Biosynthesis of Natural Flavanones in Saccharomyces cerevisiae

A four-step flavanone biosynthetic pathway was constructed and introduced into Saccharomyces cerevisiae. The recombinant yeast strain was fed with phenylpropanoid acids and produced the flavanones naringenin and pinocembrin 62 and 22 times more efficiently compared to previously reported recombinant prokaryotic strains. Microbial biosynthesis of the flavanone eriodictyol was also achieved.     

Effect of Low pH and Aluminum Toxicity on the Photosynthetic Characteristics of Different Fast-Growing Eucalyptus Vegetatively Propagated Clones

Knowing how acid soils and aluminum in soils may limit the growth of Eucalyptus trees in plantations is important because these plantations grow in many tropical and subtropical regions. Seedlings of four vegetatively propagated Eucalyptus clones, E. grandis × E. urophylla ‘GLGU9’(G9), E. grandis × E. urophylla ‘GLGU12’ (G12), E. urophylla × E. camaldulensis ‘GLUC3’ (G3) and E. urophylla ‘GLU4’(G4), were subjected to liquid culture with Hoagland nutrient solution for 40 days, then treated with four different treatments of acid and aluminum for 1 day. The four treatments used either pH 3.0 or 4.0 with or without added aluminum (4.4 mM) in all possible combinations; a control used no added aluminum at pH 4.8. Subsequently, the photosynthetic parameters and morphology of leaves from eucalypt seedlings were determined and observed. The results showed that the tested chlorophyll content, net photosynthetic rate, transpiration rate and water use efficiency were apparently inhibited by aluminum. Under uniform Al concentration (4.4 mM), the Al-induced limitation to photosynthetic parameters increased with pH, indicating acid stimulation to Al toxicity. Among all treatments, the most significant reduction was found in the combination of pH 3.0 and 4.4 mM Al. The photosynthetic and transpiration rates showed similar trends with G9 > G12 > G3 > G4, suggesting that G9 and G12 had higher Al-tolerance than other two clones. Microscopic observation revealed changes in leaf morphology when exposed to Al stress; for example, a reduced thickness of leaf epidermis and palisade tissue, the descendant palisade tissue/spongy tissue ratio and leaf tissue looseness. Overall, the acid and aluminum stress exerted negative effects on the photosynthetic activity of eucalypt seedlings, but the differences in tolerance to Al toxicity between the clones were favorable, offering potential to improve Eucalyptus plantation productivity by selecting Al tolerant clones.     

Cyanogenic polymorphism in Eucalyptus polyanthemos Schauer subsp. vestita L. Johnson and K. Hill (Myrtaceae)

Plant cyanogenesis, the release of cyanide from endogenous cyanide-containing compounds, is an effective herbivore deterrent. This paper characterises cyanogenesis in the Australian tree Eucalyptus polyanthemos Schauer subsp. vestita L. Johnson and K. Hill for the first time. The cyanogenic glucoside prunasin ((R)-mandelonitrile β-D-glucoside) was determined to be the only cyanogenic compound in E. polyanthemos foliage. Two natural populations of E. polyanthemos showed quantitative variation in foliar prunasin concentration, varying from zero (i.e. acyanogenic) to 2.07 mg CN g^-1 dry weight in one population and from 0.17 to 1.98 mg CN g^-1 dry weight in the other. No significant difference was detected between the populations with respect to the mean prunasin concentration or the degree of variation in foliar prunasin, despite significant differences in foliar nitrogen. Variation between individuals was also observed with respect to the capacity of foliage to catabolise prunasin to form cyanide. Moreover, variation in this capacity generally correlated with the amount of prunasin in the tissue, suggesting genetic linkage between prunasin and β-glucosidase.     

Stable carbon and nitrogen isotope ratios of Eucalyptus and Acacia species along a seasonal rainfall gradient in Western Australia

Key message

Eucalyptus and Acacia species were surprisingly similar with respect to variations in δ ¹³ C, δ ¹⁵ N. Both genera respond with speciation and associated changes in leaf structure to drought.

