Surface attachment of nitrifying bacteria and their inhibition by potassium ethyl xanthate

Ion exchange resins and glass microscope slides were used to investigate factors affecting attachment of nitrifying bacteria to solid surfaces and the effect of attachment on inhibition ofNitrobacter by potassium ethyl xanthate. The ammonium oxidizerNitrosomonas attached preferentially to cation exchange resins while the nitrite oxidizerNitrobacter colonized anion exchange resins more extensively. Colonization was always associated with growth, and the site of substrate (NH₄ ⁺ or NO₂ ^–) adsorption was the major factor in attachment and colonization. The specific growth rate of cells colonizing either ion exchange resin beads or glass surfaces was greater than that of freely suspended cells, butNitrobacter populations colonizing glass surfaces were more sensitive to the inhibitor potassium ethyl xanthate. The findings indicate that surface growth alone does not protect soil nitrifying bacteria from inhibition by potassium ethyl xanthate and explain different patterns of inhibition for ammonium and nitrite oxidizers in the soil.     

Enhanced Reactivity of Rhizopus oryzae Lipase Displayed on Yeast Cell Surfaces in Organic Solvents: Potential as a Whole-Cell Biocatalyst in Organic Solvents

Immobilization of enzymes on some solid supports has been used to stabilize enzymes in organic solvents. In this study, we evaluated applications of genetically immobilized Rhizopus oryzae lipase displayed on the cell surface of Saccharomyces cerevisiae in organic solvents and measured the catalytic activity of the displayed enzyme as a fusion protein with α-agglutinin. Compared to the activity of a commercial preparation of this lipase, the activity of the new preparation was 4.4 × 10⁴-fold higher in a hydrolysis reaction using p-nitrophenyl palmitate and 3.8 × 10⁴-fold higher in an esterification reaction with palmitic acid and n-pentanol (0.2% H₂O). Increased enzyme activity may occur because the lipase displayed on the yeast cell surface is stabilized by the cell wall. We used a combination of error-prone PCR and cell surface display to increase lipase activity. Of 7,000 colonies in a library of mutated lipases, 13 formed a clear halo on plates containing 0.2% methyl palmitate. In organic solvents, the catalytic activity of 5/13 mutants was three- to sixfold higher than that of the original construct. Thus, yeast cells displaying the lipase can be used in organic solvents, and the lipase activity may be increased by a combination of protein engineering and display techniques. Thus, this immobilized lipase, which is more easily prepared and has higher activity than commercially available free and immobilized lipases, may be a practical alternative for the production of esters derived from fatty acids.     

Phosphorus fertilizer recovery from calcareous soils amended with humic and fulvic acids

Precipitation of Ca phosphates negatively affects recovery by plants of P fertilizer applied to calcareous soils, but organic matter slows the precipitation of poorly soluble Ca phosphates. To study the effect of high molecular weight organic compounds on the recovery of applied P, a mixture of humic and fulvic acids was applied to calcareous soils with different levels of salinity and Na saturation which were fertilized with 200 and 2000 mg P kg^–1 as NH₄H₂PO₄. Recovery was measured as the ratio of increment in Olsen P-to-applied P after 30, 60 and 150 days, and associated P forms were studied using sequential chemical fractionation and ³¹P NMR spectroscopy. Application of the humic-fulvic acid mixture (HFA) increased the amount of applied P recovered as Olsen P in all the soils except in one soil with the highest Na saturation. In soils with high Ca saturation and high Olsen P, recovery increased from < 15% in the absence of amendment to > 40% at a 5 g HFA kg^–1 amendment rate (30 days incubation and 200 mg P kg^–1 fertilizer rate). This is ascribed to inhibition of the precipitation of poorly soluble Ca phosphates, consistent with the sequential chemical extraction (reduction of the HCl extractable P) and P concentration in 0.01 M CaCl₂ (1:10 soil:solution ratio) extracts. ³¹P NMR spectra revealed that in non-amended samples, most spectral shifts were due to poorly soluble P compounds (carbonate apatite); on the other hand, at the 5 g HFA kg^–1 rate, significant amounts of amorphous Ca phosphate and dicalcium phosphate dihydrate (DCDP) were identified. The increase in the recovery of applied P due to HFA reveals a positive effect of the application of organic matter as soil amendments on the efficiency of P fertilizers and also explains that manures and other organic sources of P were more efficient increasing available P than inorganic P fertilizers in calcareous soils.     

