Specificity of soil hydrolytically microbial complex under different moisture conditions

It has been established that soil moisture has a significant impact on the activity of chitinolytic microbial processes, rather than pectinolytic processes. The degradation of polysaccharides with an increase in soil moisture in microbial complex markedly increases the role of prokaryotic microorganisms, especially actinomycetes. For the first time, using the FISH method, the amount of detected phylogenetic composition of a metabolically active hydrolytic complex of humus horizons of grey forest and gley and weakly podzolic soil and humus has been estimated depending on the humidity. At optimum moisture, phylogenetic groups Actinobacteria and Firmicutes dominated in the chitinolytic process. An increase in the proportion of proteobacteria is observed with an increase in humidity. The role of gamma- and alphaproteobacteria and actino-bacteria is heightened with the drying of soil in the hydrolytic complex. A quantitative estimate of the rate of degradation of polysaccharides (pectin and chitin) in different types of soils at different levels of moisture is given. The dependence of the phylogenetic composition of an active microbial hydrolytic complex of humus horizons of grey forest and gley, weakly podzolic soils and humus on humidity is revealed.     

Microbial destruction of chitin in soils under different moisture conditions

The most favorable moisture conditions for the microbial destruction of chitin in soils are close to the total water capacity. The water content has the most pronounced effect on chitin destruction in soils in comparison with other studied substrates. It was found using gas-chromatographic and luminescent-microscopic methods that the maximum specific activity of the respiration of the chitinolytic community was at a rather low redox potential with the soil moisture close to the total water capacity. The range of moisture values under which the most intense microbial transformation of chitin occurred was wider in clayey and clay loamy soils as compared with sandy ones. The increase was observed due to the contribution of mycelial bacteria and actinomycetes in the chitinolytic complex as the soil moisture increased.     

The microbial destruction of chitin,pectin, and cellulose in soils

The most intensive degradation of polysaccharides takes place upon low and moderate temperatures in typical chernozems and gray forest soils and upon high temperatures in brown desert-steppe soils. This regularity is related to the structure of soil microbial complexes. The soil water content exerts a more pronounced effect on chitin decomposition in comparison with cellulose and pectin decomposition. The most favorable conditions for pectin decomposition by microbes are created at the water content close to the field capacity. Model experiments indicate that the range of moisture, upon which the transformation of chitin by microbes is most active, is wider in clay and loamy soils than in sandy soils. Direct study of microorganisms in the investigated soils under microscope has shown that actinomycetes, bacteria, and fungi participate in the transformation of polysaccharides. The role of actinomycetes in chitin decomposition increases in parallel with the rise in the soil water content and temperature. The role of fungi in pectin decomposition becomes higher under higher moistening and lower temperatures. The use of the FISH method makes it possible to reveal differences in the structure and number of metabolically active representatives of Bacteria and Archaea chitinolytic and pectinolytic prokaryotic complexes in the investigated soils under the impact of different ecological factors.     

Effects of chitin amendment of soil on microorganisms,nematodes, and growth of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.)

Effects of soil amendment with crabshell chitin on the growth of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.), and on populations of soil bacteria, fungi, and plant-parasitic and free-living nematodes were investigated in a pot trial. Five soil samples were collected from Te Puke (Paengaroa Shallow Sand, a Typic Hapludand) and five from Hamilton (Bruntwood silt loam, an Aquic Hapludand), New Zealand. Subsamples of each soil were either amended with chitin or unamended and planted with white clover and ryegrass. The ryegrass shoot weight in amended soil was greater (P<0.01), most probably due to N mineralised from chitin. A significantly lower (P<0.01) root: shoot ratio of ryegrass in the amended soil also suggested improved N availability, and therefore less root mass was needed to support a given shoot mass. A reduction in nodulation was observed in 12-day-old white clover seedlings (P<0.05) and also in 6-week-old seedlings (P<0.01). The shoot weight of white clover was significantly lower (P<0.05) in amended soil, possibly due to phytotoxic effects of chitin. Chitin increased (P<0.01) the populations of bacteria and fungi by 13-fold and 2.5-fold, respectively. The cyst nematode of white clover, Heterodera trifolii, was significantly reduced in chitin-amended soil, possibly due to increased levels of chitinase produced by rhizosphere microorganisms. Two other plant-parasitic nematodes, Pratylenchus spp. and Tylenchus spp., were also reduced in ryegrass roots and in soil as a result of the chitin amendment. However, the total number of free-living nematodes increased 5.4-fold in amended soil.     

