The influence of cadmium on life-history parameters and gut microflora of <Emphasis Type="Italic">Archegozetes longisetosus</Emphasis> (Acari: Oribatida) under laboratory conditions

We tested the effect of cadmium (25, 130 μg Cd g⁻¹), administered via Chinese cabbage (Brassica chinensis L.) as food on life-history parameters and gut microflora of tritonymphs and adults of the oribatid mite, Archegozetes longisetosus Aoki. Both concentrations of Cd had an adverse effect on offspring mortality, and the higher concentration also reduced female fecundity, as well as the number of bacteria, fungi and actinomycetes, and it changed the community structure of bacteria; the proportion of gram-negative bacteria increased while that of gram-positive bacteria declined. Interestingly, at the lower Cd concentration microflora was more abundant and diverse than in the control group, especially in the tritonymphs, although the mean activity of gut microflora was reduced. The higher Cd concentration reduced microflora activity both in the tritonymphs and adults.     

Antagonistic activity of soil acidophilic actinomycetes

It has been shown that soil acidophilic actinomycetes (mycelial prokaryotes with a growth optinum between pH 3 and 7) markedly differ from neutrophilic actinomycetes in antimicrobial activity: the former are more active against fungi and yeasts, whereas the latter effectively suppress Gram-positive bacteria. Acidophilic streptomycetes actively inhibit the growth of phytopathogenic fungi, especially on acidic media.     

Arbuscular mycorrhizal adaptation,spore germination,root colonization,and host plant growth and mineral acquisition at low pH

Arbuscular mycorrhizal (AM) fungi colonize plant roots and often enhance host plant growth and mineral acquisition, particularly for plants grown under low nutrient and mineral stress conditions. Information about AM fungi and mycorrhizal ( +AM) host plant responses at low pH ( < 5) is limited. Acaulospora are widely reported in acid soil, and Gigaspora sp. appear to be more common in acid soils than Glomus sp. Spores of some AM fungi are more tolerant to acid conditions and high Al than others; t Acaulospora sp., Gigaspora sp., and Glomus manihotis are particularly tolerant. Root colonization is generally less in low than in high pH soils. Percentage root colonization is generally not related to dry matter (DM) produced. Maximum enhancement of plant growth in acid soil varies with AM fungal isolate and soil pH, indicating adaptation of AM isolates to edaphic conditions. Acquisition of many mineral nutrients other than P and Zn is enhanced by +AM plants in acid soil, and the minerals whose concentration is enhanced are those commonly deficient in acid soils (Ca, Mg, and K). Some AM fungal isolates are effective in overcoming soil acidity factors, especially Al toxicity, that restrict plant growth at low pH.     

Biosorption and recycling of gold using various microorganisms

In order to obtain basic information on the biosorption and recycling of gold from aqueous systems using microbial cells, the biosorption of gold by various microorganisms was investigated. Of 75 strains of microorganisms tested (25 bacteria, 19 actinomycetes, 17 fungi and 14 yeasts), high abilities of gold biosorption from a solution containing hydrogen tetrachloroaurate (III) were found in some gram-negative bacterial strains, such as Acinetobacter calcoaceticus, Erwinia herbicola, Pseudomonas aeruginosa, and P. maltophilia. Most of the gram-positive bacteria, actinomycetes, fungi and yeasts had a lower ability for gold biosorption than gram-negative bacteria. On the other hand, all of the microorganisms tested adsorbed far smaller amounts of gold from a solution containing gold dicyanoaurate (I). The biosorption of gold from a solution containing hydrogen tetrachloroaurate (III) using P. maltophilia having a high adsorbing ability for gold was very rapid and was affected by the pH of the solution, external gold concentration, and cell amounts. P. maltophilia cells immobilized with polyacrylamide gel also have a high ability for gold biosorption. The gold adsorbed on the immobilized cells is easily desorbed with 0.1 M thiourea solution. The immobilized P. maltophilia cells can be used repeatedly in biosorption-desorption cycles.     

Effect of Cadmium Stress on the Growth,Physiology, Stress Markers,Antioxidants and Stomatal Behaviour of Two Genotypes of Chickpea ( <i>Cicer arietinum </i>L.)

