Growth,lipid content,productivity, and fatty acid composition of tropical microalgae for scale‐up production

Biomass and lipid productivity, lipid content, and quantitative and qualitative lipid composition are critical parameters in selecting microalgal species for commercial scale‐up production. This study compares lipid content and composition, and lipid and biomass productivity during logarithmic, late logarithmic, and stationary phase of Nannochloropsis sp., Isochrysis sp., Tetraselmis sp., and Rhodomonas sp. grown in L1‐, f/2‐, and K‐medium. Of the tested species, Tetraselmis sp. exhibited a lipid productivity of 3.9–4.8 g m^?2 day^?1 in any media type, with comparable lipid productivity by Nannochloropsis sp. and Isochrysis sp. when grown in L1‐medium. The dry biomass productivity of Tetraselmis sp. (33.1–45.0 g m^?2 day^?1) exceeded that of the other species by a factor 2–10. Of the organisms studied, Tetraselmis sp. had the best dry biomass and/or lipid production profile in large‐scale cultures. The present study provides a practical benchmark, which allows comparison of microalgal production systems with different footprints, as well as terrestrial systems. Biotechnol. Bioeng. 2010;107: 245–257. © 2010 Wiley Periodicals, Inc.     

Survival,growth and reproduction of Daphnia galeata feeding on single and mixed Pseudomonas and Rhodomonas diets

1. Bacteria can be an important resource for zooplankton production in aquatic food webs, although the degree to which bacteria sustain zooplankton growth and reproduction is not clear. We performed a growth experiment with Daphnia galeata feeding on different ratios of P‐replete Pseudomonas and Rhodomonas, ranging from a 100% bacterial to a 100% algal diet. 2. A pure bacterial diet did not support survival, growth or reproduction of D. galeata. While a 20% share of Rhodomonas in the food allowed survival of daphniids, the occurrence of offspring on a 50% algal diet indicated that the threshold for successful reproduction was between those two proportions of algal food. Increasing the proportion of the alga further increased growth and reproductive output, indicating that Rhodomonas was a higher‐quality food than Pseudomonas. 3. A subsequent labelling experiment demonstrated that D. galeata incorporated phosphorus from Pseudomonas and Rhodomonas with similar efficiency, whereas carbon was incorporated more efficiently from Pseudomonas than from Rhodomonas. 4. we hypothesise that inadequate levels of essential biochemicals in pure bacterial diets led to decreased Daphnia performance. Concentrations of fatty acids in general, and especially of polyunsaturated fatty acids, were much lower in Pseudomonas than in Rhodomonas. This difference could explain the different growth and reproduction responses, although limitation by other essential biochemicals (e.g. sterols) cannot be ruled out. 5. Hence, where they dominate, bacteria may provide a significant part of the elemental flux to species feeding higher in the food web on the short term. However, the performance of consumers may be constrained by essential biochemicals.     

INTENSE GRAZING AND PREY‐DEPENDENT GROWTH OF PFIESTERIA PISCICIDA (DINOPHYCEAE)1

Grazing and growth of Pfiesteria piscicida (Pfiest) were investigated using batch and cyclostat cultures with Rhodomonas sp. (Rhod) as prey. Observed maximum growth rates (1.4 d^?1) and population densities (2 × 10⁵ cells·mL^?1) corresponded to values predicted by Monod functions (1.76 d^?1; 1.4 × 10⁵ cells·mL^?1). In batch cultures under a range of prey‐to‐predator ratios (0.1:1 to 180:1) and prey concentrations (1000–71,000 cells·mL^?1), Rhodomonas sp. was always depleted rapidly and P. piscicida concentrations increased briefly. The rate of Rhodomonas sp. depletion and the magnitude of P. piscicida population maxima depended on the prey‐to‐predator ratio and prey concentration. Starvation resulted in cell cycle arrest at G1 and G2+M and ultimately the demise of both P. piscicida and Rhodomonas sp. populations, demonstrating the dependence of P. piscicida on the supply of appropriate prey. The depletion of Rhodomonas sp. populations could be attributed directly to grazing, because P. piscicida did not exert detectable inhibitory effects on the growth of Rhodomonas sp. but grazed intensely, with maximum grazing rates>10 Rhod·Pfiest^?1·d^?1 and with no apparent threshold prey abundance for grazing. The results suggest that 1) the abundance of appropriate prey may be an important factor regulating P. piscicida abundance in nature, 2) P. piscicida may control prey population, and 3) high growth and grazing potentials of P. piscicida along with cell cycle arrest may confer survival advantages.     

