Respiration in cell development

Summary Dark oxygen uptake was measured manometrically for cells of green high-temperature alga, Chlorella 7-11-05, separated from nonsynchronized populations by centrifugation into fractions of predominantly small or large cells. In the presence of exogenous glucose, respiration activity of the smaller (younger) cell fraction was invariably higher than that of the larger (older) cell fraction. In the absence of exogenous substrate, the difference in respiration rates in two fractions of cells was inconsistent from one experiment to another both in size and in sign. The dependence of dark respiration on the amount of available substrate makes the endogenous respiration rate unsuitable as an indicator of the inherent capacity of respiratory mechanisms.In observations on synchronized heterotrophically grown cells, the glucose respiration rate expressed per dry weight of cells gradually declined over the developmental period irrespective of the adequate exogenous supply of glucose or illumination by weak light. Observations on synchronized heterotrophically grown Chlorella cells thus corroborated studies of glucose respiration in cells separated into are groups by centrifugation.The decline in metabolic activity in the course of cell development previously established for growth and photosynthesis extends to include respiration activity. Disagreements among several investigators in regard to the course of respiration during cell development are probably due to the effects of accessory factors such as strong light during the preceding growth period or the scarcity of respiratory substrate during respiration measurements which affect and distort changes in the inherent capacity of metabolic mechanisms in the course of cell development.     

Synthesis of plasmalemmal glycoproteins in intestinal epithelial cells. Separation of Golgi membranes from villus and crypt cell surface membranes; glycosyltransferase activity of surface membrane

The relationship between Golgi and cell surface membranes of intestinal cells was studied. These membranes were isolated from intestinal crypt cells and villus cells. The villus cell membranes consisted of microvillus membrane, a Golgi-rich fraction, and two membrane fractions interpreted as representing lateral-basal membranes. The villus cell microvillus membrane was purified by previously published techniques while the other membranes were obtained from isolated cells by differential centrifugation and density gradient velocity sedimentation. The two membrane fractions obtained from villus cells and considered to be lateral-basal membranes were enriched for Na+,K+-ATPase activity, but one also showed enrichment in glycosyltransferase activity. The Golgi membrane fraction was enriched for glycosyltransferase activity and had low to absent Na+,K+-ATPase activity. Adenylate cyclase activity was present in all membrane fractions except the microvillus membrane but co-purified with Golgi rather than lateral-basal membranes. Electron microscopy showed that the Golgi fraction consisted of variably sized vesicles and cisternalike structures. The two lateral-basal membrane fractions showed only vesicles of smaller, more uniform size. After 125I labeling of isolated intact cells, radioactivity was found associated with the lateral-basal and microvillus membrane fractions and not with the Golgi fraction. Antibody prepared against lateral-basal membrane fractions reacted with the surface membrane of isolated villus cells. The membrane fractions from isolated crypt cells demonstrated that all had high glycosyltransferase activity. The data show that glycosyltransferase activity, in addition to its Golgi location, may be a significant property of the lateral-basal portion of the intestinal villus cell plasma membrane. Data obtained with crypt cells support earlier data and show that the crypt cell surface membrane possesses glycosyltransferase activity.     

Differential distribution of nitric oxide synthase between cell fractions isolated from the rat gastric mucosa.

Cells isolated from the rat gastric mucosa were resolved into two fractions on a percoll density gradient, and into five fractions using counterflow centrifugation (elutriation). Ca(2+)-dependent nitric oxide synthase (NOS) activity was found in the high density percoll fraction but not in the parietal cell enriched low density fraction. This activity was inhibited by NG-monomethyl-L-arginine with an IC50 of 3.7 microM. Cells in the elutriator fraction rich in mucous-epithelial cells exhibited the highest NOS activity, while the smaller cell fractions had no detectable NOS yet had the highest basal release of prostaglandin E2. The parietal cell enriched elutriator fraction again had low NOS activity. The activity of a constitutive NOS in the mucous-cell fraction may indicate a role of NO in the regulation of epithelial cell integrity or secretion.     