Effects of chitin degradation products N-acetylglucosamine and N,Nʹ-diacetylchitobiose on chitinase activity and bacterial community structure in an incubated upland soil

ABSTRACT

Chitin, which is the polymer of N-acetylglucosamine (GlcNAc) linked by β1,4 glycoside bonds, has been reported as a soil amendment to mitigate plant soil diseases, increasing the population of chitin-degrading bacteria, and chitinolytic enzymatic activity in the soil. In some chitin-degrading bacteria, whose chitinolytic systems have been intensively studied, the chitin degradation product N,N?-diacetylchitobiose {(GlcNAc)₂} induces expression of genes for chitinases whereas GlcNAc does not. To evaluate the effects of these mono- and disaccharides on the population and activity of chitinolytic bacteria in soil, we investigated the chitinolytic enzyme activity and bacterial community structure in an incubated upland soil supplemented with GlcNAc or (GlcNAc)₂. The added GlcNAc and (GlcNAc)₂ (2 mg g^?1) were consumed within 1 d when incubated at 25°C. Chitinase activity was induced by (GlcNAc)₂ and chitin after 1-d and 7-d incubation, respectively, but not by GlcNAc. N-acetylglucosaminidase (GlcNAcase) activity was induced by GlcNAc but was lower than those by (GlcNAc)₂ and chitin. Amplicon sequencing analysis targeting 16S rRNA genes demonstrated that both GlcNAc and (GlcNAc)₂ significantly increased the rate of the order Bacillales, but the compositions of Bacillales differed from each other: the family Planococcaceae significantly increased in either GlcNAc- or (GlcNAc)₂-added soil, but the genera Bacillus and Paenibacillus were increased mainly by GlcNAc and (GlcNAc)₂, respectively. The family Streptomycetaceae of the order Actinomycetales was significantly increased by (GlcNAc)₂ and chitin, but GlcNAc did not. Thus, GlcNAc and (GlcNAc)₂, which were promptly consumed in the incubated soil, indicated partly similar but distinctive effects on chitinolytic enzyme activity and bacterial communities. Both aminosugars increased GlcNAcase activity and the population size of Planococcaceae. GlcNAc increased Bacillus. Chitinase activity and the populations of Paenibacillus and Streptomycetaceae, a number of strains of which are known as potent chitin-degraders, were increased by (GlcNAc)₂, but not by GlcNAc.     

Autolysis of chlamydospores of Fusarium solani f. sp. cucurbitae in chitin and laminarin amended soils

Lysis of chlamydospores of Fusarium solani f. sp. cucurbitae is enhanced both in chitin and in laminarin amended soils. In soil amended with both chitin and laminarin, lysis of chlamydospores resembles that in control soil. Addition of chitin and laminarin to soil stimulates the growth of both bacteria and actinomycetes. In soils amended with chitin and with both chitin and laminarin, a chitinolytic microflora is stimulated. Penetration of chlamydospore cells by soil microorganisms has not been observed using the electron microscope. The mechanism of lysis of chlamydospores in soil is discussed.     

多氯联苯复合污染土壤的土著微生物修复强化措施研究

通过室内模拟试验,以不同C源、C/N比、水分及通透性为调控因子,对多氯联苯(PCBs)长期复合污染土壤的土著微生物强化修复进行了初步研究。结果表明,PCBs长期复合污染土壤中,在土壤水分含量为田间持水量的60%时,加入淀粉、葡萄糖和琥珀酸钠均在一定程度上增加了细菌和真菌数量,从而促进土壤中PCBs的土著微生物降解。不同种类的C源对PCBs污染土壤的土著微生物降解效果存在明显差异,且其降解效果与C源的施用剂量密切相关。当淀粉加入量为C1.0g/kg土时,土壤中PCBs的降解效果较好,而葡萄糖和琥珀酸钠加入量为C0.2g/kg土时,PCBs的降解效果明显。土壤C/N比为10:1的处理效果优于C/N比为25:1和40:1。土壤人为翻动有利于PCBs污染土壤中细菌和真菌的生长,提高土著微生物的代谢活性,从而促进土壤中PCBs的自然降解。这为进一步探讨加速土壤中PCBs降解的最适条件和研发POPs污染土壤的生物修复技术提供了科学依据。     

