Aphanomyces macrosporus sp. nov. Causing Root Rot in Barley and Some Other Plants

In recent years, a new root rot disease in barley, which is caused by an Aphanomyces species, was found in field surveys in Southern Sweden and Denmark. Its symptoms occurred at the early tillering stage, around the BBCH 21 growth stage, and included the yellowing of leaves, brown coleoptiles, and the discolouration of roots. Prolonged soil wetness after rainfall favoured disease development, which sometimes advanced the yellowing patches to entire fields, resulting in lower yields. Oospores were found in the fine roots of diseased plants, and Aphanomyces isolates were obtained from these roots, as well as from the roots of barley plants grown in the greenhouse in soil samples from infected fields. Based on morphological analysis, we found that the new isolates were similar to those already obtained from barley and spinach roots in the 1990s in the same growing area. The morphological and molecular analyses performed in this study clearly separated and distinguished these barley isolates from other known Aphanomyces, and hereby Aphanomyces macrosporus sp. nov. is proposed as a new plant pathogenic species. It has larger oogonia and oospores than A. euteiches, A. cochlioides, and A. cladogamus, with one up to eight diclinous antheridia per oogonium. The phylogenetic analysis of the ITS rDNA region sequences grouped these new Aphanomyces isolates in a monophyletic clade, which was clearly distinguished from other plant pathogenic Aphanomyces species. The further pathogenicity of A. macrosporus on other plants is currently under investigation, but it is clear that it can at least infect barley, spinach, and sugar beet, indicating a wide host range for this species. The widespread presence and presumably broad host range of this new pathogenic Aphanomyces species must be considered in crop rotations.

Low health-related quality of life in adult individuals with multiple limb deficiencies compared with population-based reference values

BACKGROUND

Knowledge on health-related quality of life (HRQoL) in multiple limb deficiencies (LDs) is limited.

OBJECTIVES

To investigate self-reported HRQoL in multiple LDs, assess differences between congenital LD and acquired LD and sex, and to evaluate associations between the types of LDs, demographic variables, and HRQoL.

STUDY DESIGN

Cross-sectional cohort study.

METHODS

A total of 106 individuals with multiple limb deficiencies treated at the EX-Center were invited by mail to fill out the Short Form-36 survey.

RESULTS

Responses from 62 participants, mean age ± SD 49.5 ± 14.2, showed that 43 had congenital LD and 19 had acquired LD. Responders reported reduced HRQoL in all Short Form-36 domains except Role-Emotional, compared with reference values (P < 0.05-<0.001). Individuals with a congenital LD reported worse Bodily Pain than acquired LD (P < 0.05), and women reported lower Physical Function than men (P < 0.05). Sick leave was negatively associated with physical composite score. Living in a rural area was positively associated with Mental Health (P < 0.01), and congenital LD was negatively associated with Vitality (P < 0.05).

CONCLUSIONS

Individuals with multiple LDs in Sweden have lower HRQoL compared with reference values. There are significant associations between sick leave and physical function, rural living and mental health, and the type of LD and vitality.

Verticillium Wilt in Oilseed Rape-the Microbiome is Crucial for Disease Outbreaks as Well as for Efficient Suppression

Microbiome management is a promising way to suppress verticillium wilt, a severe disease in Brassica caused by Verticillium longisporum. In order to improve current biocontrol strategies, we compared bacterial Verticillium antagonists in different assays using a hierarchical selection and evaluation scheme, and we integrated outcomes of our previous studies. The result was strongly dependent on the assessment method chosen (in vitro, in vivo, in situ), on the growth conditions of the plants and their genotype. The most promising biocontrol candidate identified was a Brassica endophyte Serratia plymuthica F20. Positive results were confirmed in field trials and by microscopically visualizing the three-way interaction. Applying antagonists in seed treatment contributes to an exceptionally low ecological footprint, supporting efficient economic and ecological solutions to controlling verticillium wilt. Indigenous microbiome, especially soil and seed microbiome, has been identified as key to understanding disease outbreaks and suppression. We suggest that verticillium wilt is a microbiome-driven disease caused by a reduction in microbial diversity within seeds and in the soil surrounding them. We strongly recommend integrating microbiome data in the development of new biocontrol and breeding strategies and combining both strategies with the aim of designing healthy microbiomes, thus making plants more resilient toward soil-borne pathogens.

The structure of the Brassica napus seed microbiome is cultivar-dependent and affects the interactions of symbionts and pathogens

BACKGROUND

Although the plant microbiome is crucial for plant health, little is known about the significance of the seed microbiome. Here, we studied indigenous bacterial communities associated with the seeds in different cultivars of oilseed rape and their interactions with symbiotic and pathogenic microorganisms.

RESULTS

We found a high bacterial diversity expressed by tight bacterial co-occurrence networks within the rape seed microbiome, as identified by llumina MiSeq amplicon sequencing. In total, 8362 operational taxonomic units (OTUs) of 40 bacterial phyla with a predominance of Proteobacteria (56%) were found. The three cultivars that were analyzed shared only one third of the OTUs. The shared core of OTUs consisted mainly of Alphaproteobacteria (33%). Each cultivar was characterized by having its own unique bacterial structure, diversity, and proportion of unique microorganisms (25%). The cultivar with the lowest bacterial abundance, diversity, and the highest predicted bacterial metabolic activity rate contained the highest abundance of potential pathogens within the seed. This data corresponded with the observation that seedlings belonging to this cultivar responded more strongly to the seed treatments with bacterial inoculants than other cultivars. Cultivars containing higher indigenous diversity were characterized as having a higher colonization resistance against beneficial and pathogenic microorganisms. Our results were confirmed by microscopic images of the seed microbiota.

CONCLUSIONS

The structure of the seed microbiome is an important factor in the development of colonization resistance against pathogens. It also has a strong influence on the response of seedlings to biological seed treatments. These novel insights into seed microbiome structure will enable the development of next generation strategies combining both biocontrol and breeding approaches to address world agricultural challenges.

Dental Plaque pH and Micro-organisms during Hyposalivation

We have previously reported that minor gland and whole saliva flow rates and salivary proteins showed differences in individuals with primary Sjögren’s syndrome or head and neck radiation therapy, compared with controls ( Eliasson et al., 2005 ). We now hypothesize that pH and number of acidogenic micro-organisms in dental plaque as well as saliva buffering capacity also differ in these individuals. Plaque pH was measured by the microtouch method up to 60 min after a sucrose rinse. Plaque collected from the same sites was analyzed for counts of total and acidic micro-organisms. Compared with their controls, the irradiated group but not the Sjögren’s syndrome group displayed significantly lower plaque pH, increased numbers of lactobacilli and Candida species, as well as reduced buffering capacity. Stepwise regression tests suggested that the buccal minor-salivary-gland secretion rate in the test groups and counts of mutans streptococci in the controls were of significant importance for dental plaque pH.