A Cell Kinetic and Cytological Study on the Asymmetric Cell Division of Thymic Lymphoblasts of the Embryonic Rat

Cell division of thymus lymphoid cells from embrynonic and young rats was investigated cytologically on cell smears, focusing attention on asymmetric cell division. Some of thymic lymphoblasts displayed features implicating asymmetric cell division. At the telophase of such cells, two immature daughter cells looked dissimilar: one of them was smaller in size and possessed a more condensed nucleus, compared with the counterpart cell. Furthrmore, in most cases the cytoplasm of the smaller daughter cell was stained with Giemsa more deeply. It was suggested that the asymmetry of the nucleus emerges at anaphase and telophase probably due to some polarized situation of the cytoplasm. Asymmetrically-dividing cells were relatively frequently observed during the developmental period when large lymphoblasts actively transform into smaller lymphocytes :16% to 17% of whole dividing cells were under asymmetric cell division on days 16 and 17 of gestation, while less than 5% on day 19 or thereafter. In correlation with this observation, asymmetrically-dividing cells were more frequently observed among large lymphoblasts than among other smaller cell fractions. These results support the view that the asymmetric cell division may play some essential role in the transformation of large lymphoblasts into smaller lymphocytes.     

Preferential localisation of elastase in cytosol of human myeloid leukemia HL-60 cells.

The subcellular distribution of the elastase in human myeloid leukemia HL-60 cells was studied in comparison with that in normal leukocytes. On differential centrifugation, most of the elastase activity of HL-60 cell lysates was recovered in the 105,000 x g supernatant, while that of human peripheral blood leukocyte lysates was recovered in the 500 x g precipitate (azurophil granule-rich fraction). Moreover, on Percoll density gradient centrifugation, the elastase activity in HL-60 cell extracts was recovered in the lightest fraction with none in the azurophil granule-rich fractions, whereas most of the activity in leukocyte extracts was recovered in the azurophil granule-rich fractions. This subcellular localization of elastase did not change when HL-60 cells differentiated into monocytes and granulocytes by induction with 12-O-tetradecanoyl phorbol-13-acetate and retinoic acid, respectively. Furthermore, on Sephadex G-75 gel filtration, the elastase activity in HL-60 cell extracts was eluted earlier than that in leukocyte extracts. The size estimation indicated that the elastase of HL-60 cells was 36-30 kDa, corresponding to the size of an elastase precursor reported. The relevance of a large form of the elastase in HL-60 cells to its subcellular localization is discussed.     

DNA POLYMERASES IN FRACTIONATED RAT BRAIN NUCLEI

Abstract— —Adult rat brain nuclei were separated by discontinuous sucrose gradient centrifugation into astrocyte enriched, neuron enriched, and oligodendrocyte/microglia fractions. Nuclear fractions were subjected to velocity sucrose gradient centrifugation and gradient fractions assayed using relatively specific reaction mixtures for DNA polymerase-α, -β and TdT. NEM resistant DNA polymerase activity (DNA polymerase-β) was detected in equivalent amounts in all nuclear fractions. High molecular weight NEM sensitive activity (DNA polymerase-α) was found primarily in the neuron enriched fraction. The significance of the presence of DNA polymerase-α, an enzyme thought to be involved in DNA replication, in a cell incapable of cell division is unknown. TdT was detected in all fractions with increased activity in the neuron enriched fraction. The finding of TdT in thymocytes and neurons further supports the hypothesis that this enzyme is involved in the storage of noninherited information.     

NEURONAL AND NEUROPIL FRACTIONS FROM DEVELOPING RAT BRAIN

Abstract— A method is described for the preparation of enriched fractions containing isolated neuronal and glial cells from brains derived from 1 to 20-day-old rats. The method is based on mechanical disaggregation in a medium containing Ficoll-PVP followed by centrifugation on a single-stage two-step gradient at 13,000 g for 30min. The neuronal and neuropil (glial) fractions are approx 70–80% pure in cellular terms.
The cells showed well-preserved cytoplasmic and nuclear morphology at the light and electron microscope level and between 70 and 80% excluded trypan blue. Despite changes in the total cell population with age due to glial proliferation, the proportionate recovery of cells in the separated fractions was fairly constant: based on DNA determination, 23 and 29% of all neurons and 15 and 17% of glia were recovered in the purified fractions from Day 1 and Day 20 animals respectively.
Changes in neuronal cell size with age were reflected in a 2.5-fold increase in protein recovered in the neuronal fraction per mg DNA. Protein and RNA levels/mg DNA in the neuropil fraction reached a maximum at Day 10. It is concluded that the method produces a defined and reliable purification of cells in the separated fractions throughout the studied age range and therefore provides a sound basis for studies on the distribution of biochemical systems between cell types during post-natal development.     

