Does Pseudomonas aeruginosa use intercellular signalling to build biofilm communities?

Pseudomonas aeruginosa is a Gram-negative bacterial species that causes several opportunistic human infections. This organism is also found in the environment, where it is renowned (like other Pseudomonads) for its ability to use a wide variety of compounds as carbon and energy sources. It is a model species for studying group-related behaviour in bacteria. Two types of group behaviour it engages in are intercellular signalling, or quorum sensing, and the formation of surface-associated communities called biofilms. Both quorum sensing and biofilm formation are important in the pathogenesis of P. aeruginosa infections. Quorum sensing regulates the expression of several secreted virulence factors and quorum sensing mutant strains are attenuated for virulence in animal models. Biofilms have been implicated in chronic infections. Two examples are the chronic lung infections afflicting people suffering from cystic fibrosis and colonization of indwelling medical devices. This review will discuss quorum sensing and biofilm formation and studies that link these two processes.     

Species traits and climate velocity explain geographic range shifts in an ocean‐warming hotspot

Species' ranges are shifting globally in response to climate warming, with substantial variability among taxa, even within regions. Relationships between range dynamics and intrinsic species traits may be particularly apparent in the ocean, where temperature more directly shapes species' distributions. Here, we test for a role of species traits and climate velocity in driving range extensions in the ocean‐warming hotspot of southeast Australia. Climate velocity explained some variation in range shifts, however, including species traits more than doubled the variation explained. Swimming ability, omnivory and latitudinal range size all had positive relationships with range extension rate, supporting hypotheses that increased dispersal capacity and ecological generalism promote extensions. We find independent support for the hypothesis that species with narrow latitudinal ranges are limited by factors other than climate. Our findings suggest that small‐ranging species are in double jeopardy, with limited ability to escape warming and greater intrinsic vulnerability to stochastic disturbances.     

EFFECTS OF INCREASED TEMPERATURE AND CO2 ON PHOTOSYNTHESIS,GROWTH, AND ELEMENTAL RATIOS IN MARINE SYNECHOCOCCUS AND PROCHLOROCOCCUS (CYANOBACTERIA)1

Little is known about the combined impacts of future CO₂ and temperature increases on the growth and physiology of marine picocyanobacteria. We incubated Synechococcus and Prochlorococcus under present‐day (380 ppm) or predicted year‐2100 CO₂ levels (750 ppm), and under normal versus elevated temperatures (+4°C) in semicontinuous cultures. Increased temperature stimulated the cell division rates of Synechococcus but not Prochlorococcus. Doubled CO₂ combined with elevated temperature increased maximum chl a–normalized photosynthetic rates of Synechococcus four times relative to controls. Temperature also altered other photosynthetic parameters (α, Φ_max, E_k, and ) in Synechococcus, but these changes were not observed for Prochlorococcus. Both increased CO₂ and temperature raised the phycobilin and chl a content of Synechococcus, while only elevated temperature increased divinyl chl a in Prochlorococcus. Cellular carbon (C) and nitrogen (N) quotas, but not phosphorus (P) quotas, increased with elevated CO₂ in Synechococcus, leading to ～20% higher C:P and N:P ratios. In contrast, Prochlorococcus elemental composition remained unaffected by CO₂, but cell volume and elemental quotas doubled with increasing temperature while maintaining constant stoichiometry. Synechococcus showed a much greater response to CO₂ and temperature increases for most parameters measured, compared with Prochlorococcus. Our results suggest that global change could influence the dominance of Synechococcus and Prochlorococcus ecotypes, with likely effects on oligotrophic food‐web structure. However, individual picocyanobacteria strains may respond quite differently to future CO₂ and temperature increases, and caution is needed when generalizing their responses to global change in the ocean.     

Molecular and morphological diversity of Trebouxia microalgae in sphaerothallioid Circinaria spp. lichens1

Three vagrant (Circinaria hispida, Circinaria gyrosa, and Circinaria sp. ‘paramerae’) and one crustose (semi‐vagrant, Circinaria sp. ‘oromediterranea’) lichens growing in very continental areas in the Iberian Peninsula were selected to study the phycobiont diversity. Mycobiont identification was checked using nrITS DNA barcoding: Circinaria sp. ‘oromediterranea’ and Circinaria sp. ‘paramerae’ formed a new clade. Phycobiont diversity was analyzed in 50 thalli of Circinaria spp. using nrITS DNA and LSU rDNA, with microalgae coexistence being found in all the species analyzed by Sanger sequencing. The survey of phycobiont diversity showed up to four different Trebouxia spp. as the primary phycobiont in 20 thalli of C. hispida, in comparison with the remaining Circinaria spp., where only one Trebouxia was the primary microalga. In lichen species showing coexistence, some complementary approaches are needed (454 pyrosequencing and/or ultrastructural analyses). Five specimens were selected for high‐throughput screening (HTS) analyses: 22 Trebouxia OTUs were detected, 10 of them not previously known. TEM analyses showed three different cell morphotypes (Trebouxia sp. OTU A12, OTU S51, and T. cretacea) whose ultrastructure is described here in detail for the first time. HTS revealed a different microalgae pool in each species studied, and we cannot assume a specific pattern between these pools and the ecological and/or morphological characteristics. The mechanisms involved in the selection of the primary phycobiont and the other microalgae by the mycobiont are unknown, and require complex experimental designs. The systematics of the genus Circinaria is not yet well resolved, and more analyses are needed to establish a precise delimitation of the species.     