Abstract

Stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) in leaves of eucalypts (Corymbia and Eucalyptus) and Acacia (and some additional Fabaceae) species were investigated together with specific leaf area (SLA), leaf nitrogen (N) and leaf phosphorous (P) concentration along a north–south transect through Western Australia covering winter- and summer-dominated rainfall between 100 and 1,200 mm annually. We investigated 62 eucalypts and 78 woody Fabaceae species, mainly of the genus Acacia. Leaf δ¹³C values of Eucalyptus and Acacia species generally increased linearly with latitude from ?29.5 ± 1.3 ‰ in the summer-dominated rainfall zone (15°S–18°S) to about ?25.7 ± 1.1 ‰ in the winter-dominated rainfall zone (29°S–31°S). δ¹⁵N increased initially with southern latitudes (0.5 ± 1.6 ‰ at 15°S; 5.8 ± 3.3 ‰ at 24–29°S) but decreased again further South (4.6 ± 3.5 ‰ at 31°S). The variation in δ¹³C and δ¹⁵N was probably due to speciation of Eucalyptus and Acacia into very local populations. There were no species that were distributed over the whole sampling area. The variation in leaf traits was larger between species than within species. Average nitrogen concentrations were 11.9 ± 1.05 mg g^?1 in Eucalyptus, and were 18.7 ± 4.1 mg g^?1 in Acacia. Even though the average nitrogen concentration was higher in Acacia than Eucalyptus, δ¹⁵N gave no clear indication for N₂ fixation in Acacia. In a multiple regression, latitude (as a surrogate for rainfall seasonality), mean rainfall, leaf nitrogen concentration, specific leaf area and nitrogen fixation were significant and explained 69 % of the variation of δ¹³C, but only 36 % of the variation of δ¹⁵N. Higher nitrogen and phosphorus concentration could give Acacia an advantage over Eucalyptus in arid regions of undefined rainfall seasonality.     

Topographical influences on foliar nitrogen concentration and stable isotope composition in a Mediterranean-climate catchment

Nitrogen (N) oligotrophication is increasing globally across terrestrial ecosystems and manifested in decreasing nitrogen concentration ([N]) and changes in the stable nitrogen isotope composition (δ¹⁵N) of foliage. Heterogeneity in plant nitrogen sources makes it challenging to detect the effects of N oligotrophication even at a small catchment scale with complex topography. Understanding the spatial and temporal variation of foliar δ¹⁵N and [N] at such a scale is required to develop useful ecological indicators and monitoring methods to support catchment management with a potential N oligotrophication problem. This study examined spatial and high-resolution temporal variation of foliar δ¹⁵N and [N] and their influencing factors in ten trees grouped by Eucalyptus and Acacia in a native forest vegetation catchment. Over 16 sampling campaigns within a 12-month period, foliar δ¹⁵N and [N] increased in Eucalyptus but were constant in the N₂-fixing Acacia. The higher foliar [N] and δ¹⁵N in Acacia reflected its N₂-fixation ability. Topographic flow accumulation area (NDVI) explained 46% (77%) of spatial variation in dry-season Eucalyptus foliar δ¹⁵N ([N]). For Eucalyptus, foliar δ¹⁵N was higher at the downslope than the upslope locations, but no hillslope location differences were observed for foliar [N]. These results suggest that in the non-N₂-fixing Eucalyptus, seasonal water stress related nitrogen availability may be reflected in foliar δ¹⁵N rather than foliar [N]. As such, foliar δ¹⁵N of non-N₂-fixing plants potentially is a more sensitive indicator of seasonal or topographical N availability than foliar [N].     