THE PREPARATION AND PROPERTIES OF BACTERIAL CHROMATOPHORE FRACTIONS

Chromatophore material from the bacterium Rhodopseudomonas spheroides was freed of ribosomes by centrifugation in 27 per cent RbCl and then separated into "heavy" and "light" fractions by centrifugation through a sucrose gradient. The fractions differed from one another in the following ways. (a) The isopycnic density of the heavy fraction was between 1.15 and 1.18 gm/ml and that of the light fraction was 1.14 gm/ml. (b) The heavy fraction was able to bind ribosomes; the light fraction was not. (c) The light fraction was homogeneous in the ultracentrifuge and had a sedimentation constant, extrapolated to infinite dilution, of 153 s_20,w. The heavy fraction was grossly heterogeneous. (d) Both the amount of bacteriochlorophyll relative to protein and the ratio of bacteriochlorophyll to carotenoids were greater in the light fraction. (e) The spectra of the two fractions in the near infra-red were different. Comparisons of the chromatophore fractions from cells with different amounts of bacteriochlorophyll showed that the specific bacteriochlorophyll contents of the two fractions did not change to the same extent as did that of the whole cells. The amount of heavy fraction from pigmented cells was roughly independent of the cellular pigment content and was about equal to that from pigment-free cells. The amount of light fraction depended on the pigment content of the cells; no light fraction was obtained from cells devoid of bacteriochlorophyll. The cytochrome complements of both fractions underwent quantitative as well as qualitative changes with varying growth conditions. The size of the photosynthetic unit in R. spheroides appeared to increase as the total cellular bacteriochlorophyll content increased; however, the number of units per light fraction particle remained constant.     

Biochemical and immunological properties of Coxiella burnetii cell wall and peptidoglycan-protein complex fractions.

Coxiella burnetii morphological cell types were fractionated into large-cell variant cell walls, two fractions of small-cell variant cell walls, and one fraction of small-cell variant whole cells. Based on the contents of peptidoglycan (PG)-constituents and the yields of the sodium dodecyl sulfate-insoluble PG-protein complex (PG-PC) from cell walls, the fraction of large-cell variant cell walls contained significantly less PG than did the fraction of small-cell variant cell walls. The yields of PG-PC from the fractions of large-cell variant cell walls and small-cell variant cell walls were 2 and 32%, respectively. These results indicated that the PG of the large-cell variant cell walls may be partially digested by PG-lytic enzymes or incompletely synthesized, whereas the small-cell variant cell walls appeared to have intact PG. Proteins associated with PG-PC were resistant to proteolysis by trypsin, protease VI, and proteinase K. Saturated and unsaturated fatty acids were detected in whole cells and cell walls but not in PG-PC, which contained a 3-deoxy-D-mannooctulosonic acid-like component that is also present in phase I lipopolysaccharide. Immunogenicity of the fractions was tested by measuring the temporal sequence of phase II and phase I antibody responses in vaccinated rabbits. Both phase II and phase I antibody responses were demonstrated with all fractions except the sodium dodecyl sulfate supernatant of the small-cell variant cell walls, whereas PG-PC elicited a pure phase II antibody response up to 29 days postvaccination. The immunogenicity of these fractions may reflect a quantitative difference in antigen concentration or may be due to a qualitative difference in phase II and I determinants.     

Subfractionation of rat liver plasma membrane. Uneven distribution of plasma membrane-bound enzymes on the liver cell surface.

