Aerobic biodegradation of biphenyl and polychlorinated biphenyls by Arctic soil microorganisms.

We examined the degradation of biphenyl and the commercial polychlorinated biphenyl (PCB) mixture Aroclor 1221 by indigenous Arctic soil microorganisms to assess both the response of the soil microflora to PCB pollution and the potential of the microflora for bioremediation. In soil slurries, Arctic soil microflora and temperate-soil microflora had similar potentials to mineralize [14C]biphenyl. Mineralization began sooner and was more extensive in slurries of PCB-contaminated Arctic soils than in slurries of uncontaminated Arctic soils. The maximum mineralization rates at 30 and 7 degrees C were typically 1.2 to 1.4 and 0.52 to 1.0 mg of biphenyl g of dry soil-1 day-1, respectively. Slurries of PCB-contaminated Arctic soils degraded Aroclor 1221 more extensively at 30 degrees C (71 to 76% removal) than at 7 degrees C (14 to 40% removal). We isolated from Arctic soils organisms that were capable of psychrotolerant (growing at 7 to 30 degrees C) or psychrophilic (growing at 7 to 15 degrees C) growth on biphenyl. Two psychrotolerant isolates extensively degraded Aroclor 1221 at 7 degrees C (54 to 60% removal). The soil microflora and psychrotolerant isolates degraded all mono-, most di-, and some trichlorobiphenyl congeners. The results suggest that PCB pollution selected for biphenyl-mineralizing microorganisms in Arctic soils. While low temperatures severely limited Aroclor 1221 removal in slurries of Arctic soils, results with pure cultures suggest that more effective PCB biodegradation is possible under appropriate conditions.     

New Criteria for the Evaluation of Soil Bacterial Complexes

The initial concentration of prokaryotic microorganisms, the type of their growth, doubling time, and the growth dynamics of bacteria and actinomycetes in three types of soil (meadow, chestnut, and soddy forest) were evaluated by the luminescence microscopic analysis of soil samples incubated in a humid chamber for 1 day. Soddy forest and chestnut soils differed in most of the parameters analyzed. Meadow soil was close to soddy forest soil in some parameters and to chestnut soil in other parameters. All soil suspensions exhibited high growth rates of bacteria and actinomycetes, indicating that the fraction of viable microorganisms in the soils was high.     

New criteria for evaluation of soil bacterial complexes

The initial concentration of prokaryotic microorganisms, the type of their growth, doubling time, and the growth dynamics of bacteria and actinomycetes in three types of soil (meadow, chestnut, and soddy forest) were evaluated by the luminescence microscopic analysis of soil samples incubated in a humid chamber for 1 day. Soddy forest and chestnut soils differed in most of the parameters analyzed. Meadow soil was close to soddy forest soil in some parameters and to chestnut soil in other parameters. All soil suspensions exhibited high growth rates of bacteria and actinomycetes, indicating that the fraction of viable microorganisms in the soils was high.     

高黎贡山土壤微生物生态分布及其生化特性的研究

研究了高黎贡山东坡不同海拔高度的自然林、不同海拔高度和人为干扰强度的集体林、不同权属森林和不同土地利用类型土壤微生物数量及某些生化特性。结果表明,在高黎贡山上半部,自然林随海拔降低,土壤微生物数量及活性升高。而下半部,集体林随海拔降低,人为干扰强度和频率增加,土壤微生物数量和活性降低;森林权属从国有集体个人,土壤微生物数量及活性降低;森林被纯林替代后,土壤微生物数量及活性迅速降低,但耕作通常更有利于微生物繁殖。高黎贡山中部(海拔2000m左右)的自然植被下土壤微生物含量丰富且活性较高,但海拔高气温低不利于土壤微生物生长繁殖及进行生物化学变化。另一方面,森林植被的过份砍伐和利用也使土壤微生物数量和活性降至较低水平。     

Temperature as an autoecological factor of chitinolytic microbial complex formation in soils

