The relationship between cell size and viability of soil bacteria

The number of bacterial cells in soil that form colonies on nutrient agar represent a small fraction of the direct microscopic counts (DMC). The colony-forming cells have larger cell dimensions than the very small (dwarf) cells which represent the majority of the DMC. This may indicate that the dwarf cells are species unable to form visible colonies on agar, or that they swell to normal dimensions when growing. Indigenous bacterial cells were separated from soil by density gradient centrifugation and fractionated according to diameter by filtration through polycarbonate filters. Each filtrate was studied with respect to DMC, cell dimensions, colony-forming cells (visible colonies and microcolonies), and cell dimensions during growth on the agar. The calculated average percent viability was only 0.2% for cells with diameters below 0.4m, about 10% for cells with diameters between 0.4 and 0.6m, and 30–40% for cells with diameters above 0.6m. Only 10–20% of the viable cells with diameters <0.4m increased their diameter to >0.4m prior to growth. Thus, size change during starvation and growth cycles did not explain the high numbers of dwarf cells observed by microscopy. The results show that despite the relatively low number of colony-forming bacteria in soil, the species that form colonies may be fairly representative for the medium size and large cells, which constitute a major part of the bacterial biovolume. Thus plate counting could be a useful method to count and isolate the bacteria accounting for much of the biovolume in soil. The origin of the dwarf cells is still unclear, but the low number of small cells that increased in size seems to indicate that the majority of these bacterial cells are not small forms of ordinary sized bacteria.     

Dynamics of nitrogen remobilization in defoliated Phleum pratense and Festuca pratensis under short and long photoperiods

The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy (Phleum pratense L. cv. Bodin) and meadow fescue (Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 mM NH₄NO₃ and pre-treated by extending the 11 h photosynthetically significant light period either by 1 h (short-day or SD plants) or 7 h (long-day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, ¹⁵N-labelled NH₄⁺ or NH₄⁺+ NO₃^? was supplied over a 20-day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO₃^? reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO₃^? uptake restarting 1 or 2 days earlier than NH₄⁺ uptake, even when NH₄⁺ was the only form of N supply. LD timothy plants supplied solely with NH₄⁺ were slowest to resume uptake of mineral N. Supplying NO₃^? in addition to NH₄⁺ after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short-term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink-driven rates of N remobilization and their interactions with mineral N uptake following defoliation.     

Evolutionary stasis and lability in thermal physiology in a group of tropical lizards

Understanding how quickly physiological traits evolve is a topic of great interest, particularly in the context of how organisms can adapt in response to climate warming. Adjustment to novel thermal habitats may occur either through behavioural adjustments, physiological adaptation or both. Here, we test whether rates of evolution differ among physiological traits in the cybotoids, a clade of tropical Anolis lizards distributed in markedly different thermal environments on the Caribbean island of Hispaniola. We find that cold tolerance evolves considerably faster than heat tolerance, a difference that results because behavioural thermoregulation more effectively shields these organisms from selection on upper than lower temperature tolerances. Specifically, because lizards in very different environments behaviourally thermoregulate during the day to similar body temperatures, divergent selection on body temperature and heat tolerance is precluded, whereas night-time temperatures can only be partially buffered by behaviour, thereby exposing organisms to selection on cold tolerance. We discuss how exposure to selection on physiology influences divergence among tropical organisms and its implications for adaptive evolutionary response to climate warming.     

Hummingbirds fuel hovering flight with newly ingested sugar

We sought to characterize the ability of hummingbirds to fuel their energetically expensive hovering flight using dietary sugar by a combination of respirometry and stable carbon isotope techniques. Broadtailed hummingbirds (Selasphorus platycercus) were maintained on a diet containing beet sugar with an isotopic composition characteristic of C3 plants. Hummingbirds were fasted and then offered a solution containing cane sugar with an isotopic composition characteristic of C4 plants. By monitoring the rates of CO2 production and O2 consumption, as well as the stable carbon isotope composition of expired CO2, we were able to estimate the relative contributions of carbohydrate and fat, as well as the absolute rate at which dietary sucrose was oxidized during hovering. The combination of respirometry and carbon isotope analysis revealed that hummingbirds initially oxidized endogenous fat following a fast and then progressively oxidized proportionately more carbohydrates. The contribution from dietary sources increased with each feeding bout, and by 20 min after the first meal, dietary sugar supported approximately 74% of hovering metabolism. The ability of hummingbirds to satisfy the energetic requirements of hovering flight mainly with recently ingested sugar is unique among vertebrates. Our finding provides an example of evolutionary convergence in physiological and biochemical traits among unrelated nectar-feeding animals.     

