Sorption of lead and copper from an aqueous phase system by marine-derived Aspergillus species

A total of 47 cultures of Aspergillus representing 13 species were screened for their ability to tolerate 7.5 mM Pb²⁺ and 2 mM Cu²⁺, all of which were positive, with growth of 31 of the cultures being enhanced by low concentrations of lead. The isolates of Aspergillus versicolor, A. niger and A. flavus were tolerant to concentrations as high as 10 - 12.5 mM Pb²⁺ and 3 – 4 mM Cu²⁺. Selected cultures displayed a good sorption capacity of 32 - 41 mg Pb²⁺ and 3.5 - 6.5 mg Cu²⁺ g^-1 dry weight of mycelia, which was improved by alkali pretreatment of the biomass and negatively affected by mild dry heat treatment. The sequestration of the metal occurred mainly by sorption to the cell-surface with very little intracellular uptake. FTIR analysis indicated the involvement of hydroxyl, amino, and carbonyl groups in Pb²⁺ and Cu²⁺ biosorption by fungal biomass of the different species of Aspergillus.     

Aerobic decolorization of Acid Brilliant Scarlet GR by microbial community and the community dynamics during sequencing batch processes

In this research, aerobic decolorization of Acid Brilliant Scarlet GR by microbial community was studied. Effects of conditions and dye concentraion on decolorization processes were investigated. Additionally, continuous decolorization was evaluated through sequencing batch tests and the microbial dynamics during this process was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis. The results showed that 100 mg l^?1 of the dye was completely decolorized within 12 h, which was mainly caused by biodegradation. The optimal decolorization conditions were as follows: inoculation size 2.07 g l^?1 (wet cell pellet), rotation speed 150 r min^?1, pH 5.0–7.0 and 30 °C. The processes were well described by zero-order kinetics, and more than 700 mg l^?1 of the dye would inhibit the activity of the consortium. Furthermore, the microbial community exhibited high efficiency in sequencing batch processes for continuous decolorization. Microbial community structure shifted obviously when exposed to higher concentration of the dye (500 mg l^?1), and all the dominant microorganisms were affiliated with four different phyla of Actinobacteria, Bacteroidetes, Proteobacteria and Firmicutes.     

Lead accumulation and distribution in maize seedlings: Relevance to biomass production and metal phytoextraction

Among trace metals, lead is a highly toxic contaminant, being hazardous to humans and animals. Application of maize plants for phytoremediation of polluted soils and waters has recently been of particular interest. The aim of this work is to investigate the Pb-phytoextraction potential of the maize cv. Tzariza used widely in Eastern European agriculture. Maize seedlings were exposed in a nutrient solution to 1–10000 µM of Pb²⁺ for 21 days. Lead accumulated mostly in conductive tissues and shoots at 0.1 mM and higher concentrations of Pb in growth medium. Pb at concentrations of 1 and 10 mM caused an increase in the superoxide anion level and the catalase activity in maize leaves. Lead ions were tolerable to maize seedlings within a concentration range up to 1000 µM of Pb^2+. The levels of lead in the nutrient solution above 1 mM resulted in inhibition of the growth of axial organs, decrease in leaf area, inhibition of water absorption, and reduction in accumulation of biomass. Theoretical considerations indicate that in the temperate climates of the phytoremediation with maize may allow annual removal up to 90 kg of Pb per km², depending on the initial level of soil contamination.     

Formation,regeneration, and transformation of protoplasts of Streptomyces diastatochromogenes 1628

Toyocamycin exhibits effective biological activities for use against plant pathogenic fungi thanks to its structural similarity to nucleoside. It has been recognized as a promising agricultural antibiotic utilized in controlling the occurrence of plant diseases. In our previous study, a strain that was isolated was identified and designated as Streptomyces diastatochromogenes whose major secondary metabolite was toyocamycin, but the production was largely limited. Protoplast transformation is a useful technique in the improvement of streptomycete. In this study, we optimized some key factors necessary for protoplast formation, regeneration, and transformation of S. diastatochromogenes. When mycelium was cultivated in CP medium with 1 % glycine, harvested at 48 h old, and then treated with 3 mg lysozyme/mL in P buffer for 1 h, the greatest regeneration frequency (42.5 %) of protoplasts was obtained. By using 1?×?10⁹/mL protoplasts with polyethylene glycol 1000 at a concentration of 30 % (w/v), the best performance of protoplast transformation efficiency was 4.8?×?10³/μg DNA transformants.     