The dynamics of carbon dioxide emission from soil was studied during chitinolytic succession induced by humidification and chitin introduction at different temperatures (5, 27, and 50°C) using gas chromatography. The abundance and biomass of the chitinolytic bacterial and actinomycete complex in soil were evaluated by luminescent microscopy. Active development of the chitinolytic microbial complexes was observed at all studied temperatures. The most active growth of chitinolytic microorganisms was observed at high temperature during early succession and at low temperature during late succession. High and low temperatures provided for active development of the chitinolytic microbial complex in soils confined to warm climatic zones (brown desert-steppe soil) and soils of temporary zones (gray forest soil). Actinomycetes demonstrated the most active growth among chitinolytic microorganisms in the studied soil samples both at low and high temperatures.     

The allelopathic potential of alfalfa root medicagenic acid glycosides and their fate in soil environments

Summary The allelopathic effect of alfalfa (Medicago media Pers.) and red clover (Trifolium pratense L.) root saponins on winter wheat seedling growth and the fate of these chemicals in soil environments were studied. Seed germination, seedling and test fungus growth were suppressed by water and by alcohol extracts of alfalfa roots, and by crude saponins of alfalfa roots, indicating that medicagenic acid glycosides are the inhibitor. Powdered alfalfa roots inhibited wheat seedling growth when added to sand. At concentrations as low as 0.25% (w/w) the root system was completely destroyed whereas seedling shoots suffered little damage. Red clover roots caused some wheat growth inhibition when incorporated to sand, but their effect was much lower than in the alfalfa root treatment. Soil textures had a significant influence on the inhibitory effect of alfalfa roots. The inhibition of seedling growth was more pronounced on light than on heavy soils. This was attribted to the higher sorption of inhibitors by heavy soils. Incubation of alfalfa roots mixed into loose sand, coarse sand, loamy sand and clay loam for a period of 0–8 days resulted in decreased toxicity to bothT. viride and wheat seedlings. This decrease occurred more quickly in heavier soils than in loose sand, due to the hydrolysis of glycosides by soil microorganisms. Soil microbes were capable of detoxifying medicagenic acid glycosides by partial hydrolysis of sugar chain to aglycone. These findings illustrate the importance of medicagenic acid glycosides as an inhibitor of wheat seedling growth, and of their fate in different soil environments.     

THE EFFECT OF CERTAIN SOIL TREATMENTS ON DIDYMELLA STEM-ROT OF TOMATOES

About 93% of Didymella lycopersici spores were destroyed after 4 weeks incubation in unsterilized soil. A survey of the microflora of glasshouse soil receiving different treatments and inoculated with D. lycopersici showed no clear relation between numbers of any group of organisms and the incidence of stem rot. Sterilized soil was not made toxic to D. lycopersici by the growth of a number of soil microorganisms even after 9 months incubation, but addition of unsterilized soil or of a suspension of unsterilized soil quickly restored toxicity. Direct observations of spores in soil on slides showed that their fate varied with the treatment of the soil before inoculation. With fresh soil or air-dry soil moistened 2 or more days before inoculation, lysis of spores occurred. With air-dry soil moistened and inoculated simultaneously, some spores germinated but growth of germ tubes soon ceased. No direct connexion could be seen between the fate of the spores and soil microorganisms. Addition of glucose to unsterilized soil reduced its toxicity to D. lycopersici. Soils steamed for 1 min. or longer were not toxic to D. lycopersici , but soils steamed for very short periods were as toxic as unsterilized soils although the soil microflora was much reduced.     