华南十种桉树的热值与灰分含量比较

桉树是林业生物质能源的原料之一,了解桉树的热值和灰分含量能为合理利用桉树能源林提供理论参考。该研究采用热量计和马福炉对华南尾巨桉等10种桉树的不同器官进行热值和灰分含量测定。结果表明：10种桉树树叶、树枝、树根、树干和树皮的干质量热值、去灰分热值分别为15.10~21.06 kJ.g-1和16.50~22.11 kJ.g-1,器官的平均干质量热值、去灰分热值以树叶最高(19.50和20.56 kJ.g-1)、树皮的最低(17.32和18.09 kJ.g-1),说明树叶所含的高能有机物质比其它器官多;不同器官的干质量热值与去灰分热值在不同品种中的大小排序不完全一致。灰分含量在0.14％~8.5％之间,器官平均的灰分含量以树叶最高(5.13％)、树干最低(0.30％),说明树叶所含的矿质元素较多。不同器官的热值与灰分含量均差异显著(P<0.05)。植株个体的干质量热值与去灰分热值均以尾叶桉最高(18.99和19.18 kJ.g-1),以托里桉最低(17.53和17.86 kJ.g-1);灰分含量则以托里桉最高(1.90％)、巨桉最低(0.61％)。相关分析结果表明,灰分含量与干质量热值、去灰分热值存在一定的负相关,但未达显著水平;干质量热值与去灰分热值呈极显著的正相关关系(P<0.01)。由于理想的植物燃料应具备热值高与灰分含量低的特点,结合该研究的结果分析,托里桉作为燃料资源利用不理想,以尾叶桉较为适宜。     

Naringin levels in citrus tissues : I. Comparison of different antibodies and tracers for the radioimmunossay of naringin

The preparation of a tritiated radiotracer that was used in the radioimmunoassay of naringin (naringenin-7-O-α-rhamnosyl- (1-2)-β-d-glucopyranoside) and which was synthesized by reduction of the carbonyl group of the flavanone is reported. The resulting assay has a detection limit of 0.5 picomole per 0.1 milliliter, is specific for the 7-neohesperidoside substitution on flavanones, and can measure naringin in crude extracts of plant tissues. This radioimmunoassay is compared with three other naringin immunoassays which use antibodies raised against two different haptens and different tracers labeled with ¹²⁵I or ³H. The applicability of the methods to the quantification of naringin and other flavanone neohesperidosides in citrus tissue is discussed.     

Chemical composition and antibacterial activities of seven Eucalyptus species essential oils leaves

Background

In this paper, we have studied the essential oils chemical composition of the leaves of seven Eucalyptus species developed in Tunisia. Eucalyptus leaves were picked from trees growing in different arboretums in Tunisia. Choucha and Mrifeg arboretums located in Sedjnene, region of Bizerte (Choucha: E. maideni, E. astrengens et E. cinerea; Mrifeg : E. leucoxylon), Korbous arboretums located in the region of Nabeul, North East Tunisia with sub-humid bioclimate, (E. lehmani), Souiniet-Ain Drahem arboretum located in region of Jendouba (E. sideroxylon, E. bicostata). Essential oils were individually tested against a large panel of microorganisms including Staphylococcus aureus (ATCC 6539), Escherichia coli (ATCC 25922), Enterococcus faecalis (ATCC29212), Listeria ivanovii (RBL 30), Bacillus cereus (ATCC11778).

Results

The yield of essential oils ranged from 1.2% to 3% (w/w) for the different Eucalyptus species. All essential oils contain α-pinene, 1,8-cineol and pinocarveol-trans for all Eucalyptus species studied. The 1,8-cineol was the major compound in all species (49.07 to 83.59%). Diameter of inhibition zone of essential oils of Eucalyptus species varied from 10 to 29 mm. The largest zone of inhibition was obtained for Bacillus cereus (E. astrengens) and the lowest for Staphylococcus aureus (E. cinerea). The essential oils from E. maideni, E. astrengens, E. cinerea (arboretum of Bizerte), E. bicostata (arboretum of Aindraham) showed the highest antibacterial activity against Listeria ivanovii and Bacillus cereus.

Conclusion

The major constituents of Eucalyptus leaves essential oils are 1,8-cineol (49.07 to 83.59%) and α-pinene (1.27 to 26.35%). The essential oils from E. maideni, E. astrengens, E. cinerea, E. bicostata showed the highest antibacterial activity against Listeria ivanovii and Bacillus cereus, they may have potential applications in food and pharmaceutical products.     