Effective bioremoval and detoxification of textile dye mixture by Alishewanella sp. KMK6

Alishewanella sp. strain KMK6 was able to degrade mixture of textile dyes (0.5–2.0 g?l^?1) within 8 h. An initial 28 % reduction in COD was observed immediately after decolorization at static anoxic conditions which on further incubation at shaking conditions reduced by 90 %. Partially purified azoreductase was able to utilize different azo dyes as substrates. The HPLC profile of dye degradation showed formation of metabolic products. Further FTIR analysis showed significant changes in the peaks corresponding to functional groups present in dye mixture and its degradation products. The genotoxicity assessment showed that the dye degradation products were non-toxic compared to dye mixture.     

混合白腐真菌的固定化及其在治理铅污染废水中的应用

【目的】为缓解重金属废水污染对全球食品安全和人类健康的威胁,降低铅(plumbum, Pb)在土壤及动植物体内的积累,借助固定化技术提高菌株的重金属去除效率。【方法】以白腐真菌(white rot fungi)为实验材料,通过混菌兼容性及铅离子(Pb²⁺)去除能力筛选出吸附效果好且兼容性优的复合菌种,探究最优混菌类型及其比例,优化菌球最佳固定化助剂配方,在此基础上深入探究菌球在实际应用中的最优吸附条件。【结果】黄孢原毛平革菌(Phanerochaete chrysosporium)、云芝(Coriolus versicolor)、凤尾菇(Lentinus sajor-caju)和平菇(Pleurotus ostreatus) 4种菌株兼容效果佳,可进行后续实验;其中云芝和凤尾菇以体积1:1混合后对Pb²⁺去除效果显著优于各单菌作用;固定化条件优化实验中,20.0 g/L海藻酸钠、15.0 g/L生物炭和2.0×10⁶个/mL白腐真菌组成混菌体系,辅以二氧化硅及沸石制得的固定化菌球在96 h Pb²⁺...     

Removal of Cd2+, Pb2+, and Zn2+ from contaminated water using dolomite powder

Dolomite collected from Surat Thani Province in Thailand was investigated for use as a sorbent for the removal of divalent heavy metal cations from an aqueous solution. The sorbent had a surface area of 2.46 m²/g and a pH of zero point charge (pHzpc) of 9.2. Batch sorption was used to examine the effect of the pH (pH 3–7) on the sorption capacity of Cd²⁺, Pb²⁺ and Zn²⁺, alone or together as an equimolar mixture at various concentrations. Alone, each heavy metal cation was adsorbed faster at a higher pH, where the sorption of Cd²⁺ and Pb²⁺ fitted a Langmuir isotherm, but Zn²⁺ sorption best fitted a Freundlich isotherm. Under equimolar competitive sorption, the sorption capacity of each cation was decreased by 75.8% (0.29–0.07 mM/g), 82.8% (0.53–0.09 mM/g), and 95.7% (0.84–0.04 mM/g) for Cd²⁺, Pb²⁺ and Zn²⁺, respectively, compared to that with the respective single cation. Desorption of these heavy metal cations from dolomite was low, with an average desorption level of 0.06–17.4%. Furthermore, since dolomite is readily available and rather cheap, it is potentially suitable for use as an efficient sorbent to sorb Cd²⁺ and Pb²⁺, and perhaps Zn²⁺, from contaminated water.     

Immobilization of <Emphasis Type="BoldItalic">Irpex lacteus</Emphasis> to liquid-core alginate beads and their application to degradation of pollutants

White rot fungi (WRF) are applicable to biodegradation of recalcitrant pollutants. However, excessive biomass growth typical for WRF cultivation can hinder their large scale applications. Therefore, immobilization of Irpex lacteus to liquid-core alginate beads restricting excessive mycelium growth and simultaneously keeping high degradation rate of pollutants was tested. Effective diffusivities of dyes to the beads varied from (2.98 ± 0.69) × 10^?10 to (10.27 ± 2.60) × 10^?10 m²/s. Remazol Brilliant Blue R (RBBR), Reactive Orange 16 (RO16), and Naphthol Blue Black (NBB) were used as model dyes. The immobilized fungus decolorized model dyes when applied both in microwell plates and in fluidized bed reactors. Using the microwell plates, the apparent reaction rate constants ranged from (2.06 ± 0.11) × 10^?2 to (11.06 ± 0.27) × 10^?2 1/h, depending on the dye used and its initial concentration. High initial concentrations negatively affected the dye decolorization rate. No fungal growth outside the beads was observed in fluidized bed reactors and thus no operational problems linked to an excessive biomass growth occurred. When RBBR was decolorized in subsequent batches in the fluidized bed reactor, the apparent reaction rate constant increased from (11.63 ± 0.35) × 10^?2 to (29.26 ± 7.19) × 10^?2 1/h.     