Conversion of biomass hydrolysates and other substrates to ethanol and other chemicals by Lactobacillus buchneri*

Aims: A Lactobacillus buchneri strain NRRL B‐30929 can convert xylose and glucose into ethanol and chemicals. The aims of the study were to survey three strains (NRRL B‐30929, NRRL 1837 and DSM 5987) for fermenting 17 single substrates and to exam NRRL B‐30929 for fermenting mixed substrates from biomass hydrolysates. Methods and Results: Mixed acid fermentation was observed for all three L. buchneri strains using various carbohydrates; the only exception was uridine which yielded lactate, acetate and uracil. Only B‐30929 is capable of utilizing cellobiose, a desired trait in a potential biocatalyst for biomass conversion. Flask fermentation indicated that the B‐30929 strain can use all the sugars released from pretreated hydrolysates, and producing 1·98–2·35 g l^?1 ethanol from corn stover hydrolysates and 2·92–3·01 g l^?1 ethanol from wheat straw hydrolysates when supplemented with either 0·25× MRS plus 1% corn steep liquor or 0·5× MRS. Conclusions: The L. buchneri NRRL B‐30929 can utilize mixed sugars in corn stover and wheat straw hydrolysates for ethanol and other chemical production. Significance and Impact of the Study: These results are valuable for future research in engineering L. buchneri NRRL B‐30929 for fermentative production of ethanol and chemicals from biomass.     

Nitrogen‐rich microbial products provide new organo‐mineral associations for the stabilization of soil organic matter

Understanding the cycling of C and N in soils is important for maintaining soil fertility while also decreasing greenhouse gas emissions, but much remains unknown about how organic matter (OM) is stabilized in soils. We used nano‐scale secondary ion mass spectrometry (NanoSIMS) to investigate the changes in C and N in a Vertisol and an Alfisol incubated for 365 days with ¹³C and ¹⁵N pulse labeled lucerne (Medicago sativa L.) to discriminate new inputs of OM from the existing soil OM. We found that almost all OM within the free stable microaggregates of the soil was associated with mineral particles, emphasizing the importance of organo‐mineral interactions for the stabilization of C. Of particular importance, it was also found that ¹⁵N‐rich microbial products originating from decomposition often sorbed directly to mineral surfaces not previously associated with OM. Thus, we have shown that N‐rich microbial products preferentially attach to distinct areas of mineral surfaces compared to C‐dominated moieties, demonstrating the ability of soils to store additional OM in newly formed organo‐mineral associations on previously OM‐free mineral surfaces. Furthermore, differences in ¹⁵N enrichment were observed between the Vertisol and Alfisol presumably due to differences in mineralogy (smectite‐dominated compared to kaolinite‐dominated), demonstrating the importance of mineralogy in regulating the sorption of microbial products. Overall, our findings have important implications for the fundamental understanding of OM cycling in soils, including the immobilization and storage of N‐rich compounds derived from microbial decomposition and subsequent N mineralization to sustain plant growth.     