Salt tolerant screening in eucalypt genotypes (Eucalyptus spp.) using photosynthetic abilities, proline accumulation, and growth characteristics as effective indices

Eucalypts are highly regarded plantation trees due to their fast growing nature, high water consumption, tolerance to abiotic stresses, and ease of conversion to pulp and paper. We screened five genotypes of Eucalyptus camaldulensis (T5, BD4, 1-7-1, H1, and SH4) and three genotypes of the E. camaldulensis × Eucalyptus urophylla hybrid (H4, 58H2, and 27A2) for salt tolerance. Fresh weight and leaf area in hybrid genotypes (H4, 58H2, and 27A2) were greater than those in the E. camaldulensis population after plantlets were subjected to 200 mM NaCl for 14 d. The chlorophyll a content in hybrid genotypes decreased by 19.71–37.11% compared to 51.45–66.00% decline in E. camaldulensis. Similarly, total chlorophyll content was retained at a high level in the hybrid population, leading to stabilization of the net photosynthetic rate. The amount of proline, an osmolyte, was significantly increased in all Eucalyptus genotypes when exposed to 200 mM NaCl. Multivariate analyses of proline accumulation, photosynthetic pigment degradation, diminishing chlorophyll fluorescence, P _n reduction, and growth inhibition in salt-stressed plantlets of Eucalyptus genotypes were performed to classify salt-tolerant- and salt-sensitive groupings. The hybrid eucalypt genotypes H4, 58H2, and 27A2 were identified as salt tolerant while the selection genotypes of E. camaldulensis, T5, BD4, 1-7-1, H1, and SH4, were classified as salt susceptible.     

Biosynthesis of natural flavanones in Saccharomyces cerevisiae

A four-step flavanone biosynthetic pathway was constructed and introduced into Saccharomyces cerevisiae. The recombinant yeast strain was fed with phenylpropanoid acids and produced the flavanones naringenin and pinocembrin 62 and 22 times more efficiently compared to previously reported recombinant prokaryotic strains. Microbial biosynthesis of the flavanone eriodictyol was also achieved.     

Relationships between C3 Plant Foliar Carbon Isotope Composition and Element Contents of Grassland Species at High Altitudes on the Qinghai-Tibet Plateau,China

Relationships of foliar carbon isotope composition (δ¹³C) with foliar C, N, P, K, Ca, Mg contents and their ratios of 219 C₃ species leaf samples, obtained in August in 2004 to 2007 from 82 high altitude grassland sites on the Qinghai-Tibet Plateau China, were examined. This was done with reference to the proposition that foliar δ¹³C increases with altitude and separately for the life-form groups of graminoids, forbs and shrubs and for the genera Stipa and Kobresia. For all samples, foliar δ¹³C was negatively related to foliar K, P and ∑_{K+ Ca+ Mg}, and positively correlated to foliar C, C/N and C/P. The significance of these correlations differed for the taxonomic and life-form groups. Lack of a relationship of foliar δ¹³C with foliar N was inconsistent with the majority of studies that have shown foliar δ¹³C to be positively related to foliar N due to a decrease of C_i/C_a (the ratio between intercellular and atmospheric concentration of CO₂) and explained as a result of greater photosynthetic capacity at higher foliar N concentration. However this inconsistency relates to other high altitude studies that have found that photosynthetic capacity remains constant as foliar N increases. After accounting for the altitudinal relationship with foliar δ¹³C, of the elements only the K effect was significant and was most strongly expressed for Kobresia. It is concluded that factors critical to plant survival and growth at very high altitudes, such as low atmospheric pressure and low temperatures, may preclude expression of relationships between foliar δ¹³C and foliar elements that have been observed at lower altitudes.     

The Relative Concentrations of Nutrients and Toxins Dictate Feeding by a Vertebrate Browser,the Greater Glider Petauroides volans

