Biomedical subjects

M Farina

Publications and source records attributed to M Farina.

At least 73 records · Page 4Linked to original sources

PubMed2000

Nitric oxide inhibits prostanoid synthesis in the rat oviduct.

We have studied the effect of nitric oxide (NO) on the production of arachidonic acid ([14C]-AA) metabolites in the rat oviduct. The basal synthesis of eicosanoids was measured by the conversion of ([14C]-AA) to the different radiolabeled products of cyclooxygenase (COX). The oviducts incubated for 1 h with the labeled substrate of COX were able to convert 3.3 +/- 0.3% of ([14C]-AA) to 6-ceto-PGF1alpha, 10.7 +/- 1.0% to PGF2alpha, 13.5 +/- 1.2% to PGE2 and 6.3 +/- 0.5% to TXB2. The tissues were incubated with different doses of two NO donors: SIN-1 and Spermine NONOate. The results indicated that SIN-1 produces a significant decrease (50%; P < 0.05) in all prostanoids evaluated in a dose-response fashion. The inhibitory effect was completely reversed by addition of 20 microg/ml of hemoglobin (Hb), a NO scavenger. The addition of Spermine NONOate to the incubation medium diminished significantly (65%) the synthesis of COX metabolites suggesting that NO acts by inhibiting COX activity in the rat oviduct. However, NOS inhibitors, N(G)-L-arginine-methyl-ester (L-NAME) nd N(G)-L-monomethyl-arginine (L-NMMA) had no effect on basal production of the prostanoids. These results indicate that in the rat oviduct the synthesis of COX metabolites is negatively regulated by nitric oxide.

Animals↗

PubMed2000

IL1alpha augments prostaglandin synthesis in pregnant rat uteri by a nitric oxide mediated mechanism.

This study aims to examine the possible relationship between cytokines, nitric oxide (NO) and prostaglandins in the pregnant rat uterus. Results indicate that 1) IL1alpha enhances the synthesis of prostaglandins and augments NO production in pregnant rat uteri and 2) the effect of IL1alpha on prostaglandin synthesis is abolished by NMMA, a NOS inhibitor, by aminoguanidine, an iNOS inhibitor, and by NS-398, a COX-2 inhibitor. These results suggest that there is an interaction between IL1alpha, NO and prostaglandins and that are involved COX-2 and iNOS in this interrelationship. This mechanism might be important in the regulation of uterine contractility during pregnancy and labor.

Animals↗

PubMed2000

Effect of high-flux dialysis on the anaemia of haemodialysis patients.

BACKGROUND: Anaemia is one of the major clinical characteristics of patients with chronic renal failure, and has a considerable effect on morbidity and mortality. Adequate dialysis is of paramount importance in correcting anaemia by removing small and medium-sized molecules, which may inhibit erythropoiesis. However, high-molecular-weight inhibitors cleared only by means of highly porous membranes have also been found in uraemic serum and it has been claimed from uncontrolled studies that high-flux dialysis could improve anaemia in haemodialysis patients. METHODS: We therefore planned this multicentre randomized controlled trial with the aim of testing whether the use of a large-pore biocompatible membrane for a fixed 12-week follow-up improves anaemia in haemodialysis patients in comparison with the use of a conventional cellulose membrane. Eighty-four (5.3%) of a total of 1576 adult haemodialysed patients attending 13 Dialysis Units fulfilled the entry criteria and were randomly assigned to the experimental treatment (42 patients) or conventional treatment (42 patients). RESULTS: Haemoglobin levels increased non-significantly from 9.5+/-0.8 to 9.8+/-1.3 g/dl (dP=0. 069) in the population as a whole, with no significant difference between the two groups (P:=0.485). Erythropoietin therapy was given to 32/39 patients (82%) in the conventional group, and 26/35 (74%) in the experimental group (P:=0.783) with subcutaneous administration to 26/32 patients in conventional and to 23/26 patients in experimental group, P:=0.495. Dialysis dose (Kt/V) remained constant in both groups (from 1.30+/-0.17 to 1.33+/-0.20 in the conventional group and from 1.28+/-0.26 to 1.26+/-0.21 in the experimental group, P:=0.242). Median pre- and post-dialysis beta(2)-microglobulin levels remained constant in the conventional group (31.9 and 34.1 mg/dl at baseline) and decreased in the experimental group (pre-dialysis values from 31.1 to 24.7 mg/dl, P:=0.004 and post-dialysis values from 24.8 to 20.8 mg/dl, P:=0.002). Median erythropoietin doses were not different at baseline (70 IU/kg/week in conventional treatment and 90 IU/kg/week in experimental treatment, P:=0.628) and remained constant during follow-up (from 70 to 69 IU/kg/week in the conventional group and from 90 to 91 IU/kg/week in the experimental group, P:=0.410). Median erythropoietin plasma levels were in the normal range and remained constant (from 12.1 to 12.9 mU/ml in the conventional group and from 13.2 to 14.0 mU/ml in the experimental group, P:=0.550). CONCLUSIONS: This study showed no difference in haemoglobin level increase between patients treated for 3 months with a high-flux biocompatible membrane in comparison with those treated with a standard membrane. When patients are highly selected, adequately dialysed, and have no iron or vitamin depletion, the effect of a high-flux membrane is much less than might be expected from the results of uncontrolled studies.