Monitoring of Desulfitobacterium frappieri PCP-1 in pentachlorophenol-degrading anaerobic soil slurry reactors

Anaerobic biodegradation of pentachlorophenol (PCP) was studied in rotative bioreactors containing 200 g of PCP-contaminated soil and 250 ml of liquid medium. Reactors were bioaugmented with cells of Desulfitobacterium frappieri strain PCP-1, a bacterium able to dehalogenate PCP to 3-chlorophenol. Cells of strain PCP-1 were detected by quantitative PCR for at least 21 days in reactors containing 500 mg of PCP per kg of soil but disappeared after 21 days in reactors with 750 mg of PCP per kg of soil. Generally, PCP was completely removed in less than 9 days in soils contaminated with 189 mg of PCP per kg of soil. Sorption of PCP to soil organic matter reduced its toxicity and enhanced the survival of strain PCP-1. In some non-inoculated reactors, the indigenous microorganisms of some soils were also able to degrade PCP. These results suggest that anaerobic dechlorination of PCP in soils by indigenous PCP-degrading bacteria, or after augmentation with D. frappieri PCP-1, should be possible in situ and ex situ when the conditions are favourable for the survival of the degrading microorganisms.     

Biological activity of the soils of the rice irrigation systems in the southern Ukraine

The biological activity of soils was studied in the irrigation systems of the Southern Ukraina. Aerobic microorganisms were found to be widely distributed in all these soils. The cell number of Azotobacter and the activity of nitrogen fixation differed among various irrigation systems. Active nitrogen-fixing microbial associations were isolated from the soils; some of them were capable of fixation of 19.4 mg N per 1 g of assimilated glucose. The microbiological processes of certain irragation systems were characterized by reductive processes such as the intensive growth of sulphate reducing bacteria and the high activity of denitrification. The activities of protease, catalase and dehydrogenase differed among various soils, and were the lowest at a level of ground waters being 0.8 m. Flooding is one of ecological factors affecting the biological activity of the soils of irrigation systems.     

Cyanuric acid--a s-triazine derivative as a nitrogen source for some soil microorganisms

Cyanuric acid was not toxic for soil microorganisms examined and was even observed to stimulate the growth of Azotobacter in chernozem. Some isolated fungi were capable of cleaving the ring of cyanuric acid. With the use of 15N-labeled cyanuric acid it was found that the nitrogen taken from this compound by Aspergillus minutus and Pseudogymnoascus sp. was incorporated into their proteins. About 70-90% of 15N derived from cyanuric acid was detected in the biomass of the examined fungi. The ability of soil microorganisms to cleave the triazine ring is of importance in the detoxication of soils treated with triazine herbicides.     

Microbial Growth in a Steady-State Model of Ethylene Glycol-Contaminated Soil

Biodegradation of ethylene glycol was tested in a laboratory-scale, steady-state infiltration system of two arid region soil types by monitoring indigenous microbial growth after the infiltration of three concentrations of ethylene glycol. Microorganisms in the soils were able to adapt to the ethylene glycol in several cases, resulting in higher numbers of microorganisms and lower pHs in the effluents. These microorganisms were identified and were able to use ethylene glycol as a sole carbon source. The adaptation was seen best with high-moisture-content soils when the ethylene glycol concentrations were 1% or 10%. However, acclimation to 0.1% and 10% ethylene glycol did not occur in low-moisture-content clay soil, but did occur in low-moisture-content silt soil, indicating that soil type and moisture content are important factors. In all cases, microbial diversity decreased over time. Received: 23 June 1997 / Accepted: 11 August 1997     

Limitations to the Potential of Transgenic Trifolium subterraneum L. Plants that Exude Phytase when Grown in Soils with a Range of Organic P Content