Plasma membranes were isolated from rat liver mainly under isotonic conditions. As marker enzymes for the plasma membrane, 5'-nucleotidase and (Na+ + K+)-ATPase were used. The yield of plasma membrane was 0.6-0.9 mg protein per g wet weight of liver. The recovery of 5'-nucleotidase and (Na+ +K+)-ATPase activity was 18 and 48% of the total activity of the whole-liver homogenate, respectively. Judged from the activity of glucose-6-phosphatase and succinate dehydrogenase in the plasma membrane, and from the electron microscopic observation of it, the contamination by microsomes and mitochondria was very low. A further homogenization of the plasma membrane yielded two fractions, the light and heavy fractions, in a discontinuous sucrose gradient centrifugation. The light fraction showed higher specific activities of 5'-nucleotidase, alkaline phosphatase, (Na+ +K+)-ATPase and Mg2+-ATPase, whereas the heavy one showed a higher specific activity of adenylate cyclase. Ligation of the bile duct for 48 h decreased the specific activities of (Na2+ +K+)-ATPase and Mg2+-ATPase in the light fraction, whereas it had no significant influence on the activities of these enzymes in the heavy fraction. The specific activity of alkaline phosphate was elevated in both fractions by the obstruction of the bile flow. Electron microscopy on sections of the plasma membrane subfractions showed that the light fraction consisted of vesicles of various sizes and that the heavy fractions contained membrane sheets and paired membrane strips connected by junctional complexes, as well as vesicles. The origin of these two fractions is discussed and it is suggested that the light fraction was derived from the bile front of the liver cell surface and the heavy one contained the blood front and the lateral surface of it.     

Effect of ageing on enzymes of phenylpropanoid metabolism in Solanum tuberosum discs

-Separation of cell fractions or cell organelles of potato tuber by differential centrifugation and by sucrose density gradient centrifugation showed that, in dormant tissue, nearly all the activity of shikimate and prephenate dehydrogenases, phenylalanine ammonia lyase, cinnamate-4-hydroxylase and an O-methyltransferase for caffeate was in the soluble fraction. All these enzymes increased in activity in slices aged in light for 18 hr. In contrast to the other enzymes, cinnamate hydroxylase becomes associated with the microsomal fraction in aged discs.     

Plasma-membrane location of phosphatidylinositol hydrolysis in rabbit neutrophils stimulated with formylmethionyl-leucylphenylalanine.

Rabbit peritoneal neutrophils, disrupted by sonication, were separated into three subcellular fractions by sucrose-step-gradient centrifugation and these were analysed with respect to biochemical markers. They comprised a high-speed supernatant containing the cytosol, a light particulate fraction enriched in Golgi and plasma membranes and a heavy particulate fraction enriched in granules and nuclei. The light particulate fraction was further separated into its components, which were identified as Golgi membranes (galactosyltransferase activity) and plasma membranes ((radioactivity derived from labelling intact cells with [125I]di-iodosulphanilic acid diazonium salt and [3H]formylmethionyl-leucylphenylalanine ([3H]fMet-Leu-Phe) binding)). In cells prelabelled with [3H]glycerol, the hydrolysis of phosphatidylinositol due to cell stimulation with fMet-Leu-Phe (10 nM) was shown to occur in the light particulate fraction. The [32P]Pi-labelling of phosphatidate, which is an early consequence of phosphatidylinositol hydrolysis, also occurred in this fraction. Analytical sucrose-gradient centrifugation of the light particulate fraction showed that the stimulated increment in [32P]phosphatidate (and thus by implication the initial phosphatidylinositol breakdown) was localized in the plasma membrane.     

Influence of the elimination of lymphocytes from tumor cell suspensions on the calculation of S-phase fractions by flow cytometry

Contaminating lymphocytes were eliminated from enzymatically obtained cell suspensions of 260 surgical biopsy specimens by density gradient centrifugation using lymphocyte separation medium (LSM) in an attempt to improve the determination of S-phase fractions by flow cytometry. The elimination of lymphocytes from the cell suspensions was ascertained on cytologic smears prepared from the suspensions before and after LSM centrifugation. Following the elimination of lymphocytes, the calculated S-phase fractions increased significantly in DNA-diploid tumors, but not in DNA-aneuploid ones. The increase of the S-phase fraction was correlated to the numbers of lymphocytes in the tumor cell suspensions before LSM centrifugation. Furthermore, in 12 tumors originally classified as diploid, an aneuploid cell line was detected after LSM centrifugation. These results indicate that samples from diploid tumors containing large numbers of lymphocytes should have the lymphocytes eliminated by methods such as LSM centrifugation in order to obtain reliable results for the calculations of the S-phase fractions.     

