Cells Of Different Ages Research Articles

Distribution of Red Blood Cells Deformability: Study on Density-Separated Cell Subpopulations

Aging-related processes lead to significant metabolic and structural changes in red blood cells (RBCs) and, as a result, to heterogeneity in cell populations. Using the Percoll linear density gradient, separating the RBC population and obtaining fractions enriched with cells of different ages is possible. Previously, cells from the “light” fraction were characterized by increased deformability. However, the distribution of RBC deformability in subpopulations possessing a different density has not been studied. In this study, we measured the deformability of RBCs from cell fractions characterized by different densities. RBC deformability was determined using a computerized cell flow-properties analyzer, which provides the deformability distribution in a population of 10,000–15,000 cells. Our results demonstrate a strong correlation between the cytosol hemoglobin concentration and the cell deformation indexes. In addition, we show that the “lightest” fraction of RBCs contains the lowest number of deformable and the highest number of highly deformable cells. In contrast, the “dense” fraction is enriched with undeformable RBCs, with a minimal presence of highly deformable cells. In summary, we have shown that RBC fractions depleted or enriched with undeformable cells can be obtained by using a density gradient. However, these fractions are not homogeneous in their deformability properties.

Cell Level- Modeling of Aging and Rejuvenation

Understanding processes related to human aging and rejuvenation relies on experimental data and advanced models operating at different levels. There are several existing conceptual and specific modeling approaches. However, one of the existing tasks is compiling generic models linking properties at cell and cell-element levels to properties at systemic levels - tissue, organ, and whole body. One of the critical issues in the relevant models is the enormity of interacting components at the cell and sub-cell levels needed to represent the properties of high-level systems properly. This paper describes a promising approach to modeling and simulation at the cell population level for studying aging and rejuvenation. It also presents initial conclusions formulated based on the results of modeling and experiments coupled to it. The model is based on the concepts of the proliferation niche and homeostatic cell number stabilization in the cell population through the associated action of proliferation and apoptosis. Importantly, we address the issue of defining “aging” and “rejuvenation” for cell populations containing large numbers of cells of different ages. It is possible to demonstrate that homeostatic regulation can be performed by maintaining the concentration of a single regulatory substance. Predictions and simulations of the proposed model are compared to data from existing publications and experiments specifically conducted to validate the model. Currently, none of the available data contradicts the modeling results at the proposed level of detail. However, an inadequate number of elements and the employed statistical approach further limit progress in such modeling. Expanding the proposed method to include a realistic number of features representing human tissues, organs, and body and to allow for proper modeling of aging and rejuvenation processes requires more advanced modeling techniques.

Threshold behavior of an age-structured tumor immune model

In this paper, we present and analyze an age-structured tumor immune model. Based on the fact that tumor cells of different ages tend to exhibit different physiological behaviors, we consider the age structure of tumor cells, age-based proliferation function and age-dependent death function in the model. The threshold R0 for the existence of tumor-free steady state is derived. It is found that if R0 > 1, the tumor-free steady state is not only locally stable but also globally stable. Moreover, numerical simulation shows that the threshold R0 may be regarded as an index to reflect the ability of “tumor immune surveillance”, that is, the smaller the R0, the better the ability of tumor immune surveillance. If R0 > 1, it is proved that the tumor steady state is existent and uniformly persistent. The local stability of the tumor steady state is investigated under some further conditions besides R0 > 1. In the end, we estimate the system parameters, verify the theoretical results and analyze some system parameters’ sensitivities.

Landscape of transcription and expression regulated by DNA methylation related to age of donor and cell passage in adipose-derived mesenchymal stem cells.

