Effects of microbial population and culture phosphate composition on the activity of pyrophosphatases from soil microorganisms

The quantity of intracellular pyrophosphatases produced in mixed cultures was not related to pyrophosphate or orthophosphate concentration in the culture medium, but high pyrophosphate concentration initially depressed microbial growth, delayed the first signs of pyrophosphate hydrolysis and gave rise to a lower initial rate of pyrophosphate hydrolysis in the culture.Not all cultures produced intracellular pyrophosphatases, but when they were present, the same functional kinds of enzymes appeared to be present when compared on the basis of activation by five cations. All cultures inoculated with fresh soil were able to hydrolyse pyrophosphate in the culture medium, but not all cultures inoculated with stored soil displayed culture pyrophosphatase activity. There was evidence that intracellular pyrophosphatases were responsible for culture pyrophosphatase activity.It was found that cultures showing low intracellular and culture pyrophosphatase activity were dominated by Gram +ve rods. When intracellular and culture phosphatase activities were high, Gram ?ve rods and Gram ?ve cocci dominated the culture populations. As cultures dominated by Gram +ve rods were obtained only from stored soil inoculum, it is considered that during soil storage, Gram +ve rods became dominant in the soil because of the ability of some members of this group to form resistant endospores.     

Nature of the transient activation of soil microorganisms by ethanol or acetaldehyde

Low molecular weight alcohols and aldehydes emanating from undecomposed plant residues cause a rapid activation of microbial respiration and growth in soil. To determine the relative utilization of added volatile or endogenous microbial reserves during a transient period of activation, ethanol-1,2-¹⁴C or acetaldehyde was added to soil. With concentrations of ethanol giving near maximal respiration, 80–90 per cent of the CO₂ evolved in excess of the control came from labelled ethanol. For comparison, similar experiments were performed with spores of Fusarium solani under conditions where ethanol was a required substrate for germination. About 70–90 per cent of the CO₂ evolved in excess of the control came from added ethanol. In both the soil and spore systems enhanced respiration continued for less than 5 hr and ceased when the volatile substrate was depleted. Few endogenous reserves were utilized, and substantial amounts of cellular materials apparently were accumulated during this process. No changes in numbers of soil microorganisms were observed either during the transient activation or during the subsequent 2 weeks.     

土壤中耐铅微生物的筛选

通过在培养基中加入一定浓度的Pb(300mg／kg),从土壤中分离到12株耐Pb微生物菌株。其中细菌菌株为1～5号,放线菌为6～9号,真菌为10～12号。经过形态学观察、拮抗试验以及液体培养和土壤模拟试验中降低Pb效果测试,发现12株菌对有效态铅都有一定的降低作用。在液体培养中3号、4号、6号、7号、8号和10号菌株的降低效果最好,降低率超过70％,在土壤培养中3号和7号的降低作用最明显,降低率分别为63．8％和66％。     

Microenvironments of soil microorganisms

Summary Ultrastructural studies of soil micro-organisms and the microenvironments surrounding them are reviewed. Soil microfauna, and bacteria, actinomycetes and fungi, fixed and embedded in situ, were examined by electron microscopy (both transmission and scanning). In some cases ultrastructural histochemistry was used to detect and identify the organic matter with which microorganisms were associated and to examine the polymeric microbial materials (enzymes, extracellular polysaccharides) they produced. Although some small organisms (0.3 m diameter) occurred singly in dense fabrics of clay or humified organic matter, larger bacteria occurred in rhizospheres, in small colonies in the larger micropores or associated with substantial deposits of organic matter (faecal pellets, carbohydrate-rich plant cell-wall debris). Whereas rhizospheres had mixed microbial populations, individual microvoids in the bulk soil usually contained only one type of micro-organism. Following chloroform treatment, microorganisms were found only in mucigel deposits or deep in the interiors of micropores, suggesting that these constitute protected sites where microorganisms survive temporarily adverse conditions. Soil microfauna and fungi were mainly confined to the larger voids. Although some live hyphae occurred in the outer regions of aggregates, hyphae deep within soil fabrics were usually devoid of cytoplasmic organelles. Faecal pellets, plant tissues and cell-wall remnants comprised the most frequent, larger organic masses, while the most common micron- and submicron-sized organic matter consisted of fibrous or amorphous humified matter. Unequivocal detection of enzymes was limited to the surface of microorganisms.     