Aged↗

PubMed2000

Haematopoietic progenitors from umbilical cord blood.

BACKGROUND/AIM: The aim of this study is to improve the obstetrician-based cord blood collection system and an efficient recovery of CD34+ haematopoietic progenitor stem cells. METHODS: CD34+ cells were purified from total blood using a positive selection enrichment method, called Mini-Macs. RESULTS: The final yield of CD34+ cells we obtained was 10(4) cells/ml, with a CD34+ purity of 99%. CONCLUSION: Our results confirm that, by using this method, it is possible to get a significant stem cell number, thus improving transplanting both peripheral stem cells and umbilical cord ones.

Antigens, CD34↗

PubMed2000

Zinc accumulation in phosphate granules of Ucides cordatus hepatopancreas.

Amorphous phosphate granules are present in vertebrate and invertebrate organisms. The functions attributed to these structures depend on their mineral contents and organic matrix composition. In the present study we have determined zinc concentrations in the hepatopancreas of the crab Ucides cordatus from regions contaminated with zinc, and the elemental composition of hepatopancreal phosphate granules. Organisms were collected from the contaminated areas of Sepetiba Bay (SB) and Guanabara Bay (GB), and from a non-contaminated area, Ribeira Bay (RB). The first two sites are located near the metropolitan region of Rio de Janeiro city, Brazil. Atomic absorption spectroscopy (AAS) showed a significant difference (P<0.05) for zinc concentration in the hepatopancreas from organisms collected at the contaminated sites GB (210 +/- 20 microg/g dry weight) and SB (181 +/- 16 microg/g dry weight) compared to the non-contaminated site RB (76 +/- 14 microg/g dry weight). Phosphate granules isolated from hepatopancreatic tissue were studied by electron diffraction (ED), energy dispersive X-ray analysis (EDX) and electron spectroscopic imaging (ESI). ED of granules presented no diffraction spots, indicating that these structures are in an amorphous state, while EDX of granules isolated from a contaminated area contained P, Ca and Zn. Mg, Cl and Fe were also found in some of the spectra. ESI showed that O, P and Ca were colocalized in the mineralized layers of most granules observed. The correlation between the results obtained by AAS and those obtained by microanalytical techniques suggests that the hepatopancreatic granules of U. cordatus may be related to the phenomenon of heavy metal retention.

Animals↗

PubMed2000

[Differential action of non-steroidal antiinflammatory drugs on human gallbladder cyclooxygenase and lipoxygenase].

Lysine clonixinate (LC) is a non-steroidal antiinflammatory agent (NSAID) with only few adverse effects. This characteristic has prompted us to suggest that its administration, at levels equivalent to those found in human plasma following therapeutic doses, slightly inhibits cyclooxygenase I (COX I). Three experiments were performed. Experiment 1: to study the in vitro effect of LC at concentrations of 4 and 6 micrograms/ml, comparable with those found in plasma following an oral therapeutic dose of 125 mg. Gallbladder tissue segments were incubated with 0.25 microCi of 14C-arachidonic acid and the production of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha) and 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) was measured. LC did not affect basal production of any of the 3 prostaglandins (PGs) but at 6 micrograms/ml slightly reduced the levels of 5-hidroxyeicosatetraenoic acid (5-HETE). Experiment 2: LC was administered preoperatively to 6 patients by continuous perfusion, to achieve a steady-state concentration between 4 and 6 micrograms/ml. Gallbladder segments from the 6 treated and another 6 control patients were incubated in 14C-arachidonic acid. Gallbladder segments treated with LC did not show a decreased production of any of the three PGs whereas 5-HETE released to the medium was significantly lower. Experiment 3: 18 patients received an i.v. bolus of LC 100 mg (n1 = 6) or LC 200 mg (n2 = 6) or indomethacin (INDO) 50 mg (n3 = 6). Unlike the administration of INDO bolus, LC in the above doses did not inhibit PG synthesis. Both NSAIDs showed different effects when the production of 5-HETE synthesis was assessed. Treatment with INDO did not alter the production of 5-HETE while LC elicited significant inhibition. The three studies conducted, namely in vitro and in vivo continuous perfusion and i.v. bolus, revealed that LC had no effect on prostaglandin synthesis while reducing significantly the levels of 5-HETE.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2000