Adipose-derived mesenchymal stem cells (ADSCs) are pluripotent stromal cells that can differentiate into a variety of cell types, including skin cells. High-throughput sequencing was performed on cells of different ages and cell passage, obtaining their methylation, mRNA expression, and protein profile data. The stemness of each sample was then calculated using the TCGAbiolinks package in R. Co-expression modules were identified using WGCNA, and a crosstalk analysis was performed on the corresponding modules. The ClusterProfile package was used for the functional annotation of module genes. Finally, the regulatory network diagram was visualized using the Cytoscape software. First, a total of 16 modules were identified, where 3 modules were screened that were most relevant to the phenotype. 29 genes were screened in combination of the RNA seq, DNA methylation seq and protein iTRAQ. Finally, a comprehensive landscape comprised of RNA expression, DNA methylation and protein profiles of age relevant ADSCs was constructed. Overall, the different omics of ADSCs were comprehensively analyzed in order to reveal mechanisms pertaining to their growth and development. The effects of age, cell passage, and stemness on the therapeutic effect of ADSCs were explored. Additionally, a theoretical basis for selecting appropriate ADSC donors for regenerative medicine was provided.

Accounting for red blood cell accessibility reveals distinct invasion strategies in Plasmodium falciparum strains.

The growth of the malaria parasite Plasmodium falciparum in human blood causes all the symptoms of malaria. To proliferate, non-motile parasites must have access to susceptible red blood cells, which they invade using pairs of parasite ligands and host receptors that define invasion pathways. Parasites can switch invasion pathways, and while this flexibility is thought to facilitate immune evasion, it may also reflect the heterogeneity of red blood cell surfaces within and between hosts. Host genetic background affects red blood cell structure, for example, and red blood cells also undergo dramatic changes in morphology and receptor density as they age. The in vivo consequences of both the accessibility of susceptible cells, and their heterogeneous susceptibility, remain unclear. Here, we measured invasion of laboratory strains of P. falciparum relying on distinct invasion pathways into red blood cells of different ages. We estimated invasion efficiency while accounting for red blood cell accessibility to parasites. This approach revealed different tradeoffs made by parasite strains between the fraction of cells they can invade and their invasion rate into them, and we distinguish “specialist” strains from “generalist” strains in this context. We developed a mathematical model to show that generalist strains would lead to higher peak parasitemias in vivo compared to specialist strains with similar overall proliferation rates. Thus, the ecology of red blood cells may play a key role in determining the rate of P. falciparum parasite proliferation and malaria virulence.

CARBON DIOXIDE AND METHANE FLUX MEASUREMENTS AT A LARGE UNSANITARY DUMPING SITE IN THE AMAZON REGION

Dumps are important anthropogenic sources of greenhouse gas emissions into the atmosphere, mostly CH4. However, few studies on the subject have been carried out in the Amazon region. Several factors affect the production and emission of dumps gas. The objective of this study was to quantify the spatial variation of CO2 and CH4 production in an Amazon dump and try to associate the relative importance of some environmental factors with the fluxes. This study was carried out in an open-air dump in the metropolitan region of Belém, where approximately 11.0 million Mg of waste was deposited in 25 years, of which 6.4 million Mg was organic. The emission rates of CH4 and CO2 from the surface of the dump were determined using the closed dynamic flux chamber technique. The study was conducted in three cells of different ages, sampled in two moments between the Amazon rainy and dry season. The Aura dump has an area of 30 ha and emits a total of 51.49 Mg CO2 ha-1 month-1 and 3.16 Mg CH4 ha-1 month-1 to the atmosphere. This results in an expressive production of 1,359,961.04 Mg CO2-e year-1, being that 58.54% is due to CH4 flux. The spatial variability in CO2 and CH4 flux is very large, especially for CH4, forming hotspots of high concentrations, and perhaps because of this, the flow has not been correlated with micrometeorological variations.

Metabolic kinetic model for dibenzothiophene desulfurization through 4S pathway using intracellular compound concentrations

Dibenzothiophene desulfurization with Pseudomonas putida CECT5279 in resting cells has been studied. A rational evolution of the kinetic modeling of the 4S desulfurization route is presented based on the recent advances in the knowledge of this bioprocess. Taking into account the influence of some intracellular compounds in the kinetics of the reactions involved in the 4S route, in particular ATP and NADH, a new kinetic model including this information has been formulated. The resulting kinetic model is able to satisfactorily predict the evolution of the 4S route compounds in a wide range of conditions that previous models were unable to describe correctly. These wide conditions include the use of cells of a single age and the mixture of cells of different ages. The model is able to describe process evolution when acetic acid is used as co-substrate, both in batch and fed-batch operations.