Growth and P-nutrition of transgenic Trifolium subterraneum L. which express a chimeric fungal phytase gene (ex::phyA) was compared to azygous and wild-type controls in a range of soils that differed in organic P content. Shoot and root growth by plant lines were measured and effects of reducing the influence of soil microorganisms were investigated by pasteurising the soils. Plants that expressed phyA did not have better P-nutrition than control plants after 56 days growth, except in a soil that contained a large concentration of both total organic P and organic P that was amenable to hydrolysis by a plant-derived phytase. Pasteurisation had little effect on the relative P-nutrition of the various plant lines in any of the soils. Roots of transgenic plants that expressed ex::phyA were shorter than controls up to 21 days growth in a number of soils, which resulted in an initial greater P accumulation efficiency. However, greater P accumulation efficiency was only maintained in the soil where significant growth and P nutrition responses were also observed. Availability of inositol phosphates in soil is a major factor that limits the effectiveness of expressing fungal phytase genes in plants as a means to improve P-nutrition. Reducing the influence of rhizosphere microorganisms appeared to have little effect on the P-nutrition of plant lines, but the longer root system produced by control plants may have initially provided them with greater access to soil P resources. This research highlights the inherent difficulty in improving the P-nutrition of plants by the manipulation of single traits in isolation, but does provide some evidence that such approaches can be successful under certain edaphic conditions.     

Survival of Macrophomina phaseoli (Maubl.) Ashby on cucurbit roots

Summary Experiments on the survival ofM. phaseoli on cucurbit root pieces were carried out. The sclerotia ofM. phaseoli were almost unaffected by 10 months dry storage in the laboratory. Under dry to moderately moist soil conditions it survived for 2 months with little loss of viability. In wet soils however, the buried root pieces were colonized by other soil microorganisms which prevented the growth ofM. phaseoli.     

Effects of soil pH on rhizoctonia damping-off of sugar beet and disease suppression induced by soil amendment with crop residues

Effects of soil pH on damping-off of sugar beet by R. solani (AG2-2) and soil suppressiveness against the disease were studied by comparing disease incidences in pasteurized versus non-pasteurized, infested soils. Soil pH was correlated neither to disease incidence in five soils ranging from pH 4.5 to 7.2 nor to indigenous disease suppressiveness, the difference in disease incidences between non-treated soil and its pasteurized counterpart. When an alkaline soil was acidified with H₂SO₄, disease suppression markedly declined, increasing disease incidence in the non-pasteurized soil. Inversely, disease suppression was enhanced when an acidic soil was neutralized by adding Ca(OH)₂. Soil amendment with dried peanut plant residue suppressed the disease in two pasteurized, near-neutral soils, lowering the incidence to the levels in the non-pasteurized soils, but was less effective in two pasteurized, acidic soils. In vitro mycelial growth of the pathogen and seedling growth was optimal at pH 4.5–5.5 and 6.0–6.5, respectively, and declined as the pH became higher or lower. (Conclusions) These results suggest that the seedlings were inhibited more than the pathogen at low pH, and that indigenous disease suppressiveness through the activity of antagonistic soil microorganisms operates effectively in near-alkaline soils, but is weakened or nullified in acidic soils.     

Cyclodextrin effects on the ex-situ bioremediation of a chronically polychlorobiphenyl-contaminated soil

The possibility of enhancing the intrinsic ex-situ bioremediation of a chronically polychlorinated biphenyl-contaminated soil by using cyclodextrins was studied in this work. The soil, contaminated with a large array of polychlorinated biphenyls and deriving from a dump site where it has been stored for about 10 years, was found to contain indigenous cultivable aerobic bacteria capable of utilising biphenyl and chlorobenzoic acids. The soil was amended with inorganic nutrients and biphenyl, saturated with water, and treated in aerobic batch slurry- and fixed-phase reactors. Hydroxypropyl-beta-cyclodextrin and gamma-cyclodextrin, added to both reactor systems at the concentration of 10 g/L at the 39th and 100th days of treatment, were found to generally enhance the depletion rate and extent of the soil polychlorobiphenyls. Despite some abiotic losses could have affected the depletion data, experimental evidence, such as the production of metabolites tentatively characterized as chlorobenzoic acids and chloride ion accumulation in the reactors, indicated that cyclodextrins significantly enhanced the biological degradation of the soil polychlorobiphenyls. This result has been ascribed to the capability of cyclodextrins of enhancing the availability of polychlorobiphenyls in the hydrophilic soil environment populated by immobilised and suspended indigenous soil microorganisms. Both cyclodextrins were metabolised by the indigenous soil microorganisms at the concentration at which they were used. Therefore, cyclodextrins, both for their capability of enhancing the biodegradation of soil polychlorobiphenyls and for their biodegradability, can have the potential of being successfully used in the bioremediation of chronically polychlorinated biphenyl-contaminated soils. Copyright 1998 John Wiley & Sons, Inc.     

