Studies on the susceptibility of different culture morphotypes of Listeria monocytogenes to uptake and survival in human polymorphonuclear leukocytes

This study demonstrated that atypical virulent filaments of Listeria monocytogenes (rough variant type II and designated FR for this study), isolated from clinical specimens or generated during exposure to pulsed-plasma gas discharge in liquids, were shown to be capable of survival when engulfed by human polymorphonuclear leukocytes (PMNLs). Factors shown to significantly influence the maximal respiratory burst response in PMNLs and survival of different internalized cell or filament forms of L. monocytogenes were bacterial strain, culture form, degree of opsonization (with and without the use of 10% serum) and composition of the bacterial growth media used before uptake by PMNLs. Opsonized regular-sized L. monocytogenes cells grown on blood agar (BA) elicited the greatest respiratory burst response and survived best in PMNLs. The filamentous (FR) and multiple cell chain (MCR) rough variants were significantly less susceptible to uptake and survival in PMNLs. Supplementation of tryptone soya agar with hemin resulted in significantly reduced chemiluminescence responses in phagocytosing PMNLs compared with the maximal levels observed from prior bacterial growth on BA or brain heart infusion agar that also contained a source of iron. The MCR variants secreting decreased levels of a peptidoglycan hydrolase CwhA protein exhibited the lowest percentage survival when internalized in PMNLs compared with wild-type smooth or FR culture variants as determined by the macrophage-killing assay.     

The immunobiology of the innate response to Toxoplasma gondii

Toxoplasma gondii is a unique intracellular parasite. It can infect a variety of cells in virtually all warm-blooded animals. It has a worldwide distribution and, overall, around one-third of people are seropositive for the parasite, with essentially the entire human population being at risk of infection. For most people, T. gondii causes asymptomatic infection but the parasite can cause serious disease in the immunocompromised and, if contracted for the first time during pregnancy, can cause spontaneous abortion or congenital defects, which have a substantial emotional, social and economic impact. Toxoplasma gondii provokes one of the most potent innate, pro-inflammatory responses of all infectious disease agents. It is also a supreme manipulator of the immune response so that innate immunity to T. gondii is a delicate balance between the parasite and its host involving a coordinated series of cellular interactions involving enterocytes, neutrophils, dendritic cells, macrophages and natural killer cells. Underpinning these interactions is the regulation of complex molecular reactions involving Toll-like receptors, activation of signalling pathways, cytokine production and activation of anti-microbial effector mechanisms including generation of reactive nitrogen and oxygen intermediates.     

Use of Galleria mellonella larvae to evaluate the in vivo anti-fungal activity of [Ag2(mal)(phen)3]

Larvae of the insect Galleria mellonella were employed to assess the in vivo antifungal efficacy of ([Ag₂(mal)(phen)₃]), AgNO₃ and 1,10-phenanthroline. Larvae pre-inoculated with these compounds were protected from a subsequent lethal infection by the yeast Candida albicans while larvae inoculated 1 and 4 h post-infection showed significantly increased survival (P < 0.01) compared to control larvae. Administration of these compounds resulted in an increase over 48 h in the density of insect haemocytes (immune cells) but there was no widespread activation of genes for antimicrobial peptides. This work demonstrates that G. mellonella larvae may be employed to ascertain the antifungal efficacy of silver(I) compounds and offers a rapid and effective means of assessing the in vivo activity of inorganic antimicrobial compounds.     

Sarcomere dynamics in skeletal muscle myofibrils during isometric contractions

The main goal of this study was to evaluate the dynamics of sarcomeres during isometric activation of skeletal muscle myofibrils. Rabbit psoas myofibrils (n=14) were attached between a pair of cantilevers for force measurements at one side and a rigid glass needle at the other side, and their images were used for measurements of individual sarcomere lengths (SL) during contractions. Myofibrils were set at average SL between 2.13 and 3.06 μm, and were activated and held isometric for 20–35 s during which SL and force were continuously measured. SL dispersion increased from the rest state to activation, but it remained mostly constant during the activation period. Even with the length non-uniformity developed during myofibril activation, most sarcomeres stabilized their length changes during the isometric contraction. As a result, sarcomeres contracted at different degrees of filament overlap while producing similar forces. When the myofibrils were separated in two groups that produced force at averaged short (≤2.5 μm) or long (≥2.5 μm) SL, the initial non-uniformity was greater in long lengths, but changes observed in sarcomeres during the activation period were similar, suggesting that sarcomere stability is not length-dependent.     

A multiple-method approach reveals a declining amount of chloroplast DNA during development in Arabidopsis

Background  

A decline in chloroplast DNA (cpDNA) during leaf maturity has been reported previously for eight plant species, including Arabidopsis thaliana. Recent studies, however, concluded that the amount of cpDNA during leaf development in Arabidopsis remained constant.     