Nitrogen and phosphorus requirements for raising mycorrhizal seedlings of Leucaena leucocephala in containers

A greenhouse study was undertaken to determine the nitrogen and phosphorus fertilization requirements for raising mycorrhizal seedlings in soil in containers. Seedlings of Leucaena leucocephala were grown for 40 days in dibble tubes containing fumigated or nonfumigated soil uninoculated or inoculated with Glomus aggregatum. The soil was fertilized with NH₄NO₃ solution to obtain 25–200 mg N kg^-1 soil, and with a KH₂PO₄ solution to establish target soil solution P concentrations of 0.015–0.08 mg P l^-1. At the end of 40 days, seedlings were transplanted into pots containing 5-kg portions of fumigated soil. Posttransplant vesicular arbuscular mycorrhizal fungal (VAMF) effectiveness, measured as pinnule P content, plant height, shoot dry weight and tissue N and P concentrations, was significantly increased by pretransplant VAMF colonization in both soils. The best posttransplant mycorrhizal colonization and mycorrhizal growth responses were observed if the nonfumigated pretransplant soil was amended with 50 mg N kg^-1 soil and 0.04 mg P l^-1 or if the fumigated pretransplant soil was amended with 100 mg N kg^-1 soil and 0.04 mg P 1^-1. There was no relationship between NP ratios of nutrients added to the pretransplant soil medium and shoot NP ratios observed after transplanting. Shoot NP ratio was also not correlated with root colonization level.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 4025     

Mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) in soil inoculated with Pseudomonas cepacia DBO1(pRO101), Alcaligenes eutrophus AEO106(pRO101) and Alcaligenes eutrophus JMP134(pJP4): effects of inoculation level and substrate concentration

Mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) by two Alcaligenes eutrophus strains and one Pseudomonas cepacia strain containing the 2,4-D degrading plasmids pJP4 or pRO101 (=pJP4::Tn1721) was tested in 50 g (wet wt) samples of non-sterile soil. Mineralization was measured as ¹⁴C-CO₂evolved during degradation of uniformly-ring-labelled ¹⁴C-2,4-D. When the strains were inoculated to a level of approximately 10⁸ CFU/g soil, between 20 and 45% of the added 2,4-D (0.05 ppm, 10 ppm or 500 ppm) was mineralized within 72 h. Mineralization of 0.05 ppm and 10 ppm, 2,4-D by the two A. eutrophus strains was identical and rapid whereas mineralization by P. cepacia DBO1(pRO101) occurred more slowly. In contrast, mineralization of 500 ppm 2,4-D by the two A. eutrophus strains was very slow whereas mineralization by P. cepacia DBO1 was more rapid. Comparison of 2,4-D mineralization at different levels of inoculation with P. cepacia DBO1(pRO101) (6×10⁴, 6×10⁶ and 1×10⁸ CFU/g soil) revealed that the maximum mineralization rate was reached earlier with the high inoculation levels than with the low level. The kinetics of mineralization were evaluated by nonlinear regression analysis using five different models. The linear or the logarithmic form of a three-half-order model were found to be the most appropriate models for describing 2,4-D mineralization in soil. In the cases in which the logarithmic form of the three-half-order model was the most appropriate model we found, in accordance with the assumptions of the model, a significant growth of the inoculated strains.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - CFU colony forming units - PTYG peptone, tryptone, yeast & glucose - DPM disintegrations per minute     