Effects of volatile oils from aromatic shrubs on soil microorganisms

Volatile oils from Thymus capitatus, Satureja thymbra and, to a lesser extent, Rosmarinus officinalis stimulate soil respiration. The S. thymbra oil is fungistatic to the germination of Penicillium citrinum spores in soil, and to mycelial growth of Mucor hiemalis in liquid culture. Addition of the S. thymbra oil and, to a lesser extent, R. officinalis oil to soil result in increased bacterial numbers. Bacteria appear to use the oils as carbon and energy sources. Thus the oils appear to have an ecological effect by shifting the soil population balance from fungi to bacteria.     

Transport of microorganisms through soil

Microorganisms migrating into and through soil from sources on the land surface may cause a serious threat to both ground and surface waters. It has been estimated that microorganisms can migrate significant distances in the field. Results from various studies suggested that preferential flow through macropores, worm holes, cracks, and fractures is the main reason for such observations. However, a quantitative representation of this phenomenon has not been provided. Microorganisms migrate through soil by advection and dispersion, while being subjected to effects of filtration, adsorption, desorption, growth, decay, sedimentation and chemotaxis. Both laboratory and field investigations have contributed important information on bacterial movement in soils. Qualitative comparisons are generally transferable from laboratory to field situations. Quantitative agreement is much more difficult to establish. Available mathematical modelling of microbial transport is limited in practical application because of the simplifying assumptions used in its development.     

Paclobutrazol effects on soil microorganisms

The side effects of paclobutrazol, a plant growth regulator, on soil microbial community and activity were assessed in soil samples from Petrolina (PE), Pernambuco State and from Lins (SP), São Paulo State, in Brazil. The first experiment was carried out with soils from mango orchards of Petrolina, subjected to frequent field applications of paclobutrazol. A second experiment was conducted with soils from Petrolina and Lins with application of paclobutrazol under greenhouse conditions. For orchard soils, plate counting of soil microorganisms was carried out, while for the greenhouse experiment the parameters evaluated were: microbial biomass C, living hyphal length, dehydrogenase activity, and paclobutrazol dissipation. The paclobutrazol addition to soils of mango orchards in Petrolina, affected negatively the soil microbial community. The average values for total number of bacteria, fungi and actinomycetes were reduced by 58, 28, and 28%, respectively, compared to the paclobutrazol unamended soil. For the greenhouse experiment, the paclobutrazol application in the soils from Petrolina influenced negatively the dehydrogenase activity and the living hyphal length, but not the microbial biomass C. The addition of this substance to the Lins soils had no effect on the microbial parameters evaluated.     

Metabolism of fluorodifen by soil microorganisms

The metabolism of fluorodifen (p-nitrophenyl α,α,α,-trifluoro-2-nitro-p-tolyl ether) by soil microorganisms in the presence or absence of other carbon and nitrogen sources was studied. The degradation of this herbicide continued for 5 days, when benzoate or acetate and ammonium sulphate were included in the cultures, and for more than 5 weeks when fluorodifen was used as a sole source of carbon and nitrogen.Under all conditions nitrite ions were produced at concentrations ranging between 5 and 80 per cent of the nitro-nitrogen of the fluorodifen present. The highest concentration of nitrite was obtained when added carbon sources were used with fluorodifen. The lowest nitrite concentration accumulated when the fluorodifen was used as sole source of carbon and nitrogen. The nitrite reached a maximum value after a few days of incubation, followed by rapid disappearance.p-Nitrophenol and quinol were identified in the acid-ether extract of cultures. It is suggested that the first step in the degradation of fluorodifen is the hydrolysis of the ether linkage followed by the direct elimination of the nitro-groups as nitrite ions.     

Degradation of Sevin by soil microorganisms

Microorganisms capable of transforming the pesticide 1-naphthyl N-methyl-carbamate (Sevin) were isolated from soil. Three isolates were able to accelerate the hydrolysis of Sevin to 1-naphthol. Several unidentified intermediates were separated by thin-layer chromatography and also by following the decomposition of Sevin-methyl-¹⁴C. Since 1-naphthol is a biological as well as a chemical decomposition product of Sevin, its transformation by the isolated microbes was also studied. A fungus, identified as Fusarium solani, altered 1-naphthol rapidly. Whereas one strain of bacterium degraded the hydrolysis product gradually, another strain accumulated it under certain conditions. Mixed cultures of the investigated microbes were more effective in transforming Sevin than pure cultures, and this phenomenon was also observed with 1-naphthol as substrate with the exception of one bacterial strain.     

