The effect of nitrogen source on photosynthesis of carob at high CO2 concentrations

Carob seedlings ( Ceratonia siliqua L. cv. Mulata), fed with nitrate or ammonium, were grown in growth chambers containing two levels of CO₂ (360 or 800 μl l⁻¹), three root temperatures (15, 20 or 25°C), and the same shoot temperature (20/24°C, night/day temperature). The response of the plants to CO₂ enrichment was affected by environmental factors such as the type of inorganic nitrogen in the medium and root temperature. Increasing root temperature enhanced photosynthesis rate more in the presence of nitrate than in the presence of ammonium. Differences in photosynthetic products were also observed between nitrate- and ammonium-fed carob seedlings. Nitrate-grown plants showed an enhanced content of sucrose, while ammonium led to enhanced storage of starch. Increase in root temperature caused an increase in dry mass of the plants of similar proportions in both nitrogen sources. The enhancement of the rates of photosynthesis by CO₂ enrichment was proportionally much larger than the resulting increases in dry mass production when nitrate was the nitrogen source. Ammonium was the preferred nitrogen source for carob at both ambient and high CO₂ concentrations. The level of photosynthesis of a plant is limited not only by atmospheric CO₂ concentration but also by the nutritional and environmental conditions of the root.     

Isolation and characterization of methanogenic bacteria from rice paddies

Abstract Enrichment cultures for H₂-CO₂, methanol- or acetate-utilizing methanogens were prepared from two rice field soil samples. All the cultures except one acetate enrichment showed significant methane production. Pure cultures of Methanobacterium - and Methanosarcina -like organisms were isolated from H₂-CO₂ and methanol enrichment cultures, respectively, and were characterized for various nutritional and growth conditions. The organisms had an optimal pH range of 6.4–6.6 and a temperature optimum of 37°C. The Methanobacterium isolates were able to utilize H₂-CO₂ but no other substrates as sole energy source, while the Methanosarcina isolates were able to utilize methanol, methylamines or H₂-CO₂ as sole energy sources. Both Methanobacterium isolates and one isolate of Methanosarcina were able to use dinitrogen as the sole source of nitrogen for growth. The isolates used several sulfur compounds as sole sources of sulfur.     

Na_2SeO_4对蛹虫草子实体生长的影响

蛹虫草是一种药食两用真菌,具有与冬虫夏草相似的功能,且富硒能力较强。本研究通过大量的人工栽培试验,旨在探究不同浓度Na_2SeO_4对新疆本地蛹虫草子实体生长的影响。试验表明,质量浓度为20 mg/L的Na_2SeO_4对蛹虫草的生长不产生显著影响,但蛹虫草各项生物学指标均随着培养基中外源Na_2SeO_4浓度的增加而呈下降趋势,说明随着外源Na_2SeO_4浓度的增加会对蛹虫草的生长产生抑制效应,当外源Na_2SeO_4质量浓度达到200 mg/L时,生产的蛹虫草已不具备商品价值。由此可见,20 mg/L的质量浓度是以Na_2SeO_4为硒源进行蛹虫草富硒研究的安全浓度。该研究为富硒产品开发寻找新的硒源开辟了新思路,为新疆地区进一步大规模栽培富硒蛹虫草提供一定的参考,但是对以Na_2SeO_4为硒源的最佳富硒浓度还有待于进一步研究。     

Effect of different carbon sources on community composition of bacterial enrichments from soil

Soil is a highly heterogeneous matrix, which can contain thousands of different bacterial species per gram. Only a small component of this diversity (maybe <1%) is commonly captured using standard isolation techniques, although indications are that a larger proportion of the soil community is in fact culturable. Better isolation techniques yielding greater bacterial diversity would be of benefit for understanding the metabolic activity and capability of many soil microorganisms. We studied the response of soil bacterial communities to carbon source enrichment in small matrices by means of terminal restriction fragment length polymorphism (TRFLP) analysis. The community composition of replicate enrichments from soil displayed high variability, likely attributable to soil heterogeneity. An analysis of TRFLP data indicated that enrichment on structurally similar carbon sources selected for similar bacterial communities. The same analysis indicated that communities first enriched on glucose or benzoate and subsequently transferred into medium containing an alternate carbon source retained a distinct community signature induced by the carbon source used in the primary enrichment. Enrichment on leucine presented a selective challenge that was able to override the imprint left by primary enrichment on acetate. In a time series experiment community change was most rapid 18 hours after inoculation, corresponding to exponential growth. Community composition did not stabilize even 4 days after secondary enrichment. Four different soil types were enriched on four different carbon sources. TRFLP analysis indicated that in three out of four cases communities enriched on the same carbon source were more similar regardless of which soil type was used. Conversely, the garden soil samples yielded similar enrichment communities regardless of the enrichment carbon source. Our results indicate that in order to maximize the diversity of bacteria recovered from the environment, multiple enrichments should be performed using a chemically diverse set of carbon sources.     

