Spreading of a mycobacterial cell-surface lipid into host epithelial membranes promotes infectivity

Several virulence lipids populate the outer cell wall of pathogenic mycobacteria. Phthiocerol dimycocerosate (PDIM), one of the most abundant outer membrane lipids, plays important roles in both defending against host antimicrobial programs and in evading these programs altogether. Immediately following infection, mycobacteria rely on PDIM to evade Myd88-dependent recruitment of microbicidal monocytes which can clear infection. To circumvent the limitations in using genetics to understand virulence lipids, we developed a chemical approach to track PDIM during Mycobacterium marinum infection of zebrafish. We found that PDIM's methyl-branched lipid tails enabled it to spread into host epithelial membranes to prevent immune activation. Additionally, PDIM’s affinity for cholesterol promoted this phenotype; treatment of zebrafish with statins, cholesterol synthesis inhibitors, decreased spreading and provided protection from infection. This work establishes that interactions between host and pathogen lipids influence mycobacterial infectivity and suggests the use of statins as tuberculosis preventive therapy by inhibiting PDIM spread.

Spreading of a mycobacterial cell surface lipid into host epithelial membranes promotes infectivity

ABSTRACTSeveral virulence lipids populate the outer cell wall of pathogenic mycobacteria (Jackson, 2014). Phthiocerol dimycocerosate (PDIM), one of the most abundant outer membrane lipids (Anderson, 1929), plays important roles in both defending against host antimicrobial programs (Camacho et al., 2001; Cox et al., 1999; Murry et al., 2009) and in evading these programs altogether (Cambier et al., 2014a; Rousseau et al., 2004). Immediately following infection, mycobacteria rely on PDIM to evade toll-like receptor (TLR)-dependent recruitment of bactericidal monocytes which can clear infection (Cambier et al., 2014b). To circumvent the limitations in using genetics to understand virulence lipid function, we developed a chemical approach to introduce a clickable, semi-synthetic PDIM onto the cell wall of Mycobacterium marinum. Upon infection of zebrafish, we found that PDIM rapidly spreads into host epithelial membranes, and that this spreading inhibits TLR activation. PDIM’s ability to spread into epithelial membranes correlated with its enhanced fluidity afforded by its methyl-branched mycocerosic acids. Additionally, PDIM’s affinity for cholesterol promoted its occupation of epithelial membranes; treatment of zebrafish with statins, cholesterol synthesis inhibitors, decreased spreading and provided protection from infection. This work establishes that interactions between host and pathogen lipids influence mycobacterial infectivity and suggests the use of statins as tuberculosis preventive therapy by inhibiting PDIM spread.

Carpellary appendages in Nymphaea and Victoria (Nymphaeaceae): evidence of their role as osmophores based on morphology, anatomy and ultrastructure

In flowers of Nymphaea and Victoria, carpellary appendages are regarded as structures related to pollination by deceit of night-blooming species. In this study, the anatomy, histochemistry and ultrastructure of carpellary appendages were analysed to investigate their possible role in the production of volatile compounds in nocturnal species Nymphaea amazonum, N. gardneriana, N. prolifera (Nymphaea subgenus Hydrocallis) and Victoria cruziana, and in diurnal species N. caerulea (Nymphaea subgenus Brachyceras). Carpellary appendages were studied using light microscopy and scanning and transmission electron microscopy from pre-anthesis to the second day of anthesis. Anatomical and ultrastructural features are characteristic of osmophores. In all species, the most frequent components in secretory cells are amyloplasts, lipid bodies, mitochondria, rough endoplasmic reticulum and elaioplasts. The epidermis and multilayered parenchyma accumulate abundant starch grains and lipophilic substances, both of which vanish during anthesis. Amorphous substances are deposited between the plasmalemma and the outer cell wall of epidermal cells, and are then released by cuticular diffusion. Odour production in carpellary appendages might be an ancient role of primary importance both in diurnal and nocturnal species that are pollinated by deceit. Olfactory and visual cues of small carpellary appendages in Nymphaea subgenus Brachyceras correspond to bee pollination, and large carpellary appendages in subgenus Hydrocallis and Victoria represent parallel functional specializations of the flowers to the attraction and reward for exclusive beetle pollination.

Potamosiphon australiensis gen. nov., sp nov. (Oscillatoriales), a new filamentous cyanobacterium from subtropical north-eastern Australia

A new filamentous cyanobacterium, Potamosiphon australiensis gen. et sp. nov., was isolated from a small coastal stream in subtropical north-eastern Australia, and characterised using combined morphological and phylogenetic attributes. It was found growing on the benthos of Fat Hen Creek amongst cobbles, gravel and large woody debris, mostly as single straight or variously flexuous filaments amongst other algae, but occasionally formed loose aggregations amongst littoral vegetation. Morphologically, Potamosiphon is most similar to members of the genus Lyngbya. Filaments were isopolar, cylindrical, not or slightly constricted at the cross walls. Vegetative cells were discoid, broader than long with finely granular contents, aerotopes were not present. Apical cells were rounded, without calyptra or a thickened outer cell wall. Reproduction occurred via motile hormogonia, which formed often in series, after the occurrence of necridic cells. Trichome fragmentation also occurred following a diagonal division. Following this division trichomes often continued to grow past each other within a common sheath. Thylakoids were irregularly arranged throughout the whole cell volume. Phylogenetic analyses using partial 16S rRNA sequences obtained from three strains of P. australiensis showed that it formed a well supported monophyletic clade, sharing less than 94% nucleotide similarity with other cyanobacterial sequences, including putatively related taxa within the Oscillatoriaceae. It also formed a novel clade in the nifH phylogeny, which was associated with the genus Microseira G.B. McGregor & Sendall.