The current work was performed to know the impact of cadmium (Cd) toxicity on two different genotypes of chickpea (Cicer arietinum L.) namely Pusa-BG1053 and Pusa-BG372. Cadmium was applied in the form of cadmium chloride (CdCl₂), in varying levels, 0, 25, 50, 75, and 100 mg Cd kg^-1 soil. Plant growth as well as physiological attributes were decreased with increasing concentration of Cd. Both genotypes showed the maximum and significant reduction at the maximum dose of Cd (100 mg Cd kg^-1 soil). Results of this study proved that the genotype Pusa-BG1053 was more tolerant and showed a lower decline in growth, photosynthetic and biochemical attributes than Pusa-BG372. This later genotype showed the maximum reduction and was sensitive to Cd stress. A better activity of antioxidants protected Pusa-BG1053 from Cd toxicity; on the other hand, the activity of antioxidants was much lower in Pusa-BG372. Scanning electron microscopic studies showed differences in both genotypes. In Pusa-BG1053, stomatal quantity was higher and stomata were slightly close to the characteristic guard cells. In Pusa-BG372 stomata were lower, slightly open and with highly affected guard cells. Root cell mortality due to the harsh effects of Cd appeared to be more evident in Pusa-BG372 than Pusa-BG1053, which was visible under a confocal microscope. As a result of this study, Pusa-BG1053 was a more tolerant genotype, and exhibited a minimum reduction in terms of all studied parameters than Pusa-BG372, which was a sensitive genotype to Cd toxicity.

     

Variation in Microbial Community Structure in Two Boreal Peatlands as Determined by Analysis of Phospholipid Fatty Acid Profiles

Analyses of phospholipid fatty acids (PLFAs) were used to assess variation in community structure and total microbial biomass in two boreal peatlands in Sweden. The total PLFA concentration in peat ranged from 0.16 to 7.0 nmol g of wet peat(sup-1) (median, 0.70 nmol g of wet peat(sup-1)). Principal-component analysis of PLFA data revealed that the degree of depth-related variation in PLFA composition was high among peatland habitats, with general differences between wet sites, with water tables within a few centimeters of the moss surface, and dry sites, with water tables >10 cm below the moss surface. However, variation in PLFA composition over the growing season was negligible. In the principal-component analyses, most PLFAs were determined to be parts of clusters of covarying fatty acids, suggesting that they originated in the same functional groups of microorganisms. Major clusters were formed by monounsaturated (typical of gram-negative eubacteria), terminally branched (gram-positive or anaerobic gram-negative eubacteria), methyl-branched and branched unsaturated (sulfate-reducing bacteria and/or actinomycetes), (omega)8 monounsaturated (methane-oxidizing bacteria), and polyunsaturated (eucaryotes) PLFAs. Within the clusters, PLFAs had rather distinct concentration-depth distributions. For example, PLFAs from sulfate-reducing bacteria and/or actinomycetes and those from methane-oxidizing bacteria had maximum concentrations slightly below and at the average water table depth, respectively.     

废弃铅锌矿区圆叶无心菜根际真菌的分离及其镉铅耐性研究

采用常规的和分别含Cd2+、Pb2+的马丁氏培养基,对云南省会泽县废弃铅锌矿区圆叶无心菜(Arenar-ia orbiculata)根际真菌进行分离和鉴定,将分离的菌株分别接种在含不同浓度Pb2+(0,0.1,1,10mmol/L)和Cd2+(0,0.05,0.5,5mmol/L)的马铃薯葡萄糖培养液(PSB)中,研究废弃铅锌矿区圆叶无心菜根际真菌的镉铅耐性,结果表明:从铅锌矿区圆叶无心菜根际共分离获得6个属的真菌,其中青霉属(Penicillinm)真菌为优势种群;Cd2+和Pb2+显著减少根际真菌在平板上生长的菌落数量,抑制菌株的生长;含Cd2+和含Pb2+的马丁氏培养基分离的根际真菌镉铅耐性强于常规马丁氏培养基分离的菌株。     

Isolation and Characterization of Actinomycete Antagonists of a Fungal Root Pathogen