MR Imaging of Gadolinium-DTPA-BMA-Enhanced Reperfused and Nonreperfused Porcine Myocardial Infarction

To investigate whether Gd-DTPA-BMA-enhanced MR imaging permits differentiation between reperfused and nonreperfused myocardial infarction, myocardial infarction was induced in 12 domestic pigs. In 6 pigs, Gd-DTPA-BMA, 0.3 mmol/kg b.w. was administered i.v. 60 min after the occlusion. In 6 other pigs, the infarctions were reperfused 80 min after the occlusion, followed by injection of Gd-DTPA-BMA after 20 min of reperfusion. Radiolabeled microspheres were used to confirm zero-flow during the occlusion period and reperfusion in the infarcted myocardium. All pigs were killed 20 min after injection of contrast medium, and the hearts were excised and imaged with MR. The Gd concentration was measured in infarcted and nonischemic myocardium by ICPAES. In the reperfused hearts, the infarctions were strongly highlighted, corresponding to a 5-fold higher Gd concentration in infarcted vis-à-vis nonischemic myocardium. In the hearts subjected to occlusion without reperfusion, there was only a rim of enhancement in the peripheral part of the infarctions.

Magnetic Resonance Imaging of Acute Myocardial Infarction in Pigs Using Gd-Dtpa

Six pigs with coronary artery occlusion were investigated with MR imaging before and subsequently for about 2.5 hours at repeated intervals after the intravenous administration of Gd-DTPA (0.4 mmol/kg). The animals were sacrificed after a total occlusion time of 6 hours and the hearts were excised. The excised hearts were then reexamined in the MR equipment and stained with TTC (triphenyl tetrazolium) in order to define areas of infarction. Four control hearts with 6-hour-old infarctions were only imaged ex vivo without any previous administration of contrast media. In vivo, there was no clear demarcation of infarction with or without Gd-DTPA. Ex vivo, without any contrast media, the infarctions were poorly discriminated with a discretely increased signal intensity relative to normal myocardium in the T2 weighted images. Gd-DTPA was found to accumulate in the infarctions, which caused an elevated signal intensity most pronounced in the T1 weighted images. This considerably improved the delineation of the infarcted area.

Double-Contrast Enhanced Mr Imaging of Myocardial Infarction in the Pig

Myocardial infarction was induced by ligating a diagonal branch of the left anterior descending artery in 18 pigs. All pigs were sacrificed 6 h after the occlusion. Dysprosium diethylenetriaminepentaacetic acid bismethylamide (Dy-DTPA-BMA, 1.0 mmol/kg) was administered i.v. to 6 pigs, starting 3 min before sacrifice (injection time approximately 1 min). In a second group of 6 pigs, a double-contrast technique was used, consisting of an i.v. injection of gadolinium-DTPA-BMA (0.4 mmol/kg) 2 h before sacrifice, followed by an i.v. injection of Dy-DTPA-BMA (1.0 mmol/kg) 3 min before sacrifice. Six additional pigs, subjected to 6 h of coronary artery occlusion without administration of contrast medium, served as controls. The hearts were excised and imaged with MR. In the control animals, the infarctions demonstrated an increased signal intensity in the proton density- and T2-weighted images. Administration of Dy-DTPA-BMA primarily improved infarct visualization in the proton density- and T2-weighted images, due to reduction of signal intensity in nonischemic myocardium. The double-contrast technique further improved infarct visualization in all sequences.

Mr Imaging of Acute Myocardial Infarction in Pigs Using GD-Dtpa-Labeled Dextran

Myocardial infarctions were induced in 12 pigs. In 6 pigs, dextran-(Gd-DTPA)15 (≈0.1 mmol Gd/kg b.w.) was injected i.v. 4 to 4.5 hours after coronary artery occlusion. ECG gated MR images were obtained repeatedly before (n = 4) and after (n = 6) contrast medium injection. Relaxation times in blood samples were measured repeatedly. The animals were sacrificed 2 hours after contrast medium administration. The hearts were excised, reexamined in the MR equipment and stained with triphenyltetrazolium chloride (TTC) in order to define areas of infarction. The remaining 6 pigs were sacrificed 6 hours after occlusion without administration of contrast medium. These hearts were only imaged ex vivo. In vivo, the infarctions could not be identified with or without dextran-(Gd-DTPA)15. Ex vivo, without contrast medium, the infarctions had an increased signal intensity, most pronounced in the T2-weighted images. Dextran-(Gd-DTPA)15 caused a prolonged, pronounced shortening of T1 and T2 in blood samples. The infarct demarcation improved in the T1-weighted images after injection of dextran-(Gd-DTPA)15, due to a moderate enhancement in normal myocardium and a stronger enhancement at the periphery of the infarctions, while the central parts of the infarctions were only weakly enhanced.

Root Rot of Pea and Faba Bean in Southern Sweden Caused by Phytophthora pisi sp. nov

A root rot disease of pea and faba bean caused by a Phytophthora sp. was observed in fields and field soil samples in southern Sweden. Observations of the disease in pea root rot greenhouse assays were systematically recorded, and incidence and geographic distribution data were compared with the pea root rot caused by Aphanomyces euteiches. Following one successful isolation of the pathogen, isolation procedures and selective media were optimized to retrieve more isolates. Phylogenetic analysis showed that the isolates belong to a novel lineage, closely related to Phytophthora sojae, and proposed here as a new species, P. pisi sp. nov. In a collection of 13 isolates from separate fields, intraspecific variation was detected in both nuclear and mitochondrial loci. Pathogenicity tests on a range of crop plants and wild legumes suggest that the host range of the pathogen is restricted to a group of legumes closely related to pea which, in addition to pea, include the crop species faba bean, lentil, common vetch, and chickpea. Morphology, growth requirements, and pathogenicity traits indicate that the species may be identical to the organism previously described as P. erythroseptica var. pisi. The work characterizes a novel Phytophthora sp. causing root rot of legume crops.

Microflora in oral ecosystems in subjects with radiation-induced hyposalivation

AIM

To analyse the microbial flora in specific oral sites in 13 dentate subjects, 6-8 months after completed radiation therapy (RT group) and in 13 matched controls.