Isolation and characterization of the Neurospora crassa endoplasmic reticulum

The endoplasmic reticulum from Neurospora crassa was identified by monitoring the activity of the putative enzyme marker phosphatidylcholine glyceride transferase. After differential centrifugation of a cell homogenate, phosphatidylcholine glyceride transferase activity initially copurified with plasma membrane H+-ATPase. However, isopycnic centrifugation of the whole-cell homogenate on a linear sucrose gradient separated the two enzyme activities into different fractions. The lighter membrane fraction exhibited characteristics that have been associated with the endoplasmic reticulum in other organisms: (i) the inclusion of magnesium caused this light membrane fraction to shift to a higher density on the gradient; (ii) it was highly enriched in cytochrome c reductase, an endoplasmic reticulum marker in other systems; and (iii) the morphology of the light fraction with and without added magnesium was clearly distinguishable from that of the plasma membrane fraction by electron microscopy. A reinvestigation of the location of chitin synthetase confirmed its association with the plasma membrane fraction even after separation of the lighter fractions.     

Leghaemoglobin biosynthesis in a new single cell system from soybean root nodules

Single cells were effectively released from 35–45-day-old soybean ( Glycine max L. cv. Yaefusanari) nodules by treatment with an enzymic solution containing 1 mg/ml maceration enzyme (Pectolyase Y-23), 0.5 M mannitol, 2% (w/v) sucrose and 0.5% (w/v) potassium dextran sulfate. Bacteroid-containing cells were purified by Percoll density gradient centrifugation. Electron microscopic observation showed that these cells were protoplasts enclosed by a thin wall and with well preserved internal structures including bacteroids. The single cells obtained were stable against centrifugation and vigorous pipetting. The cells retained the ability to synthesize proteins including leghaemoglobin. The ratio of leghaemoglobin components synthesized in the single cells was similar to that of components synthesized in the nodules. The bacteroidal cell fraction was further separated into three fractions by a Percoll density gradient centrifugation. Comparison of the absolute and relative leghaemoglobin content, the activity of glutamine synthetase in the cytoplasm and the activity of 3-hydroxybutyrate dehydrogenase in the bacteroid suggests that these fractions contained cells in different stages of symbiosis. This new single cell system should provide a useful experimental system for analyzing events in the root nodule.     

The significance of promitochondrial structures in rat liver for mitochondrial biogenesis

1. The heavy, light and fluffy mitochondrial fractions obtained by differential centrifugation were further characterized with respect to their protein synthesizing ability in vitro, their nucleic acid content, buoyant density of their DNA and ultrastructure. 2. The light mitochondrial fraction synthesized proteins in vitro at a rate 4-5 times as high as heavy and fluffy mitochondria. The incorporation ability of this fraction was also maximally affected by the thyroid status of the animal. The radioactivity in leucyl-tRNA of the light mitochondrial fraction was about 3-4 times as high as that of the other two fractions. 3. The heavy, light and fluffy mitochondrial fractions contained small but consistent amounts of RNA and DNA. Although the DNA content was the same in all mitochondria fractions, the light mitochondria contained relatively more RNA. The buoyant density of DNA from all the fractions was 1.701g/cm(3). 4. Electron microscopy revealed that the heavy mitochondria have a typical mitochondrial architecture, with densely packed cristae and a well developed double membrane. Light mitochondria were also surrounded by double membranes, but were smaller in size and contained less cristae. The fluffy fraction consisted of a mixture of well formed mitochondria and those in the process of degradation. 5. The significance of these findings in relation to mammalian mitochondrial genesis is discussed.     

Comparative studies of two membrane fractions isolated from chemotrophically and phototrophically grown cells of Rhodopseudomonas capsulata.

Light and heavy membrane fractions have been isolated by equilibrium sucrose density centrifugation from Rhodopseudomonas capsulata 938 GCM grown aerobically in the dark (chemotrophically) and anaerobically in the light (phototrophically). The densities of the light and heavy fractions from phototrophic cells were 1.1004 to 1.1006 and 1.1478, respectively, and the densities of the light and heavy fractions from chemotrophic cells were 1.0957 to 1.0958 and 1.1315, respectively. Both fractions were active in photochemical and respiratory functions and in electron transport-coupled phosphorylation. The light membrane fraction isolated from chemotrophic cells contained the reaction center and the light-harvesting pigment-protein complex B 870, but not the variable light-harvesting complex B 800-850. A small amount of the complex B 800-850 was present in the light fraction isolated from phototrophically grown cells, but it was not energetically coupled to the photosynthetic apparatus. From inhibitor studies, difference spectroscopy, and measurement of enzyme activities it was tentatively concluded that the light membrane fraction contains only the reduced nicotinamide adenine dinucleotide-oxidizing electron transport chain having a KCN-insensitive, low-potential cytochrome c oxidase, whereas the heavy fraction contains additionally the succinate dehydrogenase and a high-potential cytochrome b terminal oxidase sensitive to KCN. The light membrane fraction was more labile than the heavy fraction in terms of phosphorylating activity.     

