated in the presence of the serine protease inhibitor PMSF and accumulation of large autophagosomes and electrodense structures in the Δpep4 mutant cell vacuoles took place. These results demonstrate that the homologues of both, the proteinase B and the protease A, are involved in the autophagosomes degradation process in U. maydis.

Genetics and Pathogenicity Factors of Group C and G Streptococci.

Of the eight phylogenetic groups comprising the genus Streptococcus, Lancefield group C and G streptococci (GCS and GGS, resp.) occupy four of them, including the Pyogenic, Anginosus, and Mitis groups, and one Unnamed group so far. These organisms thrive as opportunistic commensals in both humans and animals but may also be associated with clinically serious infections, often resembling those due to their closest genetic relatives, the group A streptoccci (GAS). Advances in molecular genetics, taxonomic approaches and phylogenomic studies have led to the establishment of at least 12 species, several of which being subdivided into subspecies. This review summarizes these advances, citing 264 early and recent references. It focuses on the molecular structure and genetic regulation of clinically important proteins associated with the cell wall, cytoplasmic membrane and extracellular environment. The article also addresses the question of how, based on the current knowledge, basic research and translational medicine might proceed to further advance our understanding of these multifaceted organisms. Particular emphasis in this respect is placed on streptokinase as the protein determining the host specificity of infection and the Rsh-mediated stringent response with its potential for supporting bacterial survival under nutritional stress conditions.

Inyecciones de glucosa en Jacaranda mimosifolia D. Don en áreas urbanas de Texcoco de Mora

Los árboles de jacaranda son comunes en áreas urbanas del valle de México y se desarrollan frecuentemente bajo condiciones de estrés nutricional o hídrico, lo que restringe el crecimiento del arbolado. El suministro de carbohidratos a través del sistema vascular recientemente se ha recomendado como una opción para mejorar el crecimiento y vitalidad. Por lo anterior, el objetivo del trabajo fue evaluar el efecto de la glucosa sobre crecimiento y vitalidad de árboles de Jacaranda mimosifolia inyectada al tronco en cuatro concentraciones: 0 (testigo), 30, 55 y 80 g L-1 Se midieron incrementos en diámetro (cm) y altura (m), se monitoreó la condición de copa y producción de follaje y además se evaluó el contenido de carbohidratos en brotes, troncos y raíces, así como la fluorescencia de la clorofila (Fv/Fm). Se encontraron diferencias significativas (P≤0.05) en el incremento en diámetro y altura con la aplicación de 80 g L-1 de glucosa. La condición de copa mostró valores significativamente más altos en densidad y bajos en transparencia, así como una buena producción de follaje, con la concentración más alta del carbohidrato (80 g L-1). Su contenido presentó diferencias significativas (P≤0.05) en tronco, no así en brotes, raíces, ni en valores de fluorescencia de la clorofila. Las inyecciones de glucosa al tronco tienen un efecto significativo en el crecimiento de árboles de esta especie y afectan en menor medida la vitalidad del arbolado.

Glucose-restriction increases Trichomonas vaginalis cellular damage towards HeLa cells and proteolytic activity of cysteine proteinases (CPs), such as TvCP2.

Trichomonas vaginalis induces cellular damage to the host cells (cytotoxicity) through the proteolytic activity of multiple proteinases of the cysteine type (CPs). Some CPs are modulated by environmental factors such as iron, zinc, polyamines, etc. Thus, the goal of this study was to assess the effect of glucose on T. vaginalis cytotoxicity, proteolytic activity and the particular role of TvCP2 (TVAG_057000) during cellular damage. Cytotoxicity assays showed that glucose-restriction (GR) promotes the highest HeLa cell monolayers destruction (~95%) by trichomonads compared to those grown under high glucose (~44%) condition. Zymography and Western blot using different primary antibodies showed that GR increased the proteolytic activity, amount and secretion of certain CPs, including TvCP2. We further characterized the effect of glucose on TvCP2. TvCP2 increases in GR, localized in vesicles close to the plasma membrane and on the surface of T. vaginalis. Furthermore, pretreatment of GR-trichomonads with an anti-TvCP2r polyclonal antibody specifically reduced the levels of cytotoxicity and apoptosis induction to HeLa cells in a concentration-dependent manner. In conclusion, our data show that GR, as a nutritional stress condition, promotes trichomonal cytotoxicity to the host cells, increases trichomonad proteolytic activity and amount of CPs, such as TvCP2 involved in cellular damage.

Serum and nutrient deprivation increase autophagic flux in intervertebral disc annulus fibrosus cells: an in vitro experimental study.