By use of selective media, 267 actinomycete strains were isolated from four rhizosphere-associated and four non-rhizosphere-associated British soils. Organic media with low nutrient concentrations were found to be best for isolating diverse actinomycetes while avoiding contamination and overgrowth of isolation media by eubacteria and fungi. While all isolates grew well at pHs 6.5 to 8.0, a few were unable to grow at pH 6.0 and a significant number failed to grow at pH 5.5. Eighty-two selected isolates were screened for in vitro antagonism towards Pythium ultimum by use of a Difco cornmeal agar assay procedure. Five isolates were very strong antagonists of the fungus, four were strong antagonists, and ten others were weakly antagonistic. The remaining isolates showed no antagonism by this assay. Additional studies showed that several of the P. ultimum antagonists also strongly inhibited growth of other root-pathogenic fungi. Twelve isolates showing antifungal activity in the in vitro assay were also tested for their effects on the germination and short-term growth of lettuce plants in glasshouse pot studies in the absence of pathogens. None of the actinomycetes prevented seed germination, although half of the isolates retarded seed germination and outgrowth of the plants by 1 to 3 days. During 18-day growth experiments, biomass yields of some actinomycete-inoculated plants were reduced in comparison with untreated control plants, although all plants appeared healthy and well rooted. None of the actinomycetes significantly enhanced plant growth over these short-term experiments. For some, but not all, actinomycetes, some correlations between delayed seed germination and reduced 18-day plant biomass yields were seen. For others, plant biomass yields were not reduced despite an actinomycete-associated delay in seed germination and plant outgrowth. Preliminary glasshouse experiments indicated that some of the actinomycetes protect germinating lettuce seeds against damping-off caused by P. ultimum.     

喀斯特地区三种人工林土壤微生物群落结构特征

为揭示不同人工植被修复模式对喀斯特土壤微生物群落的影响,采用氯仿熏蒸提取法和磷脂脂肪酸(phospholipid fatty acid, PLFA)法研究人工构建的降香黄檀(Dalbergia odorifera)纯林(PDOP)、顶果木(Acrocarpus fraxinifolius)纯林(PAFP)、顶果木×降香黄檀混交林(MADP)对土壤微生物生物量及土壤微生物群落结构的影响。结果表明:(1)PDOP的土壤微生物生物量碳(MBC)和微生物生物量氮(MBN)含量显著高于PAFP和MADP,PAFP显著高于MADP。(2)三种人工林土壤真菌、丛枝菌根真菌和总PLFA含量无显著差异,但PDOP土壤细菌、放线菌、丛枝菌根真菌和总PLFA含量均高于PAFP和MADP,PAFP高于MADP。PDOP的土壤细菌、革兰氏阳性菌、革兰氏阴性菌、放线菌的PLFA含量显著高于MADP。MADP的真菌细菌比显著高于PDOP,但与PAFP无显著差异。(3)冗余分析表明,土壤阳离子交换量、pH和C:N是影响土壤微生物群落组成的最主要影响因子。从三种人工林的土壤微生物生物量及微生物群落结构来看,在喀斯特地区MADP并未显示出酸性土地区混交林提高土壤微生物生物量、改善土壤微生物群落结构的优势,但混交林的真菌细菌比最高,更有利于提高土壤生态系统的稳定性。     

Antibacterial Action of Spermine: Effect on Urinary Tract Pathogens

The basic polyamine spermine was tested for antibacterial activity at two pH levels by the modified cup method against a variety of gram-positive and gram-negative organisms isolated from urine. At pH 6.4, with concentrations ranging from 39 to 2,500 mug per 0.1 ml, there were no clear zones of inhibition seen with any of the gram-negative test organisms, although some adverse effect on growth within the area of the cylinder was noted in 36%. Three of 17 gram-positive strains were inhibited at this pH. Spermine was more active at pH 7.4, but even at the highest concentrations only 16% of the gram-negative and 47% of the gram-positive bacteria tested showed definite zones of inhibition. It is concluded that spermine probably plays little, if any, role in natural resistance to urinary tract infections in vivo.     

Positive selection of antibiotic-producing soil isolates.