Phosphorus-deficiency reduces aluminium toxicity by altering uptake and metabolism of root zone carbon dioxide

The role of phosphorus (P) status in root-zone CO₂ utilisation for organic acid synthesis during Al³⁺ toxicity was assessed. Root-zone CO₂ can be incorporated into organic acids via Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31). P-deficiency and Al³⁺ toxicity can induce organic acid synthesis, but it is unknown how P status affects the utilisation of PEPC-derived organic acids during Al³⁺ toxicity. Two-week-old Solanum lycopersicum seedlings were transferred to hydroponic culture for 3 weeks. The hydroponic culture consisted of a standard Long Ashton nutrient solution containing either 0.1 μM or 1 mM P. Short-term Al³⁺ toxicity was induced by a 60-min exposure to a pH-buffered solution (pH 4.5) containing 2 mM CaSO₄ and 50 μM AlCl₃. Al³⁺ toxicity induced a decline in root respiration, adenylate concentrations and an increase in root-zone CO₂ utilisation for both P sufficient and P-deficient plants. However during Al³⁺ toxicity, P deficiency enhanced the incorporation and metabolism of root-zone CO₂ via PEPC. Moreover, P deficiency led to a greater proportion of the PEPC-derived organic acids to be exuded during Al³⁺ toxicity. These results indicate that P-status can influence the response to Al³⁺ by inducing a greater utilisation of PEPC-derived organic acids for Al³⁺ detoxification.     

Fermentative production of P(3HB-co-3HV) from propionic acid by Alcaligenes eutrophus in fed-batch culture with pH-stat continuous substrate feeding method

The feeding of propionic acid for production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] by Alcaligenes eutrophus ATCC17697 was optimized using a fed-batch culture system. The concentration of propionic acid was maintained at 3 g l^–1 as growth was inhibited by propionic acid in the broth. A pH-stat substrate feeding system was used in which propionic acid was fed automatically to maintain a pH of the culture broth at 7.0. By feeding a substrate solution containing 20% (w/v) propionic acid, 4.9% (w/v) ammonia water [at a molar ratio of carbon to nitrogen (C/N molar ratio) of 10] in cell growth phase, the concentration of propionic acid in the broth was maintained at 3 g l^–1 giving a specific growth rate of 0.4 h^–1. To promote P(3HB-co-3HV) production, two stage fed-batch culture which consisted of the stage for the cell growth and the stage for the P(3HB-co-3HV) accumulation was carried out. When the substrate solution whose C/N molar ratio was 50 was fed in P(3HB-co-3HV) accumulation phase, the cell concentration and the P(3HB-co-3HV) content in the cells reached 64 g l^–1 and 58% (w/w) in 55.5 h, respectively.     

Response of Stylosanthes guianensis to endomycorrhizal fungi inoculation as affected by lime and phosphorus applications

The effect of 3 different species of vesicular-arbuscular mycorrhizal fungi on the growth of Stylosanthes guianensis (Aubl.) Sw. cultivated in a sterilized acid and dystrophic soil (Quartzipsament), with 4 levels of lime (0; 0.27; 0.63 and 1.10 meq Ca²⁺/100 g air-dried soil, as Ca(OH)₂) and 2 P levels (0 and 20 mg P/kg soil, as KH₂PO₄) was evaluated under greenhouse conditions. Plants were harvested 40, 60, and 80 days after planting. Stylosanthes guianensis was highly mycotrophic, especially in soil without P fertilization. Mycotrophism was highest in plants inoculated with Acaulospora scrobiculata in soil receiving no P fertilizer and with 0.63 meq Ca²⁺/100 g air-dried soil. Shoot growth increment was as high as 5129% at the third harvest. Inoculation with Glomus macrocarpum presented intermediate results, whereas inoculation with Gigaspora margarita had no significant effect on plant growth. Root per cent colonization and shoot dry weight, as well as root percent colonization and shoot to root ratio were significantly correlated. The occurrence of S. guianensis in very acid and dystropic soils, containing toxic levels of Al³⁺, requires the association with VAM fungi for the plant tolerate such conditions.     