Analysis of microbial community structure and composition in leachates from a young landfill by 454 pyrosequencing.

Microorganisms are responsible for degrading the raw leachate generated in sanitary landfills, extracting the soluble fraction of the landfill waste and biotransforming organic matter and toxic residues. To increase our understanding of these highly contaminated ecosystems, we analyzed the microbial communities in the leachate produced by three landfill cells of different ages. Using high-throughput 454 pyrosequencing of the 16S rRNA gene, we describe the structure of the leachate communities and present their compositional characteristics. All three communities exhibited a high level of abundance but were undersampled, as indicated by the results of the rarefaction analysis. The distribution of the taxonomic operational units (OTUs) was highly skewed, suggesting a community structure with a few dominant members that are key for the degradation process and numerous rare microorganisms, which could act as a resilient microorganism seeder pool. Members of the phylum Firmicutes were dominant in all of the samples, accounting for up to 62% of the bacterial sequences, and their proportion increased with increasing landfill age. Other abundant phyla included Bacteroidetes, Proteobacteria, and Spirochaetes, which together with Firmicutes comprised 90% of the sequences. The data illustrate a microbial community that degrades organic matter in raw leachate in the early stages, before the methanogenic phase takes place. The genera found fit well into the classical pathways of anaerobic digestion processes.

Paradoxical response to mechanical unloading in bone loss, microarchitecture, and bone turnover markers.

Background: Sclerostin, encoded by the SOST gene, has been implicated in the response to mechanical loading in bone. Some studies demonstrated that unloading leads to up-regulated SOST expression, which may induce bone loss.Purpose: Most reported studies regarding the changes caused by mechanical unloading were only based on a single site. Considering that the longitudinal bone growth leads to cells of different age with different sensitivity to unloading, we hypothesized that bone turnover in response to unloading is site specific.Methods: We established a disuse rat model by sciatic neurectomy in tibia. In various regions at two time-points, we evaluated the bone mass and microarchitecture in surgically-operated rats and control rats by micro-Computed Tomography (micro-CT) and histology, sclerostin/SOST by immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), and quantitative reverse transcription polymerase chain reaction (qPCR), tartrate resistant acid phosphatase 5b (TRAP 5b) by ELISA and TRAP staining, and other bone markers by ELISA. Results: Micro-CT and histological analysis confirmed bone volume in the disuse rats was significantly decreased compared with those in the time-matched control rats, and microarchitecture also changed 2 and 8 weeks after surgery. Compared with the control groups, SOST mRNA expression in the diaphysis was down-regulated at both week 2 and 8. On the contrary, the percentage of sclerostin-positive osteocytes showed an up-regulated response in the 5 - 6 mm region away from the growth plate, while in the 2.5 - 3.5 mm region, the percentage was no significant difference. Nevertheless, in 0.5 - 1.5 mm region, the percentage of sclerostin-positive osteocytes decreased after 8 weeks, consistent with serum SOST level. Besides, the results of TRAP also suggested that the expression in response to unloading may be opposite in different sites or system.Conclusion: Our data indicated that unloading-induced changes in bone turnover are probably site specific. This implies a more complex response pattern to unloading and unpredictable therapeutics which target SOST or TRAP 5b.

