Prolonged Nutrient Starvation Research Articles

The yeast VAPs Scs2 and Scs22 are required for NVJ integrity and micronucleophagy

Microautophagy degrades cargos in the vacuole by direct engulfment of the vacuolar membrane. Micronucleophagy selectively degrades a portion of the nucleus in budding yeast. The vacuole contacts the nucleus via the nucleus–vacuole junction (NVJ), and in micronucleophagy a portion of the nucleus containing nucleolar proteins is made to protrude into the vacuole at the NVJ, followed by abscission and degradation. Microautophagy and micronucleophagy are induced by inactivation of target of rapamycin complex 1 (TORC1) protein kinase after nutrient starvation. Here, we show that the VAMP-associated proteins (VAPs) Scs2 and its paralog Scs22 are required for NVJ integrity and micronucleophagic degradation of nucleolar proteins. On the other hand, nucleolar dynamics prerequisite for micronucleophagy were not impaired in VAP mutant cells. Finally, yeast VAPs were critical for viability during prolonged nutrient starvation. This study sheds light on the emerging role of VAP in adaptation in responses to nutrient starvation.

Special issue in honour of Prof. Reto J. Strasser - Gradual changes in the photosynthetic apparatus triggered by nitrogen depletion during microalgae cultivation in photobioreactor

Changes of photosynthetic activity during natural depletion of nitrogen in a batch culture of Chlorella vulgaris were studied using chlorophyll a fluorescence-based methods. Complex analysis including JIP-test, multiexponential approximation, and the analysis of differential curves was carried out on the recorded fluorescence transients. Three pivot points were detected in dynamics of the JIP-test parameters during culture growing. We associated these time points with different stages of mineral stress progress. Immediately after nitrogen exhaustion in the cultivation medium, a transient increase in the efficiency of PSII was detected. During this short period, the photosynthetic apparatus acclimated to the stress by reducing the number of PSII reaction centers, simultaneously increasing the effective cross section of the light-harvesting antenna per reaction center. However, prolonged nutrient starvation impaired the structure of the photosynthetic apparatus, deactivating the oxygen-evolving complex and impairing the overall electron transport.

Increasing AMPK activity supports enhanced oxidative metabolism, proliferation, and in vitro recovery of human CD4+ T cells

Abstract Background In adoptive immunotherapy, treatment success correlates with the in vivo expansion and subsequent persistence of transferred cells. In T cells, survival and memory formation are both enhanced when cells exhibit higher levels of oxidative metabolism. AMP-activated protein kinase (AMPK) is a master regulator of metabolism, promoting oxidative phosphorylation when nutrients are scarce. We hypothesized that enhanced AMPK signaling would improve T cell therapeutic potential by increasing their oxidative potential and prolonging their persistence. Results Jurkat and primary human T cells were transduced with a lentiviral construct encoding either AMPKγ2 or an empty vector. All AMPKγ2 transduced cells showed increased activation of the AMPK pathway, with AMPK-transduced Jurkat T cells exhibiting increased baseline and maximal oxygen consumption as measured on a Seahorse Metabolic Analyzer. Furthermore, they were able to maintain this enhanced oxidative metabolism despite prolonged nutrient starvation. In addition, AMPK-transduced primary human T cells increased their mitochondrial density and improved their in vitro proliferation, with significantly increased recovery of CD4+ T cells. Discussion Increasing AMPK activity by over-expressing AMPKγ2 increases the in vitro oxidative potential, proliferation, and recovery of human T cells, particularly CD4+ T cells. These changes are all attractive features for subsequent adoptive immunotherapy. Further work will evaluate the mechanism underlying the phenotype and metabolome of AMPK-transduced cells and will assess their metabolic activity and persistence in vivo.

Reversible solidification of fission yeast cytoplasm after prolonged nutrient starvation.

ABSTRACTCells depend on a highly ordered organisation of their content and must develop strategies to maintain the anisotropic distribution of organelles during periods of nutrient shortage. One of these strategies is to solidify the cytoplasm, which was observed in bacteria and yeast cells with acutely interrupted energy production. Here, we describe a different type of cytoplasm solidification fission yeast cells switch to, after having run out of nutrients during multiple days in culture. It provides the most profound reversible cytoplasmic solidification of yeast cells described to date. Our data exclude the previously proposed mechanisms for cytoplasm solidification in yeasts and suggest a mechanism that immobilises cellular components in a size-dependent manner. We provide experimental evidence that, in addition to time, cells use intrinsic nutrients and energy sources to reach this state. Such cytoplasmic solidification may provide a robust means to protect cellular architecture in dormant cells.