Biosensor for acrylamide based on an ion-selective electrode using whole cells of Pseudomonas aeruginosa containing amidase activity

The aim of this work was to develop a biosensor for toxic amides using whole cells of Pseudomonas. aeruginosa containing amidase activity, which catalyses the hydrolysis of amides such as acrylamide producing ammonia and the corresponding organic acid. Whole cells immobilized in several types of membrane in the presence of glutaraldehyde and an ammonium ion-selective electrode, were used for biosensor development. This biosensor exhibited a linear response in the range of 0.1–4.0×10^?3 M of acrylamide, a detection limit of 4.48×10^?5 M acrylamide, a response time of 55 s, a sensitivity of 58.99 mV mM^?1 of acrylamide and a maximum t_1/2 of 54 days. The selectivity of this biosensor towards other amides was investigated, which revealed that it cross-reacted with acetamide and formamide, but no activity was detected with phenylacetamide, p-nitrophenylacetamide and acetanilide. It was successfully used for quantification of acrylamide in real industrial effluents and recovery experiments were carried out which revealed an average substrate recovery of 93.3%. The biosensor is cheap since whole cells of P. aeruginosa can be used as source of amidase activity.     

Fundamental aspects of waste sewage sludge treatment: Microbial solids biodegradation in an aerobic thermophilic semi-continuous system

The solubilization and biodegradation of whole microbial cells by an aerobic thermophilic microbial population was investigated over a 72 h period. Various parameters were followed including total suspended solids reduction, changes in the dissolved organic carbon, protein and carbohydrate concentrations, and carboxylic acid production and utilisation. From the rates of removal of the various fractions a simple model for the biodegradation processes is proposed and verified with respect to acetic acid production and utilization, and total suspended solids removal. The process is initiated by enzymic degradation of the substrate microbe cell walls followed by growth on the released soluble substrates at low dissolved oxygen concentration with concommitant carboxylic acid production. Subsequent utilization of the unbranched, lower molecular weight carboxylic acids allows additional energy supply following exhaustion of the easily utilisable soluble substrate from microbial cell hydrolysis.List of Symbols Y _Xp/Xs kg/kg yield process microbes on substrate yeast cells - Y _Xp/Ac kg/kg yield process microbes on acetate - Y _Ac/Ss kg/kg yield acetate produced by process microbes growing on substrate yeast cells - Y _Ss/Xs kg/kg yield soluble substrate from lysis of yeast cells - Y _Ss/Xp kg/kg yield soluble substrate from lysis of process microbes - Y _P/Xs kg/kg yield particulates from lysis of yeast cells - Y _P/Xp kg/kg yield particulates from lysis of process microbes - _{max (Ss)} h^–1 maximum specific growth rate constant for growth of process microbes on soluble substrate - _{max (Ac)} h^–1 maximum specific growth rate constant for growth of process microbes on acetate - Ks _Ss kg/m³ saturation coefficient for growth of process microbes on soluble substrate - Ks _Ac kg/m³ saturation coefficient for growth of process microbes on acetate - K _d h^–1 death/lysis rate constant for process microbes - K _i kg/m³ inhibition constant for growth of process microbes on acetate - K _L h^–1 lysis rate constant for whole yeast cells - K _h h^–1 hydrolysis rate constant for particulate biomass     

Ectomycorrhizal and arbuscular mycorrhizal colonization of Alnus acuminata from Calilegua National Park (Argentina)