Effects of rhizosphere remediation and bioaugmentation on carbofuran removal from soil

Rhizosphere soil contains important sources of nutrients for microorganisms resulting in high number of microorganisms capable of degrading various types of chemicals in the soil. Thus, this study investigated a carbofuran dissipation in rhizosphere soils of 6 weeds namely, umbrella sedge (Cyperus iria L.), fuzzy flatsedge (C. pilosus V.), small flower umbrella plant (C. difformis L.), tall-fringe-rush hoorah grass (Fimbristylis miliacea V.), cover fern (Marsilea crenata P.), and water primrose (Jussiaea linifolia V.). Rhizosphere soil of fuzzy flatsedge showed the shortest half-life (t_1/2) of carbofuran (15 days) among other soils. So, it was selected to be used in the bioaugmentation experiment using carbofuran degrader namely Burkholderia cepacia, PCL3, as inoculum in order to examine whether they would improve carbofuran degradation in soil. The results showed that the addition of PCL3 into rhizosphere soil did not improve carbofuran degradation suggesting that microorganisms in rhizosphere soil might be capable enough to remove carbofuran from soil. The number of carbofuran degraders in the rhizosphere soils was greater than in bulk soil 10–100 times which might be responsible to a rapid degradation of carbofuran in rhizosphere soils without the addition of PCL3. The ability of PCL3 to degrade carbofuran was evident in bulk soil (t_1/2 of 12 days) and autoclaved soils (t_1/2 13–14 days) when compared to soils without an inoculation (t_1/2 of 58 days) indicated that the addition of a degrader was useful in improving carbofuran degradation in soil.     

Biodegradation of Dinoseb (2-sec-Butyl-4,6-Dinitrophenol) in Several Idaho Soils with Various Dinoseb Exposure Histories

We examined the ability of native microorganisms in various Idaho soils to degrade dinoseb and studied some physical and chemical soil characteristics which might affect the biodegradation process. Dinoseb biodegradation rates were higher in silt-loam soils than in loamy-sand soils. Biodegradation rates were not influenced by previous exposure of the soils to dinoseb. Bacterial numbers, measured by standard plate counts on soil extract agar, were the best predictors of biodegradation rates, accounting for 53% of the variability between soils. Soil nitrate-N inhibited dinoseb biodegradation and accounted for 39% of the variability. Sorption of dinoseb to soil surfaces also appeared to influence biodegradation rates. No other soil parameter contributed significantly to the variability in biodegradation rates. Persistence of dinoseb in one soil was due to inhibition of biodegradation by nitrate, while in another soil persistence appeared to be due to lack of native degradative microorganisms.     

Glyphosate tolerance and utilization by the microflora of soils treated with the herbicide

Summary The effect of recurrent applications of the herbicide glyphosate on a garden soil was investigated. Compared to an adjacent untreated soil the microbial population showed reduced sensitivity to glyphosate when grown in mineral salts medium. In both populations inhibition could be partially reversed by addition to the medium of the end products of the aromatic amino acid biosynthetic pathway, but the effect was more pronounced in the population from the treated site. However, all isolates from both soils were capable of growth in unsupplemented medium in the presence of as much as 10 mM glyphosate. No evidence for glyphosate metabolism was obtained from enrichment experiments carried out using inocula from the untreated soil; at the treated site organisms capable of using glyphosate as sole C or N source could not be isolated but a variety of Gram-negative bacteria able to use its phosphonate moiety were obtained. Many of these organisms were identified as Pseudomonas spp.     