Physicochemical and transfection properties of cationic Hydroxyethylcellulose/DNA nanoparticles

In this study the physicochemical and transfection properties of cationic hydroxyethylcellulose/plasmid DNA (pDNA) nanoparticles were investigated and compared with the properties of DNA nanoparticles based on polyethylene imine (PEI), which is widely investigated as a gene carrier. The two types of cationic hydroxyethylcelluloses studied, polyquaternium-4 (PQ-4) and polyquaternium-10 (PQ-10), are already commonly used in cosmetic and topical drug delivery devices. Both PQ-4 and PQ-10 spontaneously interact with pDNA with the formation of nanoparticles approximately 200 nm in size. Gel electrophoresis and fluorescence dequenching experiments indicated that the interactions between pDNA and the cationic celluloses were stronger than those between pDNA and PEI. The cationic cellulose/pDNA nanoparticles transfected cells to a much lesser extent than the PEI-based pDNA nanoparticles. The low transfection property of the PQ-4/pDNA nanoparticles was attributed to their neutrally charged surface, which does not allow an optimal binding of PQ-4/pDNA nanoparticles to cellular membranes. Although the PQ-10/pDNA nanoparticles were positively charged and thus expected to be taken up by cells, they were also much less efficient in transfecting cells than were PEI/pDNA nanoparticles. Agents known to enhance the endosomal escape were not able to improve the transfection properties of PQ-10/pDNA nanoparticles, indicating that a poor endosomal escape is, most likely, not the major reason for the low transfection activity of PQ-10/pDNA nanoparticles. We hypothesized that the strong binding of pDNA to PQ-10 prohibits the release of pDNA from PQ-10 once the PQ-10/pDNA nanoparticles arrive in the cytosol of the cells. Tailoring the nature and extent of the cationic side chains on this type of cationic hydroxyethylcellulose may be promising to further enhance their DNA delivery properties.     

Cytosolic RNA:DNA hybrids activate the cGAS–STING axis

Intracellular recognition of non‐self and also self‐nucleic acids can result in the initiation of potent pro‐inflammatory and antiviral cytokine responses. Most recently, cGAS was shown to be critical for the recognition of cytoplasmic dsDNA. Binding of dsDNA to cGAS results in the synthesis of cGAMP(2′–5′), which then binds to the endoplasmic reticulum resident protein STING. This initiates a signaling cascade that triggers the induction of an antiviral immune response. While most studies on intracellular nucleic acids have focused on dsRNA or dsDNA, it has remained unexplored whether cytosolic RNA:DNA hybrids are also sensed by the innate immune system. Studying synthetic RNA:DNA hybrids, we indeed observed a strong type I interferon response upon cytosolic delivery of this class of molecule. Studies in THP‐1 knockout cells revealed that the recognition of RNA:DNA hybrids is completely attributable to the cGAS–STING pathway. Moreover, in vitro studies showed that recombinant cGAS produced cGAMP upon RNA:DNA hybrid recognition. Altogether, our results introduce RNA:DNA hybrids as a novel class of intracellular PAMP molecules and describe an alternative cGAS ligand next to dsDNA.     

Lipid content and apoptosis of in vitro-produced bovine embryos as determinants of susceptibility to vitrification

The objective was to evaluate supplementation of fetal calf serum (FCS) and phenazine ethosulfate (PES), a metabolic regulator that inhibits fatty acid synthesis, in culture media during in vitro production (IVP) of bovine embryos. Taking oocyte fertilization (n = 4,320) as Day 0, four concentrations of FCS (0, 2.5, 5, and 10%) and three periods of exposure to PES (without addition—Control; after 60 h—PES Day 2.5 of embryo culture; and after 96 h—PES Day 4) were evaluated. Increasing FCS concentration in the culture media enhanced lipid accumulation (P < 0.05), increased apoptosis in fresh (2.5%: 19.1 ± 1.8 vs 10%: 28.4 ± 2.3, P < 0.05; mean ± SEM) and vitrified (2.5%: 42.8 ± 2.7 vs 10%: 69.2 ± 3.4, P < 0.05) blastocysts, and reduced blastocoele re-expansion after vitrification (2.5%: 81.6 ± 2.5 vs 10%: 67.3 ± 3.5, P < 0.05). The addition of PES in culture media, either from Days 2.5 or 4, reduced lipid accumulation (P < 0.05) and increased blastocoele re-expansion after vitrification (Control: 72.0 ± 3.0 vs PES Day 2.5: 79.9 ± 2.8 or PES Day 4: 86.2 ± 2.4, P < 0.05). However, just the use of PES from D4 reduced apoptosis in vitrified blastocysts (Control: 52.0 ± 3.0 vs PES Day 4: 39.2 ± 2.4, P < 0.05). Independent of FCS withdrawal or PES addition to culture media, the in vivo control group had lesser lipid accumulation, a lower apoptosis rate, and greater cryotolerance (P < 0.05). The increased lipid content was moderately correlated with apoptosis in vitrified blastocysts (r = 0.64, P = 0.01). In contrast, the increased apoptosis in fresh blastocysts was strongly correlated with apoptosis in vitrified blastocysts (r = 0.94, P < 0.0001). Therefore, using only 2.5% FCS and the addition of PES from Day 4, increased the survival of IVP embryos after vitrification. Moreover, embryo quality, represented by the fresh apoptosis rate, was better than lipid content for predicting embryo survival after vitrification.