The objective of this study was to determine patterns of ectomycorrhizas (ECM) and arbuscular mycorrhizas (AM) colonization associated with Alnus acuminata (Andean alder), in relation to soil parameters (electrical conductivity, field H₂O holding capacity, pH, available P, organic matter, and total N) at two different seasons (autumn and spring). The study was conducted in natural forests of A. acuminata situated in Calilegua National Park (Jujuy, Argentina). Nine ECM morphotypes were found on A. acuminata roots. The ECM colonization was affected by seasonality and associated positively with field H₂O holding capacity, pH, and total N and negatively associated with organic matter. Two morphotypes (Russula alnijorullensis and Tomentella sp. 3) showed significant differences between seasons. Positive and negative correlations were found between five morphotypes (Alnirhiza silkacea, Lactarius omphaliformis, Tomentella sp. 1, Tomentella sp. 3, and Lactarius sp.) and soil parameters (total N, pH, and P). A significant negative correlation was found between field H₂O holding capacity and organic matter with AM colonization. Results of this study provide evidence that ECM and AM colonization of A. acuminata can be affected by some soil chemical edaphic parameters and indicate that some ECM morphotypes are sensitive to changes in seasonality and soil parameters.     

Aerobic metabolic potential of microbial populations indigenous to deep subsurface environments

Subsurface sediment samples, collected from three boreholes ranging in depths from 0.1 to 260 m, were used in substrate mineralization studies to examine the aerobic metabolic potential of microbial populations indigenous to the deep subsurface. Mineralization was measured by quantifying the amount of ¹⁴CO₂ released from radiolabeled acetate, phenol, or 4‐methoxybenzoate added to subsurface sediments at 10 μg g^‐1. Mineralization of the three compounds was observed in all but a few of the subsurface samples and did not decrease with depth. In addition, mineralization data collected from similar geologic formations from the different boreholes indicated that there was significant lateral continuity of microbial activity. Regression analyses were performed to determine which environmental factors were related to microbial metabolic potential. Mineralization was positively correlated with heterotrophic abundance as measured by plate counts. Other parameters that appeared to influence metabolic potential included pH and clay content.     

Structure and content of pollutants in temporal surface sediments in small watersheds

ABSTRACT

Formation of gel-like surface sediments has been observed during spring and autumn in small watersheds in boreal areas with pH <5.7 and concentrations of humic substances above 3 mg L^?1. This structure efficiently accumulates dissolved, colloidal and particulate constituents. The gel consists of ferric (hydr)oxides and fulvic acid and has high viable counts of bacteria (notably Gallionella spp.) as well as fungal hyphae. The solid/solution distribution (log K_d; l kg^?1) for trace metals (Cd, Cu, Pb, V, Zn) ranges from 4 to 6.5 which indicate an efficient accumulation during periods with gel. The concentrations of adsorbable organic halogens in the gel were not different from forest soils in general.     

The Influence of the Chemical Composition of Typha Domingensis and Nymphaea Ampla Detritus on Invertebrate Colonization During Decomposition in a Brazilian Coastal Lagoon

The aims of this study were to investigate the structure and composition of the invertebrate community during the detritus decomposition (colonization features) of the two most abundant aquatic macrophytes Typha domingensis Pers. and Nymphaea ampla in Jurubatiba Lagoon and verify if the chemical composition of the substratum has any influence on invertebrate colonization and which are the functional groups possibly affected by these compounds. The substratum T. domingensis had higher percentages of cell wall fraction (F= 108.33; p < 0.0001) and organic matter (F= 225.77; p < 0.0001), while nitrogen (F= 408.61; p < 0.0001) and phosphorus (F= 224.59; p < 0.0001) contents were higher in N. ampla. These differences in the chemical composition of the substrata influenced the decomposition rate, and the detritus of N. ampla(4.37% DW day^–1) decomposed approximately 26 times faster than the T. domingensis(0.17% DW day^–1) detritus. The main groups of invertebrates that colonized both substrate were Chironomidae, with more than 50% of the total, followed by Oligochaeta, Nematoda, Copepoda and Cladocera. The results showed that the slow breakdown rate of T. domingensis detritus provided a higher probability for colonization and that the main driving force structuring the invertebrates' community was degradative ecological succession (DES).     