N‐ACYL HOMOSERINE LACTONe LACTONASE,AiiA, INACTIVATION OF QUORUM‐SENSING AGONISTS PRODUCED BY CHLAMYDOMONAS REINHARDTII (CHLOROPHYTA) AND CHARACTERIZATION OF aiiA TRANSGENIC ALGAE1

Eukaryotes such as plants and the unicellular green alga Chlamydomonas reinhardtii P. A. Dang. produce and secrete compounds that mimic N‐acyl homoserine lactone (AHL) bacterial quorum‐sensing (QS) signals and alter QS‐regulated gene expression in the associated bacteria. Here, we show that the set of C. reinhardtii signal‐mimic compounds that activate the CepR AHL receptor of Burkholderia cepacia are susceptible to inactivation by AiiA, an AHL lactonase enzyme of Bacillus. Inactivation of these algal mimics by AiiA suggests that the CepR‐stimulatory class of mimics produced by C. reinhardtii may have a conserved lactone ring structure in common with AHL QS signals. To examine the role of AHL mimic compounds in the interactions of C. reinhardtii with bacteria, the aiiA gene codon optimized for Chlamydomonas was generated for the expression of AiiA as a chimeric fusion with cyan fluorescent protein (AimC). Culture filtrates of transgenic strains expressing the fusion protein AimC had significantly reduced levels of CepR signal‐mimic activities. When parental and transgenic algae were cultured with a natural pond water bacterial community, a morphologically distinct, AHL‐producing isolate of Aeromonas veronii was observed to colonize the transgenic algal cultures and form biofilms more readily than the parental algal cultures, indicating that secretion of the CepR signal mimics by the alga can significantly affect its interactions with bacteria it encounters in natural environments. The parental alga was also able to sequester and/or destroy AHLs in its growth media to further disrupt or manipulate bacterial QS.     

Characterization of centrin genes from Ochromonas danica (Chrysophyceae) and Scytosiphon lomentaria (Phaeophyceae)

Centrin, the EF‐hand Ca²⁺‐binding protein is localized at the basal apparatus of flagella and in centrioles in many eukaryotic cells. In the present study, centrin genes of the heterokont algae have been clarified for the first time. We isolated and analyzed cDNA and genomic DNA of centrin genes from the crysophycean alga Ochromonas danica Prings (UTEX LB1298) and the brown alga Scytosiphon lomentaria (Lyngbye) Link. The centrin gene of Ochromonas contained an open reading frame of 163 amino acids. The deduced protein, named Odcen, exhibited 85%, 78% and 59% homology to Chlamydomonas, human and Arabidopsis centrin, respectively. The centrin genes of Scytosiphon contained an open reading frame of 164 amino acids. The deduced protein, named Slcen, exhibited 84%, 77% and 59% homology to Chlamydomonas, human and Arabidopsis centrin, respectively. Both Odcen and Slcen possessed N‐terminal extensions before the conserved amino acid among various centrins, four EF‐hand domains and an aromatic amino acid at the C‐terminus. Southern blot hybridization suggested that the centrin gene occurs as a single copy gene in both Ochromonas and Scytosiphon genomes. Comparison of the sequence of the cDNA and the genomic DNA revealed that the Odcen gene was split into three fragments by introns and Slcen gene consisted of five fragments. The junctions of all introns of both genes conformed to the GT–AG rule. The introns of Slcen gene were considerably long and, as a result, the Slcen gene was approximately seven times longer than Odcen gene.     