At term pregnancies in transfusion-dependent beta-thalassemic women.

The health background management and outcome of five pregnancies in women affected by Cooley Disease are described and the preconceptual guidance and care are considered. The patients were selected from a group of 103 thalassemic women divided into three subgroups according to their first and successive menstruation characteristics. Only one woman needed induction of ovulation. A precise and detailed pre-pregnancy assessment was done before each conception. All the women were in labour at 38 weeks' gestation, and five healthy babies were born at term, weighing between 2,600 and 3,200 g. The improvement in current treatments will result in a continuous increase in pregnancies in thalassemic women, making pregnancy a real eventuality for them. Furthermore, we are studying the possibility of collecting foetus umbilical cord blood after delivery, with the aim of obtaining complete marrow reconstitution in an attempt at heterologous transplantation to the mother.

Adolescent↗

PubMed1999

Morphometric and densitometric study of the biogenesis of electron-dense granules in Fonsecaea pedrosoi.

Fonsecaea pedrosoi is a polymorphic pathogenic fungus, etiological agent of chromoblastomycosis, that synthesizes a melanin-like pigment. Although this pigment has been described as a component of the outer layers of the cell wall, electron-dense cytoplasmic bodies have also been visualized. In this work, we have correlated the appearance of intracellular electron-dense granules with the melanization process in F. pedrosoi. For this, conidial forms were grown under conditions where melanin was not synthesized. Afterwards, cells were incubated in Hank's medium supplemented with bovine fetal serum, at 37 degrees C, to stimulate the pigment production. The genesis of cytoplasmic bodies, with different stages of electron density, was demonstrated by transmission electron microscopy. The appearance of fungal acidic compartments, visualized by confocal laser scanning microscopy in cells stained with acridine orange, was time coincident with the formation of electron-dense granules observed by transmission electron microscopy. The quantification of granule numbers as well as morphometric and densitometric studies were performed.

Ascomycota↗

PubMed1999

Thrombospondin-1 is a mediator of the neurotypic differentiation induced by EGF in thymic epithelial cells.

Thymic epithelial cell component originates from cranial neural crest as well as from endoderm and ectoderm of the third pharyngeal pouch and branchial cleft. Epidermal growth factor (EGF) has been previously shown to play a crucial role in directing thymic epithelial cells toward a neural-oriented cell fate. To identify genes that are involved in the EGF-induced neurotypic differentiation of the thymic stroma-derived TC-1S cell line, we studied EGF-treated and untreated cells by RNA fingerprinting PCR-based differential screening. We obtained 23 distinct sequences including 18 known genes and 5 sequences previously unreported, which are currently under characterization. Here, we describe the involvement of one of the isolated genes, the thrombospondin-1, as a mediator of the neurotypic differentiation induced by EGF in TC-1S cells. We show that thrombospondin-1 mRNA and protein levels are increased by EGF. Moreover, exogenous thrombospondin-1 is able to enhance the outgrowth of neurite-like processes as well as the expression of neurofilaments and neural cell adhesion molecule in TC-1S cells. These observations suggest that the up-regulation of thrombospondin-1 synthesis induced by EGF contributes to the differentiation choice of thymic epithelial cells toward a neural fate, reminiscent of their neural crest origin.

Animals↗

PubMed1999

Atomic force microscopy study of tooth surfaces.