Although ecologists believe that vertebrate herbivores must select a diet that allows them to meet their nutritional requirements, while avoiding intoxication by plant secondary metabolites, this is remarkably difficult to show. A long series of field and laboratory experiments means that we have a good understanding of the factors that affect feeding by leaf-eating marsupials. This knowledge and the natural intraspecific variation in Eucalyptus chemistry allowed us to test the hypothesis that the feeding decisions of greater gliders (Petauroides volans) depend on the concentrations of available nitrogen (incorporating total nitrogen, dry matter digestibility and tannins) and of formylated phloroglucinol compounds (FPCs), potent antifeedants unique to Eucalyptus. We offered captive greater gliders foliage from two species of Eucalyptus, E. viminalis and E. melliodora, which vary naturally in their concentrations of available nitrogen and FPCs. We then measured the amount of foliage eaten by each glider and compared this with our laboratory analyses of foliar total nitrogen, available nitrogen and FPCs for each tree offered. The concentration of FPCs was the main factor that determined how much gliders ate of E. viminalis and E. melliodora, but in gliders fed E. viminalis the concentration of available nitrogen was also a significant influence. In other words, greater gliders ate E. viminalis leaves with a particular combination of FPCs and available nitrogen that maximised the nutritional gain but minimised their ingestion of toxins. In contrast, the concentration of total nitrogen was not correlated with feeding. This study is among the first to empirically show that browsing herbivores select a diet that balances the potential gain (available nutrients) and the potential costs (plant secondary chemicals) of eating leaves. The major implication of the study is that it is essential to identify the limiting nutrients and relevant toxins in a system in order to understand feeding behaviour.     

Engineering Central Metabolic Pathways for High-Level Flavonoid Production in Escherichia coli

The identification of optimal genotypes that result in improved production of recombinant metabolites remains an engineering conundrum. In the present work, various strategies to reengineer central metabolism in Escherichia coli were explored for robust synthesis of flavanones, the common precursors of plant flavonoid secondary metabolites. Augmentation of the intracellular malonyl coenzyme A (malonyl-CoA) pool through the coordinated overexpression of four acetyl-CoA carboxylase (ACC) subunits from Photorhabdus luminescens (PlACC) under a constitutive promoter resulted in an increase in flavanone production up to 576%. Exploration of macromolecule complexes to optimize metabolic efficiency demonstrated that auxiliary expression of PlACC with biotin ligase from the same species (BirA_Pl) further elevated flavanone synthesis up to 1,166%. However, the coexpression of PlACC with Escherichia coli BirA (BirA_Ec) caused a marked decrease in flavanone production. Activity improvement was reconstituted with the coexpression of PlACC with a chimeric BirA consisting of the N terminus of BirA_Ec and the C terminus of BirA_Pl. In another approach, high levels of flavanone synthesis were achieved through the amplification of acetate assimilation pathways combined with the overexpression of ACC. Overall, the metabolic engineering of central metabolic pathways described in the present work increased the production of pinocembrin, naringenin, and eriodictyol in 36 h up to 1,379%, 183%, and 373%, respectively, over production with the strains expressing only the flavonoid pathway, which corresponded to 429 mg/liter, 119 mg/liter, and 52 mg/liter, respectively.     

Measurement of Leaf Hydraulic Conductance and Stomatal Conductance and Their Responses to Irradiance and Dehydration Using the Evaporative Flux Method (EFM)

Water is a key resource, and the plant water transport system sets limits on maximum growth and drought tolerance. When plants open their stomata to achieve a high stomatal conductance (g_s) to capture CO₂ for photosynthesis, water is lost by transpiration^1,2. Water evaporating from the airspaces is replaced from cell walls, in turn drawing water from the xylem of leaf veins, in turn drawing from xylem in the stems and roots. As water is pulled through the system, it experiences hydraulic resistance, creating tension throughout the system and a low leaf water potential (Ψ_leaf). The leaf itself is a critical bottleneck in the whole plant system, accounting for on average 30% of the plant hydraulic resistance³. Leaf hydraulic conductance (K_leaf = 1/ leaf hydraulic resistance) is the ratio of the water flow rate to the water potential gradient across the leaf, and summarizes the behavior of a complex system: water moves through the petiole and through several orders of veins, exits into the bundle sheath and passes through or around mesophyll cells before evaporating into the airspace and being transpired from the stomata. K_leaf is of strong interest as an important physiological trait to compare species, quantifying the effectiveness of the leaf structure and physiology for water transport, and a key variable to investigate for its relationship to variation in structure (e.g., in leaf venation architecture) and its impacts on photosynthetic gas exchange. Further, K_leaf responds strongly to the internal and external leaf environment³. K_leaf can increase dramatically with irradiance apparently due to changes in the expression and activation of aquaporins, the proteins involved in water transport through membranes⁴, and K_leaf declines strongly during drought, due to cavitation and/or collapse of xylem conduits, and/or loss of permeability in the extra-xylem tissues due to mesophyll and bundle sheath cell shrinkage or aquaporin deactivation^5-10. Because K_leaf can constrain g_s and photosynthetic rate across species in well watered conditions and during drought, and thus limit whole-plant performance they may possibly determine species distributions especially as droughts increase in frequency and severity^11-14.We present a simple method for simultaneous determination of K_leaf and g_s on excised leaves. A transpiring leaf is connected by its petiole to tubing running to a water source on a balance. The loss of water from the balance is recorded to calculate the flow rate through the leaf. When steady state transpiration (E, mmol • m^-2 • s^-1) is reached, g_s is determined by dividing by vapor pressure deficit, and K_leaf by dividing by the water potential driving force determined using a pressure chamber (K_leaf= E /- Δψ_leaf, MPa)¹⁵.This method can be used to assess K_leaf responses to different irradiances and the vulnerability of K_leaf to dehydration^14,16,17.     