Cryopreserving human peripheral blood progenitor cells

High-dose chemotherapy followed by autologous peripheral blood progenitor cell (PBPC) transplantation is used in the treatment of chemosensitive malignancies. Cryopreservation of PBPC in 10% dimethyl sulfoxide (DMSO) has been the standard procedure in most institutions. Infusion of PBPC cryopreserved with DMSO can be associated with toxic reactions such as vomiting, cardiac dysfunction, anaphylaxia and acute renal failure. The grade of toxicity experienced by patients is related to the amount of DMSO present in the PBPC. Cryopreservation with lower DMSO concentrations would be expected to reduce the toxicity. In recent studies done with PBPC cells cryopreserved with 5%, 4% and 2% DMSO, using 10% DMSO as a reference control, CD34+ cells were investigated for preservation of viability, apoptosis, and necrosis. Also preservation of mature colony-forming (CFU) cells, specifically mature myeloid, erythroid progenitors, CFU-megakaryocytes and long-term culture-initiating cells (LTC-ICs) were investigated, using 5% and 10% DMSO as cryoprotectant. All samples were frozen in a rate-controlled programmed freezer and stored in the vapor phase of liquid nitrogen until used. Conclusion: 5% DMSO is the optimal concentration for cryopreserving human PBPC in vitro. Consequently, some hospitals have started using 5% DMSO as cryoprotectant for the autologous PBPC as a standard procedure.     

Proteomic profile of culture filtrate from the Brazilian vaccine strain <Emphasis Type="Italic">Mycobacterium bovis</Emphasis> BCG Moreau compared to <Emphasis Type="Italic">M. bovis</Emphasis> BCG Pasteur

Background  

Bacille Calmette-Guerin (BCG) is currently the only available vaccine against tuberculosis (TB) and comprises a heterogeneous family of sub-strains with genotypic and phenotypic differences. The World Health Organization (WHO) affirms that the characterization of BCG sub-strains, both on genomic and proteomic levels, is crucial for a better comprehension of the vaccine. In addition, these studies can contribute in the development of a more efficient vaccine against TB. Here, we combine two-dimensional electrophoresis (2DE) and mass spectrometry to analyse the proteomic profile of culture filtrate proteins (CFPs) from M. bovis BCG Moreau, the Brazilian vaccine strain, comparing it to that of BCG Pasteur. CFPs are considered of great importance given their dominant immunogenicity and role in pathogenesis, being available for interaction with host cells since early infection.     

A tumor-associated mutation of FYVE-CENT prevents its interaction with Beclin 1 and interferes with cytokinesis

The tumor suppressor activity of Beclin 1 (BECN1), a subunit of class III phosphatidylinositol 3-kinase complex, has been attributed to its regulation of apoptosis and autophagy. Here, we identify FYVE-CENT (ZFYVE26), a phosphatidylinositol 3-phosphate binding protein important for cytokinesis, as a novel interacting protein of Beclin 1. A mutation in FYVE-CENT (R1945Q) associated with breast cancer abolished the interaction between FYVE-CENT and Beclin 1, and reduced the localization of these proteins at the intercellular bridge during cytokinesis. Breast cancer cells containing the FYVE-CENT R1945Q mutation displayed a significant increase in cytokinetic profiles and bi-multinuclear phenotype. Both Beclin 1 and FYVE-CENT were found to be downregulated in advanced breast cancers. These findings suggest a positive feedback loop for recruitment of FYVE-CENT and Beclin 1 to the intercellular bridge during cytokinesis, and reveal a novel potential tumor suppressor mechanism for Beclin 1.