Atomic force microscopy (AFM) was used to study tooth surfaces in order to compare the pattern of particle distribution in the outermost layer of the tooth surfaces. Human teeth and teeth from a rodent (Golden hamster), from a fish (piranha), and from a grazing mollusk (chiton) with distinct feeding habits were analyzed in terms of particle arrangement, packing, and size distribution. Scanning electron microscopy and transmission electron microscopy were used for comparison. It was found that AFM gives high-contrast, high-resolution images and is an important tool as a source of complementary and/or new structural information. All teeth were cleaned and some were etched with acidic solutions before analysis. It was observed that human enamel (permanent teeth) presents particles tightly packed in the outer surface, whereas enamel from the hamster (continuously growing teeth) shows particles of less dense packing. The piranha teeth have a thin cuticle covering the long apatite crystals of the underlying enameloid. This cuticle has a rough surface of particles that have a globular appearance after the brief acidic treatment. The similar appearance of the in vivo naturally etched tooth surface suggests that the pattern of globule distribution may be due to the presence of an organic material. Elemental analysis of this cuticle indicated that calcium, phosphorus, and iron are the main components of the structure while electron microdiffraction of pulverized cuticle particles showed a pattern consistent with hydroxyapatite. The chiton mineralized tooth cusp had a smooth surface in an unabraded region and a very rough structure with the magnetite crystals (already known to make part of the structure) protruding from the surface. It was concluded that the structures analyzed are optimized for efficiency in feeding mechanism and life span of the teeth.

Acids↗

PubMed1999

Can prolonged treatment improve the prognosis in adults with focal segmental glomerulosclerosis?

Eighty nephrotic adults with focal segmental glomerulosclerosis (FSGS) and plasma creatinine lower than 3 mg/dL were given corticosteroids (53 patients) or immunosuppressive agents (27 patients) for a median of 16 and 75 weeks, respectively. Forty-two patients responded with complete remission (29 patients, 36%) or partial remission (13 patients, 16%). Twenty-six patients who did not respond were treated again. Two patients obtained complete remission and 13 partial remission. The probability of remission was associated with treatment with corticosteroids (P = 0.0001; RR, 3. 93; 95% CI, 2.00 to 7.72), absence of arterial hypertension (P = 0. 0023; RR, 2.59; 95% CI, 1.41 to 4.79), and a percentage of hyaline glomeruli lower than 5% (P = 0.0152; RR, 2.04; 95% CI, 1.15 to 3.64). The probability of being alive at 110 months without doubling of plasma creatinine was 69%. The risk of renal insufficiency was correlated with mesangial proliferation (P = 0.0025; RR, 5.50; 95% CI, 1.82 to 16.60) and with interstitial fibrosis (P = 0.0231; RR, 4. 44; 95% CI, 1.23 to 16.08) at initial biopsy. Considering partial or complete remission as a time-dependent variable, only the lack of remission (P = 0.0027; RR, 7.23; 95% CI, 1.98 to 26.33) and mesangial proliferation (P = 0.0069; RR, 4.59; 95% CI, 1.52 to 13. 88) were correlated with renal failure. Major side effects were observed in 11 patients (5 infections, 1 peptic ulcer, 2 diabetes, 3 neoplasias). This study shows that 70% of nephrotic adults with FSGS may obtain complete or partial remission and maintain stable renal function for about 10 years when given a prolonged therapy with corticosteroids or immunosuppressive drugs.

Adrenal Cortex Hormones↗

PubMed1999

Structural basis for mechanical transduction in the frog vestibular sensory apparatus: III. The organization of the otoconial mass.

The saccule and the utricle of the vestibular system detect linear acceleration and gravity. Sensory transduction in these organs depends on myriads of calcium carbonate crystals of high specific gravity, called otoconia, embedded in a filament matrix that overlies the sensory epithelium. The coexistence of hard crystals and slender filaments in this complex extracellular matrix makes it difficult to analyze by conventional electron microscopy. We have now examined this structure in the bullfrog saccule using the quick-freeze, deep-etch replica technique. The otoconia in their typical aragonite polymorph shape exhibit smooth surfaces and are embedded in a loose matrix made of two types of filaments. The regular surface of the otoconia forms a natural smooth background against which we could observe with unprecedented detail the network organization and substructure of the filaments. One type of filament is 8 nm in diameter, while the other, which has a characteristic beaded appearance, is 15 nm in diameter. Both types of filaments either make lateral connections with or end directly on the surface of the otoconia. A consistent observation was the presence of short filaments that directly cross-link adjacent otoconia. Very few otoconia were fractured in an orientation that would allow the study of their internal architecture. These otoconia presented a typical conchoidal cleavage of aragonite. Although crystallites were not clearly apparent, thin lamellar microstructures appeared oriented both perpendicularly and longitudinally to the major otoconial axis. This structural study establishes a framework for the identification of the molecular components present in this unique extracellular matrix and may also help elucidate their role in mechanical transduction.