Effect of Different Carbon Sources on Community Composition of Bacterial Enrichments from Soil

Soil is a highly heterogeneous matrix, which can contain thousands of different bacterial species per gram. Only a small component of this diversity (maybe <1%) is commonly captured using standard isolation techniques, although indications are that a larger proportion of the soil community is in fact culturable. Better isolation techniques yielding greater bacterial diversity would be of benefit for understanding the metabolic activity and capability of many soil microorganisms. We studied the response of soil bacterial communities to carbon source enrichment in small matrices by means of terminal restriction fragment length polymorphism (TRFLP) analysis. The community composition of replicate enrichments from soil displayed high variability, likely attributable to soil heterogeneity. An analysis of TRFLP data indicated that enrichment on structurally similar carbon sources selected for similar bacterial communities. The same analysis indicated that communities first enriched on glucose or benzoate and subsequently transferred into medium containing an alternate carbon source retained a distinct community signature induced by the carbon source used in the primary enrichment. Enrichment on leucine presented a selective challenge that was able to override the imprint left by primary enrichment on acetate. In a time series experiment community change was most rapid 18 hours after inoculation, corresponding to exponential growth. Community composition did not stabilize even 4 days after secondary enrichment. Four different soil types were enriched on four different carbon sources. TRFLP analysis indicated that in three out of four cases communities enriched on the same carbon source were more similar regardless of which soil type was used. Conversely, the garden soil samples yielded similar enrichment communities regardless of the enrichment carbon source. Our results indicate that in order to maximize the diversity of bacteria recovered from the environment, multiple enrichments should be performed using a chemically diverse set of carbon sources.     

Investigation on the regulation of aniline utilization in Pseudomonas multivorans strain An 1

Summary Pseudomonas multivorans strain An 1 was isolated from forest soil after enrichment in a medium containing 0.1% aniline as the sole source of carbon and energy. Increasing aniline concentrations increasingly inhibited bacterial growth. At pH 7, aniline concentrations greater than 16mM were toxic enough to completely arrest growth. The optimal pH for growth on aniline was 6.5.On binary mixtures of aniline and additional carbon sources, diauxic growth was observed. The addition carbon sources caused various degrees of repression of the aniline catabolizing enzyme system. The fastest induction of this system occurred at pH 4, suggesting that protonization of the aniline molecule is crucial.     

Nitrogen Source Activates TOR (Target of Rapamycin) Complex 1 via Glutamine and Independently of Gtr/Rag Proteins

The evolutionary conserved TOR complex 1 (TORC1) activates cell growth in response to nutrients. In yeast, TORC1 responds to the nitrogen source via a poorly understood mechanism. Leucine, and perhaps other amino acids, activates TORC1 via the small GTPases Gtr1 and Gtr2, orthologs of the mammalian Rag GTPases. Here we investigate the activation of TORC1 by the nitrogen source and how this might be related to TORC1 activation by Gtr/Rag. The quality of the nitrogen source, as defined by its ability to promote growth and glutamine accumulation, directly correlates with its ability to activate TORC1 as measured by Sch9 phosphorylation. Preferred nitrogen sources stimulate rapid, sustained Sch9 phosphorylation and glutamine accumulation. Inhibition of glutamine synthesis reduces TORC1 activity and growth. Poor nitrogen sources stimulate rapid but transient Sch9 phosphorylation. A Gtr1 deficiency prevents the transient stimulation of TORC1 but does not affect the sustained TORC1 activity in response to good nitrogen sources. These findings suggest that the nitrogen source must be converted to glutamine, the preferred nitrogen source in yeast, to sustain TORC1 activity. Furthermore, sustained TORC1 activity is independent of Gtr/Rag. Thus, the nitrogen source and Gtr/Rag activate TORC1 via different mechanisms.     