Emission characteristics and air–surface exchange of gaseous mercury at the largest active landfill in Asia

The emission characteristics and air-surface exchange of gaseous elemental mercury (GEM) at Laogang landfill in Shanghai, China, the largest active landfill in Asia, has been investigated during two intensive field campaigns in 2011 and 2012. The mercury (Hg) content in municipal solid waste (MSW) varied widely from 0.19 to 1.68 mg kg−1. Over the closed cell in the landfill, the mean ambient air GEM concentration was virtually indistinguishable from the hemispherical background level (1.5–2.0 ng m−3) while the concentration downwind of ongoing landfill operation (e.g. dumping, burying and compacting of MSW) was clearly elevated. GEM emission through landfill gas (LFG) was identified as a significant source. GEM concentrations in LFGs collected from venting pipes installed in different landfill cells varied widely from 3.0 to 1127.8 ng m−3. The GEM concentrations were found negatively correlated to the age of LFG cells, suggesting GEM released through LFG declined readily with time. The GEM emission from this source alone was estimated to be 1.23–1.73 mg h−1. GEM emission from cover soil surfaces was considerably lower and at a scale comparable to that of background soil surfaces. This is in contrast to earlier reports showing enhanced GEM emissions from landfill surfaces in Southern China, probably due to the difference in soil Hg content and gas permeability characteristics of soils at different sites. Vertical concentration profiles of GEM in the interstitial gas of buried MSW were sampled, perhaps for the first time, which exhibited a wide spatial variability (4.9–713.1 ng m−3) in the 3-year-old landfill cell investigated. GEM emission from landfill operation was estimated to be 290–525 mg h−1 using a box model. This suggests that GEM degassing from Laogang landfill is quantitatively largely dominated by emissions from daily landfilling operations with a much smaller contribution from LFG venting and insignificant (bi-directional fluxes near zero) contribution from surfaces capped with a soil layer. This study reveals divergent GEM emission patterns among landfill cells of different ages, and provides essential emission estimates for formulating Hg emission reduction strategies for a large landfill.

Expressions of p16INK4a gene and Bmi1 gene in human corneal endothelial cells of different ages

Background p16INK4a gene plays an important role during the aging and senility. So it was well known to be a leading gene associated with aging. Corneal endothelial cells（CECs） always get trapped in the G1 phase due to the lack of proliferative ability. Whether it is relative with cell senescence is unclear. Objective This study was to investigate the expression of p16INK4a gene and Broil gene in human CECs from different aged donors ex vivo. Methods The corneal rims,the residual of corneal tissue preserved in DX solution after penetrating keratoplasty,was used in the present study. Parameters were recorded for the donor, including the age, death to preservation interval and preservation to surgery interval. Corneal endothelium survival rate and endothelial cell density were evaluated by trypan blue-alizarin red dying immediately after penetrating keratoplasty. Routine haematoxylin and eosin staining was also performed to proof the normal structure of the cornea. Sections of corneas from different aged donors were classified into 〈 30 years group, 30-50 years group and 〉 50 years group and were immunostained to assess the expressions of p16INK4a protein, Bmil protein and Ki67 protein in CECs. Total RNA was extracted from independent corneal sampie for the evaluation of p16INK4a mRNA,Bmil mRNA and Ki67 mRNA expression in CECs by quantitative real-time PCR（qRT-PCR）. Results The endothelial cell density of each group was（3069±172） , （2748±64） , （2444 ± 178 ）cells/ram2, respectively. Haematoxylin and eosin staining showed the normal structure of corneal epithelium, stroma and endothelium, qRT-PCR examination revealed an age-related increase in p16~NK4a mRNA expression in the CECs（ F = 5. 703, P = 0. 014 ） and a decrease in Bmil mRNA and Ki67 mRNA expression （ F -- 3. 950 ,P= 0. 042;F--548. 500, P = 0. 000 ）. The further comparison verified a significant elevation in the expression of p16~NK4a mRNA in the CECs of the 〉50 years group compared with 〈30 years group and significant decline in Broil mRNA and Ki67 mRNA the expression （ P = 0. 006,0. 013,0. 000）. Immunohistochemistry in situ confirmed the expression and nuclear localization of p16INK4a protein in CECs, and the expressing intensities of Bmil and Ki67 proteins in the elder donors were weaker than those of the younger donors. The immunofluorescence exhibited that the expressing intensity of p16INK4a protein in CECs of 58 years old donor was higher than that of 23 years old donor, showing a consistent result with that of qRT-PCR. Conclusions Expression of p16INK4a gene increases and that of Bmil gene decreases upon age. These results suggest that p16INK4a gene is associated with senescence of human CECs. Key words: Corneal endothelial cell; Senescence; p16INK4a gene; Broil gene