Changes in Mycobacterium spp. population structure and pyrene mineralization in polycyclic aromatic hydrocarbon-amended soils

The effect of pyrene and phenanthrene contamination on soil Mycobacterium spp. community structure was examined using PCR-amplification of 16S rRNA genes with primers specific for the fast-growing group of Mycobacterium spp. and separation of phylotypes by temperature gradient gel electrophoresis (TGGE). The degradative potential of the soil microbial community was measured over time by mineralization of ¹⁴C-pyrene added to the contaminated soils. PCR-TGGE profiles, in combination with band sequencing and phylogenetic analysis of the prominent phylotypes, indicated shifts in the Mycobacterium spp. community during incubation. Reductions in species diversity and enrichments of specific populations were observed in all pyrene- and phenanthrene-treated soils, in contrast to the relatively stable control soil profiles. Mineralization studies indicated the shortest acclimation periods and the highest initial rates of pyrene degradation occurred in soils pre-exposed to phenanthrene, or a mixture of phenanthrene and pyrene, for 14 weeks. Pre-exposure of soil microorganisms to a single dose of pyrene for the same length of time also decreased the acclimation period for the degradation of pyrene. Monthly application of either pyrene or phenanthrene to soils, however, resulted in an increase in pyrene degradative potential 6 weeks after the first pre-exposure, but a decrease in degradative potential 14 weeks after the first pre-exposure. Similar PCR-TGGE profiles were obtained from soils with comparable pyrene mineralization curves or degradative potentials.     

Sphingobium属细菌土壤中降解异丙隆的特性

通过在不同环境条件的土壤中接入异丙隆降解菌悬液,研究了Sphingobium属的3株细菌—YBL1、YBL2和YBL3在土壤中降解异丙隆的特性,分析了土壤类型、温度、碳氮源、土壤含水量和菌株接种量等因素对3株细菌降解土壤中异丙隆的影响。结果表明,3株细菌在马肝土(pH 6.7)中能够高效降解异丙隆,在红壤(pH 4.5)中不能降解异丙隆,菌株YBL3在潮土(pH 8.2)中也有较好的降解效果;当接种量低于105CFU g-1土时,3株细菌均不能降解马肝土中的异丙隆,接种量高于106CFU g-1土时,菌株可以高效地降解土壤中的异丙隆;马肝土含水量低于40%时,3株细菌降解土壤中异丙隆的速率与土壤含水量呈正相关关系;在16~37℃范围内,菌株降解马肝土中异丙隆的速率与温度亦呈正相关关系。     

Nodulation status of native woody legumes and phenotypic characteristics of associated rhizobia in soils of southern Ethiopia

The nodulation of provenances of Acacia seyal, Acacia tortilis and Faidherbia albida, and other indigenous multipurpose tree species were tested in 14 different soil samples collected from diverse agro-ecological zones in southern Ethiopia. Associated rhizobia were isolated from these and from excavated nodules of field standing mature trees, and phenotypically characterized. Indigenous rhizobia capable of eliciting nodules on at least one or more of the woody legume species tested were present in most of the soils. Tree species were markedly different in nodulation in the different site soils. Sesbania sesban and Acacia abyssinica showed higher nodulation ability across the different sites indicating widespread occurrence of compatible rhizobia in the soils. The nodulation patterns of the different provenances of Acacia spp. suggested the existence of intraspecific provenance variations in rhizobial affinity which can be exploited to improve N fixation through tree selection. Altogether, 241 isolates were recovered from the root nodules of trap host species and from excavated nodules. Isolates were differentiated by growth rate and colony morphology and there were very fast-, fast-, slow-, and very slow-growing rhizobia. The bulk of them (68.5%) were fast-growing acid-producing rhizobia while 25.3% were slow-growing alkali-producing types. Fast-growing alkali-producing (2.9%) and slow-growing acid-producing strains (3.3%) were isolated from trap host species and excavated nodules, respectively. All isolates fell into four colony types: watery translucent, white translucent, dull glistering and milky (curdled) type. The diversity of indigenous rhizobia in growth rate and colony morphology suggested that the collection probably includes several rhizobial genera.     