Effects of CO2 enrichment on mineral accumulation and nitrogen relations in a submersed macrophyte

1. Six- to eight-week greenhouse experiments with independent control of pH and dissolved CO₂ evaluated the potential for CO₂ enrichment to stimulate the accumulation of Al, Fe, P and N in shoots of Vallisneria americana , particularly at pH 5. These minerals were provided only as they occurred in natural lake sediments.
2. The effect of CO₂ enrichment at pH 5 v pH 7.3 on growth and tissue N concentration was also determined.
3. CO₂ enrichment at pH 5 effected 5.5- and 7-fold increases in total shoot accumulation of Al and Fe, respectively. In a two-way factorial experiment, CO₂ enrichment yielded 6- to 11-fold greater total shoot P accumulation in plants grown on less and more fertile sediments, respectively.
4. In a three-way factorial experiment, CO₂ enrichment stimulated Vallisneria growth, especially at pH 5, and resulted in a 31–58% reduction in tissue [N] for different pH × sediment combinations. These are greater reductions than previously reported. It also increased total shoot N accumulation up to 6-fold, and there were significant interactions with pH and sediment source: the CO₂ enrichment effect on shoot N accumulation was greater at pH 5 than at pH 7.3, and it was greater with the more fertile sediment at pH 5.
5. Water chemistry (pH and/or [CO₂]) and sediment fertility thus both indirectly influenced the accumulation of sediment-derived minerals in macrophyte shoots within the water column.     

Effects of CO2 enrichment on mineral accumulation and nitrogen relations in a submersed macrophyte

1. Six- to eight-week greenhouse experiments with independent control of pH and dissolved CO₂ evaluated the potential for CO₂ enrichment to stimulate the accumulation of Al, Fe, P and N in shoots of Vallisneria americana , particularly at pH 5. These minerals were provided only as they occurred in natural lake sediments.
2. The effect of CO₂ enrichment at pH 5 v pH 7.3 on growth and tissue N concentration was also determined.
3. CO₂ enrichment at pH 5 effected 5.5- and 7-fold increases in total shoot accumulation of Al and Fe, respectively. In a two-way factorial experiment, CO₂ enrichment yielded 6- to 11-fold greater total shoot P accumulation in plants grown on less and more fertile sediments, respectively.
4. In a three-way factorial experiment, CO₂ enrichment stimulated Vallisneria growth, especially at pH 5, and resulted in a 31–58% reduction in tissue [N] for different pH × sediment combinations. These are greater reductions than previously reported. It also increased total shoot N accumulation up to 6-fold, and there were significant interactions with pH and sediment source: the CO₂ enrichment effect on shoot N accumulation was greater at pH 5 than at pH 7.3, and it was greater with the more fertile sediment at pH 5.
5. Water chemistry (pH and/or [CO₂]) and sediment fertility thus both indirectly influenced the accumulation of sediment-derived minerals in macrophyte shoots within the water column.     

Mineralization of Trichloroethylene by Heterotrophic Enrichment Cultures

Microbial consortia capable of aerobically degrading more than 99% of exogenous trichloroethylene (TCE) (50 mg/liter) were collected from TCE-contaminated subsurface sediments and grown in enrichment cultures. TCE at concentrations greater than 300 mg/liter was not degraded, nor was TCE used by the consortia as a sole energy source. Energy sources which permitted growth included tryptone-yeast extract, methanol, methane, and propane. The optimum temperature range for growth and subsequent TCE consumption was 22 to 37°C, and the pH optimum was 7.0 to 8.1. Utilization of TCE occurred only after apparent microbial growth had ceased. The major end products recovered were hydrochloric acid and carbon dioxide. Minor products included dichloroethylene, vinylidine chloride, and, possibly, chloroform.     

Effect of Carbon and Energy Source on Bacterial Chromate Reduction

Studies were conducted to evaluate carbon and energy sources suitable to support hexavalent chromium (Cr(VI)) reduction by a bacterial consortium enriched from dichromate-contaminated aquifer sediments. The consortium was cultured under denitrifying conditions in a minimal, synthetic groundwater medium that was amended with various individual potential carbon and energy sources. The effects of these individual carbon and energy sources on Cr(VI) reduction and growth were measured. The consortium was found to readily reduce Cr(VI) with sucrose, acetate, L-asparagine, hydrogen plus carbon dioxide, ethanol, glycerol, glycolate, propylene glycol, or D-xylose as a carbon and energy source. Minimal Cr(VI) reduction was observed when the consortium was cultured with citrate, 2-ketoglutarate, L-lactate, pyruvate, succinate, or thiosulfate plus carbon dioxide as a carbon and energy source when compared with abiotic controls. The consortium grew on all of the above carbon and energy sources, with the highest cell densities reached using D-xylose and sucrose, demonstrating that the consortium is metabolically diverse and can reduce Cr(VI) using a variety of different carbon and energy sources. The results suggest that the potential exists for the enrichment of Cr(VI)-reducing microbial populations in situ by the addition of a sucrose-containing feedstock such as molasses, which is an economical and readily available carbon and energy source.     