Nuclear gene targeting in Chlamydomonas using engineered zinc‐finger nucleases

The unicellular green alga Chlamydomonas reinhardtii is a versatile model for fundamental and biotechnological research. A wide range of tools for genetic manipulation have been developed for this alga, but specific modification of nuclear genes is still not routinely possible. Here, we present a nuclear gene targeting strategy for Chlamydomonas that is based on the application of zinc‐finger nucleases (ZFNs). Our approach includes (i) design of gene‐specific ZFNs using available online tools, (ii) evaluation of the designed ZFNs in a Chlamydomonas in situ model system, (iii) optimization of ZFN activity by modification of the nuclease domain, and (iv) application of the most suitable enzymes for mutagenesis of an endogenous gene. Initially, we designed a set of ZFNs to target the COP3 gene that encodes the light‐activated ion channel channelrhodopsin‐1. To evaluate the designed ZFNs, we constructed a model strain by inserting a non‐functional aminoglycoside 3′‐phosphotransferase VIII (aphVIII) selection marker interspaced with a short COP3 target sequence into the nuclear genome. Upon co‐transformation of this recipient strain with the engineered ZFNs and an aphVIII DNA template, we were able to restore marker activity and select paromomycin‐resistant (Pm‐R) clones with expressing nucleases. Of these Pm‐R clones, 1% also contained a modified COP3 locus. In cases where cells were co‐transformed with a modified COP3 template, the COP3 locus was specifically modified by homologous recombination between COP3 and the supplied template DNA. We anticipate that this ZFN technology will be useful for studying the functions of individual genes in Chlamydomonas.     

Chemoreception in the green algaDunaliella tertiolecta

A capillary assay was employed to quantify positive chemotactic responses in the motile, unicellular, marine algaDunaliella tertiolecta. Among a wide range of inorganic and organic compounds tested, only ammonium ion,l-tyrosine,l-tryptophan, andl-phenylalanine were found to be major atractants for the chlorophyte.l-Methionine andl-cysteine weakly attracted the alga at 10⁻³ M. The minimum concentration of the major attractants needed to elicit an observable chemotactic response was approximately 10⁻⁶ M. The maximum response occurred when the capillaries contained 10⁻⁵ Ml-tyrosine orl-tryptophan, 10⁻⁴ Ml-phenylalanine, and 10⁻³ M ammonium chloride. The other amino acids, carbohydrates, B-vitamins, urea, and nitrate were among the chemicals that failed to attractD. tertiolecta. The alga apparently possesses one chemoreceptor that binds ammonium ion only, and another chemoreceptor that binds the three aromatic amino acids.     

Biotechnological production of polyamines by bacteria: recent achievements and future perspectives

In Bacteria, the pathways of polyamine biosynthesis start with the amino acids l-lysine, l-ornithine, l-arginine, or l-aspartic acid. Some of these polyamines are of special interest due to their use in the production of engineering plastics (e.g., polyamides) or as curing agents in polymer applications. At present, the polyamines for industrial use are mainly synthesized on chemical routes. However, since a commercial market for polyamines as well as an industry for the fermentative production of amino acid exist, and since bacterial strains overproducing the polyamine precursors l-lysine, l-ornithine, and l-arginine are known, it was envisioned to engineer these amino acid-producing strains for polyamine production. Only recently, researchers have investigated the potential of amino acid-producing strains of Corynebacterium glutamicum and Escherichia coli for polyamine production. This mini-review illustrates the current knowledge of polyamine metabolism in Bacteria, including anabolism, catabolism, uptake, and excretion. The recent advances in engineering the industrial model bacteria C. glutamicum and E. coli for efficient production of the most promising polyamines, putrescine (1,4-diaminobutane), and cadaverine (1,5-diaminopentane), are discussed in more detail.     

The effect of nutrients and environmental conditions on biomass and oil production in Botryococcus braunii Race B strains