Separation of rabbit epiphyseal chondrocytes in various stages of differentiation

Summary Separation of fractions enriched in hypertrophic cells and proliferative cells has been achieved by density gradient centrifugation of cells from collagenase digests of rabbit epiphyseal cartilage. Concentrated suspensions of cells are centrifuged on a continuous Percoll density gradient. Hypertrophic cells remain in the upper part of the gradient and proliferative zone cells move to the lower regions. The resultant fractions show differences in mean cell diameter, alkaline phosphatase activity, morphology and synthetic activity in culture. Fractions rich in hypertrophic cells contain larger cells and more alkaline phosphatase activity than those enriched in proliferative cells. In culture the hypertrophic cells flatten as large irregular polygonal cells, whereas proliferative fractions form smaller spindle-shaped cells. In micromass culture hypertrophic fractions incorporate less ³⁵S-sulphate and ¹⁴C-proline, and less tritiated thymidine than do proliferative fractions. These results suggest a general reduction in matrix and DNA synthesis with the attainment of the fully differentiated hypertrophic state, coincident with the expression of alkaline phosphatase activity and mineralisation of the cartilage matrix.     

Size distribution and photophosphorylation of chromatophores from t Rhodospirillum rubrum

Morphology and photophosphorylation of chromatophores from t Rhodospirillum rubrum have been investigated by dynamic light scattering (DLS) and in situ ³¹P-NMR measurement. Two components, designated as light and heavy fractions, with different average sizes and size distributions were detected by the DLS and can be separated by sucrose density gradient centrifugation. The light fraction has an average size of about 140 nm in diameter with a narrow distribution and shows a high activity of photophosphorylation. About 70 of ADP were found to be converted to ATP purely by the photophosphorylative reaction. In contrast, the heavy fraction has a broad size distribution centered around 350 nm and a low activity of photophosphorylation. Only about 50 of ADP was converted into ATP and AMP with a ratio of 7:3, indicating that most membrane-bound adenylate kinase are attached on the particles of the heavy fraction. Effect of physical disruption on the structural integrity of chromatophores has been examined by using sonication with various oscillating strengths. The result shows that the morphology of chromatophores for both light and heavy fractions is relatively stable to the disruption, while the photophosphorylative activity of the light fraction is very sensitive to the disrupting strength, suggesting that the internal structure of the purified chromatophores could be partially damaged by the disruption.     

Microbial population structures in soil particle size fractions of a long-term fertilizer field experiment

Soil structure depends on the association between mineral soil particles (sand, silt, and clay) and organic matter, in which aggregates of different size and stability are formed. Although the chemistry of organic materials, total microbial biomass, and different enzyme activities in different soil particle size fractions have been well studied, little information is available on the structure of microbial populations in microhabitats. In this study, topsoil samples of different fertilizer treatments of a long-term field experiment were analyzed. Size fractions of 200 to 63 microm (fine sand fraction), 63 to 2 microm (silt fraction), and 2 to 0.1 microm (clay fraction) were obtained by a combination of low-energy sonication, wet sieving, and repeated centrifugation. Terminal restriction fragment length polymorphism analysis and cloning and sequencing of 16S rRNA genes were used to compare bacterial community structures in different particle size fractions. The microbial community structure was significantly affected by particle size, yielding higher diversity of microbes in small size fractions than in coarse size fractions. The higher biomass previously found in silt and clay fractions could be attributed to higher diversity rather than to better colonization of particular species. Low nutrient availability, protozoan grazing, and competition with fungal organisms may have been responsible for reduced diversities in larger size fractions. Furthermore, larger particle sizes were dominated by alpha-Proteobacteria, whereas high abundance and diversity of bacteria belonging to the Holophaga/Acidobacterium division were found in smaller size fractions. Although very contrasting organic amendments (green manure, animal manure, sewage sludge, and peat) were examined, our results demonstrated that the bacterial community structure was affected to a greater extent by the particle size fraction than by the kind of fertilizer applied. Therefore, our results demonstrate specific microbe-particle associations that are affected to only a small extent by external factors.