Resistance of soil microorganisms to starvation

Most groups of soil microorganisms died when exposed to prolonged starvation in a carbon-free solution, but the relative abundance of Bacillus and actinomycetes increased with time. Certain non-sporeforming bacteria also persisted. The ability of individual soil isolates to endure starvation in solution was not correlated with their glycogen content or rate of endogenous respiration. However, cells of the resistant populations were rich in poly-β-hydroxybutyrate, whereas the starvation-susceptible bacteria generally contained little of this substance. Poly-β-hydroxybutyrate was used rapidly in cells deprived of exogenous sources of carbon.     

Decomposition of atmospheric hydrogen by soil microorganisms and soil enzymes

The decomposition of atmospheric hydrogen in different types of soil was measured. The decomposition of H₂ was apparently a first-order reaction. H₂ decomposition activity was proportional to the amount of soil with maximum activities at soil water contents of approx. 6–11% (w/w). The activity was lower under anaerobic conditions, but was constant between 1–20% O₂. It was destroyed by autoclaving and was partially inactivated by fumigation with NH₃, CHC1₃ or acetone, by u.v. irradiation and by treatment with NaCN or NaN₃, indicating that biological processes in the soil were responsible for the observed H₂ decomposition. Treatment of soil with toluene or CHCl₃ caused only a partial inactivation. Incubation of soil in the presence of streptomycin or actidione reduced H₂ decomposition by less than 50%, whereas CO consumption was abolished. The H₂ decomposition rates showed H₂ saturation curves with apparent Michaelis-Menten kinetics. Cooperative effects were not observed. V_max was reached at approx. 200 μl1^?1. The K_m values for H₂ were in the range of 30μl 1^?1, but increased to higher values, when the soil had been pretreated with high H₂ mixing ratios. Apparently, the observed H₂ decomposition by soil is not only due to the activity of viable microorganisms, but soil enzymes as well.     

Oxalate-metabolizing microorganisms in sagebrush steppe soil

Oxalate metabolization by soil microorganisms was assessed using a calcium oxalate clearing medium and¹⁴CO₂ release from [¹⁴C]-oxalate. Three saprophytic fungi, two bacteria, and one actinomycete tested produced¹⁴CO₂ when grown in culture with [¹⁴C]-oxalate, yet failed to test positive for oxalate degradation using a calcium-clearing medium. A field plot was then established to determine the effects of oxalate inputs on oxalate metabolism. The amount of [¹⁴C]-oxalate metabolized by soil microorganisms and the number of bacteria metabolizing oxalate increased within 24 h after the addition of oxalic acid at a concentration of 11.1 mol g^-1 soil. Oxalate metabolism and bacterial numbers returned to the baseline within 84 days. Soil phosphate concentrations increased significantly above baseline 7 days after the addition of oxalate and did not return to prespike levels. Fungi, bacteria, and actinomycetes were able to metabolize oxalate. Therefore, while oxalate can influence P cycles by increasing the amount of available phosphates, that increase is mediated by microbes that metabolize the oxalates.     

Sampling soil microfloras: Optimization of density gradient centrifugation in percoll to separate microorganisms from soil suspensions

Suspensions of non-filamentous microorganisms and clay were prepared by dispersing soil with an ion-exchange resin, sieving, elutriation and ultrafiltration. Cells were separated from clay by density gradient centrifugation in linear gradients of Percoll (limiting densities 1.101 and l.139 gcm⁻³). By fractionating the density gradient, the mixed population could be separated into components of differing density. Percoll could be separated from microorganisms by gel chromatography on columns of Sephacryl S-1000 or centrifugation after dilution.     

Effect of pesticide application on soil microorganisms

Modern agriculture largely relies on the extensive application of agrochemicals, including inorganic fertilizers and pesticides. Indiscriminate, long-term and over-application of pesticides have severe effects on soil ecology that may lead to alterations in or the erosion of beneficial or plant probiotic soil microflora. Weathered soils lose their ability to sustain enhanced production of crops/grains on the same land. However, burgeoning concern about environmental pollution and the sustainable use of cropping land have emphasized inculcation of awareness and the wider application of tools, techniques and products that do not pollute the environment at all or have only meager ecological concerns. This review covers the types of, concerns about and current issues regarding the extensive application of agrochemicals, in particular pesticides, on a variety of microorganisms integrated in successive food chains in the soil food web.     