Rhizobia in tropical legumes—XIII. Biochemical basis of acid and alkali reactions

Three fast-growing rhizobia (Rhizobium meliloti isolated from Medicago saliva, R. trifolii from Trifolium subterraneum, and Rhizohium sp. from Leucaena leucocephala) and three slow-growing rhizobia R. japonicum from Glycine max, Rhizobium spp from Centrosema pubescens and Crotolaria anagyroides) were grown in defined media. The mean generation times of the fast-growing and slowgrowing strains were 3.8 h and 8.6 h respectively. Slow-growing organisms raised the initial pH of the defined medium while the fast-growing organisms lowered it. Rates of oxygen consumption tended to be higher in the slow-growing organisms.UMKL 19 (isolated from L. leucocephala) possessed all the normal reactions of fast-growing rhizobia but had a single sub-polar flagellum, similar to the three slow-growing strains studied.Certain combinations of amino acids and sugars (e.g. glutamine and galactose) induced an acidic reaction in the fast-growing organisms while the slow-growing ones changed the media to alkaline. Fast-growing organisms utilized more galactose for growth compared to slow-growing ones. Both types of organisms synthesized and released a wide range of amino acids into the medium.We suggest that pH changes produced by rhizobia growing on yeast-extract mannitol media are caused by the preferential utilization of sugars by fast-growing organisms and nitrogenous compounds by slow-growing ones.     

Intrinsic antibiotic resistance and competition in fast- and slow-growing soybean rhizobia on a hybrid of Asian and US cultivars

Summary Six fast-growing soybean rhizobia (Rhizobium fredii) and thirteen slow-growing soybean rhizobia (Bradyrhizobium japonicum) were examined for resistance to 10 antibiotics. Axenic studies were carried out to determine the competitiveness of dual-strain inocula consisting of fast- and slow-growing rhizobia isolated from subtropical-tropical soils for nodule occupancy on a hybrid of Asian and US soybean cultivars. Nodule occupancy was determined by intrinsic resistance to erythromycin and neomycin. The results showed wide variability in resistance to 10 antibiotics for fast- and slow-growing rhizobia. The intrinsic antibiotic resistance of fast- and slow-growing rhizobia was extremely high against nalidixic acid (400 g ml^–1) and penicillin (200 g ml^–1). The competitive ability of inoculant strains for nodule occupancy varied for different combination sets and with the plant growing media. Our results show that fast-growing rhizobia nodulate a hybrid of Asian and US soybean cultivars. Fast-growing soybean rhizobia did not completely exclude nodulation by the slow-growing strains, which formed 0–79% nodules, depending on the strain used in the inoculum.     

Symbiosis with bacteria enhances the use of chitin by the springtail,Folsomia candida (Collembola)

Summary The relationship between Folsomia candida and chitin-degrading microorganisms was studied. On chitin agar, 10¹⁰ bacteria were isolated per g faeces, and 3.8×10¹¹ bacteria per g gut contents, 1/3 of them showing a clear (chitin-free) zone around the colony. The most abundant chitin-degrading bacteria were Xanthomonas maltophilia and Curtobacterium sp. To determine the bacterial contribution in the use of chitin by F. candida, a feeding experiment was carried out. F. candida were fed with chitin, either amended with or without tetracycline as an inhibitor of bacteria. When tetracycline was omitted the biomass of F. candida was increased compared to those fed chitin with tetracycline. However, this result was observed only when the food replacement intervals were long enough to allow bacterial colonization before ingestion of the food. In a food-selection experiment, a preference for chitin colonized with microorganisms as opposed to sterile chitin was found. The results indicate that a mutualistic symbiosis of F. candida with chitinolytic microorganisms is likely to enhance chitin degradation. This relationship is not only intra-intestinal but also involves an extra-intestinal phase.Dedicated to the late Prof. Dr. W. Kühnelt     