Soil micro-habitat effects on fine roots of Chamaecyparis obtusa Endl.: A field experiment using root ingrowth cores

Ingrowth cores in the field were used to compare fine root characteristics of hinoki cypress (Chamaecyparis obtusa) among rooting substrate in the form of needle leaf litter, decomposing organic material, and mineral soil. Fine root growth, morphology, arbuscular mycorrhizal (AM) associations, and tissue C and N concentration were determined. The inorganic N leaching from each soil substrate was taken as a measure of N availability. Although there was no significant difference in total N leaching among substrates, more NH ₊ ⁴ -N leached from the decomposing organic material than other substrates. Rapid fine root production was observed in the organic material, whereas root production in the litter substrate was suppressed. Annual net fine root productions in litter, organic material, and mineral soil were 51, 193, and 132 g m⁻², respectively. In the leaf litter substrate, AM colonization was suppressed and specific root length was higher than in the other substrates, indicating severe nutrient limitation in the litter. These responses of hinoki cypress roots seemed to be a soil exploitation pattern whereby absorptive fine roots were arranged to maximize nutrient acquisition.     

Measles Virus Fusion Protein Is Palmitoylated on Transmembrane-Intracytoplasmic Cysteine Residues Which Participate in Cell Fusion

[³H]palmitic acid was metabolically incorporated into the viral fusion protein (F) of Edmonston or freshly isolated measles virus (MV) during infection of human lymphoid or Vero cells. The uncleaved precursor F₀ and the F₁ subunit from infected cells and extracellular virus were both labeled, indicating that palmitoylation can take place prior to F₀ cleavage and that palmitoylated F protein was incorporated into virus particles. [³H]palmitic acid was released from F protein upon hydroxylamine or dithiothreitol treatment, indicating a thioester linkage. In cells transfected with the cloned MV F gene, in which the cysteines located in the intracytoplasmic and transmembrane domains (Cys 506, 518, 519, 520, and 524) were replaced by serine, a major reduction of [³H]palmitic acid incorporation was observed for F mutated at Cys 506 and, to a lesser extent, at Cys 518 and Cys 524. We also observed incorporation of [³H]palmitic acid in the F₁ subunit of canine distemper virus F protein. Cell fusion induced by cotransfection of cells with MV F and H (hemagglutinin) genes was significantly reduced after replacement of Cys 506 or Cys 519 with serine in the MV F gene. Transfection with the F gene with a mutation for Cys 518 abolished cell fusion, although less mutant protein was detected on the cell surface. These results suggest that the F protein transmembrane domain cysteines 506 and 518 participate in structures involved in cell fusion, possibly mediated by palmitoylation.     

Association of Potassium and Some Other Monovalent Cations with Occurrence of Polyphosphate Bodies in Chlorella pyrenoidosa

Phosphate-starved Chlorella pyrenoidosa cells formed polyphosphate bodies (PB) upon transfer into nutrient solutions containing phosphate and potassium, or another monovalent cation, such as Na⁺, NH₄⁺, Li⁺, or Rb⁺. The phenomenon was studied by chemical analyses, light microscopy, and electron microscopy.

When the P-starved cells were transferred into a complete nutrient solution containing 100 micromolar P, they accumulated large quantities of P and K within several hours. The accumulation was accompanied by a corresponding appearance of PB in the cells. The absence of K from the medium prevented appreciable P accumulation and PB formation, but omitting Ca or Mg did not.

The P-starved cells exposed to a simple solution of at least 20 micromolar H₃PO₄ and 100 micromolar KHCO₃ responded in a similar manner as the cells exposed to the complete nutrient solution. However, the PB appeared structurally different.