Regeneration and transformation of Eucalyptus camaldulensis

Reliable regeneration protocols for Eucalyptus camaldulensis using leaf explants from in vitro-grown plants have been developed. Out of the 24 clones tested 13 were regenerated and of these, 6 showed regeneration from more than 60% of the explants. Identical protocols were also successful in the regeneration of some clones of E. microtheca, E. ochrophloia, E. grandis and E. marginata, but at lower frequencies. Co-cultivation of E. camaldulensis leaf explants with Agrobacterium tumefaciens strains carrying a kanamycin resistance gene and the reporter gene β-glucuronidase (GUS), followed by selection on kanamycin at 9 mg l^–1, allowed the selection of transformed shoots that could be rooted on selective media. Transformation of the plants was verified by staining for the GUS enzyme in various plant tissues, NptII assays and by Southern blotting on isolated DNA using specific probes for both the GUS and selectable marker genes. Transformed tissue was obtained with 5 clones of E. camaldulensis tested and a number of A. tumefaciens strains. However, only 1 clone regenerated transformed whole plants reliably. Received: 14 October 1996 / Revision received: 18 February 1997 / Accepted: 1 April 1997     

Suitability of Eucalyptus and Corymbia for Mnesampela privata (Guenée) (Lepidoptera: Geometridae) larvae

Abstract 1 Mnesampela privata (Guenée) has a host list of 40 Eucalyptus and at least one Corymbia species. Larval survival and performance was studied on 19 species to investigate how certain leaf traits influence the suitability of different species. 2 After 7 days, survival on Eucalyptus aggregata and Eucalyptus camphora is greater than 70% even though the toughness of leaves is 0.15–0.19 mg/mm². However, after the same time, survival on genotypes of Eucalyptus melliodora and Eucalyptus sideroxylon was less than 60%, or even 0%, even though the toughness of some leaves was as low as 0.11 mg/mm². An unmeasured allelochemical, rather than toughness, may reduce survival on these species. 3 Dry weights of first‐instar larvae were negatively correlated with leaf toughness for 13 of the species studied. Species that produced the heaviest first‐instar larvae were not the same hosts that produced the heaviest second‐instar larvae. 4 Dry weights of female pupae were negatively correlated with total oil content for five of the species studied. 5 Larvae exhibit age‐related changes in feeding behaviour. Neonates skeletonize leaves (avoid leaf veins and oil glands) and post‐third‐instar larvae ingest whole leaf fragments (consume small leaf veins and oil glands). These findings suggest that neonates are sensitive to high leaf toughness and non‐oil plant secondary metabolites whereas older larvae are less sensitive to high leaf toughness and are likely to become larger adults on hosts with lower oil contents.     