The loss of nutrient supply is a suspected contributor of intervertebral disc degeneration. However, the extent to which low nutrition affects disc annulus fibrosus (AF) cells is unknown as nutrient deprivation has mainly been investigated in disc nucleus pulposus cells. Hence, an experimental study was designed to clarify the effects of limited nutrients on disc AF cell fate, including autophagy, the process by which cells recycle their own damaged components. Rabbit disc AF cells were cultured in different media with varying serum concentrations under 5% oxygen. Cellular responses to changes in serum and nutrient concentrations were determined by measuring proliferation and metabolic activity. Autophagic flux in AF cells was longitudinally monitored using imaging cytometry and Western blotting for LC3, HMGB1, and p62/SQSTM1. Apoptosis (TUNEL staining and cleaved caspase-3 immunodetection) and cellular senescence (senescence-associated β-galactosidase assay and p16/INK4A immunodetection) were measured. Markers of apoptosis and senescence increased, while cell proliferation and metabolic activity decreased under the withdrawal of serum and of nutrients other than oxygen, confirming cellular stress. Time-dependent increases in autophagy markers, including LC3 puncta number per cell, LC3-II expression, and cytoplasmic HMGB1, were observed under conditions of reduced nutrition, while an autophagy substrate, p62/SQSTM1, decreased over time. Collectively, these findings suggest increased autophagic flux in disc AF cells under serum and nutrient deprivation. Disc AF cells exhibit distinct responses to serum and nutrient deprivation. Cellular responses include cell death and quiescence in addition to reduced proliferation and metabolic activity, as well as activation of autophagy under conditions of nutritional stress. These slides can be retrieved under Electronic Supplementary Material.

Potential prebiotic activity of Tenebrio molitor insect flour using an optimized in vitro gut microbiota model.

The Tenebrio molitor insect flour (TMIF) is considered a nutritive food ingredient, but its impact at the gut microbiota level and its potential prebiotic activity still need be assessed. For such studies, an in vitro simulation model of gut microbiota was optimized. Pure cultures of Lactobacillus and Bifidobacterium strains in monocultures and co-cultures (pairs and consortium) were used in this model to evaluate the effect of TMIF on the viability and metabolic activity of those bacteria. The optimization of the in vitro model of the gut microbiota was successful, and growth of the most important groups of bacteria in the gut microbiota was observed. So this model can be used to study the effects of other ingredients at that level. It also enabled pinpointing the prebiotic effects of the studied TMIF suggesting possible symbiotic interactions. In addition, the direct effect of the TMIF on bacterial cells, when in nutritive stress was also evaluated. In terms of TMIF effects on probiotic bacteria viability and growth, no negative effects were observed, and even an enhancement of growth and an increase of production of short chain fatty acids (SCFA) and lactate, in most of the cases, was observed. Also, this study showed that TMIF helps in maintaining the viability of bacteria during incubation time when these are under nutritional stress conditions. A potential prebiotic effect of TMIF is then predictable with this study, opening a path to new research on this subject.

Mycoplasmas are no exception to extracellular vesicles release: Revisiting old concepts.

Release of extracellular vesicles (EV) by Gram-negative and positive bacteria is being frequently reported. EV are nano-sized, membrane-derived, non-self-replicating, spherical structures shed into the extracellular environment that could play a role in bacteria-host interactions. Evidence of EV production in bacteria belonging to the class Mollicutes, which are wall-less, is mainly restricted to the genus Acholeplasma and is scanty for the Mycoplasma genus that comprises major human and animal pathogens. Here EV release by six Mycoplasma (sub)species of clinical importance was investigated. EV were obtained under nutritional stress conditions, purified by ultracentrifugation and observed by electron microscopy. The membrane proteins of EV from three different species were further identified by mass spectrometry as a preliminary approach to determining their potential role in host-pathogen interactions. EV were shown to be released by all six (sub)species although their quantities and sizes (30–220 nm) were very variable. EV purification was complicated by the minute size of viable mycoplasmal cells. The proteins of EV-membranes from three (sub)species included major components of host-pathogen interactions, suggesting that EV could contribute to make the host-pathogen interplay more complex. The process behind EV release has yet to be deciphered, although several observations demonstrated their active release from the plasma membrane of living cells. This work shed new light on old concepts of “elementary bodies” and “not-cell bound antigens”.