Microcosm study for revegetation of barren land with wild plants by some plant growth-promoting rhizobacteria

Growth promotion of wild plants by some plant growth-promoting rhizobacteria (PGPR) was examined in the microcosms composed of soils collected separately from a grass-covered site and a nongrass-covered site in a lakeside barren area at Lake Paro, Korea. After sowing the seeds of eight kinds of wild plants and inoculation of several strains of PGPR, the total bacterial number and microbial activity were measured during 5 months of study period, and the plant biomasses grown were compared at the end of the study. Acridine orange direct counts in the inoculated microcosms, 1.3-9.8 x 10(9) cells x g soil(-1) in the soil from the grass-covered area and 0.9-7.2 x 10(9) cells x g soil(-1) in the soil from the nongrass-covered site, were almost twice higher than those in the uninoculated microcosms. The number of Pseudomonas sp., well-known bacteria as PGPR, and the soil dehydrogenase activity were also higher in the inoculated soils than the uninoculated soils. The first germination of sowed seeds in the inoculated microcosm was 5 days earlier than the uninoculated microcosm. Average lengths of all plants grown during the study period were 26% and 29% longer in the inoculated microcosms starting with the grass-covered soil and the nongrass-covered soil, respectively, compared with those in the uninoculated microcosms. Dry weights of whole plants grown were 67-82% higher in the inoculated microcosms than the uninoculated microcosms. Microbial population and activity and growth promoting effect by PGPR were all higher in the soils collected from the grass-covered area than in the nongrass-covered area. The growth enhancement of wild plants seemed to occur by the activities of inoculated microorganisms, and this capability of PGPR may be utilized for rapid revegetation of some barren lands.     

Effects of Resource-Island Soils, Competition, and Inoculation with Azospirillum on Survival and Growth of Pachycereus pringlei, the Giant Cactus of the Sonoran Desert

Resource‐island soils formed by some plants in arid lands are capable of supporting certain plants that do not normally establish in surrounding areas free of vegetation. We determined growth responses of Pachycereus pringlei (cardon), the giant columnar cactus, whose widespread, finely branched, subsurface root systems stabilize desert soils, to four soils collected from within or outside of resource islands. Traits of cardon grown in soils from mature (MM) or young (YM) Prosopis articulata (mesquite), mature Olnea testosa (ironwood, MI), or bare areas (BA) were compared, to determine differences between the effects of soils due to the identity or the stage of development of nurse plants. The levels of soil N, P, and C contents were in the order MM> > YM > MI BA. The BA soil had the coarsest and MM soil the finest texture. Cardon was also grown in pot cultures inoculated with the plant‐growth‐promoting bacterium Azospirillum brasilense, or in association with a competing grass, Sorghum bicolor (sorghum). Competition did not affect survival rates of cardon in any of the soils after six months of growth, but decreased biomass accumulation by up to 90% in the best (MM) soil. Inoculation of cardon seeds with A. brasilense did not affect survival but resulted in significantly better root and shoot growth, and this effect increased linearly as soil nutrients declined. In the best soil (MM), A. brasilense had no effect on cardon growth, but in the poorest soil (BA) shoot dry mass was almost 60% and root length over 100% greater as a result of inoculation, with responses in the other two soils intermediate. This effect did not appear to be owing to N₂ fixation, as nitrogenase activity (acetylene reduction) was not detected in any of the treatments. Soil formation by selected nurse trees in arid areas is an important factor in plant establishment and growth, and the present results indicate that these processes can be impeded or facilitated by the introduction of competing or beneficial organisms. The use of beneficial microorganisms associated with roots may accelerate the restoration of disturbed areas. Key words: Azospirillum, desert soils, nitrogen fixation, nurse plant, Pachycereus pringlei, plant survival, resource‐island.