Rhizobia in tropical legumes—XIV. Ion uptake differences between fast- and slow-growing strains

We compared the uptake of nitrogen, potassium and phosphorus (as well as ¹⁴C-labelled mannitol, ³H-labelled glutamate, and ³²P-labelled phosphate) in three fast- and three slow-growing rhizobia. The fast-growing strains used were Rhizobium meliloti (isolated from Medicago sativa), R. trifolii (from Trifolium subterraneum), and Rhizobium spp from Leucaena leucocephala, while the slow-growing strains were R. japonicum (Glycine max), and two Rhizobium spp (from Centrosema pubescens and Crotolaria anagyroides). Slow-growing organisms preferentially utilized glutamate in the medium. Both fast- and slow-growing strains took up more NH⁺₄-N than NO^?₃-N on a per cell basis. In the presence of mannitol, fast-growing strains can cause either acid or alkaline reactions, an effect that is dependent only on the N-source (NH⁺₄ or NO^?₃). Uptake preferences of the fast-growing Leucaena isolate (UMKL 19) resembled those of the slow-growing rhizobia, further strengthening the argument that this organism (and others like it) may be intermediate between the normal fast- and slow-growing groups. Generally, the efficiency of uptake of N (either as NH⁺₄ or NO^?₃), P, and therefore K, was greater in the fast-growing organisms.     

采用通气堆沤对石油烃污染土壤进行生物修复

Laboratory simulation studies and a composting pilot study were conducted to evaluate the capacity of three strains of fungi, indigenous fungus Fusarium sp. and Phanerochaete chrysosporium and Coriolus Versicolor, to remediate petroleum-contaminated soils. In laboratory, the fungi were inoculated into a liquidculture medium and the petroleum-contaminated soil samples for incubation of 40 and 50 days 5 respectively. In the 200-day pilot study, nutrient contents and moisture were adjusted and maintained under aerobiccondition in composting units using concrete container (118.5 cm × 65.5 cm × 12.5 cm) designed specially for this study. The laboratory simulation results showed that all the three fungi were effective in degrading petroleum in the liquid culture medium and in the soil. At the end of both the laboratory incubations, the degradation rates by Phanerochaete chrysosporium were the highest, reaching 66% after incubation in liquid culture for 50 days. This was further demonstrated in the composting pilot study where the degradation rate by P. chrysosporium reached 79% within 200 days, higher than those of the other two fungi (53.1% and 46.1%), indicating that P. chrysosporium was the best fungus for bioremediation of soil contaminated with petroleum. Further research is required to increase degradation rate.     

Soil moisture and the rates of biodegradation of diallate and triallate

Degradation experiments were combined with biomass measurements and adsorption tests to determine how soil moisture content influences the rates of degradation of ⁴¹C-labelled diallate and triallate. In soils treated with 1 μg^?1 herbicide and incubated at constant temperature and moisture, degradation rates were regulated by two variables: the quantity of microbial biomass in the soil; and the quantity of herbicide dissolved in the soil solution. The quantity of biomass was influenced by soil water content and the duration of incubation. The amounts of herbicide in solution were determined by the amount of water present and the total quantity of herbicide in the soil. In all soil samples, the rates of degradation increased with increasing water content but decreased with prolonged incubation. The factors responsible for decrease with time were the loss of biomass during incubation and the decline in herbicide concentration in the soils as degradation proceeded.     

Microbial destruction of chitin in different soils

Chitinolytic prokaryotic and eukaryotic complexes were studied in the course of succession initiated by an introduction of chitin and moistening of the soil. An increase in the number and biomass of chitinolytic microorganisms and stronger carbon dioxide emission were observed in the experimental variants with chitin as compared with the control without chitin. The increase was recorded for the prokaryotes (actinomycetes and bacteria) and not due to the eukaryotes in the course of the succession initiated by chitin. It was first found that the chitinolytic actinomycetal complex in an ordinary chernozem has a specific taxonomic structure. The representatives of the Streptosporangium genus were the dominating actinomycetes in the chitinolytic complex.     