MATERIAL AND METHODS

The microflora on the tongue, buccal mucosa, vestibulum, supragingival plaque and subgingival region was analysed using duplicate sampling and cultivation technique. A clinical examination was also performed.

RESULTS

Candida albicans was found in one or more sites in 54% of the RT subjects and in 15% of the controls. In three RT subjects, C. albicans was found at all four sites analysed. An unexpected finding was that enterococci were found in all RT subjects and in high number in 38%. None of the controls harboured enterococci. In supragingival plaque, Lactobacillus spp. were detected in 92% of the RT subjects and the number and proportion of Lactobacillus spp. were extremely high compared with the controls. Mutans streptococci were detected in high numbers in 31% of the RT subjects, while they were not detected in 23%.

CONCLUSION

The microbial results explain why some RT subjects have an increased susceptibility to oral diseases and stress that site-specific microbial analysis is an important diagnostic tool when planning oral health preventive care for RT subjects.

Adhesion and invasion to epithelial cells by fimA genotypes of Porphyromonas gingivalis

Adhesion to and invasion of epithelial cells by the periodontopathogen Porphyromonas gingivalis is promoted by the major fimbriae, encoded by fimA. The microorganism can be classified in six genotypes, based on fimA sequence, and genotype II strains are more prevalent than others in periodontitis patients. This study aimed to determine the adhesive and invasive abilities on KB cells of different fimA allelic variants of P. gingivalis isolates. Twenty-two isolates and six reference strains representing the six fimA genotypes and non-typeable strains were screened for their adhesion and invasion abilities on KB cells, using standard methods. All strains were able to adhere and, except for one, to invade KB cells. However, these properties were not homogeneous among strains belonging to the same genotype. There was no correlation between adhesion and invasion efficiencies. Isolate KdII 865 (fimA genotype II) was the most invasive and the second most adhesive strain, whereas reference strain ATCC 33277 (fimA I) showed a low adhesion ability but was highly invasive. These data indicated that fimA genotypes of P. gingivalis are not related to the adhesion and invasion abilities on KB cells, suggesting that the increased prevalence and proportion of certain genotypes may be attributed to other characteristics besides FimA variation.

First Report in Sweden of Downy Mildew on Parsley Caused by Plasmopara petroselini

During September 2004, downy mildew of parsley caused by a species of Plasmopara was observed in an experimental field of parsley (Petroselinum crispum subsp. crispum L. cv. Gigante d'Italia/Hilmar) in Borgeby in southern Sweden. The summer of 2004 was exceptionally wet and humid. Disease became widespread throughout the field in just a few days. Local growers reported that symptoms consistent with downy mildew had appeared in their parsley fields every year since 2001. Plasmopara, under P. nivea, has been reported on parsley in Europe since the middle of the 19th century (4). In recent years, this disease has caused severe damage to parsley grown in several European countries, e.g., France, Germany, Switzerland, and Belgium (1,3). The first symptoms appeared as faint chlorotic spots on the upper surfaces of the leaves. On the corresponding lower surfaces, mycelium and sporangiophores grew profusely and developed a white mat that in part turned dark gray. Eventually, the leaves and stalks became necrotic and died. The sporangiophores were monopodially branched, 248.4 ± 13.36 μm long (n = 17), each branch ending in 2 to 5 ultimate branchlets tapered toward the tip. The trunk diameter measured 7.0 ± 0.77 μm (n = 9) above the basal part and 6.1 ± 0.81 μm just below the first branch. The sporangia were broadly ellipsoidal to ellipsoidal, hyaline, 22.5 ± 0.73 μm long and 16.6 ± 0.48 μm wide (n μ 40). They were mostly nonpapillate when young, although exit pores 4.8 ± 0.32 μm (n = 10) were visible. Mature sporangia exhibited a dehiscence apparatus and a plug in the exit pore. On the basis of the characteristics above, the pathogen was identified as P. petroselini (= P. nivea pro parte [2]). Independent verification of the identity was done by O. Constantinescu at the Botanical Museum, Uppsala, Sweden. A voucher specimen was deposited at the Herbarium UPS, in Uppsala under the number UPS F-118873. To our knowledge, this is the first report of P. petroselini on parsley in Sweden. References: (1) E. Bèliard and J. Thibault. Phytoma 554:2, 2002. (2) O. Constantinescu. Taxon 54:813, 2005. (3) C. Crepel and S. Inghelbrecht. Plant Dis. 87:1266, 2003. (4) A. de Bary, Ann. Sci. Nat. Bot., Sér. 4, 20:5, 1863.

Minor gland saliva flow rate and proteins in subjects with hyposalivation due to Sjögren's syndrome and radiation therapy

In this study, the secretion rate and IgA, albumin and lactoferrin concentrations in minor labial and buccal gland saliva were investigated in individuals with hyposalivation due to primary Sjogren's syndrome (pSS; 10 subjects) or head and neck radiation therapy (RT; 10 subjects) and in their matched controls. Whole saliva was similarly examined. The minor gland saliva flow was measured using the Periotron method. IgA, albumin and lactoferrin concentrations were analysed by ELISA techniques. A general finding was that the flow rate and protein concentrations were lower in labial than in buccal gland saliva. In both hyposalivation groups, the labial minor gland saliva secretion rate was lowered compared to their respective controls. The buccal gland saliva flow rate was significantly reduced in the RT group only. IgA and albumin concentrations were not different from the controls in the labial secretions. The concentration of lactoferrin was increased in the RT group. In buccal saliva, the concentrations of all proteins examined but pSS IgA, were increased compared to the controls. Reduced flow rate and increased protein concentrations were seen for whole saliva where the lactoferrin concentration was higher in RT than in pSS subjects. Thus, our findings suggested that minor gland saliva flow rate and protein concentrations are affected in RT and pSS subjects and to highest extent in the former.

Oral bacteria and clinical variables in dependent individuals at a special facility*

The oral health of dependent residents at special facilities has often been reported as being poor, but it is difficult to relate oral health to general health and define the need for oral health care. Microbiological analyses of the oral flora have been suggested as a suitable method for evaluating oral health in this group of patients. A study was performed at a nursing facility where 33 individuals participated. The aim was to describe their oral flora in relation to other health variables and to classify the residents on different risk levels. An oral examination of the residents was made at the facility, together with a 3-day food record and an oral microbiological analysis. The analysis classified the residents in different categories according to both acid-producing bacteria and the flora correlated with a reduction in general health. The categories were based on previous studies conducted at the Department of Microbiology (Faculty of Odontology in Göteborg). The present study revealed that the level for acid-producing bacteria was high in 12 individuals and the micriobial level according to decreased general health was high in seven individuals. A high level of acid-producing bacteria was related to functional impairment, which was in turn related to nutritional problems and help with oral hygiene. The microbial level according to the reduction in general health did not significantly correlate with other variables.