Stress-Tolerant <Emphasis Type="Italic">Viridibacillus arenosi</Emphasis> Strain IHB B 7171 from Tea Rhizosphere as a Potential Broad-Spectrum Microbial Inoculant

Viridibacillus arenosi strain IHB B 7171 identified based on 16S rRNA gene sequence produced colony forming units (cfu/ml) ranging from 3.3 × 10⁴ to 1.2 × 10¹⁰ under pH 5–11, 2.2 × 10² to 1.4 × 10¹⁰ for temperature 5–40 °C, 2.4 × 10² to 1.1 × 10¹⁰ for PEG 6000 10–30%, 2.2 × 10² to 1.4 × 10¹⁰ for 2.5–10% NaCl, 3.1 × 10³ to 1.7 × 10⁹ for 2.5–7.5 mM CaCl₂, 2.2 × 10² to 1.4 × 10⁷ for 2.5–7.5 mM AlCl₃, and 3.2 × 10² to 1.2 × 10⁷ for 2.5–7.5 mM FeCl₃. The activities of plant growth-promoting attributes with the increasing acidity, desiccation and salinity ranged from 408 to 101, 20 to 8, 14 to 5 µg/ml P-liberated from tri-calcium phosphate, aluminium phosphate and iron phosphate, 20–9% siderophore units, 14–4 µg/ml IAA and 190–16 α-ketobutyrate h/mg protein ACC-deaminase activity. Plant height, leaf number, and leaf weight on treatment with bacterial inoculum showed an increment of 9.5, 17.6, 54.5 and 31.0% in tea seedlings, respectively. The bacterium also enhanced plant height and yield by 10 and 13% in pea and 2.8 and 13.9% in wheat. The results exhibited stress-tolerance and plant growth-promoting activities by the strain under stressed growth-conditions with potential as a broad-spectrum plant growth-promoting rhizobacterium.     

Green synthesis of gold nanoparticles by a newly isolated strain <Emphasis Type="Italic">Trichosporon</Emphasis><Emphasis Type="Italic">montevideense</Emphasis> for catalytic hydrogenation of nitroaromatics

Objective

To investigate green synthesis of gold nanoparticles (AuNPs) by Trichosporon montevideense, and to study their reduction of nitroaromatics.

Results

AuNPs had a characteristic absorption maximum at 535 nm. Scanning electron microscopy images revealed that the biosynthesized nanoparticles were attached on the cell surface. X-ray diffraction analysis indicated that the particles formed as face-centered cubic (111)-oriented crystals. The average size of AuNPs decreased from 53 to 12 nm with increasing biomass concentration. The catalytic reduction of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, o-nitrophenylamine and m-nitrophenylamine (0.1 mM) by NaBH₄ had reaction rate constants of 0.32, 0.44, 0.09, 0.24 and 0.39 min^?1 with addition of 1.45 × 10^?2 mM AuNPs.

Conclusions

An eco-friendly approach for synthesis of AuNPs by T. montevideense is reported for the first time. The biogenic AuNPs could serve as efficient catalysts for hydrogenation of various nitroaromatics.

     

Effect of the metals iron, copper and silver on fluorobenzene biodegradation by Labrys portucalensis

Organic and metallic pollutants are ubiquitous in the environment. Many metals are reported to be toxic to microorganisms and to inhibit biodegradation. The effect of the metals iron, copper and silver on the metabolism of Labrys portucalensis F11 and on fluorobenzene (FB) biodegradation was examined. The results indicate that the addition of 1 mM of Fe²⁺ to the culture medium has a positive effect on bacterial growth and has no impact in the biodegradation of 1 and 2 mM of FB. The presence of 1 mM of Cu²⁺ was found to strongly inhibit the growth of F11 cultures and to reduce the biodegradation of 1 and 2 mM of FB to ca. 50 %, with 80 % of stoichiometrically expected fluoride released. In the experiments with resting cells, the FB degraded (from 2 mM supplied) was reduced ca. 20 % whereas the fluoride released was reduced to 45 % of that stoichiometrically expected. Ag⁺ was the most potent inhibitor of FB degradation. In experiments with growing cells, the addition of 1 mM of Ag⁺ to the culture medium containing 1 and 2 mM of FB resulted in no fluoride release, whereas FB degradation was only one third of that observed in control cultures. In the experiments with resting cells, the addition of Ag⁺ resulted in 25 % reduction in substrate degradation and fluoride release was only 20 % of that stoichiometrically expected. The accumulation of catechol and 4-fluorocatechol in cultures supplemented with Cu²⁺ or Ag⁺ suggest inhibition of the key enzyme of FB metabolism—catechol 1,2-dioxygenase.     