Vital mitochondrial functions show profound changes during yeast culture ageing

During a 10-day culture ageing, cells of the wild-type Saccharomyces cerevisiae strain JC 482 retain their viability, while mitochondrial function and morphology change. Cell routine and uncoupled respiration rates increase to a maximum on day 4 and then decline to near zero. The decline, which occurs also in mitochondria isolated from cells of different age, is not due to increasing proportion of petites. Rhodamine 123 fluorescence intensity reporting on mitochondrial membrane potential appears to drop slightly for 4days and then more sharply at the time when respiration rate also decreases. The MitoTracker Green fluorescent signal related to the mitochondrial content per cell also decreases. The branched tubular mitochondrial network of 1-day-old cells dissolves into short fragments; during the first 4days, this fragmentation is associated with increasing function of mitochondria, while later on, it accompanies functional decline, which is also indicated by the decreasing ratio of Rhodamine 123 fluorescence to MitoTracker Green fluorescence. As shown by cell counting, microscopy and flow cytometry, the cell size distribution in the population broadens, and the population thus becomes more heterogeneous. The changes in respiration rate, mitochondrial membrane potential, mass and structure point to changes in the mitochondrial status during ageing.

Activation and interruption of the reproduction of Varroa destructor is triggered by host signals (Apis mellifera)

The reproductive cycle of the parasitic mite Varroa destructor is closely linked to the development of the honey bee host larvae. Using a within colony approach we introduced phoretic Varroa females into brood cells of different age in order to analyze the capacity of certain stages of the honey bee larva to either activate or interrupt the reproduction of Varroa females. Only larvae within 18h (worker) and 36h (drones), respectively, after cell capping were able to stimulate the mite’s oogenesis. Therewith we could specify for the first time the short time window where honey bee larvae provide the signals for the activation of the Varroa reproduction. Stage specific volatiles of the larval cuticle are at least part of these activation signals. This is confirmed by the successful stimulation of presumably non-reproducing mites to oviposition by the application of a larval extract into the sealed brood cells. According to preliminary quantitative GC–MS analysis we suggest certain fatty acid ethyl esters as candidate compounds.If Varroa females that have just started with egg formation are transferred to brood cells containing host larvae of an elder stage two-thirds of these mites stopped their oogenesis. This confirms the presence of an additional signal in the host larvae allowing the reproducing mites to adjust their own reproductive cycle to the ontogenetic development of the host. From an adaptive point of view that sort of a stop signal enables the female mite to save resources for a next reproductive cycle if the own egg development is not sufficiently synchronized with the development of the host.The results presented here offer the opportunity to analyze exactly those host stages that have the capacity to activate or interrupt the Varroa reproduction in order to identify the crucial host signals.

Spatial differences within the membrana granulosa in the expression of focimatrix and steroidogenic capacity