Stepwise discriminant analysis was used to identify the most powerful selective substrates which could be used to formulate media capable of enriching for antibiotic-producing soil isolates. This was achieved by characterizing a collection of 74 soil bacteria, including eubacteria and actinomycetes, according to their ability to produce antibacterial antibiotics and their growth responses to 43 physiological and nutritional tests. The characters which were selective for actinomycetes relative to eubacteria included growth on proline (1%, w/v) and humic acid (0.1%) as sole sources of both carbon and nitrogen, growth on nitrate as a nitrogen source, and growth at pH 7.7-8.0. Growth on proline (1%) and humic acid (0.1%) as sole carbon/nitrogen sources, growth on asparagine as a nitrogen source, and growth in the presence of vitamins were among the characteristics which allowed antibiotic-producing actinomycetes to be differentiated from non-antibiotic-producing strains. Several simple isolation media which incorporated the selective substrates identified by discriminant analysis succeeded in increasing the proportion of actinomycetes isolated from soil samples. Furthermore, the percentage of isolates capable of antibiotic production was considerably increased.     

Effect of cadmium on growth of potentially pathogenic soil fungi

The effect of Cd on the mycelial growth of some potentially pathogenic soil fungi was investigated. Sixty-four strains from twenty-five fungal species were tested for their susceptibility to Cd. Final colony diameter, radial growth rate and final dry mass of mycelium (for Cd: 1–200 ppm) were measured. EcD₅₀ values were calculated from these parameters. The intra- and interspecific variability in the results obtained is presented. Among the keratinolytic fungal group, the genera Arthrographis, Trichophyton and Chrysosporium (including the Chrysosporium anamorph of Aphanoascus reticulisporus) were the most resistant to Cd. T. mentagrophytes was the most sensitive of all Trichophyton species tested. Among the nonkeratinolytic fungal group, the genera Pseudallescheria, Absida and Rhizopus were highly resistant to Cd. Strains of Aspergillus were more resistant to Cd than strains of Penicillium. Zygomycetes were more resistant to Cd than Ascomycetes with Fungi Imperfecti. Nonkeratinolytic fungi showed higher resistance to Cd than keratinolytic fungi. The two last differences resulted from the extremely high EcD₅₀ values for R. oryzae and A. corymbifera. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Interactions Between Cadmium and Lead on Growth, Nitrogen Fixation, Phytochelatin, and Glutathione Production in Mycorrhizal Cajanus cajan (L.) Millsp.

Heavy metals (HM) are a unique class of toxicants because they cannot be broken up into nontoxic forms. Excess HM causes stunted growth, upsets mineral nutrition, and affects membrane structure and permeability. High tolerance to HM toxicity is based on reduced metal uptake or increased internal sequestration in a genotype. Arbuscular mycorrhizal (AM) fungi are important rhizospheric microorganisms that occur in metal-contaminated soils and perhaps detoxify the potential effects of metals. The aim of this work was to study the role of the AM fungus Glomus mosseae in the alleviation of cadmium (Cd) and lead (Pb) toxicities in Cajanus cajan (L.) Millsp. (pigeonpea) genotypes. The effects of interactions between Cd (25 and 50 mg/kg) and Pb (500 and 800 mg/kg) on plant dry mass, nitrogen metabolism, and production of phytochelatins (PCs) and glutathione (GSH) were monitored with and without AM fungus in genotypes Sel-85N (relatively tolerant) and Sel-141-97 (sensitive). Cd treatments were more toxic than Pb, and their combinations led to synergistic inhibitions to growth and nitrogen-fixing potential (acetylene reduction activity [ARA]) in both genotypes. However, the effects were less deleterious in Sel-85N than in Sel-141-97. Exposure to Cd and Pb significantly increased the levels of PCs in a concentration- and genotype-dependent manner, which could be directly correlated with the intensity of mycorrhizal infection (MI). Stimulation of GSH production was observed under Cd treatments, although no obvious effects on GSH levels were observed under Pb treatments. The metal contents (Cd, Pb) were higher in roots and nodules when compared with that in shoots, which was significantly reduced in the presence of AM fungi. The results indicated that PCs and GSH might function as potential biomarkers for metal toxicity, and microbial inoculations showed bioremediation potential by helping pigeonpea plants to grow in multimetal contaminated soils.     