Animals↗

PubMed1999

The effect of epidermal growth factor on prostaglandin synthesis of oestrogenized rat uterus is mediated by nitric oxide.

We examined the possible relationship between cytokines, nitric oxide and prostaglandins (PGs) in the estrogenized rat uterus. Results indicate that epidermal growth factor (EGF) enhances the synthesis of prostaglandins in estrogenized rat uteri and induces the augmentation of nitric oxide (NO) production in this tissue by stimulating iNOS. While the effect of EGF is abolished by L-NMMA, an NO antagonist, the NS-398, a cyclooxygenase-II (COX-II) inhibitor, prevents the augmentation of prostanoids induced by EGF. These results suggest that there is an interaction among EGF, NO and PGs and that in this interrelationship are involved COX-II and iNOS. This mechanism might be important during implantation and labor.

Animals↗

PubMed1999

BsmI polymorphism of the vitamin D receptor gene in hyperparathyroid or hypoparathyroid dialysis patients.

Since bone mineral density may be influenced by the polymorphisms of the vitamin D receptor (VDR) gene, we studied whether VDR genotypes might drive the progression toward hyperparathyroidism or hypoparathyroidism in patients with end-stage renal disease. On the basis of their parathyroid hormone (PTH) levels, we divided 99 patients undergoing dialysis into 2 groups: 56 patients with hypoparathyroidism (PTH < 104 pg/mL [< 11 pmol/L]) and 43 with hyperparathyroidism (PTH > 261 pg/mL [> 27.5 pmol/L]). The BB polymorphism was more frequent in patients with hypoparathyroidism (34%) than in patients with hyperparathyroidism (16%), but the difference did not reach statistical significance. Patients with the B allele and BB genotype had a significantly lower dialytic age and serum PTH and alkaline phosphatase levels than patients with the b allele and bb genotype. These results suggest that in end-stage renal disease, the BB genotype may mark a higher risk of developing hypoparathyroidism and diminished bone turnover.

Bone Density↗

PubMed1999

The PTH-calcium curve and the set point of calcium in primary and secondary hyperparathyroidism.

BACKGROUND: The regulation of PTH secretion by calcium is altered in patients with primary hyperparathyroidism (HPT). A similar abnormality may occur in secondary HPT, but comparisons of PTH secretion in normal subjects and those with secondary HPT have given contrasting results. Differences in baseline serum ionized calcium (ICa) may partly account for these conflicting results. The aim of the present study was to evaluate whether the regulation of PTH secretion by calcium differs from normal in patients with primary and secondary HPT and to determine whether serum calcium concentration per se can affect the set point of calcium and the PTH-calcium relationship. METHODS: The PTH-ICa relationship and the set point of ICa were evaluated in 19 patients with primary HPT (1-HPT), 16 normocalcaemic patients with secondary HPT (2-HPT; PTH 344+/-191 pg/ml), 19 hypercalcaemic patients with secondary HPT (3-HPT; PTH 806+/-254 pg/ml) and 14 healthy volunteers, by inducing hypocalcaemia and hypercalcaemia in order to maximally stimulate or inhibit PTH secretion. In five 1-HPT patients the PTH-ICa curve was restudied after normalization of serum ICa by pamidronate. Parathyroid gland volume was determined by measuring gland size at parathyroidectomy or by means of high-resolution color Doppler ultrasonography. RESULTS: In 1-HPT patients the PTH-ICa curve, constructed using maximal PTH secretion induced by hypocalcaemia as 100%, was shifted to the right, the set point of ICa was increased, and the slope of the curve was reduced when compared to normal subjects. After normalization of baseline serum ICa by pamidronate, a shift of the PTH-ICa curve towards normal and a reduction in the set point of ICa was observed. However, basal PTH and maximal PTH secretion induced by hypocalcaemia increased, minimal PTH secretion induced by hypercalcaemia remained increased and the slope of the curve did not change significantly. The alterations in the PTH-ICa relationship in hypercalcaemic patients with secondary HPT were similar to those found in 1-HPT patients. In normocalcaemic patients with secondary HPT baseline PTH, maximal and minimal PTH secretion and parathyroid gland size were reduced compared to 3-HPT patients. Compared to normal subjects, 2-HPT patients showed greater calcium-induced minimal PTH secretion. The increase in non-suppressible PTH secretion resulted in a rightward shift of the PTH-ICa curve and an increase in the set point of ICa. A strong correlation was found, in both primary and secondary HPT, between the set point of ICa and baseline serum ICa, and between parathyroid gland size and baseline PTH, maximal PTH and minimal PTH. Multivariate regression analysis showed that baseline serum ICa was the main determinant of the set point of ICa in both primary and secondary HPT. CONCLUSIONS: (i) The regulation of PTH secretion by calcium is abnormal in secondary as well as in primary HPT. (ii) Parathyroid gland enlargement in secondary HPT is associated with reduced sensitivity to serum ICa and resistance of parathyroid gland to calcium-mediated PTH suppression, resulting ultimately in PTH hypersecretion, despite hypercalcaemia. (iii) The set point of calcium is strongly dependent on baseline serum calcium, and the PTH-ICa relationship can be affected by variations in serum ICa concentrations. Thus, when the set point of calcium and the PTH-ICa relationship are evaluated, possible differences in baseline serum ICa concentration among the patients should be taken into account.