Chemical anoxia delays germ cell apoptosis in the human testis

An understanding of testicular physiology and pathology requires knowledge of the regulation of cell death. Previous observation of suppression of apoptosis by hypoxia suggested a role for ATP in germ cell death. However, the exact effects of ATP production on germ cell death and of apoptosis on the levels of ATP and other adenine nucleotides (ANs) have remained unclear. We investigated the levels of ANs during human testicular apoptosis (analyzed by HPLC) and the role of chemical anoxia in germ cell death (detected by Southern blot analysis of DNA fragmentation, in situ end labeling of DNA, and electron microscopy). Incubation of seminiferous tubule segments under serum-free conditions induced apoptosis and concomitantly decreased the levels of ANs. Chemical anoxia, induced with potassium cyanide (KCN), an inhibitor of mitochondrial respiration, dropped ATP levels further and suppressed apoptosis at 4 h. After 24 h, many of the testicular cells underwent delayed apoptosis despite ATP depletion. Some cells showed signs of necrosis or toxicity. The addition of 2-deoxyglucose, an antimetabolite of glycolysis, did not alter the results obtained with KCN alone, whereas a toxic concentration of hydrogen peroxide switched apoptosis to necrosis. In most of the testicular cells, mitochondrial respiration appears to play a crucial role in controlling primary cell death cascades. In the human testis, there seem to be secondary apoptotic pathways that do not require functional respiration (or ATP).

Oral microbiota associated with hyposalivation of different origins

We analysed and compared the oral microbial flora in four groups with hyposalivation caused by radiation therapy (RT), primary Sjögren's syndrome (pSS), medication or unknown factors (Unknown), or neuroleptic treatment (Neuro). A control group with normal salivary secretion was also included. The subjects included were 54 +/- 8 years old and had 25 +/- 4 teeth. We analysed their microflora in rinsing samples using a cultivation technique. A marked increase in Lactobacillus spp. and Candida albicans was characteristic of the RT group. In the pSS group, 85% of subjects had high numbers of mutans streptococci despite good oral hygiene, frequent dental visits and fluoride use. The Unknown group had an oral flora similar to that of the controls. In the Neuro group, with a stimulated secretion rate similar to that of the Unknown group, the numbers of aciduric and acidogenic microorganisms were close to those in the pSS group. The results indicate that changes in the oral microflora associated with hyposalivation are related to the reason for the hyposalivation rather than to the magnitude of the decrease in the salivary secretion rate.

Lactoferrin, amylase and mucin MUC5B and their relation to the oral microflora in hyposalivation of different origins

There are several reasons for hyposalivation, each affecting the salivary composition in different ways. The aim of this study was to analyze and compare lactoferrin, amylase and mucin MUC5B in stimulated whole saliva collected from subjects with hyposalivation of different origins and to relate the results to the presence of some microbial species associated with oral disorders. Albumin was determined as a marker of serum leakage. The characteristic feature for subjects with radiation-induced hyposalivation was a large increase in lactoferrin, probably due to leakage through inflamed mucosal tissues, while it was a high albumin content for the group with primary Sjögren's syndrome, probably due to disruption of the fragile mucosa. The saliva composition in subjects with hyposalivation of unknown origin or due to medicines was close to that in the healthy controls. All three hyposalivation groups tended to display a decrease in the concentrations of MUC5B and amylase. None of the microbial species analyzed (streptococci, mutans streptococci, Lactobacillus spp., Fusobacterium nucleatum, Prevotella intermedia/Prevotella nigrescens, Candida albicans, Staphylococcus aureus and enterics) correlated with concentration of MUC5B in saliva. The RT group, having the highest concentration of lactoferrin, had the lowest median number of F. nucleatum and was the only group in which median number of P. intermedia/P. nigrescens was zero.

Ultrafast haem-haem electron transfer in cytochrome c oxidase

Electron transfer between the redox centres is essential for the function of the haem-copper oxidases. To date, the fastest rate of electron transfer between the haem groups has been determined to be ca. 3 x 10(5) s(-1). Here, we show by optical spectroscopy that about one half of this electron transfer actually occurs at least three orders of magnitude faster, after photolysis of carbon monoxide from the half-reduced bovine heart enzyme. We ascribe this to the true haem-haem electron tunnelling rate between the haem groups.

Deletion of one of two Escherichia coli genes encoding putative Na+/H+ exchangers (ycgO) perturbs cytoplasmic alkali cation balance at low osmolarity

Two genes in the Escherichia coli genome, b4065 (yjcE) and b1191 (ycgO), are similar to genes encoding eukaryotic Na+/H+ exchangers. Mutants were constructed in which yjcE (GRN11), ycgO (GRF55) or both (GRD22) were inactivated. There was no change in respiration-driven Na+ efflux in any of the mutants when grown in media containing 50-500 mM Na+. The only striking finding was that growth of GRF55 was impaired at low osmolarity. In complex low-salt medium, GRF55 grew at a wild-type rate for three to four generations but then stopped; the growth was partially recovered after a pause, the length of which was dependent on salt concentration. Measurement of cytoplasmic alkali cations showed that an abrupt loss of about one-half of the intracellular K+ preceded the pause. When grown in low-salt medium with only 20 mM added Na+, GRF55 also lost the ability to maintain a sodium concentration gradient. However, this phenomenon appears to be a secondary effect of the ycgO deletion. The double mutant GRD22 has the same properties as GRF55; no additional effect was found. The data indicate that neither ycgO nor yjeE participates in respiration-driven Na+ extrusion. Instead, ycgO is required for growth at low osmolarity. Hence it is concluded that ycgO participates in cell volume regulation, and accordingly it is suggested that ycgO be renamed cvrA.