Efficient protoplast isolation and transient gene expression system for <Emphasis Type="Italic">Phalaenopsis</Emphasis> hybrid cultivar ‘Ruili Beauty’

With the release of the Phalaenopsis equestris (Schauer) Rchb.f. genome database, more in-depth studies of Phalaenopsis spp. will be carried out in the future. Transient gene expression in protoplasts is a useful system for gene function analysis, which is especially true for Phalaenopsis, whose stable genetic transformation is difficult and extremely time-consuming. In this study, juvenile leaves from aseptic Phalaenopsis seedlings were used as the starting material for protoplast isolation. After protocol refinement, the highest yield of viable protoplasts [5.94 × 10⁶ protoplasts g^?1 fresh weight (FW)] was achieved with 1.0% (w/v) Cellulase Onozuka R-10, 0.7% (w/v) Macerozyme R-10, and 0.4 M D-mannitol, with an enzymolysis duration of 6 h. As indicated by transient expression of green fluorescent protein (GFP), a transformation efficiency of 41.7% was achieved with 20% (w/v) polyethylene glycol (PEG-4000), 20 μg plasmid DNA, 2 × 10⁵ mL^?1 protoplasts, and a transfection duration of 30 min. The protocol established here will be valuable for functional studies of Phalaenopsis genes.     

Development of a Murine Model with Optimal Routes for Bacterial Infection and Treatment, as Determined with Bioluminescent Imaging in C57BL/6 Mice

Mice intragastrically infected with Listeria monocytogenes EGDe and Staphylococcus aureus Xen 36 showed no visible signs of infection over 48 h. However, high numbers (6.2 × 10⁵ cfu/mg feces) of S. aureus Xen 36 were detected 4 h, and 3.3 × 10⁵ cfu/mg feces of L. monocytogenes EGDe 8 h, after administration. Mice intraperitoneally infected with S. aureus Xen 36 (1 × 10⁷ cfu) developed infection immediately after administration and for at least the following 48 h. Injection with higher cell numbers of S. aureus Xen 36 (2 × 10⁸ cfu) resulted in more intense bioluminescence (infection) of the peritoneal cavity. Injection of S. aureus Xen 36 in the tail and penile veins resulted in localized tissue infection for the first 120 h. Injection of S. aureus Xen 36 into the thigh produced a faint bioluminescent signal for 15 min. Nisin F injected into the peritoneal cavity at the same area of infection led to an immediate statistically significant decrease in infection (from 2 × 10⁶ p/s/cm²/sr to 3 × 10⁵ p/s/cm²/sr) within 2 h. Similar results were recorded when nisin F was injected subcutaneously. Intraperitoneal administration is an optimal administration route for bacterial infection and treatment with antimicrobial peptides.     

Electrochemical selective detection of dopamine on microbial carbohydrate-doped multiwall carbon nanotube-modified electrodes

Microbial carbohydrate-doped multiwall carbon nanotube (MWNT)-modified electrodes were prepared for the purpose of determining if 4-(2-aminoethyl)benzene-1,2-diol (3,4-dihydroxyphenylalanine; dopamine) exists in the presence of 0.5 mM ascorbic acid, a representative interfering agent in neurotransmitter detection. The microbial carbohydrate dopants were α-cyclosophorohexadecaose (α-C16) from Xanthomonas oryzae and cyclic-(1 → 2)-β-d-glucan (Cys) from Rhizobium meliloti. The cyclic voltammetric responses showed that the highest sensitivity (5.8 × 10^?3 mA cm^?2 μM^?1) is attained with the Cys-doped MWNT-modified ultra-trace carbon electrode, and that the α-C16-doped MWNT-modified glassy carbon electrode displays the best selectivity to dopamine (the approximate peak potential separation is 310 mV).     