降解菌HQ-C-01对克百威污染土壤的生物修复

在室内模拟条件下,研究了降解菌HQ-C-01(Pichia anomala)对克百威污染土壤的修复作用及其影响因素,同时研究了克百威及该菌株对土壤微生物的影响。结果表明,克百威降解率与降解菌HQ-C-01接种量呈正相关,降解菌接种量为2.09×108 CFU/g干土时,对土壤中50 mg/kg克百威10天降解率达82.89%;当降解菌接种量低于106 CFU/g干土时,降解菌对克百威的降解效果较弱。土壤含水量显著影响降解菌对克百威的降解率,含水量为600 g/kg时降解效果最好,降解率达85.32%,而当含水量低于200 g/kg时降解效果较差。在温度范围25℃~35℃降解菌对克百威都具有较好的降解效果。不同土壤pH值对降解菌的降解作用有显著影响,在pH值为7时,降解菌对土壤中50 mg/kg克百威10天降解率达85.62%,在较低和较高pH值下,降解效果较差。克百威使用对土壤菌落结构有一定的影响,对土壤真菌具有强烈刺激作用,从而使土壤微生物群落结构发生改变,而降解菌的使用可缓解克百威对土壤微生物的影响,修复受污染土壤。     

Effects of filter type and extraction efficiency on nitrogen mineralization measurements using the aerobic leaching soil incubation method

Aerobic incubation of soils with sequential leachings to extract mineralized N is often used to determine N mineralization potential and N availability in the laboratory. This study used tropical forest soils with differing mineralogy and texture to address: (1) the effects of filter type and equilibration time on soil moisture and N mineralization and (2) the N extraction efficiency of 0.01 M CaCl₂, minus-N nutrient solution (containing 0.004 M CaCl₂) and 2 M KCl. Use of glass microfiber filters compared to cellulose acetate or polyethersulfone membrane filters resulted in a lower moisture content for both low-and high-clay soils. However, filter type did not affect N mineralization. Under 47 kPa suction, soil moisture equilibration occurred between 240 and 360 min regardless of filter type. Extraction efficiency for mineralized N using 0.01 M CaCl₂ or minus-N nutrient solution was lower in forest soils of smectitic mineralogy and soils with a higher proportion of macroaggregates. However, with the exception of allophanic soils, the cumulative amount of N mineralized measured in a long-term incubation for approximately 1 year was not different when either a leaching or an unleached incubation method was used. These results indicate that researchers may wish to conduct preliminary evaluations to determine whether their incubation method will achieve a desired uniform moisture level and N extraction efficiency.     

Effects of fertilizer and soil components on pesticide photolysis

An environmental fate study was performed analyzing the effects of soil composition on the soil photolysis of a chemical. The study was conducted in two phases in which both moist and air-dried soils were fortified with either the common fertilizer sodium nitrate or the natural soil components iron or humic acid and dosed with niclosamide. The soils were photolyzed under a xenon lamp for 7 days. Increasing concentration of sodium nitrate did not affect the degradation pattern but did produce a lower concentration of aminoniclosamide. Soils fortified with iron displayed an unknown, which was not observed in other experiments, and the degradation of niclosamide from these soils was slower than from the sodium nitrate-fortified soils. There were no extractable degradates from any of the soils fortified with humic acid. In irradiated moist soils, the half-life of niclosamide increased when sodium nitrate was present at 20 ppm, and the half-lives of niclosamide in iron- and humic acid-fortified soil were increased slightly over that in unfortified soil. The effect of the nitrate and iron on the half-lives in dark control moist soils was minimal, but humic acid increased the dark control half-life from 420 to 611 h. No transformation of niclosamide was observed in the dark control air-dried soils. Soils with higher organic or iron contents or exposed to fertilizers do not affect as dramatically the half-life of pesticides as does the presence of moisture in the soil. Soil photolysis samples that were not maintained with moisture exhibited differences in half-life and degradation pattern. The maintenance of moisture was found to be more crucial to the reliability of soil photolysis studies than soil composition.