Solution structure of the DNA binding domain of the human forkhead transcription factor AFX (FOXO4)

AFX is a human forkhead transcription factor. Based on results from studies of the orthologous transcription factor DAF-16 in Caenorhabditis elegans, it was suggested that some of the metabolic defects in both type I and type II diabetes may be due to unregulated activity of AFX. In the present study, we report the high-resolution NMR solution structure of the DNA binding domain of AFX. It is the first structure of the DNA binding domain from a small subfamily of forkhead transcription factors (i.e., AFX, FKHR, FKHRL1, FKHRL1P1, and FKHRP1). Despite rather low sequence identity for a protein within the forkhead family, the structure is remarkably similar to those of the DNA binding domains of HNF3-gamma and FREAC-11, and to a lesser extent the DNA binding domain of Genesis which displays a slightly altered orientation of the DNA recognition helix. The high degree of structural similarity between the DNA binding domains of different forkhead transcription factors implies that the repositioning of helix 3, observed for Genesis, cannot be a general feature for modulation of the DNA binding specificity. Other mechanisms that could influence the DNA binding specificity are discussed.

Sequence properties of the 1,2-diacylglycerol 3-glucosyltransferase from Acholeplasma laidlawii membranes. Recognition of a large group of lipid glycosyltransferases in eubacteria and archaea

Synthesis of the nonbilayer-prone alpha-monoglucosyldiacylglycerol (MGlcDAG) is crucial for bilayer packing properties and the lipid surface charge density in the membrane of Acholeplasma laidlawii. The gene for the responsible, membrane-bound glucosyltransferase (alMGS) (EC ) was sequenced and functionally cloned in Escherichia coli, yielding MGlcDAG in the recombinants. Similar amino acid sequences were encoded in the genomes of several Gram-positive bacteria (especially pathogens), thermophiles, archaea, and a few eukaryotes. All of these contained the typical EX(7)E catalytic motif of the CAZy family 4 of alpha-glycosyltransferases. The synthesis of MGlcDAG by a close sequence analog from Streptococcus pneumoniae (spMGS) was verified by polymerase chain reaction cloning, corroborating a connection between sequence and functional similarity for these proteins. However, alMGS and spMGS varied in dependence on anionic phospholipid activators phosphatidylglycerol and cardiolipin, suggesting certain regulatory differences. Fold predictions strongly indicated a similarity for alMGS (and spMGS) with the two-domain structure of the E. coli MurG cell envelope glycosyltransferase and several amphipathic membrane-binding segments in various proteins. On the basis of this structure, the alMGS sequence charge distribution, and anionic phospholipid dependence, a model for the bilayer surface binding and activity is proposed for this regulatory enzyme.

Charge translocation coupled to electron injection into oxidized cytochrome c oxidase from Paracoccus denitrificans

Electrons were discretely injected into oxidized cytochrome c oxidase in liposomes by laser flash excitation of bound ruthenium [II] bispyridyl, and the membrane potential was recorded by time-resolved electrometry. Membrane potential is generated in a fast phase when an electron is transferred from the excited dye, via the CuA center, to heme a at a relative dielectric depth d inside the membrane [Zaslavsky, D., Kaulen, A. D., Smirnova, I. A., Vygodina, T., and Konstantinov, A. A. (1993) FEBS Lett. 336, 389-393]. Subsequently, membrane potential may develop further in a slower event, which is due to proton transfer into the enzyme from the opposite side of the membrane [Ruitenberg, M., Kannt, A., Bamberg, E., Ludwig, B., Michel, H., and Fendler, K. (2000) Proc. Natl. Acad. Sci. U.S.A. 97, 4632-4636]. Here, we confirm that injection of the first electron into the fully oxidized cytochrome c oxidase from Paracoccus denitrificans is associated with a fast electrogenic 11 micros phase, but there is no further electrogenic phase up to 100 milliseconds when special care is taken to ensure that only fully oxidized enzyme is present initially. A slower electrogenic 135 micros phase only becomes apparent and grows in amplitude upon increasing the number of light flashes. This occurs in parallel with a decrease in amplitude of the 11 micros phase and correlates with the number of enzyme molecules that are already reduced by one electron before the flash. The electrogenic 135 micros phase does not appear with increasing flash number in the K354M mutant enzyme, where electron and proton transfer into the binuclear center is delayed. We conclude that the 135 micros phase, and its associated proton uptake, take place on electron injection into enzyme molecules where the binuclear heme a3-CuB site is already reduced by one electron, and that it is accompanied by oxidation of heme a with a similar time constant. Reduction of heme a is not associated with electrogenic proton uptake into the enzyme, neither in the fully oxidized nor in the one-electron-reduced enzyme. The extent of the electrogenic 135 micrcos phase also rules out the possibility that reduction of the binuclear center by the second electron would be coupled to proton translocation in addition to the electrogenic uptake of a proton.

Role of the PR intermediate in the reaction of cytochrome c oxidase with O2

The first discernible intermediate when fully reduced cytochrome c oxidase reacts with O2 is a dioxygen adduct (compound A) of the binuclear heme iron-copper center. The subsequent decay of compound A is associated with transfer of an electron from the low-spin heme a to this center. This reaction eventually produces the ferryl state (F) of this center, but whether an intermediate state may be observed between A and F has been the subject of some controversy. Here we show, using both optical and EPR spectroscopy, that such an intermediate (P(R)) indeed exists and that it exhibits spectroscopic properties quite distinct from F. The optical spectrum of P(R) is similar or identical to the spectrum of the P(M) intermediate that is formed after compound A when two-electron-reduced enzyme reacts with O2. An unusual EPR spectrum with features of a CuB(II) ion that interacts magnetically with a nearby paramagnet [cf. Hansson, O., Karlsson, B., Aasa, R., Vänngård, T., and Malmström, B.G (1982) EMBO J. 1, 1295-1297; Blair, D. F., Witt, S. N., and Chan, S. I. (1985) J. Am. Chem. Soc. 107, 7389-7399] can be uniquely assigned to the P(R) intermediate, not being found in either the P(M) or F intermediate. The binuclear center in the P(R) state may be assigned as having an Fe(a3)(IV)=O CuB(II) structure, as in both the P(M) and F states. The spectroscopic differences between these three intermediates are evaluated. The P(R) state has a key role as an initiator of proton translocation by the enzyme, and the thermodynamic and electrostatic bases for this are discussed.

Heme-copper oxidases with modified D- and K-pathways are yet efficient proton pumps

The cytochrome aa(3)-type quinol oxidase from the archaeon Acidianus ambivalens and the ba(3)-type cytochrome c oxidase from Thermus thermophilus are divergent members of the heme-copper oxidase superfamily of enzymes. In particular they lack most of the key residues involved in the proposed proton transfer pathways. The pumping capability of the A. ambivalens enzyme was investigated and found to occur with the same efficiency as the canonical enzymes. This is the first demonstration of pumping of 1 H(+)/electron in a heme-copper oxidase that lacks most residues of the K- and D-channels. Also, the structure of the ba(3) oxidase from T. thermophilus was simulated by mutating Phe274 to threonine and Glu278 to isoleucine in the D-pathway of the Paracoccus denitrificans cytochrome c oxidase. This modification resulted in full efficiency of proton translocation albeit with a substantially lowered turnover. Together, these findings show that multiple structural solutions for efficient proton conduction arose during evolution of the respiratory oxidases, and that very few residues remain invariant among these enzymes to function in a common proton-pumping mechanism.