Effect of photobiomodulation on viability and proliferation of stem cells from exfoliated deciduous teeth under different nutritional conditions

This study aimed to evaluate the effect of different doses of low-level laser irradiation on the viability and proliferation of stem cells from exfoliated deciduous teeth (SHED) cultured under nutritional deficit (cellular stress) or regular nutritional conditions. SHED underwent irradiation by a red laser between 1.2 and 6.2 J cm−2. Prior to the irradiation, all groups received culture medium (MEMα, Eagle’s minimum essential medium alpha modification) supplemented with 1% of fetal bovine serum (FBS) for 1 h. After the irradiation, cells received MEMα supplemented with 10% of FBS (regular nutrition) or 1% of FBS (nutritional deficit). Cell viability and proliferation were respectively determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and crystal violet assays 6 and 24 h after irradiation (P < 0.05). At 24 h, SHED under nutritional deficit showed lower viability and proliferation after 1.2 J cm−2 irradiation. All of the irradiated groups revealed significantly higher viability and proliferation in SHED maintained under nutritional deficit than in regular nutritional conditions, except in the 3.7 and 6.2 J cm−2 groups by MTT assay. In the crystal violet assay, SHED irradiated with 1.2 J cm−2 showed no difference between the different nutritional conditions. Decrease of FBS concentration in the culture medium seems to enhance the sensitivity of SHED to the effects of photobiomodulation therapy. Nutritional stress conditions improved cell viability and proliferation of SHED after laser irradiation, except for 1.2 J cm−2.

A simple visible and near-infrared (V-NIR) camera system for monitoring the leaf area index and growth stage of Italian ryegrass

Crop growth stage is critical for making decisions in nutrient management and for evaluating crop productivity. In this study, a simple visible and near-infrared (V-NIR) camera system was developed for monitoring the leaf area index (LAI) and quantifying the quick growth stage (QGS) of Italian ryegrass. RAW format images in the red, green and NIR channels over two growing seasons of 2014–15 and 2015–16 were captured hourly each day by the V-NIR camera system installed in three Italian ryegrass fields at the farm of Hiroshima University. Multiple linear regression (MLR) models that predict the forage LAI from the imagery data were calibrated and validated, with high coefficient of determination (R2=0.79) and low root-mean-square error (RMSE=1.09) between the measured and predicted LAIs. The predicted LAI to which three vegetation indices were compared was fitted against a logistic model to extract forage QGS from smoothed time-series data under various micro-meteorological and nutrient conditions. The result shows the time-series data of LAI can be applied for monitoring seasonal changes regardless of the environmental conditions. The RMSE of the predicted phenology dates against the field-measured LAI was 0.58 and 5.2 days for the start- and end-QGS, respectively, under the high-yield condition in season 1. However, in season 2, only the start-QGS was identifiable, with an RMSE of 2.65 days under the nutritional stress condition. The forage LAI and QGS were predicted and identified with acceptable accuracy and reliability, which suggests that the V-NIR camera system can be employed as a cost-effective approach for monitoring seasonal changes in crop growth, aiding in better personalized crop and nutrient management.

Characteristics of the glucose-regulated protein 78 (grp78) gene from Bemisia tabaci MED cryptic species and its expression under thermal and nutritional stress conditions

Glucose-regulated protein 78 (GRP78) is a member of the heat shock protein 70 family that is present in the lumen of the endoplasmic reticulum (ER). Although GRP78 acts as an ER chaperone against various stresses in vertebrates, little is known about its role in insects. Herein, we determined the complete sequence of grp78 cDNA from the invasive Bemisia tabaci Mediterranean (MED) cryptic species which is a serious pest of numerous crop plants and examined transcriptional responses to thermal stress treatments and various dietary conditions using quantitative real-time RT-PCR. The grp78 level was increased under the 0°C and 40°C treatments for 1h, but not by the 10°C or 30°C treatments. In the experiment of sucrose solution ingestion, the grp78 level was increased proportional to the ingested sucrose amount. When whiteflies were reared with five different plant species (eggplant, paprika, pepper, water melon, and tomato) within the cage, the grp78 level varied according to the plant ingested. The grp78 level was the highest in whiteflies fed on eggplant and lowest in those fed on tomatoes. Overall, our results suggest that grp78 is responsive to strong thermal stress and to the change of sucrose in the diet. This study provides important insights for understanding the role of ER-specific GRP78 in thermal and nutritional physiology of insects at the molecular level.

Adaptation to Chronic Nutritional Stress Leads to Reduced Dependence on Microbiota in Drosophila melanogaster.