It is proposed that monovalent cations are essential for PB formation in C. pyrenoidosa. K is suggested to be a major component of PB formed in K-sufficient media.

     

Role of lakes for organic carbon cycling in the boreal zone

We calculated the carbon loss (mineralization plus sedimentation) and net CO₂ escape to the atmosphere for 79 536 lakes and total running water in 21 major Scandinavian catchments (size range 437–48 263 km²). Between 30% and 80% of the total organic carbon that entered the freshwater ecosystems was lost in lakes. Mineralization in lakes and subsequent CO₂ emission to the atmosphere was by far the most important carbon loss process. The withdrawal capacity of lakes on the catchment scale was closely correlated to the mean residence time of surface water in the catchment, and to some extent to the annual mean temperature represented by latitude. This result implies that variation of the hydrology can be a more important determinant of CO₂ emission from lakes than temperature fluctuations. Mineralization of terrestrially derived organic carbon in lakes is an important regulator of organic carbon export to the sea and may affect the net exchange of CO₂ between the atmosphere and the boreal landscape.     

A continuous culture study of the bioenergetic aspects of growth and production of exocellular protease in Bacillus licheniformis

Summary Bacillus licheniformis S 1684 is able to produce an alkaline serine protease exocellularly. In glucose-limited chemostat cultures the specific rate of protease production was maximal at a -value of 0.22. Above this growth rate protease production was repressed. Dependent on 10–20% of the glucose input was used for exocellular product formation. The degree of reduction of exocellular products was 4.1.Maximum molar growth yields were high and indicate a high efficiency of growth. The values of Y _glu ^max and YO ₂ ^max were 83.8 and 53.3, respectively. When Y _glu ^max was corrected for the amount of glucose used for product formation a value of 100.3 was obtained. These high maximum molar growth yields are most probably caused by a high Y _ATP ^max . Anaerobic batch experiments showed a Y _ATP of 14.6.Sometimes the used strain was instable in cell morphology and protease production. Non-protease producing cells most probably develop from producing cells by mutation in the rel-gene. Producing cells most probably are relaxed (rel ^-) and non-producing cells stringent (rel ⁺).Glossary specific growth rate (h^-1) - Y _sub growth yield permol substrate (g biomass/mol) - Y ^max maximum molar growth yield, corrected for maintenance requirements (g biomass/mol) - Y ^max(corr) Y ^max corrected for product formation (g biomass/mol) - m _sub maintenance requirements (mol/g biomass·h) - m _sub(corr) maintenance requirements corrected for product formation (mol/g biomass·h) - Y _c fraction of organic substrate converted in biomass - z fraction of organic substrate converted in exocellular products - d fraction of organic substrate converted in CO₂ (g mol/g atom C) - Crec% carbon recovery % - average degree of reduction of exocellular products - P/O amount of ATP produced during electron-transport of 2 electrons to oxygen     

Influence of Glutamic Acid Enantiomers on C‐mineralization

Seasonal dynamics in the mineralization of glutamic acid enantiomers in soils from selected ecosystems was determined and subjected to a range of treatments: ambient x elevated CO₂ level and meadow x dense x thinned forest environment. Mineralization of glutamic acid was determined by incubation of the soil with 2 mg L‐ or D‐glutamic acid g^‐1 of dry soil to induce the maximum respiration rate. Mineralization of glutamic acid enantiomers in soils fluctuates over the course of a vegetation season, following a similar trend across a range of ecosystems. Mineralization is affected by environmental changes and management practices, including elevated CO₂ level and thinning intensity. L‐glutamic acid metabolism is more dependent on soil type as compared to metabolism of its D‐enantiomer. The results support the hypothesis that the slower rate of D‐ compared to L‐ amino acid mineralization is due to different roles in anabolism and catabolism of the soil microbial community. Chirality 27:104–108, 2015. © 2014 Wiley Periodicals, Inc.