The synthesis of short- and medium-chain-length poly(hydroxyalkanoate) mixtures from glucose- or alkanoic acid-grown <Emphasis Type="Italic">Pseudomonas oleovorans</Emphasis>

Pseudomonas oleovorans NRRL B-778 accumulated mixtures of poly-3-hydroxybutyrate (PHB) and medium-chain-length poly(hydroxyalkanoates) (mcl-PHAs) when grown on glucose, octanoic acid or oleic acid, whereas growth on nonanoic acid or undecanoic acid resulted in copolymers of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-co-HV). Acetone fractionation verified the presence of PHB/mcl-PHA mixtures. The acetone-insoluble (AIS) fractions of the polymers derived from glucose (PHA-glucose), octanoic acid (PHA-octanoic) and oleic acid (PHA-oleic) were exclusively PHB while the acetone-soluble (AS) fractions contained mcl-PHA composed of differing ratios of 3-hydroxy-acid monomer units, which ranged in chain length from 6 to 14 carbon atoms. In contrast, both the AIS and AS fractions from the polymers derived from nonanoic acid (PHA-nonanoic) and undecanoic acid (PHA-undecanoic) were composed of comparable ratios of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV). The unfractionated PHA-glucose, PHA-octanoic and PHA-oleic polymers had melting temperatures (T _m) between 177 and 179°C, enthalpies of fusion (ΔH _f) of 20 cal/g and glass transition temperatures (T _g) of 3–4°C. This was due to the large PHB content in the polymer mixtures. On the other hand, the PHA-nonanoic and PHA-undecanoic polymers had thermal properties that supported their copolymer nature. In both cases, the T _m values were 161°C, ΔH _f values were 7cal/g and T _g values were −3°C. Journal of Industrial Microbiology & Biotechnology (2002) 28, 147–153 DOI: 10.1038/sj/jim/7000231 Received 30 July 2001/ Accepted in revised form 04 November 2001     

Novel Phycoerythrins in Marine Synechococcus spp. : Characterization and Evolutionary and Ecological Implications

Four clones of the marine, unicellular, cyanobacteria Synechococcus spp., were examined for the spectral and biochemical features of their phycoerythrins (PE) and their photosynthetic characteristics. Two spectral types of PE which are distinct from known PEs were found. One PE type possessed absorption maxima at 500 and 545 nm and a fluorescence emission at 560 nm. Upon denaturation in acid-urea, two chromophore absorption maxima were obtained, one corresponding to phycourobilin (A_max 500 nm) and one at 558 nm, ascribed to a phycoerythrobilin-like chromophore. The ratio of phycoerythrobilin-like to phycourobilin chromophores was 4.9:1.3. This PE possessed two subunits of M_rs of 17.0 and 19.5 kD for the α and β subunits, respectively. The other PE possessed a single symmetrical absorption at 551 nm and a fluorescence emission at 570 nm. This phycobiliprotein showed a single chromophore absorption band (A_max 558 nm) and yielded two polypeptides, an α of 17.5 kD and a β subunit of 20.8 kD. Both PEs showed a (α, β)_n structure. The presence of phycoerythrobilin-like chromophores (A_max 558 nm) appears to be diagnostic of this marine cyanobacterial group. The features of these PEs combined with additional biochemical data, suggest a possible evolutionary link between the PE-containing marine Synechococcus group and the red algal chloroplast. When the Synechococcus clones were grown under low light intensity the PE-containing clones showed higher photosynthetic performance, larger photosynthetic units sizes, reaction center I to II ratios near unity, and steeper initial slopes of photosynthesis versus irradiance curves than a non-PE-containing clone. These findings demonstrate the high photosynthetic efficiency of PE-containing clones in low light environments common to middepth neritic and oceanic habitats.     

Evolution of anaerobic ciliates from the gastrointestinal tract: phylogenetic analysis of the ribosomal repeat from Nyctotherus ovalis and its relatives

The 18S and 5.8S rDNA genes and the internal transcribed spacers ITS-1 and ITS-2 of ciliates living in the hindgut of frogs, millipedes, and cockroaches were analyzed in order to study the evolution of intestinal protists. All ciliates studied here belong to the genus Nycrotherus. Phylogenetic analysis revealed that these ciliates from a monophyletic group that includes the distantly related anaerobic free-living heterotrichous ciliates Metopus palaeformis and Metopus contortus. The intestinal ciliates from the different vertebrate and invertebrate hosts are clearly divergent at the level of their rDNA repeats. This argues for the antiquity of the associations and a predominantly vertical transmission. This mode of transmission seems to be controlled primarily by the behavior of the host. The different degrees of divergence between ciliates living in different strains of one and the same cockroach species most likely reflect the different geographical origins of the hosts. In addition, host switches must have occurred during the evolution of cockroaches, since identical ciliates were found only in distantly related hosts. These phenomena prevent the reconstruction of potential cospeciation events.      