Chronic starvation induces noncanonical pro-death stress granules.

Stress granules (SGs) assemble under stress-induced conditions that inhibit protein synthesis, including phosphorylation of eIF2α, inhibition of the RNA helicase eIF4a proteins or inactivation of mTORC1. Classically defined SGs are composed of translation initiation factors, 40S ribosomes, RNA-binding proteins and poly(A)+ mRNAs. As such, they represent an important compartment for storage of mRNAs and regulation of their translation. Emerging work on SGs indicates that these structures might promote cellular survival in diverse disease states. Yet, much work on SG formation and function employs acute stress conditions, which might not accurately reflect the chronic stresses that manifest in human disease. Here, we used prolonged nutrient starvation to model and investigate SG formation and function during chronic stress in a human cell line and mouse embryonic fibroblasts. Surprisingly, we found that SGs that form under chronic nutrient starvation lack 40S ribosomes, do not actively exchange their constituent components with cytoplasmic pools and promote cell death. We named these SGs starvation-induced SGs (stSGs). Our results on stSGs imply that SG assembly and function in the context of prolonged nutrient starvation stress differ significantly from what has been described for acute stress conditions.

Differential influence of nutrient-starved Mycobacterium tuberculosis on adaptive immunity results in progressive tuberculosis disease and pathology.

When infected with Mycobacterium tuberculosis, most individuals will remain clinically healthy but latently infected. Latent infection has been proposed to partially involve M. tuberculosis in a nonreplicating stage, which therefore represents an M. tuberculosis phenotype that the immune system most likely will encounter during latency. It is therefore relevant to examine how this particular nonreplicating form of M. tuberculosis interacts with the host immune system. To study this, we first induced a state of nonreplication through prolonged nutrient starvation of M. tuberculosis in vitro. This resulted in nonreplicating persistence even after prolonged culture in phosphate-buffered saline. Infection with either exponentially growing M. tuberculosis or nutrient-starved M. tuberculosis resulted in similar lung CFU levels in the first phase of the infection. However, between week 3 and 6 postinfection, there was a very pronounced increase in bacterial levels and associated lung pathology in nutrient-starved-M. tuberculosis-infected mice. This was associated with a shift from CD4 T cells that coexpressed gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) or IFN-γ, TNF-α, and interleukin-2 to T cells that only expressed IFN-γ. Thus, nonreplicating M. tuberculosis induced through nutrient starvation promotes a bacterial form that is genetically identical to exponentially growing M. tuberculosis yet characterized by a differential impact on the immune system that may be involved in undermining host antimycobacterial immunity and facilitate increased pathology and transmission.

Nutrient remediation rates in municipal wastewater and their effect on biochemical composition of the microalga Scenedesmus sp. AMDD

Microalgae are very efficient at removing nutrients from municipal wastewater and may be a viable tertiary wastewater treatment while additionally improving the economics of microalgal cultivation for biofuel production. The relative quantities and productivities of fatty acids, carbohydrates and proteins were determined in the microalga Scenedesmus sp. AMDD grown in treated municipal wastewater in continuous chemostats under different dilution rates or hydraulic retention times. The dilution rate of the chemostat exerted a strong control over the biochemical composition of the cultivated biomass and clear differences in the patterns of accumulation of cellular constituents were detected. Maximum carbohydrate and protein productivities were estimated to be 130 and 120mgL−1d−1, respectively, at dilution rates of 0.5d−1 and 1.05d−1, respectively. Fatty acid productivity was fairly constant at about 20mgL−1d−1 across all tested dilution rates. Total fatty acid only accumulated when growth rates were very low or when a prolonged nutrient starvation regime was imposed by interrupting the supply of wastewater to the chemostat. Monounsaturated fatty acids increased by 250%, whereas polyunsaturated fatty acids decreased by 60% and saturated fatty acids remained fairly constant, from the highest dilution rate of 1.05d−1 to nutrient starved cells. The rate of wastewater nutrient remediation therefore strongly controls the composition of the biomass, thereby controlling its commercial applicability.