Effect of feeding Actigen™ to sows during gestation and lactation and on piglet performance

SummaryActigen™ is a second generation, unique bioactive fraction derived from the outer cell wall of a specific strain of yeast, Saccharomyces cerevisiae, where it acts in the gut to bind pathogenic bacteria, preventing disease and competition for nutrients. In the current trial, 260 sows were used and fed either an unsupplemented control diet or one containing Actigen™ at 0.08% of the formulation during gestation, farrowing and lactation, to assess its impact on sow and piglet performance. Results showed significant increases in feed intake for sows fed Actigen™ pre-farrowing, but this was reversed during lactation, leading to a 7 kg saving in feed intake per animal. At birth, piglets weighed 42 g more in litters from Actigen™-fed sows compared to the control group. Weaning weight of the total litter from Actigen™ sows was significantly higher (P< 0.05) by 3.3 kg, although individual piglet weights were the same. Sows showed no significant loss in body weight during the trial, indicating that the improved piglet production was related to improved nutrient availability and perhaps Ig status of piglets due to the addition of Actigen™ in the diet.

Leaf colleters in Tabernaemontana catharinensis (Apocynaceae, Rauvolfioideae): structure, ontogenesis, and cellular secretion

Colleters, which are glands that produce sticky secretion, have ecological and taxonomic relevance in Apocynaceae. We studied the distribution, morphology, ontogenesis, and cellular secretions of leaf colleters in Tabernaemontana catharinensis A.DC. Samples from mature embryos, seedlings, and plants were processed according to usual methods for anatomical, histochemical, and ultrastructural analyses. Colleters are non-vascularized emergences that occur on the adaxial face of expanded cotyledons, eophylls, and metaphylls and at the intrapetiolar and interpetiolar positions. Standard, bifurcate, trifurcate, and sessile colleters were found, and these glands did not differ in their ontogenesis, histochemistry, or histological composition. Golgi bodies, rough endoplasmic reticulum, and plastids filled with oil droplets were the predominant organelles in the epithelial cells. Mucilage accumulated in large periplasmic spaces, traversed the outer cell wall and the permeable cuticle, which remained intact. Senescent epithelial cells were characterized by signs of cell plasmolysis, organelle degradation, membrane vesiculation, and ruptured tonoplast. Ultrastructural changes in the cell wall strengthen the argument for the involvement of this cellular compartment in the exudates’ exit. We provide the first report of the occurrence of different types of colleters in a Rauvolfioideae member. Our ontogenetic data support the hypothesis that morphological variants are deviations from the standard type.

Diploneis fenestrata sp. nov. (Bacillariophyta), a new aerophilic diatom species from Zambia, Africa

Diploneis fenestrata, a new aerophilic diatom is described from Lumangwe falls, Zambia. This novel species occurs as an epiphyte on the roots and stems of trees located within the spray zone of the falls. Its morphology was examined with both light and scanning electron microscopy. Diploneis fenestrata is distinguished from other taxa in the genus Diploneis by its prominent square openings ranging in number from 4-14 occurring within the area of the longitudinal canal only at the outer cell wall. The occurrence of these characteristic square openings found in the genus Diploneis is further discussed.

Insights into the biology and phylogeny of Chloromonas polyptera (Chlorophyta), an alga causing orange snow in Maritime Antarctica

In Antarctica, mass accumulations of psychrophilic algae cause striking phenomena like green, orange, or red snow. This occurs during summer, when coastal snowfields start to melt, become waterlogged and photoautotrophs can thrive. Chloromonas polyptera (Fritsch) Hoham, Mullet & Roemer is a unicellular species that causes orange snow in the vicinity of penguin rockeries. It has been recognized for many decades because of the distinct habitat and the characteristic morphology of cysts with elongated flanges on the outer cell wall. However, closer investigations concerning the ecology or physiology have been sparse so far. Field material was collected from two sites on the Antarctic Peninsula to find out more about metabolic and cellular strategies. The results were compared with a closely related species from high alpine locations, Chloromonas nivalis (Chodat) Hoham & Mullet. Despite the geographical distance, C. polyptera shares several physiological strategies with the alpine relative, such as the formation of cyst stages, saccharose and glycerol as main soluble carbohydrates and the abundant accumulation of the carotenoid astaxanthin. Moreover, photosynthesis is adapted to temperatures of about 1°C. The molecular phylogeny confirmed a close relationship of C. polyptera to other Chloromonas species isolated from snow. Chloromonas polyptera seems to be exclusive to coastal Antarctic ecosystems influenced by animal nutrient input.