The potential of Beauveria bassiana inoculum formulated into a polymeric matrix for a microbial control of spruce bark beetle

Two local strains of Beauveria bassiana originally isolated from naturally infected spruce bark beetles in Slovakia were tested for their virulence to Ips typographus (IT) and for their compatibility with a polymeric matrix composed of low-molecular polyethylene. Conidia could be homogenously immobilized in the low-molecular polyethylene matrix with no adverse effect on their viability and infectivity. At constant temperature (25°C), viability of immobilized conidial decreased only by 1–2% after 7 or 14 days when compared with non-formulated conidia. In field conditions, viability of conidia formulated in the matrix was even significantly higher than non-formulated conidia 35 days after their application in traps. Conidia incorporated into the polymeric matrix were infective to IT adults in laboratory bioassays. Mean values of LC₅₀ for native conidia (0.72–2.05?×?10⁶ conidia?ml^?1) and conidia immobilized in the polymeric matrix (0.64–1.03?×?10⁵ conidia?mm^?2) demonstrated high virulence. The efficacy of the local strains was significantly higher than that of B. bassiana strains from mycoinsecticides (Boverol^®, Botanigard^® ES and Naturalis-L^®). Results showed potential of this polymeric material for its use in microbial control of IT when mixed with conidia of B. bassiana.     

Establishment and characterization of Stevia rebaudiana (Bertoni) cell suspension culture: an in vitro approach for production of stevioside

A protocol has been standardized for establishment and characterization of cell suspension cultures of Stevia rebaudiana in shake flasks, as a strategy to obtain an in vitro stevioside producing cell line. The effect of growth regulators, inoculum density and various concentrations of macro salts have been analyzed, to optimize the biomass growth. Dynamics of stevioside production has been investigated with culture growth in liquid suspensions. The callus used for this purpose was obtained from leaves of 15-day-old in vitro propagated plantlets, on MS medium fortified with benzyl aminopurine (8.9 μM) and naphthalene acetic acid (10.7 μM). The optimal conditions for biomass growth in suspension cultures were found to be 10 g l^?1 of inoculum density on fresh weight basis in full strength MS liquid basal medium of initial pH 5.8, augmented with 2,4-dichlorophenoxy acetic acid (0.27 μM), benzyl aminopurine (0.27 μM) and ascorbic acid (0.06 μM), 1.0× NH₄NO₃ (24.7 mM), 3.0× KNO₃ (56.4 mM), 3.0× MgSO₄ (4.5 mM) and 3.0× KH₂PO₄ (3.75 mM), in 150 ml Erlenmeyer flask with 50 ml media and incubated in dark at 110 rpm. The growth kinetics of the cell suspension culture has shown a maximum specific cell growth rate of 3.26 day^?1, doubling time of 26.35 h and cell viability of 75 %, respectively. Stevioside content in cell suspension was high during exponential growth phase and decreased subsequently at the stationary phase. The results of present study are useful to scale-up process and augment the S. rebaudiana biological research.     

Production,characteristics and applications of phytase from a rhizosphere isolated <Emphasis Type="Italic">Enterobacter</Emphasis> sp. ACSS

Optimization of process parameters for phytase production by Enterobacter sp. ACSS led to a 4.6-fold improvement in submerged fermentation, which was enhanced further in fed-batch fermentation. The purified 62 kDa monomeric phytase was optimally active at pH 2.5 and 60 °C and retained activity over a wide range of temperature (40–80 °C) and pH (2.0–6.0) with a half-life of 11.3 min at 80 °C. The kinetic parameters K _m, V _max, K _cat, and K _cat/K _m of the pure phytase were 0.21 mM, 131.58 nmol mg^?1 s^?1, 1.64 × 10³ s^?1, and 7.81 × 10⁶ M^?1 s^?1, respectively. The enzyme was fairly stable in the presence of pepsin under physiological conditions. It was stimulated by Ca⁺², Mg⁺² and Mn⁺², but inhibited by Zn⁺², Cu⁺², Fe⁺², Pb⁺², Ba⁺² and surfactants. The enzyme can be applied in dephytinizing animal feeds, and the baking industry.     