A simple cultural method for the presumptive detection of the yeasts Brettanomyces/Dekkera in wines

AIMS: The development of a simple and reliable procedure, compatible with routine use in wineries, for the presumptive detection of Brettanomyces/Dekkera from wine and wine-environment samples. METHODS AND RESULTS: The method of detection of these yeasts employs a selective enrichment medium. The medium contains glucose (10 g l(-1)) as carbon and energy source, cycloheximide (20 mg l(-1)) to prevent growth of Saccharomyces, chloramphenicol (200 mg l(-1)) to prevent growth of bacteria and p-coumaric acid (20 mg l(-1)) as the precursor for the production of 4-ethyl-phenol. After the inoculation with wine, the medium is monitored by visual inspection of turbidity and by periodic olfactive analysis. Contaminated wines will develop visible turbidity in the medium and will produce the 4-ethyl-phenol off-odour, which can be easily detected by smelling. CONCLUSIONS: A selective enrichment liquid medium was developed to differentially promote the growth and activity of Brettanomyces/Dekkera. The method is simple to execute, employing a simple-to-prepare medium and a periodic olfactive detection. SIGNIFICANCE AND IMPACT OF THE STUDY: The characteristics of the procedure make it particularly applicable in a wine-making environment thus presenting important advantages to the wine industry.     

Inhibition of photosynthesis and export in geranium grown at two CO2 levels and infected with Xanthomonas campestris pv. Pelargonii

The effects of CO₂ enrichment on growth of Xanthomonas campestris pv. pelargonii and the impact of infection on the photosynthesis and export of attached, intact, 'source' leaves of geranium ( Pelargonium x domesticum, 'Scarlet Orbit Improved' ) are reported. Two experiments were performed, one with plants without flower buds, and another with plants which were flowering. Measurements were made on healthy and diseased leaves at the CO₂ levels (35 Pa or 90 Pa) at which the plants were grown. There were no losses of chlorophyll, or any signs of visible chlorosis or necrosis due to infection. Lower numbers of bacteria were found in leaves at high CO₂, suggesting growth at elevated CO₂ created a less favourable condition in the leaf for bacterial growth. Although high CO₂ lowered the bacterial number in infected leaves, reductions in photosynthesis and export were greater than at ambient CO₂. The capacity of infected source leaves to export photoassimilates at rates observed in the controls was reduced in both light and darkness. In summary, the severity of infection on source leaf function by the bacteria was increased, rather than reduced by CO₂ enrichment, underscoring the need for further assessment of plant diseases and bacterial virulence in plants growing under varying CO₂ levels.     

Degradation of pyrimidine ribonucleosides by Pseudomonas aeruginosa

Pyrimidine ribonucleoside degradation in the human pathogen Pseudomonas aeruginosa ATCC 15692 was investigated. Either uracil, cytosine, 5-methylcytosine, thymine, uridine or cytidine supported P. aeruginosa growth as a nitrogen source when glucose served as the carbon source. Using thin-layer chromatographic analysis, the enzymes nucleoside hydrolase and cytosine deaninase were shown to be active in ATCC 15692. Compared to (NH₄)₂SO₄-grown cells, nucleoside hydrolase activity in ATCC 15692 approximately doubled after growth on 5-methylcytosine as a nitrogen source while its cytosine deaminase activity increased several-fold after growth on the pyrimidine bases and ribonucleosides examined as nitrogen sources. Regulation at the level of protein synthesis by 5-methylcytosine was indicated for nucleoside hydrolase and cytosine deaminase in P. aeruginosa.     

Growth and sporulation of Entomophthora virulenta on semidefined media in liquid culture

Entomophthora virulenta was tested for growth and sporulation under various nutritional conditions in shake cultures containing combinations of dextrose and protein hydrolysates. Darkness, a temperature of 25°C, and a pH near 6.5 induced the formation of the greatest number of zygospores when the carbon and nitrogen sources were held constant. The influence of the total concentration of nutrients and of the ratio of the carbon and nitrogen sources depended on the nitrogen source used: The highest amount of spores under these conditions was produced with yeast extract as nitrogen source, a carbon/nitrogen source ratio of 2, and a 15% total nutrient concentration. The influence of the preinoculum and inoculum on sporulation is discussed.     

Toxic effects of toluene on the growth of activated sludge bacteria

Two bacteria were isolated from the activated sludge sample of a wastewater treatment plant in Dublin by enrichment culture technique with toluene as the sole source of carbon and energy. They were identified as Aeromonas caviae (To-4) and Pseudomonas putida (To-5). The growth of these bacteria depended on the manner in which toluene was supplied. In general, growth was better when toluene was supplied in the vapour phase. When toluene was added directly to the growth medium it was found to be toxic to the organisms but the toxic effect could be alleviated in the presence of other carbon sources and by the acclimation of the cells. The growth of To-4 on toluene has never been previously reported.     