ABSTRACTNumerous studies have shown that animal nutrition is tightly linked to gut microbiota, especially under nutritional stress. In Drosophila melanogaster, microbiota are known to promote juvenile growth, development, and survival on poor diets, mainly through enhanced digestion leading to changes in hormonal signaling. Here, we show that this reliance on microbiota is greatly reduced in replicated Drosophila populations that became genetically adapted to a poor larval diet in the course of over 170 generations of experimental evolution. Protein and polysaccharide digestion in these poor-diet-adapted populations became much less dependent on colonization with microbiota. This was accompanied by changes in expression levels of dFOXO transcription factor, a key regulator of cell growth and survival, and many of its targets. These evolutionary changes in the expression of dFOXO targets to a large degree mimic the response of the same genes to microbiota, suggesting that the evolutionary adaptation to poor diet acted on mechanisms that normally mediate the response to microbiota. Our study suggests that some metazoans have retained the evolutionary potential to adapt their physiology such that association with microbiota may become optional rather than essential.

Effects of temporary starvation and feeding on the survival and developmental time to metamorphosis in megalopa larvae of two Neotropical mangrove crab species, genus Sesarma (Sesarmidae)

Temporal variation in pelagic food supply may affect the larval development and recruitment success of many decapod crustaceans in marine coastal ecosystems. In the present study, we experimentally investigated the degree of nutritional vulnerability in megalopa larvae of two sesarmid crab species (Sesarma curacaoense and S. rectum) subjected to different conditions of nutritional stress. In the laboratory, Sesarma megalopae were initially starved for up to 9days followed by a constant feeding period in one experiment (i.e., point of no return), or they were fed at the beginning of their development for up to 9days followed by a continuous period of food deprivation in a second experiment (i.e., point of reserve saturation). Megalopae were also constantly reared in the absence and presence of food (Artemia sp. nauplii) in two control groups. The larval response to the different experimental conditions was evaluated through the percentage of survival (=% metamorphosed larvae), developmental time to metamorphosis, and Nutritional Vulnerability Index (= PRS50/PNR50). All megalopae died when reared under constant starvation whereas 100% of the larvae metamorphosed into the first juvenile crab stage after 13.1±4.4days (S. curacaoense) or 12.4±1.2days (S. rectum) when continuously fed. In the first experiment, the starvation periods did not affect the mean developmental time of the megalopae through metamorphosis (13.6±4.3days) of S. curacaoense and only those larvae initially starved for 7days presented the lowest percentage of metamorphosis to juvenile crab (73%). In S. rectum, by contrast, megalopae starved from 5 to 9days exhibited lower percentages of metamorphosis (≤86%) compared to larvae starved for 1 or 3days or those constantly fed. Furthermore, megalopae starved for 7 and 9days delayed by 1.6 and 3.5days their metamorphosis, respectively, compared to larvae constantly fed. In the second experiment, the Sesarma megalopae initially fed for only 1day presented lower percentages of metamorphosis (≤73%) than megalopae fed for 3 or more days or continually (≥93%). The mean developmental time to metamorphosis was shorter with 1day (8.1±0.7days in S. curacaoense) or 3days (11.3±1.6days in S. rectum) of temporary feeding. The estimated values of the PNR50 and PRS50 indices were respectively 7.34 and 0.93days for S. curacaoense and 9.01 and 1.78days for S. rectum. These values provided a Nutritional Vulnerability Index of 0.13 for S. curacaoense and 0.2 for S. rectum, indicating a reduced dependence on exogenous food by the megalopae of these two sesarmid crab species. This starvation tolerance associated with a short megalopal development should increase the likelihood of successful survival into the benthic life phase and avoid latent effects of the larval nutritional stress and/or delayed metamorphosis on early juvenile performance of both Sesarma species.

Modulation of Autophagy by BDNF Underlies Synaptic Plasticity

Autophagy is crucial for neuronal integrity. Loss of key autophagic components leads to progressive neurodegeneration and structural defects in pre- and postsynaptic morphologies. However, the molecular mechanisms regulating autophagy in the brain remain elusive. Similarly, while it is widely accepted that protein turnover is required for synaptic plasticity, the contribution of autophagy to the degradation of synaptic proteins is unknown. Here, we report that BDNF signaling via the tropomyosin receptor kinase B (TrkB) and the phosphatidylinositol-3' kinase (PI3K)/Akt pathway suppresses autophagy invivo. In addition, we demonstrate that suppression of autophagy is required for BDNF-induced synaptic plasticity and for memory enhancement under conditions of nutritional stress. Finally, we identify three key remodelers of postsynaptic densities as cargo of autophagy. Our results establish autophagy as a pivotal component of BDNF signaling, which is essential for BDNF-induced synaptic plasticity. This molecular mechanism underlies behavioral adaptations that increase fitness in times of scarcity.