Calcium↗

PubMed1999

Isolation of magnetic nanoparticles from pachycondyla marginata ants

We report on the presence of magnetic iron oxides in the migratory ant Pachycondyla marginata. Magnetic particles were extracted from different parts of the ant (head, thorax and abdomen) using magnetic precipitation methods. Electron spectroscopic images for iron and oxygen were obtained from the extracted particles, and, by using the corresponding electron micrographs, histograms of size distribution were constructed. Selected area diffraction patterns were also obtained from the particles, and analysis of these showed the presence of a mixture of different iron oxides, including the magnetic oxides, magnetite and maghemite. The size distribution of the particles in the abdomen is different from that in the thorax and the head. In accordance with the hypothesis of magnetic orientation based on the presence of magnetic material within the body, two regions of the ant, the head and the abdomen, could be implicated in the detection of the geomagnetic field.

Journal Article↗

PubMed1999

The value of serum CA 125 and association CA 125/CA 19-9 in endometrial carcinoma.

One hundred and twelve women with endometrial carcinoma were studied with serum sampling to determine preoperative and postoperative levels of CEA, CA 15-3, CA 19-9, TPA and CA 125. After surgical treatment 88 patients had stage I, 8 stage II, 14 stage III and 2 stage IV disease. Before treatment the sensitivity of CEA, CA 15-3, CA 19-9, TPA and CA 125 was 22.3% (25/112), 32.1% (36/112), 22.3% (25/112), 45.5% (51/112), 33.9% (38/112), respectively. According to pathological stage a statistically significant difference between intrauterine (96 cases) and extrauterine disease (16 cases) was noted only for CA 125 (28.1% vs. 68.7%) and CA 15.3 (28.1% vs. 56.2%). In relation to histological grading CA 125 rises progressively from well-differentiated cases to poorly-differentiated tumors. During the follow-up the most reliable marker was CA 125: values more than 35 U/ml of this marker resulted positive in 50% of relapsed cases and only in 5.1% of disease-free cases, thus demonstrating a high specificity. The association of various markers during the follow-up allowed us to reveal interesting results only for the CA 125/CA 19-9 combination. In fact the combined use of these markers permitted a high sensitivity (83.3%), with only 12.8% false positive cases, so with a high specificity.

Adenocarcinoma↗

PubMed1998

Magnetosome size distribution in uncultured rod-shaped bacteria as determined by electron microscopy and electron spectroscopic imaging.

We report uncultured rod-shaped magnetotactic bacteria from natural waters that biomineralize magnetic crystals in two different size ranges. Electron spectroscopic imaging of whole bacteria deposited over formvar-coated grids permitted a better visualization and measurement of the magnetosomes. All magnetosomes of individual bacteria could be observed by this technique. The magnetosomes formed one large chain, composed of three to four columns of crystals, disposed in parallel to the main axis of the bacteria. The magnetosomes ranged from 19 to 136 nm in length and 14 to 112 nm width. Smaller magnetosomes (less than 80 nm in length) localized mostly in extremities of the bacterial body while larger preferentially localized in the middle part of the cell. Electron spectroscopic diffraction and X-ray microanalysis indicate that both types of magnetosomes contain magnetite (Fe3O4). In projection, most magnetosomes seem to present pseudo-hexagonal morphologies described for magnetite. As the aspect ratios for smaller and larger magnetosomes are different, we suggest that different levels of control on biomineralization of magnetosomes may exist.

Bacteria↗