The green alga Botryococcus braunii is widely recognized as a source of non-fossil oil. However, limitations in Botryococcus biomass production hamper its commercial exploitation. This study examines the effects of nutrients (nitrogen and iron) and environmental conditions (temperature, light intensity and photoperiod) on biomass and oil production in two B. braunii Race B strains, Kossou-4 and Overjuyo-3. The highest biomass and oil production were obtained at a nitrogen concentration of 750 mg l^?1, iron concentration of 6 mg l^?1, at 25°C and at 135 µmol photons m^?2 s^?1 with a photoperiod of 16 h light:8 h darkness. Culturing the strains in Blue-green (BG11) medium containing optimized nutrients under optimal conditions resulted in an up to ~10.6-fold increase in biomass. In Kossou-4 and Overjuyo-3 strains, biomass increased from 1.647 g 10 l^?1 and 3.137 g 10 l^?1 respectively in normal BG11 medium to 17.390 g 10 l^?1 and 21.721 g 10 l^?1 in optimized BG11 media and growth conditions. This was accompanied by ~8–10.5-fold increase in oil production compared with that in normal BG11 medium. Oil (0.324 g 10 l^?1 and 0.211 g 10 l^?1) was produced in normal BG11 medium in Kossou-4 and Overjuyo-3 strains respectively, compared with 2.642 g 10 l^?1 (Kossou-4) and 2.206 g 10 l^?1 (Overjuyo-3) in modified BG11 media under optimized conditions. Therefore, optimization of nutrients and environmental conditions can increase biomass and oil production in the two strains of B. braunii.     

Fructan Biosynthesis by Intra‐ and Extracellular Zymomonas mobilis Levansucrase after Simultaneous Production of Ethanol and Levan

The chemical composition of the Zymomonas mobilis biomass and the culture liquid after ethanol and levan synthesis were studied. The activities of intra‐ and extracellular levansucrase produced by the Z. mobilis strain 113 “S” under optimum conditions both for levan and fructooligosaccharide (FOS) synthesis were also determined. It was shown that levan production relates to the reduction of the carbohydrate and lipid content in the biomass by increasing the nucleic acid and protein content. The levan producing activity of cellular levansucrase after ethanol and levan synthesis was approximately 30–40% of the total activity in the second fermentation stage. It was established that the cell free culture liquid, containing ethanol, levan, gluconic acid and sucrose (15%) at 25 °C, did not show any additional levan synthesising activity. At optimum FOS synthesis conditions (45 °C and 70% sucrose), the cell‐free culture liquid exhibited a high FOS synthesising activity (31% from total carbohydrates), with slightly reduced biomass activity. It was concluded that as a result of the simultaneous ethanol and levan production, the remaining biomass as well as the cell‐free culture liquid could be used for FOS production.     

Interactive effects of elevated CO2 and nitrogen deposition on fatty acid molecular and isotope composition of above‐ and belowground tree biomass and forest soil fractions

Atmospheric carbon dioxide (CO₂) and reactive nitrogen (N) concentrations have been increasing due to human activities and impact the global carbon (C) cycle by affecting plant photosynthesis and decomposition processes in soil. Large amounts of C are stored in plants and soils, but the mechanisms behind the stabilization of plant‐ and microbial‐derived organic matter (OM) in soils are still under debate and it is not clear how N deposition affects soil OM dynamics. Here, we studied the effects of 4 years of elevated (¹³C‐depleted) CO₂ and N deposition in forest ecosystems established in open‐top chambers on composition and turnover of fatty acids (FAs) in plants and soils. FAs served as biomarkers for plant‐ and microbial‐derived OM in soil density fractions. We analyzed above‐ and belowground plant biomass of beech and spruce trees as well as soil density fractions for the total organic C and FA molecular and isotope (δ¹³C) composition. FAs did not accumulate relative to total organic C in fine mineral fractions, showing that FAs are not effectively stabilized by association with soil minerals. The δ¹³C values of FAs in plant biomass increased under high N deposition. However, the N effect was only apparent under elevated CO₂ suggesting a N limitation of the system. In soil fractions, only isotope compositions of short‐chain FAs (C₁₆₊₁₈) were affected. Fractions of ‘new’ (experimental‐derived) FAs were calculated using isotope depletion in elevated CO₂ plots and decreased from free light to fine mineral fractions. ‘New’ FAs were higher in short‐chain compared to long‐chain FAs (C_20?30), indicating a faster turnover of short‐chain compared to long‐chain FAs. Increased N deposition did not significantly affect the quantity of ‘new’ FAs in soil fractions, but showed a tendency of increased amounts of ‘old’ (pre‐experimental) C suggesting that decomposition of ‘old’ C is retarded by high N inputs.     