Water potential affects Coniothyrium minitans growth, germination and parasitism of Sclerotinia sclerotiorum sclerotia

Water availability is an important environmental factor which has major effects on fungal activity. The effects of osmotic (KCl amended agar) and matric Polyethylene glycol ((PEG) 8000 amended agar) potentials over the range -0.1 to -5.0MPa on mycelial growth and conidial germination of eight isolates of the sclerotial parasite Coniothyrium minitans was assessed. The influence of soil water potential on the ability of three selected isolates (LU112, LU545, and T5R42i) to parasitise sclerotia of the plant pathogen Sclerotinia sclerotiorum was determined. For all eight C. minitans isolates, decreasing osmotic and matric potentials caused a reduction in mycelial growth and conidial germination. Isolates were more sensitive to decreasing matric potential than osmotic potential. Across the isolates, growth at an osmotic potential of -5.0MPa was 30-70% of the growth seen in the control, whereas less than 20% of the control growth was seen at the corresponding matric potential. Across all isolates no conidial germination was seen at matric potential of -5.0MPa. The C. minitans isolates varied in their sensitivity to decreasing water potentials. Mycelial growth and conidial germination of three isolates (LU112, Conio, and CH1) were more tolerant of low osmotic potential and matric potential with respect to mycelial growth. Isolates T5R42i and LU430 were least tolerant. In contrast, conidial germination of isolates Conio, LU545, and T5R42i were less sensitive to decreasing matric potential. Soil water potential was seen to affect infection and viability of sclerotia by the three C. minitans isolates. Isolate LU545 reduced sclerotial viability over a wider water potential range (-0.01 to -1.5MPa) compared with LU112 (-0.01 to -1.0MPa), with isolate T5R42i being intermediate. Indigenous soil fungi (Trichoderma spp. and Clonostachys rosea) were recovered from sclerotia but did not result in reduction in sclerotial viability. The relevance of these results in relation to biocontrol activity of C. minitans in soil is discussed.     

Antimicrobial properties of diacetyl.

Diacetyl preparations from three commercial sources were found to be essentially similar when tested primarily against a set of 40 cultures, including 10 of lactic acid bacteria, 4 of yeasts, 12 of gram-positive non-lactic acid bacteria, and 14 of gram-negative bacteria. The compound was effective at pH less than or equal to 7.0 and progressively ineffective at pH greater than 7.0. The lactic acid bacteria were essentially unaffected by concentrations between 100 and 350 micrograms/ml over the pH range of 5.0 to 7.0. Of the 12 gram-positive non-lactic acid bacteria, 11 were inhibited by 300 micrograms/ml at pH less than or equal to 7.0. The three yeasts and the 13 gram-negative bacteria that grew at pH 5.5 were inhibited by 200 micrograms/ml. Diacetyl was ineffective against four clostridia under anaerobic conditions. It was lethal for gram-negative bacteria and generally inhibitory for gram-positive bacteria. Nongrowing cells were not affected. The effectiveness of diacetyl was considerably less in brain heart infusion broth, Trypticase soy agar, and cooked-meat medium than in nutrient broth or plate count agar. The antimicrobial activity was antagonized by glucose, acetate, and Tween 80 but not by gluconic acid. As an antimicrobial agent, diacetyl was clearly more effective against gram-negative bacteria, yeasts, and molds than against gram-positive bacteria.     

Effect of heavy metals on the growth of selected wood-rotting basidiomycetes

Mercury, cadmium and cobalt were found to be the most toxic heavy metals, inducing strong growth inhibition of the tested basidiomycetes. The studied species differed significantly in their sensitivity to cadmium. The most sensitive fungus,Inonotus obliquus, did not grow at Cd concentrations higher than 0.1 mmol/L, whereasStereum hirsutum grew at more than 2 mmol Cd/L. Changes in mycelial morphology were observed inS. hirsutum andTrametes versicolor cultivated in the presence of cadmium and mercury. The toxicity of heavy metals was lower in rich, complex media. Presented at the 4th Mini-Symposium on Biosorption and Microbial Degradation, Prague, Czech Republic, November 26–29, 1996.     

Evaluation of freeze-substitution and conventional embedding protocols for routine electron microscopic processing of eubacteria.