In the ovarian follicular membrana granulosa there are morphological and functional differences between cells adjacent to the follicular fluid lumen, or aligning the basal lamina. Amongst the observed functional differences are steroidogenic capacity and expression levels of a novel basal lamina, focimatrix; both of which increase in the later stages of antral follicle growth. A number of different studies have produced apparently inconsistent results as to which cell layers are more steroidogenic. To examine this systematically, individual bovine follicles, confirmed as healthy by post hoc histological examination, were used to isolate populations of apical and basal granulosa cells. Cell counts revealed that the respective groups did not differ in the numbers of cells, thus confirming the separation of these populations. We measured gene expression (quantitative RT-PCR, n=8–10, follicle diameter 14.0±0.5mm) and protein levels (Western immunoblotting, n=14, follicle diameter 11.9±0.5mm) and hormone production from granulosa cells (2.5×105 viable cells/well in serum-free conditions for 24h, n=15, diameter 12±0.5mm). Levels of mRNA of HSD3B1 and CYP19A1 and three focimatrix genes COL4A1, HSPG2 and LAMB2 and LHCGR were significantly lower in apical granulosa cells (P<0.05), whereas, expression of CYP11A1 and HSD17B1 were not different (P>0.05). The protein levels of steroidogenic enzymes P450scc and P450arom were significantly higher in apical cells (P<0.05), whereas those of 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase type 1 were not different (P>0.05). Progesterone production was significantly lower and oestradiol production was significantly higher in apical granulosa cells (P<0.05). These results confirm that apical and basal cells are functionally different, and the differences might be explained by the location of cells of different ages and maturity within the membrana granulosa. Discrepancies in the literature on their steroidogenic capacity may reflect differences in the steroidogenic parameters measured.

Age-Dependent Acoustic and Microelastic Properties of Red Blood Cells Determined by Vector Contrast Acoustic Microscopy

Variations of the mechanical properties of red blood cells that occur during their life span have long been an intriguing task for investigations. The research presented is based on noninvasive monitoring of red blood cells of different ages performed by scanning acoustic microscopy with magnitude and phase contrast. The characteristic signature of fixed cells from groups of three different ages fractionated according to mass density is obtained from the acoustic microscope images, with the data represented in polar graphs. The analysis of these data enables the determination of averaged values for the velocities of ultrasound propagating in the cells from the different groups ranging from (1,681 ± 16) m s(-1) in the youngest to (1,986 ± 20) m s(-1) in the oldest group. The determined bulk modulus varies with age from (3.04 ± 0.05) GPa to (4.34 ± 0.08) GPa. An approach to determine for an age-mixed population of red blood cells, collected from a healthy person, the age of the individual cells and the age dependence of the cell parameters including density, velocity, and attenuation of longitudinal polarized ultrasonic waves traveling in the cells is demonstrated.

Extended kinetic model for DBT desulfurization using Pseudomonas Putida CECT5279 in resting cells

Dibenzothiophene desulfurization by Pseudomonas putida CECT5279, genetically modified microorganism, in resting cells is studied. In previous works, operational conditions were established and a kinetic model describing the four serial reactions was proposed. Later studies showed the existence of two characteristic growth times of this bacterium, 5 and 23h, offering maximum activities in the desulfinase and the monooxygenase enzymes of this route. The combination of cells collected at 5 and 23h of growth time was proved to be a very effective biocatalyst for desulfurization in resting cells. In this work, the previously proposed kinetic model is extended and applied to these cells with different ages. Moreover, other extension is considered, taking into account the activity loss of the enzymes involved in 4S route, and the influence of biomass concentration employed. These extensions are of considerable importance in order to scale-up the process. The kinetic model developed is able to fit the experimental results for resting cell operation with cells of different ages, in different concentration taking into account the enzyme deactivation.

Determination of nonylphenol isomers in landfill leachate and municipal wastewater using steam distillation extraction coupled with comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry

4-Nonylphenols (4-NPs) are known endocrine disruptors and by-products of the microbial degradation of nonylphenol polyethoxylate surfactants. One of the challenges to understanding the toxic effects of nonylphenols is the large number of isomers that may exist in environmental samples. In order to attribute toxic effects to specific compounds, a method is needed for the separation and quantitation of individual nonylphenol isomers. The pre-concentration methods of solvent sublimation, solid-phase extraction or liquid–liquid extraction prior to chromatographic analysis can be problematic because of co-extraction of thousands of compounds typically found in complex matrices such as municipal wastewater or landfill leachate. In the present study, steam distillation extraction (SDE) was found to be an effective pre-concentration method for extraction of 4-NPs from leachate and wastewater, and comprehensive two-dimensional gas chromatography (GC×GC) coupled with fast mass spectral data acquisition by time-of-flight mass spectrometry (ToFMS) enhanced the resolution and identification of 4-NP isomers. Concentrations of eight 4-NP isomers were determined in leachate from landfill cells of different age and wastewater influent and effluent samples. 4-NP isomers were about 3 times more abundant in leachate from the younger cell than the older one, whereas concentrations in wastewater effluent were either below detection limits or <1% of influent concentrations. 4-NP isomer distribution patterns were found to have been altered following release to the environment. This is believed to reflect isomer-specific degradation and accumulation of 4-NPs in the aquatic environment.