Biotechnological conversion of waste cooking olive oil into lipid-rich biomass using Aspergillus and Penicillium strains

Aims: In this study, we have investigated the biochemical behaviour of Aspergillus sp. (five strains) and Penicillium expansum (one strain) fungi cultivated on waste cooking olive oil. The production of lipid‐rich biomass was the main target of the work. In parallel, the biosynthesis of other extracellular metabolites (organic acids) and enzyme (lipase) and the substrate fatty acid specificity of the strains were studied. Methods and Results: Carbon‐limited cultures were performed on waste oil, added in the growth medium at 15 g l^?1, and high biomass quantities were produced (up to c. 18 g l^?1, conversion yield of c. 1·0 g of dry biomass formed per g of fat consumed or higher). Cellular lipids were accumulated in notable quantities in almost all cultures. Aspergillus sp. ATHUM 3482 accumulated lipid up to 64·0% (w/w) in dry fungal mass. In parallel, extracellular lipase activity was quantified, and it was revealed to be strain and fermentation time dependent, with a maximum quantity of 645 U ml^?1 being obtained by Aspergillus niger NRRL 363. Storage lipid content significantly decreased at the stationary growth phase. Some differences in the fatty acid composition of both cellular and residual lipids when compared with the initial substrate fat used were observed; in various cases, cellular lipids more saturated and enriched with arachidic acid were produced. Aspergillus strains produced oxalic acid up to 5·0 g l^?1. Conclusions: Aspergillus and Penicillium strains are able to convert waste cooking olive oil into high‐added‐value products. Significance and Impact of the Study: Increasing fatty wastes amounts are annually produced. The current study provided an alternative way of biovalourization of these materials, by using them as substrates, to produce added‐value compounds.     

Contrasting impacts of a native and an invasive exotic shrub on flood‐plain succession

Abstract. Question: How do Coriaria arborea, an N‐fixing native shrub, and Buddleja davidii, a non‐N‐fixing exotic shrub, affect N:P stoichiometry in plants and soils during early stages of primary succession on a flood‐plain? Location: Kowhai River Valley, northeast South Island, New Zealand. Methods: We measured soil and foliar nutrient concentrations, light levels, plant community composition and the above‐ground biomass of Coriaria and Buddleja in four successional stages: open, young, vigorous and mature. Results: Coriaria occurred at low density but dominated above‐ground biomass by the vigorous stage. Buddleja occurred at 5.3 ± 1.0 stems/m² in the young stage and reached a maximum biomass of 520–535 g.m^‐2 during the young and vigorous stages. Mineral soil N increased with above‐ground Coriaria biomass (r²= 0.45), but did not vary with Buddleja biomass. In contrast, soil P increased with Buddleja biomass (r²= 0.35), but not with Coriaria biomass. In early successional stages, 70–80% of the species present were exotic, but this declined to about 15% by the mature stage. Exotic plant species richness declined with increasing Coriaria biomass, but no other measures of diversity varied with either Coriaria or Buddleja biomass. Conclusion: These results demonstrate that Buddleja dominates early succession and accumulates P whereas Coriaria dominates later succession and accumulates N. A key ecosystem effect of the invasive exotic Buddleja is alteration of soil N:P stoichiometry.     