Electron and proton transfer in the arginine-54-methionine mutant of cytochrome c oxidase from Paracoccus denitrificans

Arginine 54 in subunit I of cytochrome c oxidase from Paracoccus denitrificans interacts with the formyl group of heme a. Mutation of this arginine to methionine (R54M) dramatically changes the spectral properties of heme a and lowers its midpoint redox potential [Kannt et al. (1999) J. Biol. Chem. 274, 37974-37981; Lee et al. (2000) Biochemistry 39, 2989-2996; Riistama et al. (2000) Biochim. Biophys. Acta 1456, 1-4]. During anaerobic reduction of the mutant enzyme, a small fraction of heme a is reduced first along with heme a(3), while most of heme a is reduced later. This suggests that electron transfer is impaired thermodynamically due to the low redox potential of heme a but that it still takes place from Cu(A) via heme a to the binuclear site as in wild-type enzyme, with no detectable bypass from Cu(A) directly to the binuclear site. Consistent with this, the proton translocation efficiency is unaffected at 1 H(+)/e(-) in the mutant enzyme, although turnover is strongly inhibited. Time-resolved electrometry shows that when the fully reduced enzyme reacts with O(2), the fast phase of membrane potential generation during the P(R )()--> F transition is unaffected by the mutation, whereas the slow phase (F --> O transition) is strongly decelerated. In the 3e(-)-reduced mutant enzyme heme a remains oxidized due to its lowered midpoint potential, whereas Cu(A) and the binuclear site are reduced. In this case the reaction with O(2) proceeds via the P(M) state because transfer of the electron from Cu(A) to the binuclear site is delayed. The single phase of membrane potential generation in the 3e(-)-reduced mutant enzyme, which thus corresponds to the P(M)--> F transition, is decelerated, but its amplitude is comparable to that of the P(R)--> F transition. From this we conclude that the completely (4e(-)) reduced enzyme is fully capable of proton translocation.

Microflora in oral ecosystems in primary Sjögren's syndrome

OBJECTIVE

Knowledge of the effect of primary Sjögren's syndrome (pSS) on the microbial flora in the different predilection sites for oral disorders is needed for planning preventive treatment. We carried out microbial analysis of samples from the dorsum of the tongue, smooth mucosa, supragingival tooth surfaces, and the gingival crevice region of 20 patients with pSS.

METHODS

A clinical oral examination was performed and whole unstimulated and stimulated secretion rates were measured.

RESULTS

Compared with healthy controls, subjects with pSS harbored higher numbers and frequencies of Streptococcus mutans, Lactobacillus spp., and Candida albicans in the supragingival plaque. On the smooth mucosa and tongue, the pSS subjects displayed an increased frequency of C. albicans, Staphylococcus aureus, enterics, and enterococci. C. albicans was detected about twice as frequently in the supragingival plaque as it was on the tongue. In the gingival crevice region, the pSS group harbored slightly lower proportions of Fusobacterium nucleatum and Prevotella intermedia/Prevotella nigrescens than controls. The clinical and microbial differences were mainly due to the pSS subjects with a stimulated secretion rate of < 0.5 ml/min. Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans were not detected in any subject with pSS.

CONCLUSION

The microbial flora in the different ecosystems reflected the status of oral disorders in the subjects with pSS. Specific site sampling and analysis in subjects with pSS revealed further differences compared with controls, and is therefore preferable to saliva sampling for oral treatment planning and for the evaluation of the effect of oral treatment and of preventive measures implemented in individuals with pSS.

Reliability and validity of a Swedish version of the Revised Leeds Disability Questionnaire for patients with ankylosing spondylitis

The aim of the study was to investigate the reliability and the validity of a Swedish version of the Revised Leeds Disability Questionnaire (RLDQ). Forty-two patients, 36 men and 6 women, median age 52.5 years, median symptom duration 24 years, with spondylarthropathy were assessed with the RLDQ, three questions on the content of the questionnaire, and range-of-motion measures. The results indicated satisfactory test-retest stability and internal consistency, and only minor internal redundancy. RLDQ items were generally considered relevant and suggested additions were similar to items already included in the questionnaire. Patients with low disability scores tended to be older and have better joint mobility than those with higher scores. Physiotherapists observed and scored disability significantly higher than patients. Correlations between subscores of the RLDQ and range-of-motion measures were in the main weak. In conclusion the Swedish version of the RLDQ may be considered as reliable and valid.

Move of adults with mental retardation from institutions to community-based living: changes in the oral microbiological flora

In the Western world, the policy of deinstitutionalization and integration of individuals with mental retardation is generally accepted. We tested the hypothesis that de-institutionalization may lead to changes of habits with a potential to influence oral health. When 57 adults with mental retardation moved from an institution to community-based living, their oral hygiene habits, gingival bleeding, and a three-day food record were registered one month before and 9 and 21 months after the move. Mutans streptococci and lactobacilli in saliva, P. intermedia/P. nigrescens, P. gingivalis, and A. actinomycetemcomitans in supragingival plaque, and C. albicans on mucous membranes were analyzed. After 21 months of community-based living, fewer persons showed high classes of mutans streptococci, growth of P. intermedia/P. nigrescens, and high frequency of sucrose intake, and more subjects showed growth of C. albicans. In a short perspective, the indicators of oral diseases suggest an unchanged or lower risk of oral diseases after the de-institutionalization of individuals with moderate or severe mental retardation.