Reactive oxygen species generated in the presence of fine pyrite particles and its implication in thermophilic mineral bioleaching

In the tank bioleaching process, maximising solid loading and mineral availability, the latter through decreasing particle size, are key to maximising metal extraction. In this study, the effect of particle size distribution on bioleaching performance and microbial growth was studied through applying knowledge based on medical geology research to understand the adverse effects of suspended fine pyrite particles. Small-scale leaching studies, using pyrite concentrate fractions (106–75, 75–25, ?25 μm fines), were used to confirm decreasing performance with decreasing particle size (D ₅₀ <40 μm). Under equivalent experimental conditions, the generation of the reactive oxygen species (ROS), hydrogen peroxide and hydroxyl radicals from pyrite was illustrated. ROS generation measured from the different pyrite fractions was found to increase with increasing pyrite surface area loading (1.79–74.01 m² L^?1) and Fe²⁺ concentration (0.1–2.8 g?L^?1) in solution. The highest concentration of ROS was measured from the finest fraction of pyrite (0.85 mM) and from the largest concentration of Fe²⁺ (0.78 mM). No ROS was detected from solutions containing only Fe³⁺ under the same conditions tested. The potential of ROS to inhibit microbial performance under bioleaching conditions was demonstrated. Pyrite-free Sulfolobus metallicus cultures challenged with hydrogen peroxide (0.5–2.5 mM) showed significant decrease in both cell growth and Fe²⁺ oxidation rates within the concentration range 1.5–2.5 mM. In combination, the results from this study suggest that conditions of large pyrite surface area loading, coupled with high concentrations of dissolved Fe²⁺, can lead to the generation of ROS, resulting in oxidative stress of the microorganisms.     

A rapid knockdown effect of Penicillium citrinum for control of the mosquito Culex quinquefasciatus in Thailand

Twenty local isolates of entomopathogenic fungi were determined for control of the larvae and adults of Culex quinquefasciatus. In a laboratory experiment, a Penicillium sp. CM-010 caused 100 % mortality of third-instar larvae within 2 h using a conidial suspension of 1 × 10⁶ conidia ml^?1. Its LC₅₀ was 3 × 10⁵ conidia ml^?1, and the lethal time (LT₅₀) was 1.06 h. Cloning and sequencing of its internal transcribed spacer region indicated that this Penicillium species is Penicillium citrinum (100 % identity in 434 bp). Mortality of the adult was highest with Aspergillus flavus CM-011 followed with Metarhizium anisopliae CKM-048 from 1 × 10⁹ conidia ml^?1. P. citrinum CM-010 at 1 × 10⁶ conidia ml^?1 killed 100 % larvae within 2 h while Bacillus thuringiensis var. israelensis at 5 ITU ml^?1 required 24 h. This P. citrinum CM-010 also greatly reduced survival of C. quinquefasciatus larvae in an unreplicated field test. Light and transmission electron micrographs showed that the fungal conidia were ingested by the larvae and deposited in the gut. The metabolite patulin was produced by P. citrinum CM-010 instead of citrinin.     

Translocation and turnover of rhizodeposit carbon within soil microbial communities of an extensive grassland ecosystem

Background and Aims

A substantial amount of photosynthesized plant-C is allocated belowground in grassland ecosystems where it influences the structure and function of the soil microbial community with potential implications for C cycling and storage. We applied stable isotope probing of microbial PLFAs and repeated soil sampling in a grassland over a period of 1 year to assess the role of microbial communities in the cycling of rhizodeposit-C.

Methods

Pulse-labeling with ¹³CO₂ was performed in a grassland site near Gent (Belgium). Soil samples were taken 24 h, 1 week, 1 month, 4 months, 9 months and 1 year following labeling and analyzed for ¹³C in soil, roots and microbial PLFAs.

Results

C enrichment of PLFAs occurred rapidly (within 24 h) but temporally varied across microbial groups. PLFAs indicative for fungi and gram-negative bacteria showed a faster ¹³C uptake compared to gram-positive bacteria and actinomycetes. However, the relative ¹³C concentrations of the latter communities increased after 1 week, while those of fungi decreased and those of gram-negative bacteria remained constant. PLFA ¹³C mean residence times were much shorter for fungi compared to bacteria and actinomycetes.

Conclusions

Our results indicate temporally varying rhizodeposit-C uptake by different microbial groups, and faster turnover rates of mycorrhizal versus saprotrophic fungi and fungi versus bacteria. Fungi appeared to play a major role in the initial processing and possible rapid channeling of rhizodeposit-C into the soil microbial community. Actinomycetes and gram-positive bacteria appeared to have a delayed utilization of rhizodeposit-C or to prefer other C sources upon rhizodeposition.