Mapping the spatial distribution of the biomass and filter‐feeding effect of invasive dreissenid mussels on the winter‐spring phytoplankton bloom in Lake Michigan

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Effects of field experimental warming on wheat root distribution under conventional tillage and no‐tillage systems

Despite the obvious importance of roots to agro‐ecosystem functioning, few studies have attempted to examine the effects of warming on root biomass and distribution, especially under different tillage systems. In this study, we performed a field warming experiment using infrared heaters on winter wheat, in long‐term conventional tillage and no‐tillage plots, to determine the responses of root biomass and distribution to warming. Soil monoliths were collected from three soil depths (0–10, 10–20, and 20–30 cm). Results showed that root biomass was noticeably increased under both till and no‐till tillage systems (12.1% and 12.9% in 2011, and 9.9% and 14.5% in 2013, in the two tillage systems, respectively) in the 0–30 cm depth, associated with a similar increase in shoot biomass. However, warming‐induced root biomass increases occurred in the deeper soil layers (i.e., 10–20 and 20–30 cm) in till, while the increase in no‐till was focused in the surface layer (0–10 cm). Differences in the warming‐induced increases in root biomass between till and no‐till were positively correlated with the differences in soil total nitrogen (R² = .863, p < .001) and soil bulk density (R² = .853, p < .001). Knowledge of the distribution of wheat root in response to warming should help manage nutrient application and cycling of soil C‐N pools under anticipated climate change conditions.     

Effects of Pseudomonas syringae pv. morsprunorum Strain C28, Outer Membrane and LPS Preparations on Cherry Callus

Callus cultures were established from cherry (Prunus avium) cvs. Napoleon and Colt, respectively susceptible and resistant to race‐1 strains of Pseudomonas syringae pv. morsprunorum, by growth on Schenk–Hildebrandt medium. On Napoleon callus, necrosis began earlier and proceeded more rapidly when inoculated with the virulent race‐1 cherry isolate strain C28, than with mutants of diminished virulence derived from it, or with the virulent plum isolates D10 and D17. Colt tissue displayed poorer viability and showed susceptibility to strain C28 and the plum isolates. Callus from both sources was somewhat susceptible to the saprophytes P. aeruginosa NCIMB 8295 and P. fluorescens NCIMB 3756. Strain C28 grew on suspended Napoleon callus cells over a period of 3–4 days, causing leakage of UV‐absorbing compounds and K⁺, with a concomitant rise in extracellular pH. P. fluorescens NCIMB 3756 showed no growth on suspended callus for 6 days. EDTA‐extracted outer membrane (OM) from strain C28 caused leakage of UV‐absorbing material and K⁺, which was later reabsorbed, with little change in pH. The presence of OM suppressed the growth of a subsequent inoculum of strain C28, possibly due to complexation of the available Ca²⁺ and/or Mg²⁺ in the surrounding medium, by the component lipopolysaccharide (LPS). OM from the rough avirulent mutant strain C28‐2 induced leakage of K⁺, but not of UV‐absorbing material, and did not prevent the growth of subsequently inoculated strain C28. Smooth LPS from strain C28 did not cause leakage of K⁺ or of UV‐absorbing material and did not prevent growth of C28. The relevance of these findings is discussed in relation to disease.     

Biomass and leaf‐level gas exchange characteristics of three African savanna C4 grass species under optimum growth conditions

C₄ savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above‐ and below‐ground biomass allocation and the response of their gas exchange to changes in light intensity, CO₂ concentration and leaf‐to‐air vapour pressure deficit gradient (D_l). Digitaria eriantha showed the largest above‐ and below‐ground biomass, high efficiency in carbon gain under light‐limiting conditions, high water use efficiency (WUE) and strong stomatal sensitivity to D_l (P = 0.002; r² = 0.5). Panicum repens had a high aboveground biomass and attained high light saturated photosynthetic rates (A_sat, 47 μmol m^?2 s^?1), stomatal conductance, (g_sat, 0.25 mol m^?2 s^?1) at relatively high WUE. Eragrostis lehmanniana had almost half the biomass of other species, and had similar A_sat and g_sat but were attained at lower WUE than the other species. This species also showed the weakest stomatal response to D_l (P = 0.19, r² = 0. 1). The potential ecological significance of the contrasting patterns of biomass allocation and variations in gas exchange parameters among the species are discussed.