Bone tissue composition, dimensions and strength in female rats given an increased dietary level of vitamin A or exposed to 3,3',4, 4',5-pentachlorobiphenyl (PCB126) alone or in combination with vitamin C

In previous studies we have described structural and functional changes in rat bone tissue caused by 3,3',4,4',5-pentachlorobiphenyl (PCB126). Some of the effects caused by PCB126 resemble those found in vitamin C-deficient rats, as well as those found in rats with a high dietary intake of vitamin A. The present investigation was designed to determine if these PCB126-induced changes could be inhibited by addition of vitamin C to the drinking water and if they could be evoked by vitamin A administration. Five groups of female rats were used in this study, which lasted for 12 weeks. Three of the groups were exposed to PCB126 (total dose 320 microgram/kg, bw), either alone or in combination with vitamin C added to the drinking water (1 and 10 g/l, respectively). One group was given feed with increased level of vitamin A (600000 U/kg pellet) and the fifth group served as controls. Using peripheral quantitative computed tomography (pQCT), it was found that PCB126 increased trabecular density and cortical thickness, but reduced the trabecular area. Furthermore, maximum torque and stiffness of the humerus during torsional testing and serum osteocalcin levels were reduced by PCB126. Of the PCB126 induced effects observed, addition of vitamin C only inhibited the reduction of serum osteocalcin. Like PCB126 vitamin A supplementation increased the inorganic content and the bone density and also reduced the trabecular area and polar moment of inertia but did not increase the cortical thickness or reduce maximum torque, stiffness or serum osteocalcin level. Apparently, the effects induced by PCB126 are not mediated either via decreased vitamin C level or increased vitamin A level.

The structure of the ubiquinol oxidase from Escherichia coli and its ubiquinone binding site

Cell respiration is catalyzed by the heme-copper oxidase superfamily of enzymes, which comprises cytochrome c and ubiquinol oxidases. These membrane proteins utilize different electron donors through dissimilar access mechanisms. We report here the first structure of a ubiquinol oxidase, cytochrome bo3, from Escherichia coli. The overall structure of the enzyme is similar to those of cytochrome c oxidases; however, the membrane-spanning region of subunit I contains a cluster of polar residues exposed to the interior of the lipid bilayer that is not present in the cytochrome c oxidase. Mutagenesis studies on these residues strongly suggest that this region forms a quinone binding site. A sequence comparison of this region with known quinone binding sites in other membrane proteins shows remarkable similarities. In light of these findings we suggest specific roles for these polar residues in electron and proton transfer in ubiquinol oxidase.

The role of the D- and K-pathways of proton transfer in the function of the haem-copper oxidases

The X-ray structures of several haem-copper oxidases now at hand have given important constraints on how these enzymes function. Yet, dynamic data are required to elucidate the mechanisms of electron and proton transfer, the activation of O(2) and its reduction to water, as well as the still enigmatic mechanism by which these enzymes couple the redox reaction to proton translocation. Here, some recent observations will be briefly reviewed with special emphasis on the functioning of the so-called D- and K-pathways of proton transfer. It turns out that only one of the eight protons taken up by the enzyme during its catalytic cycle is transferred via the K-pathway. The D-pathway is probably responsible for the transfer of all other protons, including the four that are pumped across the membrane. The unique K-pathway proton may be specifically required to aid O-O bond scission by the haem-copper oxidases.

Proton translocation by cytochrome c oxidase can take place without the conserved glutamic acid in subunit I

A glutamic acid residue in subunit I of the heme-copper oxidases is highly conserved and has been directly implicated in the O(2) reduction and proton-pumping mechanisms of these respiratory enzymes. Its mutation to residues other than aspartic acid dramatically inhibits activity, and proton translocation is lost. However, this glutamic acid is replaced by a nonacidic residue in some structurally distant members of the heme-copper oxidases, which have a tyrosine residue in the vicinity. Here, using cytochrome c oxidase from Paracoccus denitrificans, we show that replacement of the glutamic acid and a conserved glycine nearby lowers the catalytic activity to <0.1% of the wild-type value. But if, in addition, a phenylalanine that lies close in the structure is changed to tyrosine, the activity rises more than 100-fold and proton translocation is restored. Molecular dynamics simulations suggest that the tyrosine can support a transient array of water molecules that may be essential for proton transfer in the heme-copper oxidases. Surprisingly, the glutamic acid is thus not indispensable, which puts important constraints on the catalytic mechanism of these enzymes.

O-O bond splitting mechanism in cytochrome oxidase

Hybrid density functional theory (DFT) calculations have been used to investigate different mechanisms for O-O bond splitting in cytochrome oxidase. It is shown that the requirement for a low activation barrier for the O-O bond splitting is that two protons, apart from the tyrosine hydroxyl proton, are available at the binuclear center. A mechanism is suggested for the transformation from a species with a molecularly coordinated O2, to an O-O cleaved species with an oxo-ferryl group. The mechanism has a calculated activation barrier in reasonable agreement with experimental estimates, and the overall reaction is close to thermoneutral, in line with the requirement that the energy wasted as heat should be minimized. The rate limiting step in the mechanism occurs at the initial Fe-O2 intermediate, consistent with experimental observations that the decay of the oxy intermediate parallels the increase of the oxo product. The formation of a radical at the cross-linked tyrosine-histidine structure is a possible source for one of the electrons required in the bond cleavage process. Possible sources for the two protons are discussed, including a suggested key role for the hydroxyl group on the farnesyl side chain of heme a3.

Binding of O(2) and its reduction are both retarded by replacement of valine 279 by isoleucine in cytochrome c oxidase from Paracoccus denitrificans

The crystal structure of the heme-copper oxidases suggested a putative channel of oxygen entry into the heme-copper site of O(2) reduction. Changing a conserved valine near this center in cytochrome bo(3) of Escherichia coli to isoleucine caused a significant increase in the apparent K(M) for oxygen with little or no change in V(max), suggesting that oxygen diffusion had been partially blocked [Riistama, S., Puustinen, A., García-Horsman, A., Iwata, S., Michel, H., and Wikström, M. (1996) Biochim. Biophys. Acta 1275, 1-4]. To study this phenotype further using rapid kinetic methods, the corresponding change (V279I) has been made in cytochrome aa(3) from Paracoccus denitrificans. In this mutant, the apparent K(M) for oxygen is 8 times higher than in the wild-type enzyme, whereas V(max) is decreased only to approximately half of the wild-type value. Flow-flash kinetic measurements show that the initial binding of oxygen to the heme of the binuclear site is indeed much slower in the mutant than in the wild-type enzyme. However, the subsequent phases of the reaction with O(2) are also slow although the pure heme-to-heme electron transfer process is essentially unperturbed. It is suggested that the mutation sterically hinders O(2) entry into the binuclear site and that it may also perturb the structure of local water molecules involved in proton transfer to this site.