Freeze-substitution and more conventional embedding protocols were evaluated for their accurate preservation of eubacterial ultrastructure. Radioisotopes were specifically incorporated into the RNA, DNA, peptidoglycan, and lipopolysaccharide of two isogenic derivatives of Escherichia coli K-12 as representative gram-negative eubacteria and into the RNA and peptidoglycan of Bacillus subtilis strains 168 and W23 as representative gram-positive eubacteria. Radiolabeled bacteria were processed for electron microscopy by conventional methods with glutaraldehyde fixation, osmium tetroxide postfixation, dehydration in either a graded acetone or ethanol series, and infiltration in either Spurr or Epon 812 resin. A second set of cells were simultaneously freeze-substituted by plunge-freezing in liquid propane, substituting in anhydrous acetone containing 2% (wt/vol) osmium tetroxide, and 2% (wt/vol) uranyl acetate, and infiltrating in Epon 812. Extraction of radiolabeled cell components was monitored by liquid scintillation counting at all stages of processing to indicate retention of cell labels. Electron microscopy was also used to visually confirm ultrastructural integrity. Radiolabeled nucleic acid and wall components were extracted by both methods. In conventionally embedded specimens, dehydration was particularly damaging, with ethanol-dehydrated cells losing significantly more radiolabeled material during dehydration and subsequent infiltration than acetone-treated cells. For freeze-substituted specimens, postsubstitution washes in acetone were the most deleterious step for gram-negative cells, while infiltration was more damaging for gram-positive cells. Autoradiographs of specimens collected during freeze-substitution were scanned with an optical densitometer to provide an indication of freezing damage; the majority of label lost from freeze-substituted cells was a result of poor freezing to approximately one-half of the cell population, thus accounting for the relatively high levels of radiolabel detected in the processing fluids. These experiments revealed that gram-positive and gram-negative cells respond differently to freezing; these differences are discussed with reference to wall structure. It was apparent that the cells frozen first (ie., the first to contact the cryogen) retained the highest percentage of all radioisotopes, and the highest level of cellular infrastructure, indicative of better preservation. The preservation of these select cells was far superior to that obtained by more conventional techniques.     

Microbiological study of the dripping waters in Altamira cave (Santillana del Mar, Spain).

The culturable microbial populations in dripping waters from Altamira cave were studied and compared with those of the ceiling rock. Water communities have low proportions of gram-positive bacteria, and are mainly composed of gram-negative rods and cocci (Enterobacteriaceae and Vibrionaceae), while those of ceiling rocks are mainly Streptomyces spp. The community differences are probably related to environmental cave conditions: high humidity, relatively low and stable temperature, water pH close to neutrality and nature of the organic matter. All these factors seem to favor colonization and long-term growth of actinomycetes over other heterotrophic bacteria on ceiling rocks.     

Sequencing of heat shock protein 70 (DnaK) homologs from Deinococcus proteolyticus and Thermomicrobium roseum and their integration in a protein-based phylogeny of prokaryotes.

The 70-kDa heat shock protein (hsp70) sequences define one of the most conserved proteins known to date. The hsp70 genes from Deinococcus proteolyticus and Thermomicrobium roseum, which were chosen as representatives of two of the most deeply branching divisions in the 16S rRNA trees, were cloned and sequenced. hsp70 from both these species as well as Thermus aquaticus contained a large insert in the N-terminal quadrant, which has been observed before as a unique characteristic of gram-negative eubacteria and eukaryotes and is not found in any gram-positive bacteria or archaebacteria. Phylogenetic analysis of hsp70 sequences shows that all of the gram-negative eubacterial species examined to date (which includes members from the genera Deinococcus and Thermus, green nonsulfur bacteria, cyanobacteria, chlamydiae, spirochetes, and alpha-, beta-, and gamma-subdivisions of proteobacteria) form a monophyletic group (excluding eukaryotic homologs which are derived from this group via endosybitic means) strongly supported by the bootstrap scores. A closer affinity of the Deinococcus and Thermus species to the cyanobacteria than to the other available gram-negative sequences is also observed in the present work. In the hsp7O trees, D. proteolyticus and T. aquaticus were found to be the most deeply branching species within the gram-negative eubacteria. The hsp70 homologs from gram-positive bacteria branched separately from gram-negative bacteria and exhibited a closer relationship to and shared sequence signatures with the archaebacteria. A polyphyletic branching of archaebacteria within gram-positive bacteria is strongly favored by different phylogenetic methods. These observations differ from the rRNA-based phylogenies where both gram-negative and gram-positive species are indicated to be polyphyletic. While it remains unclear whether parts of the genome may have variant evolutionary histories, these results call into question the general validity of the currently favored three-domain dogma.