Biosynthesis and enantioselectivity in the production of the lilac compounds in Actinidia arguta flowers

Biosynthesis of the lilac alcohols and alcohol epoxides from linalool in ‘Hortgem Tahi’ kiwifruit (Actinidiaarguta) flowers was investigated by incubating flowers with rac-linalool, rac-[4,4,10,10,10-²H₅]linalool, (R)-8-hydroxylinalool and (R)-8-oxolinalool. All substrates were incorporated into the lilac alcohols although the (R)-configured compounds are not normally present in flowers. Biosynthesis of the lilac alcohol epoxides from rac-1,2-epoxy[4,4,10,10,10-²H₅]linalool and rac-[4′,4′, 8′, 8′,8′-²H₅]lilac aldehyde epoxide, rather than the lilac alcohols, was examined. Both substrates were non-enantioselectively converted to the lilac alcohol epoxides, suggesting two biosynthetic pathways for these compounds, contrary to previous reports. Their ability to process unnatural substrates indicates that A.arguta flowers have a greater biosynthetic capability than is suggested by their phytochemical composition. Linalool, the lilac compounds, and their biosynthetic intermediates were measured in the pistils, stamen, petals and sepals to determine if localisation in different organs contributed to only (S)-linalool being processed to the lilac compounds. Both linalool enantiomers were present in all organs, while most (97%) of the lilac compounds, and their precursors, were found in the petals. (S)-Linalool was not depleted from the flower petals, with respect to (R)-linalool, during the time of maximum production of the metabolites of (S)-linalool.     

Exploiting the engine of C(4) photosynthesis

Ever since the discovery of C(4) photosynthesis in the mid-1960s, plant biologists have envisaged the introduction of the C(4) photosynthetic pathway into C(3) crops such as rice and soybeans. Recent advances in genomics capabilities, and new evolutionary and developmental studies indicate that C(4) engineering will be feasible in the next few decades. Furthermore, better understanding of the function of C(4) photosynthesis provides new ways to improve existing C(4) crops and bioenergy species, for example by creating varieties with ultra-high water and nitrogen use efficiencies. In the case of C(4) engineering, the main enzymes of the C(4) metabolic cycle have already been engineered into various C(3) plants. In contrast, knowledge of the genes controlling Kranz anatomy lags far behind. Combining traditional genetics, high-throughput sequencing technologies, systems biology, bioinformatics, and the use of the new C(4) model species Setaria viridis, the discovery of the key genes controlling the expression of C(4) photosynthesis can be dramatically accelerated. Sustained investment in the research areas directly related to C(4) engineering has the potential for substantial return in the decades to come, primarily by increasing crop production at a time when global food supplies are predicted to fall below world demand.     

The C(4) plant lineages of planet Earth

Using isotopic screens, phylogenetic assessments, and 45 years of physiological data, it is now possible to identify most of the evolutionary lineages expressing the C(4) photosynthetic pathway. Here, 62 recognizable lineages of C(4) photosynthesis are listed. Thirty-six lineages (60%) occur in the eudicots. Monocots account for 26 lineages, with a minimum of 18 lineages being present in the grass family and six in the sedge family. Species exhibiting the C(3)-C(4) intermediate type of photosynthesis correspond to 21 lineages. Of these, 9 are not immediately associated with any C(4) lineage, indicating that they did not share common C(3)-C(4) ancestors with C(4) species and are instead an independent line. The geographic centre of origin for 47 of the lineages could be estimated. These centres tend to cluster in areas corresponding to what are now arid to semi-arid regions of southwestern North America, south-central South America, central Asia, northeastern and southern Africa, and inland Australia. With 62 independent lineages, C(4) photosynthesis has to be considered one of the most convergent of the complex evolutionary phenomena on planet Earth, and is thus an outstanding system to study the mechanisms of evolutionary adaptation.     

The occurrence of C(2) photosynthesis in Euphorbia subgenus Chamaesyce (Euphorbiaceae)

This study investigated whether Euphorbia subgenus Chamaesyce subsection Acutae contains C(3)-C(4) intermediate species utilizing C(2) photosynthesis, the process where photorespired CO(2) is concentrated into bundle sheath cells. Euphorbia species in subgenus Chamaesyce are generally C(4), but three species in subsection Acutae (E. acuta, E. angusta, and E. johnstonii) have C(3) isotopic ratios. Phylogenetically, subsection Acutae branches between basal C(3) clades within Euphorbia and the C(4) clade in subgenus Chamaesyce. Euphorbia angusta is C(3), as indicated by a photosynthetic CO(2) compensation point (Г) of 69 μmol mol(-1) at 30 °C, a lack of Kranz anatomy, and the occurrence of glycine decarboxylase in mesophyll tissues. Euphorbia acuta utilizes C(2) photosynthesis, as indicated by a Г of 33 μmol mol(-1) at 30 °C, Kranz-like anatomy with mitochondria restricted to the centripetal (inner) wall of the bundle sheath cells, and localization of glycine decarboxlyase to bundle sheath mitochondria. Low activities of PEP carboxylase, NADP malic enzyme, and NAD malic enzyme demonstrated no C(4) cycle activity occurs in E. acuta thereby classifying it as a Type I C(3)-C(4) intermediate. Kranz-like anatomy in E. johnstonii indicates it also utilizes C(2) photosynthesis. Given the phylogenetically intermediate position of E. acuta and E. johnstonii, these results support the hypothesis that C(2) photosynthesis is an evolutionary intermediate condition between C(3) and C(4) photosynthesis.