Helicobacter pylori Cholesteryl α-Glucosides Contribute to Its Pathogenicity and Immune Response by Natural Killer T Cells

Approximately 10–15% of individuals infected with Helicobacter pylori will develop ulcer disease (gastric or duodenal ulcer), while most people infected with H. pylori will be asymptomatic. The majority of infected individuals remain asymptomatic partly due to the inhibition of synthesis of cholesteryl α-glucosides in H. pylori cell wall by α1,4-GlcNAc-capped mucin O-glycans, which are expressed in the deeper portion of gastric mucosa. However, it has not been determined how cholesteryl α-glucosyltransferase (αCgT), which forms cholesteryl α-glucosides, functions in the pathogenesis of H. pylori infection. Here, we show that the activity of αCgT from H. pylori clinical isolates is highly correlated with the degree of gastric atrophy. We investigated the role of cholesteryl α-glucosides in various aspects of the immune response. Phagocytosis and activation of dendritic cells were observed at similar degrees in the presence of wild-type H. pylori or variants harboring mutant forms of αCgT showing a range of enzymatic activity. However, cholesteryl α-glucosides were recognized by invariant natural killer T (iNKT) cells, eliciting an immune response in vitro and in vivo. Following inoculation of H. pylori harboring highly active αCgT into iNKT cell-deficient (Jα18^−/−) or wild-type mice, bacterial recovery significantly increased in Jα18^−/− compared to wild-type mice. Moreover, cytokine production characteristic of Th1 and Th2 cells dramatically decreased in Jα18^−/− compared to wild-type mice. These findings demonstrate that cholesteryl α-glucosides play critical roles in H. pylori-mediated gastric inflammation and precancerous atrophic gastritis.     

Photosynthetic capacity of Eucalyptus globulus is higher when grown in mixture with Acacia mearnsii

Mixed species plantations of Eucalyptus and N₂-fixing species can be significantly more productive than monocultures. The aim of this study was to determine whether the improved growth resulted from increases in photosynthesis, light absorption and light-use efficiency, in addition to previously measured increases in leaf area, water-use efficiency and higher ratios of annual above-ground net primary production per unit of total annual below-ground carbon allocation in 1:1 mixtures near Cann River, Victoria, Australia. Light-saturated photosynthetic rate (A _max), electron transport (J), stomatal conductance (g _s) and foliar nitrogen concentrations were higher for Eucalyptus globulus trees growing in mixtures than those in monocultures. Similar increases in maximum rates of carboxylation (V _cmax), Rubisco, chlorophyll, and phosphorus concentrations were not significant. In contrast, A _max, V _cmax and J did not vary between mixtures and monocultures for A. mearnsii, whose growth was negligible by age 15 years. Mixtures also absorbed 24 and 41% more light than E. globulus and A. mearnsii., respectively, and were 38 and 154% more light-use efficient in the mixtures compared to monocultures. The increased nutrient availability in mixtures appeared to increase productivity of E. globulus by increasing the photosynthetic capacity of the foliage, as well as the leaf area, light absorption and light-use efficiency of the canopy.     

Efficient production of (2S)-flavanones by Escherichia coli containing an artificial biosynthetic gene cluster

For the fermentative production of plant-specific flavanones (naringenin, pinocembrin) by Escherichia coli, a plasmid was constructed which carried an artificial biosynthetic gene cluster, including PAL encoding a phenylalanine ammonia-lyase from a yeast, ScCCL encoding a cinnamate/coumarate:CoA ligase from the actinomycete Streptomyces coelicolor A3(2), CHS encoding a chalcone synthase from a licorice plant and CHI encoding a chalcone isomerase from the Pueraria plant. The recombinant E. coli cells produced (2S)-naringenin from tyrosine and (2S)-pinocembrin from phenylalanine. When the two subunit genes of acetyl-CoA carboxylase from Corynebacterium glutamicum were expressed under the control of the T7 promoter and the ribosome-binding sequence in the recombinant E. coli cells, the flavanone yields were greatly increased, probably because enhanced expression of acetyl-CoA carboxylase increased a pool of malonyl-CoA that was available for flavanone synthesis. Under cultural conditions where E. coli at a cell density of 50 g/l was incubated in the presence of 3 mM tyrosine or phenylalanine, the yields of naringenin and pinocembrin reached about 60 mg/l. The fermentative production of flavanones in E. coli is the first step in the construction of a library of flavonoid compounds and un-natural flavonoids in bacteria.