Contrasting modes of light acclimation in two species of the rainforest understory

In tropical rainforests, the increased light associated with the formation of treefall gaps can have a critical impact on the growth and survivorship of understory plants. Here we examine both leaf-level and whole-plant responses to simulated light gap formation by two common shade-tolerant shrubs, Hybanthus prunifolius and Ouratea lucens. The species were chosen because they differed in leaf lifespans, a trait that has been correlated with a number of leaf- and plant-level processes. Ouratea leaves typically live about 5 years, while Hybanthus leaves live less than 1 year. Potted plants were placed in the understory shade for 2 years before transfer to a light gap. After 2 days in high light, leaves of both species showed substantial photoinhibition, including reduced CO₂ fixation, F _v/F _m and light use efficiency, although photoinhibition was most severe in Hybanthus. After 17 days in high light, leaves of both species were no longer photoinhibited. In response to increased light, Ouratea made very few new leaves, but retained most of its old leaves which increased photosynthetic capacity by 50%. Within a few weeks of transfer to high light, Hybanthus had dropped nearly all of its shade leaves and made new leaves that had a 2.5-fold greater light-saturated photosynthetic rate. At 80 days after transfer, the number of new leaves was 4.9-fold the initial leaf number. After 80 days in high light, Hybanthus had approximately tenfold greater productivity than Ouratea when leaf area, photosynthetic capacity, and leaf dark respiration rate were all taken into account. Although both species are considered shade tolerant, we found that their growth responses were quite different following transfer from low to high light. The short-lived Hybanthus leaves were quickly dropped, and a new canopy of sun leaves was produced. In contrast, Ouratea showed little growth response at the whole-plant level, but a greater ability to tolerate light stress and acclimate at the leaf level. These differences are consistent with predictions based on leaf lifespan and are discussed within the context of other traits associated with shade-tolerant syndromes. Received: 25 March 1999 / Accepted: 16 August 1999     

The oxygen delivery response to acute hypoxia during incremental knee extension exercise differs in active and trained males

Background

It is well known that hypoxic exercise in healthy individuals increases limb blood flow, leg oxygen extraction and limb vascular conductance during knee extension exercise. However, the effect of hypoxia on cardiac output, and total vascular conductance is less clear. Furthermore, the oxygen delivery response to hypoxic exercise in well trained individuals is not well known. Therefore our aim was to determine the cardiac output (Doppler echocardiography), vascular conductance, limb blood flow (Doppler echocardiography) and muscle oxygenation response during hypoxic knee extension in normally active and endurance-trained males.

Methods

Ten normally active and nine endurance-trained males (VO_2max = 46.1 and 65.5 mL/kg/min, respectively) performed 2 leg knee extension at 25, 50, 75 and 100% of their maximum intensity in both normoxic and hypoxic conditions (FIO₂ = 15%; randomized order). Results were analyzed with a 2-way mixed model ANOVA (group × intensity).

Results

The main finding was that in normally active individuals hypoxic sub-maximal exercise (25 – 75% of maximum intensity) brought about a 3 fold increase in limb blood flow but decreased stroke volume compared to normoxia. In the trained group there were no significant changes in stroke volume, cardiac output and limb blood flow at sub-maximal intensities (compared to normoxia). During maximal intensity hypoxic exercise limb blood flow increased approximately 300 mL/min compared to maximal intensity normoxic exercise.

Conclusion

Cardiorespiratory fitness likely influences the oxygen delivery response to hypoxic exercise both at a systemic and limb level. The increase in limb blood flow during maximal exercise in hypoxia (both active and trained individuals) suggests a hypoxic stimulus that is not present in normoxic conditions.

     

不同退化红砂荒漠草地的水分分配格局

研究了内蒙古阿拉善盟不同过牧退化红砂草地的土壤 植物 大气系统的水分分配格局、不同退化草地和主要植物种的水分利用效率 .2 0 0 1年降雨量 12 4 .3mm ,其中试验期 119.4mm .1m深土壤水分结果表明 ,10～ 4 0cm土层受蒸散影响最大 ;由于主要共存种红砂和无芒隐子草根系分布和蒸腾强度不同等 ,含水量在 10～ 2 0cm土层以中度退化区显著低于其它样区 (P <0 .0 5 ) ,而 2 0～ 4 0cm土层以轻度退化区较低 .样地年均蒸发量为 30 .6mm ,红砂种群的年均蒸腾量为 11.9mm .随着草地退化加剧 ,裸地的蒸发量和退化指示种匍根骆驼蓬种群的蒸腾量增加 ,而红砂种群的蒸腾量降低 .与较轻度退化区比 ,中度和重度退化区的水分利用率分别下降了 14 .6 %和 4 6 .1% ,红砂水分利用率分别下降了 37.8%和 73.8% .