Proton translocation by cytochrome c oxidase: a rejoinder to recent criticism

Ten years ago, intermediate reaction steps in the catalytic cycle of cytochrome c oxidase were titrated with phosphorylation potential in isolated mitochondria, and the results were interpreted as evidence for thermodynamic linkage of proton translocation exclusively to the oxidative reaction steps of the catalytic cycle [Wikström, M. (1989) Nature 338, 776-778]. Michel has recently argued that this work was flawed, and proposed a mechanism in which one of the four steps of proton translocation is linked to the reductive phase of the catalytic cycle [Michel, H. (1999) Biochemistry 38, 15129-15140]. Here, the original data are scrutinized and related to information that has accumulated since this work was published. The analysis shows that the main conclusions from this work still hold. Michel's mechanism of proton translocation is briefly discussed, and found to be at odds with some experimental observations.

Solution structure and dynamics of the DNA-binding domain of the adipocyte-transcription factor FREAC-11

Transcription factors of the forkhead type share a highly conserved DNA-binding domain of about 100 amino acid residues. FREAC-11, expressed in adipocytes, belongs to this class. Here, we report on NMR studies that established the three-dimensional structure of the FREAC-11, DNA-binding domain. Although apparent similarities to the structures of other members within the forkhead family are observed, the structure also reveals some remarkable differences. Along with the complementary dynamics, the data provide insight into the fundamentals of sequence specificity within a highly conserved motif.

Interaction between the formyl group of heme a and arginine 54 in cytochrome aa(3) from Paracoccus denitrificans

The optical spectrum of heme a is red-shifted in aa(3)-type cytochrome c oxidases compared to isolated low-spin heme A model compounds. Early spectroscopic studies indicated that this may be due to hydrogen-bonding of the formyl group of heme a to an amino acid in the close vicinity. Here we show that most of the optical spectral shift of native heme a is due to a hydrogen-bonding interaction between the formyl group and arginine-54 in subunit I of cytochrome aa(3) from Paracoccus denitrificans, and that a smaller part is due to an electrostatic interaction between the D ring propionate of heme a and arginine-474.

Glutamate-89 in subunit II of cytochrome bo3 from Escherichia coli is required for the function of the heme-copper oxidase

Recent electrostatics calculations on the cytochrome c oxidase from Paracoccus denitrificans revealed an unexpected coupling between the redox state of the heme-copper center and the state of protonation of a glutamic acid (E78II) that is 25 A away in subunit II of the oxidase. Examination of more than 300 sequences of the homologous subunit in other heme-copper oxidases shows that this residue is virtually totally conserved and is in a cluster of very highly conserved residues at the "negative" end (bacterial cytoplasm or mitochondrial matrix) of the second transmembrane helix. The functional importance of several residues in this cluster (E89II, W93II, T94II, and P96II) was examined by site-directed mutagenesis of the corresponding region of the cytochrome bo(3) quinol oxidase from Escherichia coli (where E89II is the equivalent of residue E78II of the P. denitrificans oxidase). Substitution of E89II with either alanine or glutamine resulted in reducing the rate of turnover to about 43 or 10% of the wild-type value, respectively, whereas E89D has only about 60% of the activity of the control oxidase. The quinol oxidase activity of the W93V mutant is also reduced to about 30% of that of the wild-type oxidase. Spectroscopic studies with the purified E89A and E89Q mutants indicate no perturbation of the heme-copper center. The data suggest that E89II (E. coli numbering) is critical for the function of the heme copper oxidases. The proximity to K362 suggests that this glutamic acid residue may regulate proton entry or transit through the K-channel. This hypothesis is supported by the finding that the degree of oxidation of the low-spin heme b is greater in the steady state using hydrogen peroxide as an oxidant in place of dioxygen for the E89Q mutant. Thus, it appears that the inhibition resulting from the E89II mutation is due to a block in the reduction of the heme-copper binuclear center, expected for K-channel mutants.

Partial oxygen pressure and mitochondrial permeability transition affect germ cell apoptosis in the human testis

During regular spermatogenesis, a number of testicular germ cells degenerate by an apoptotic process that is under hormonal control. Oxidative and mitochondrial changes have been proposed to play a role in apoptosis of many cell types. Previously, whether human germ cell survival is controlled by oxygen or by effectors of the mitochondrial permeability transition has not been investigated. In the present study, apoptosis was induced in human testicular germ cells by incubating segments of seminiferous tubules without survival factors (i.e. serum or hormones; 21% oxygen). Apoptosis was significantly suppressed in an inversely dose-dependent fashion at partial oxygen pressures below 10%, as detected by Southern blot analysis of DNA fragmentation, DNA labeling in situ, and electron microscopy. Cyclosporin A and its nonimmunosuppressive derivative N-methyl-Val4-cyclosporin A prevented cell death, suggesting a key role for the mitochondrial permeability transition in apoptosis. Apoptotic cells were identified as mainly spermatocytes and spermatids, the mitochondria of which underwent morphological changes during the apoptotic process. The present results imply that to improve germ cell viability in in vitro fertilization techniques, the partial oxygen pressure should be lowered.

Infection of Potatoes by Oospores of Phytophthora infestans in Soil

Phytophthora infestans (Mont.) de Bary, causing late blight on potatoes and considered to be a typical airborne disease, was found to be infective also by oospores in the soil. P. infestans is heterothallic, and is known to reproduce asexually in Sweden since only one mating type, A1, was present until 1986. Since the 1970s, the other mating type, A2, of P. infestans has migrated to most parts of the world from its original location in central Mexico (2). When A1 and A2 meet, they may form oospores, which are thick-walled, resting structures, giving the pathogen a possibility to recombine as well as survive without its host, for instance in the soil. The soil stages of the pathogen are now therefore under intense investigation. Oospores of P. infestans were produced from two Scandinavian A1 and A2 isolates in Rye A broth mixed with talcum powder and dried for 7 weeks. The inoculum was mixed with sterile, standardized soil in concentrations of 10, 150, 250, and 400 oospores per ml of soil. Cv. Bintje plants cultivated in vitro from nodal cuttings on Murashige and Skoog medium were transplanted to the soil after rooting. Brown discolorations were obtained on the underground stems and tubers on potato plants grown in the two highest concentrations of oospores for 1 month at 15°C and 16-h day length. After 3 days of incubation on P. infestans-selective medium (3), sporangia covered the tissue from plants grown in 250 and 400 oospores per ml of soil and the pathogen was reisolated. This shows that germinating oospores of P. infestans can infect underground stems and tubers of potatoes in soil and further explains the early attack of late blight as observed in a potato crop in Sweden 1996 and 1997 (1). References: (1) B. Andersson et al. Potato Res. 41:305, 1998. (2) D. Andrivon. Phytopathology 85:1053, 1995. (3) G. W. Griffith et al. Mycologist 9:87, 1995.