Microalgae undertake a wide range of mutualistic interactions with bacteria. Here we consider how transcriptomic, metagenomic and metabolomic approaches have been combined with microbiological and biochemical analyses to expand our understanding of algal-bacterial interactions. Identification of the major bacterial species associated with algae indicates that specific bacterial groups, particularly the alpha-Proteobacteria, are found more frequently, suggesting that these may have the means to initiate and maintain symbiotic relationships. Nutrient exchange is frequently the basis of algal-bacterial mutualism, and as the compounds involved are characterised, evidence is accumulating that these are complex and specific molecules, offering opportunities for signalling processes and regulation rather than merely passive diffusion. At the same time, it is clear that the interactions are not static, but can be initiated and broken in response to environmental and developmental cues.

Ostreococcus tauri, a picoeukaryotic alga that contributes significantly to primary production in oligotrophic waters, has a highly streamlined genome, lacking the genetic capacity to grow without the vitamins thiamine (B) and cobalamin (B) Here we demonstrate that the B and B auxotrophy of O. tauri can be alleviated by co-culturing with a heterotrophic bacterial partner Dinoroseobacter shibae, a member of the Rhodobacteraceae family of alpha-proteobacteria, genera of which are frequently found associated with marine algae. D. shibae lacks the complete pathway to synthesise three other B-vitamins: niacin (B), biotin (B), and p-aminobenzoic acid (a precursor for folate, B), and the alga is in turn able to satisfy the reciprocal vitamin requirements of its bacterial partner in a stable long-term co-culture. Bioinformatics searches of 197 representative marine bacteria with sequenced genomes identified just nine species that had a similar combination of traits (ability to make vitamin B, but missing one or more genes for niacin and biotin biosynthesis enzymes), all of which were from the Rhodobacteraceae. Further analysis of 70 species from this family revealed the majority encoded the B pathway, but only half were able to make niacin, and fewer than 13% biotin. These characteristics may have either contributed to or resulted from the tendency of members of this lineage to adopt lifestyles in close association with algae. This study provides a nuanced view of bacterial-phytoplankton interactions, emphasising the complexity of the sources, sinks and dynamic cycling between marine microbes of these important organic micronutrients.

Abstract. The initial insight into electron elastic scattering off endohedral fullerenes A@C 60 is gained in the framework of a theoretical approach where the C 60 cage is modelled by a rectangular (in the radial coordinate) potential well, as in many other A@C 60 studies. The effect of a noticeably weaker electron elastic scattering off A@C 60 compared to that off empty C 60 or even the isolated atom A itself, as well as a strong sensitivity of e + A@C 60 scattering to the spin of the captured atom A are unraveled, for certain kinds of atoms. Obtained results lay out the initial qualitative basis for identifying interesting measurements and/or more rigorous calculations of e + A@C 60 elastic scattering to perform.

Electron elastic-scattering phase shifts and cross sections along with the differential and total cross sections and polarization of low-frequency bremsstrahlung upon low-energy electron collision with endohedral fullerenes A@C 60 are theoretically scrutinized versus the nature, size and spin of the encapsulated atom A. The case-study-atoms A are N, Ar, Cr, Mn, Mo, Tc, Xe, Ba, and Eu.They are thoughtfully picked out of different rows of the periodic table. The study is performed in the framework of a model static approximation. There, both the encapsulated atom A and C 60 cage are regarded as non-polarizable targets. The C 60 cage is modeled by an attractive spherical annular-potential well. The study provides the most complete initial understanding of how the processes of interest might evolve upon electron collision with various A@C 60 . Calculated results identify the most interesting and/or useful future measurements or more rigorous calculations to perform.

Summary The unicellular green alga Lobomonas rostrata requires an external supply of vitamin B12 (cobalamin) for growth, which it can obtain in stable laboratory cultures from the soil bacterium Mesorhizobium loti in exchange for photosynthate. We investigated changes in protein expression in the alga that allow it to engage in this mutualism.We used quantitative isobaric tagging (iTRAQ) proteomics to determine the L. rostrata proteome grown axenically with B12 supplementation or in coculture with M. loti. Data are available via ProteomeXchange (PXD005046).Using the related Chlamydomonas reinhardtii as a reference genome, 588 algal proteins could be identified. Enzymes of amino acid biosynthesis were higher in coculture than in axenic culture, and this was reflected in increased amounts of total cellular protein and several free amino acids. A number of heat shock proteins were also elevated. Conversely, photosynthetic proteins and those of chloroplast protein synthesis were significantly lower in L. rostrata cells in coculture. These observations were confirmed by measurement of electron transfer rates in cells grown under the two conditions.The results indicate that, despite the stability of the mutualism, L. rostrata experiences stress in coculture with M. loti, and must adjust its metabolism accordingly.

No abstract

Gaseous oxidized mercury (GOM) is a major chemical form responsible for deposition of atmospheric mercury, but its interaction with environmental surfaces is not well understood. To address this knowledge gap, we investigated the uptake of gaseous HgCl 2 , used as a GOM surrogate, by several inorganic salts representative of marine and urban aerosols. The process was studied in a fast flow reactor coupled to an ion drift−chemical ionization mass spectrometer, where gaseous HgCl 2 was quantitatively detected as HgCl 2 •NO 3 − . Uptake curves showed a common behavior, where upon exposure of the salt surface to HgCl 2 , the gas-phase concentration of the latter dropped rapidly and then recovered gradually. None of the salts produced a full recovery of HgCl 2 , indicating the presence of an irreversible chemical reaction in addition to reversible adsorption, and all salts showed reactive behavior consistent with the presence of surface sites of a high and a low reactivity. On the basis of the decrease in the uptake coefficient with increasing concentration of gaseous HgCl 2 , we conclude that the interaction follows the Langmuir−Hinshelwood mechanism. The reactivity of a deactivated salt surface after uptake could be partially restored by cycling through an elevated relative humidity at atmospheric pressure. The overall surface reactivity decreased in the series Na 2 SO 4 > NaCl > (NH 4 ) 2 SO 4 > NH 4 NO 3 . The uptake on NH 4 NO 3 was nearly fully reversible, with low values of the initial (0.4 × 10 −2 ) and steady-state (3.3 × 10 −4 ) uptake coefficients, whereas Na 2 SO 4 was significantly more reactive (3.1 × 10 −2 and 1.7 × 10 −3 ). Depending on the aerosol loading, the lifetimes of gaseous HgCl 2 on dry urban and marine particles (as pure (NH 4 ) 2 SO 4 and NaCl, respectively) were estimated to range from half an hour to about a day.

, populate the regime between frozen-in and fully kinetic plasma. Understanding such instabilities is vital to understanding fundamental particle-field energy dynamics of said regime. As has been shown (Bale et al., 2002; Curtis et al., 1982; Tang et al., 2013; Thorne, 2010), plasma instabilities represent a unique degree of freedom for energy transfer in plasmas, and mirror modes are no exception. Hydrogen plasmas whose β (particle pressure/magnetic field pressure) values are above unity (high-β) represent plasmas where mirror modes are likely to form. High-β plasmas have been found in the solar wind (