Investigating yeast cell responses to oestrogen by electrochemical detection

Candida albicans and some other yeast species are known to have an oestrogen binding protein (EBP), which oxidises NAD(P)H to NAD(P)+. 17β-oestradiol, when present, binds to the NAD(P)H oxidation site which leads to an accumulation of NAD(P)H. Our previous research has shown that oestrogens can be quantified using Saccharomyces cerevisiae cells as the detection element and a double mediator electrochemical system to measure NAD(P)H. In a modification to the whole cell method, C. albicans cell lysate and a single hydrophilic mediator was used to quantify 17β-oestradiol. This paper employs the mediated electrochemical systems to investigate the influence of growth phase on EBP production in C. albicans and the response of cells of different ages to different concentrations of oestrogen. A cell not known to possess EBP (Arxula adeninivorans) was also investigated for its response to 17β-oestradiol. As expected, A. adeninivorans did not show a detectable response to 17β-oestradiol, but surprisingly, its catabolism was inhibited.

Aerobic microbial activity and solid waste biodegradation in a landfill located in a semi-arid region of Argentina

The sanitary landfill of Bahia Blanca city, Argentina, located in a semiarid region, receives 270 tons/day of municipal solid waste. The objectives of the study were: (1) to determine aerobic microbial activity (MA) and waste biodegradation taking into account the age of the waste, and (2) to evaluate the degree of waste stabilization of the oldest cell. MA was determined by CO2 release and chemical characterization in four cells of different ages of landfill. Furthermore, enzymatic methods were used to determine the effect on MA of leachate addition. Low annual rainfall, the sandy characteristics of the soil, and the use of landfill techniques where rigorous compaction is not performed, contribute to maintaining microenvironments with a sufficient quantity of O2 to support aerobic degradation processes. Under these conditions, degrading processes are faster, thus explaining why MA in the landfill cell closed in 1992 is stabilized and behaves as an anthrosol. In areas where MA is limited by lack of water (arid and semiarid zones), refuse degradation is limited to favorable humid periods. For that reason, operations favoring fast and efficient aerobic activity should be implemented.

Pole Age Affects Cell Size and the Timing of Cell Division in Methylobacterium extorquens AM1

A number of recent experiments at the single-cell level have shown that genetically identical bacteria that live in homogeneous environments often show a substantial degree of phenotypic variation between cells. Often, this variation is attributed to stochastic aspects of biology-the fact that many biological processes involve small numbers of molecules and are thus inherently variable. However, not all variation between cells needs to be stochastic in nature; one deterministic process that could be important for cell variability in some bacterial species is the age of the cell poles. Working with the alphaproteobacterium Methylobacterium extorquens, we monitored individuals in clonally growing populations over several divisions and determined the pole age, cell size, and interdivision intervals of individual cells. We observed the high levels of variation in cell size and the timing of cell division that have been reported before. A substantial fraction of this variation could be explained by each cell's pole age and the pole age of its mother: cell size increased with increasing pole age, and the interval between cell divisions decreased. A theoretical model predicted that populations governed by such processes will quickly reach a stable distribution of different age and size classes. These results show that the pole age distribution in bacterial populations can contribute substantially to cellular individuality. In addition, they raise questions about functional differences between cells of different ages and the coupling of cell division to cell size.