Kinetics of glucose uptake by soil microorganisms

The kinetics of glucose uptake by soil microorganisms was investigated. Soil amended with an inorganic nutrient solution containing C glucose at concentrations of 2.5, 5.0, 10.0 or 20.0 mmol 1⁻¹ was maintained at 4, 12 or 25°C for varying times. The soil was analyzed for glucose, soluble ^14C, total organic ¹⁴C and evolved ¹⁴CO₂ to develop a carbon balance for the system and to define Michaelis-Menten kinetic parameters (K_m and V_max) for glucose uptake at each temperature.Glucose uptake rates, as measured by the depletion of glucose or soluble ¹⁴C from solution, were similar in soils maintained at 12 or 25°C. Based on the depletion of soluble ¹⁴C, values for K_m were 2.25 and 2.43 mmol I⁻¹ at 12 and 25°C, respectively, while V_max values were 0.25 and 1.61 h¹⁴', respectively. Glucose depletion at 4°C was faster than at 12C, while soluble ¹⁴C was removed at a significantly slower rate, suggesting soluble-C intermediates were produced in the 4°C system. Based on Chromatographie techniques and GC-MS, a soluble ¹⁴C-compound accumulating in the 4°C system was identified as maltose. The conversion of glucose to maltose resulted in K_m and V_max values of 17.29 mmol I⁻¹ and 0.12h⁻¹, respectively, for soluble ¹⁴C depletion and 4.96mmol1⁻¹ and 0.43 h⁻, respectively, for glucose depletion at 4δC. These results demonstrate the need to differentiate uptake rates for the parent compound as well as for transitory intermediates excreted into the growth medium. Evolution of CO₂ was shown to be a poor indicator of the rapid disappearance of glucose in soils.     

Effect of microorganisms on extractability of Cd from soil with NaOH and DTPA

Because Cd is extremely toxic, an understanding of the factors that allow or prevent Cd entrance into the food chain is important. The fate of Cd in soil is strongly influenced by microbial activity. Thus, an attempt was made to develop a method for studying the effect of microorganisms on Cd sorption to soil and availability to plants. It was found that the amount of Cd extracted from soil to soil suspensions with 0.1 m NaOH is related to microbial proliferation. In addition, an increase of Cd in NaOH extracts occurred concurrently with a decrease of Cd in DTPA extracts. Our observations suggest that the binding of Cd to microorganisms or their products can immobilize Cd and consequently affect its bioavailability.     

Torus-shaped pedological features associated with soil microorganisms

Torus-shaped features 1–7 urn in diameter were found on the smooth surfaces of the structural units of a Red Podzolic Soil (Udic Haplustalf) B horizon and on the smooth surfaces within the columnar structures of a Solodized Solonetz (Typic Natrustalf)-SEM & EDS were used to characterize these features, and to determine their probable pedogenesis. The size range was bimodal in the Red Podzolic B horizon, being either ∼5 μm or ∼2.0 um. In the Solodized Solonetz all tori were ∼ 1.5 μm in diameter. The larger tori consisted of fine-clay coated collapsed fungal spores, whilst the smaller tori were fine-clay coated collapsed bacteria-sized cells.     

Degradation of four phenylurea herbicides by mixed populations of microorganisms from two soil types

The metabolism of four substituted urea herbicides by microbial populations from two soils was investigated. The herbicides were two dimethylurea herbicides (fluometuron and chloroxuron) and two methoxymethylphenylurea herbicides (metobromuron and chlorbromuron), and the two soils used were Louisiana Commerce Loam and Indiana Silt Loam. The dimethyl compounds were successively N-demethylated by microorganisms from both soils. N-demethylation of the methoxymethyl herbicides, however, was significant only in the Louisiana soil, while N-demethoxylation was found in only trace amounts in all the cultures. Metabolism of these herbicides apparently was predominantly via direct hydrolysis to the aniline, which in turn underwent further transformations.     

土壤生态系统硝化微生物研究进展

微生物主导的硝化作用是生态系统中氮素循环的关键过程,其不仅与酸雨、温室气体、水体富营养化等环境问题的发生有关,还作用于土壤中氮素营养的转化,与人类生产生活密切相关。土壤生态系统中进行硝化作用的微生物包括细菌、古细菌、真菌等。这些微生物根据自身能量代谢类型的不同,利用不同的生物酶进行着不同机制的硝化作用。本文综述了目前已报道的生态系统中进行自养(经典自养硝化和全程氨氧化)和异养硝化作用的微生物类群、硝化作用关键酶及其编码基因类型、其在生态系统中多样的分布特征,以及其前沿的分子生态学研究方法。同时对不同类型硝化微生物类群今后的研究热点提出了展望,以期为系统地研究土壤生态系统中硝化微生物提供参考。