Prolonged environmental persistence requires efficient disinfection procedures to control Devriesea agamarum-associated disease in lizards

Devriesea agamarum infection causes chronic proliferative dermatitis, especially in desert dwelling lizards. The present study was concerned with evaluating persistency of D. agamarum in the environment and the evaluation of the efficacy of various disinfection procedures. First, the survival of D. agamarum was assessed both in dermal crusts obtained from clinically and naturally infected lizards, and during periods of prolonged nutrient starvation on dry surface, in moist sand and in distilled water. Secondly, a modified European Suspension Test was performed to determine the efficacy of eight procedures for the disinfection of equipment, environmental surfaces and the topical treatment of D. agamarum-associated dermal lesions. The bacterium proved to persist and remain viable for up to 57 days in dermal crusts and for more than 5months in moist sand and distilled water. In contrast, survival on dry surfaces was limited. The results of the described dilution-neutralization method demonstrated that most of the tested disinfection procedures were sufficient in achieving a 5-decimal logarithmic reduction in the number of D. agamarum colony-forming units. The use of relatively low concentrations of hydrogen peroxide and a boric and peracetic acid solution on the other hand resulted in insufficient reduction in viable counts. Devriesea agamarum can persist for long periods of time in the environment, especially under moist conditions, making the use of suitable disinfection procedures necessary. This study demonstrates the need for a dry environment for most desert lizards and the use of effective disinfection procedures next to antimicrobial treatment to eliminate D. agamarum-associated disease from captive saurian collections.

The Burkholderia cenocepacia K56-2 pleiotropic regulator Pbr, is required for stress resistance and virulence

Burkholderia cenocepacia is one of the most virulent species of the Burkholderia cepacia complex, a group of bacteria that emerged as important pathogens, especially to cystic fibrosis (CF) patients. In this study, we report the identification and characterization of a mutant strain derived form the CF isolate Burkholderia cenocepacia K56-2, carrying a plasposon insertion in a gene, located in a 3516 bp chromosomal region with an atypical G + C content, encoding a 80 amino acid putative regulatory protein named Pbr. Besides its inability to produce phenazines, the B. cenocepacia K56-2 pbr mutant exhibited a pleiotropic phenotype, including impaired survival to oxidative and osmotic stress, aromatic amino acid and prolonged nutrient starvation periods. In addition, the pbr mutant exhibited decreased virulence the nematode Caenorhabditis elegans. Altogether, our results demonstrate the involvement of Pbr on the regulation of phenazine biosynthesis, and an important role for this regulatory protein on several cellular processes related to stress resistance and virulence.

High level expression of theMagnaporthe griseamitochondrial small sub-unit rRNA during rice leaf colonization and rapid down-regulation prior to the onset of disease symptoms

Differential cDNA screening identified aMagnaporthe griseagene which is highly expressed during rice leaf colonization by the fungus. The transcript accumulatd 72 h after plant inoculation, just before symptom expression by the pathogen, but rapidly decreased in abundance after this time. DNA sequence analysis showed that the cDNA has homology to mitochondrial small sub-unit rRNAs. Consistent with this, the cDNA hybridized to purified mitochondrial DNA but did not hybridize to nuclear genomic DNA or chromosomal-sized DNA molecules. The corresponding gene also failed to segregate as a nuclear-encoded marker. To investigate expression of theM. griseasmall sub-unit mitochondrial rRNA during growth ofM. griseain axenic culture, experiments were carried out which showed that the transcript is constitutively expressed during active fungal growth but down-regulated by oxidative stress or prolonged nutrient starvation. The mitochondrial rRNA was also down-regulated developmentally during conidiation. The data are consistent with very active mitochondrial protein synthesis during colonization of rice tissue byM. grisea, followed by rapid down-regulation of mitochondrial activity prior to disease symptom outbreak and the onset of conidiogenesis.

The Survival of Coryneform Bacteria during Periods of Prolonged Nutrient Starvation

Summary: Cultures of 16 coryneform bacteria were grown to late-exponential stage in nutrient media, washed, and starved in 30 mm-potassium phosphate buffer pH 7.0, with no external energy or carbon source. After 4 weeks starvation, 20 to 98% of each culture was still viable; after 8 weeks, 5 to 70% of each culture was still viable. Little change in cell shape or size was detected in Arthrobacter globiformis, A. nicotianae, Brevibacterium linens, Corynebacterium fascians, Mycobacterium rhodochrous and Nocardia roseum when studied by electron microscopy for up to 56 d, although there was a gradual disappearance of intracellular material. No resting structures were discernible. All organisms showed an immediate decrease in endogenous respiration to less than 1% of that observed during growth. A low basal level of endogenous metabolism equivalent to 0.01 to 0.03% of cellular carbon oxidized to CO2 h−1 was maintained for 56 d. Carbohydrate, intracellular pools, protein, ribonucleic acid and deoxyribonucleic acid were utilized at varying rates by different organisms during this period. All species were effective in maintaining 20 to 70% of their Mg2+ content during a 28 d starvation period in the absence of any external Mg2+. It would appear that the soil coryneform bacteria possess similar survival characteristics in laboratory studies which could explain, in part, their ecological success in natural environments.