CO2 enrichment of soybeans. Effects of leaf/pod ratio

The effect of varying leaf number on response of soybean ( Glycine max (L.) Merr. cv. Fiskeby V) to CO₂ enrichment was studied. Plants were trimmed at pod set to 15 pods and 1 or 3 leaves (15:1 and 5:1 pod/leaf ratio) and placed in 350 or 1000 μl/l CO₂ growth chambers. Photosynthetic rates and dry weights were measured 6 times in all plants at each CO₂ concentration over a period of 39 days. Measured at treatment CO₂ concentration, photosynthetic rates deelined rapidly in enriched plants, but remained higher than those of non-enriched plants. When all plants were measured at the same CO₂ concentration, for most sampling dates, neither growth, CO₂ concentration or pod/leaf ratio significantly affected rates of photosynthesis per unit area of comparable leaves. CO₂ enrichment significantly increased total weights and pod weights in 15:1 but not 5:1 pod/leaf ratio plants. Plants with a 5:1 pod/leaf ratio had significantly higher total and pod weights than 15:1 ratio plants. Both the photosynthesis and dry weight data suggest that plants in the 5:1 ratio enriched treatment were sink-limited, but plants in all other treatments were source limited.     

Activity of sulfate-reducing bacteria in human periodontal pocket

Samples of subgingival dental tissues were examined for the presence of sulfate-reducing bacteria (SRB). Using enrichment cultures, SRBs were detected in 9 of 17 individuals. A pure culture of SRB was obtained from one sample collected from a patient with type IV periodontal disease. The characterization of this isolate showed that it belongs to the genus Desulfovibrio. The isolate used pyruvate, lactate, glucose, fructose, and ethanol as the sole source of carbon. However, the isolate was unable to use acetate and methanol as a carbon source, indicating it as an incomplete oxidizer unable to carry out the terminal oxidation of substrates. Apart from using sulfate as electron acceptor, the isolate also used thiosulfate and nitrate as an electron acceptor. It has the ability to use a variety of nitrogen sources, including ammonium chloride, nitrate, and glutamate. The optimum growth temperature of the isolate was 37 degrees C and the optimum pH for growth was 6.8. The SRB isolate contained the electron carrier desulfoviridin. The numbers of SRB in the mouth are assumed to be limited by sulfate. Potential sources of sulfate in the subgingival area include free sulfate in pocket fluid and glycosaminoglycans and sulfur-containing amino acids from periodontal tissues.     

Biodegradation of 1,4-dioxane and transformation of related cyclic compounds by a newly isolated Mycobacterium sp. PH-06

A new bacterial strain PH-06 was isolated using enrichment culture technique from river sediment contaminated with 1,4-dioxane, and identified as belonging to the genus Mycobacterium based on 16S rRNA sequencing (Accession No. EU239889). The isolated strain effectively utilized 1,4-dioxane as a sole carbon and energy source and was able to degrade 900 mg/l 1,4-dioxane in minimal salts medium within 15 days. The key degradation products identified were 1,4-dioxane-2-ol and ethylene glycol, produced by monooxygenation. Degradation of 1,4-dioxane and concomitant formation of metabolites were demonstrated by GC/MS analysis using deuterium labeled 1,4-dioxane (1,4-dioxane-d8). In addition to 1,4-dioxane, this bacterium could also transform structural analogues such as 1,3-dioxane, cyclohexane and tetrahydrofuran when pre-grown with 1,4-dioxane as the sole growth substrate. Our results suggest that PH-06 can maintain sustained growth on 1,4-dioxane without any other carbon sources.     

氮源及碳氮比对产朊假丝酵母合成谷胱甘肽的影响

研究了N源对产朊假丝酵母细胞生长和谷胱甘肽(GSH)合成的影响。在此基础上,分别以(NH4)2SO4和尿素作为单一N源,摇瓶条件下研究了不同C、N比对GSH发酵的影响。结果发现尿素有利于细胞生长,而(NH4)2SO4更有利于GSH的合成,并且酵母细胞在利用这2种N源合成GSH时,各自具有最佳的C、N比((NH4)2SO4为8.3 mol/mol,尿素为5.6 mol/mol)。最佳C、N比下的GSH分批发酵结果显示,尿素是更合适的N源,最终细胞干质量和GSH产量可以分别达到16.48 g/L和246.4 mg/L。最后分别采用发酵动力学模型和代谢网络分析对该结果产生的原因进行了定量解释。