Uncoupling Between Dinitrogen Fixation and Primary Productivity in the Eastern Mediterranean Sea

In the nitrogen (N)-impoverished photic zones of many oceanic regions, prokaryotic organisms fixing atmospheric dinitrogen (N2; diazotrophs) supply an essential source of new nitrogen and fuel primary production. We measured dinitrogen fixation and primary productivity (PP) during the thermally stratified summer period in different water regimes of the oligotrophic eastern Mediterranean Sea, including the Cyprus Eddy and the Rhodes Gyre. Low N2 fixation rates were measured (0.8-3.2μmol N m-2 d-1) excluding 10-fold higher rates in the Rhodes Gyre and Cyprus Eddy (~20μmol N m-2 d-1). The corresponding PP increased from east to west (200-2500μmol C m-2 d-1), with relatively higher productivity recorded in the Rhodes Gyre and Cyprus Eddy (2150 and 2300μmol C m-2 d-1, respectively). These measurements demonstrate that N2 fixation in the photic zone of the eastern Mediterranean Sea contributes only negligibly by direct inputs to PP (i.e., cyanobacterial diazotrophs) and is in fact uncoupled from PP. By contrast, N2 fixation is significantly coupled to bacterial productivity and to net heterotrophic areas, suggesting that heterotrophic N2 fixation may in fact be significant in this ultraoligotrophic system. This is further substantiated by the high N2 fixation rates we measured from aphotic depths and by the results of phylogenetic analysis in other studies showing an abundance of heterotrophic diazotrophs

Flood-induced multiday torpor in golden spiny mice (Acomys russatus)

Mammalian and avian torpor is widely viewed as an adaptation for survival of cold winters. However, in recent years it has been established that torpor can also be expressed in summer and that the functions of torpor are manyfold, including survival of adverse environmental events such as fires, storms, heat waves and droughts. Here we provide the first evidence on (1) torpor induction via an accidental flooding event in mammals (in captivity) and (2) expression of multiday torpor by spiny mice, lasting >7 times as long as usually observed for this desert rodent. Our data suggest yet another function of mammalian torpor, as a response to flood, in addition to many other adverse environmental events, and not just in response to cold.7 times as long as usually observed for this desert rodent. Our data suggest yet another function of mammalian torpor, as a response to flood, in addition to many other adverse environmental events, and not just in response to cold

A remote sensing approach for exploring the dynamics of jellyfish, relative to the water current

Abstract Drifting in large numbers, jellyfish often interfere in the operation of nearshore electrical plants, cause disturbances to marine recreational activity, encroach upon local fish populations, and impact food webs. Understanding the dynamic mechanisms behind jellyfish behavior is of importance in order to create migration models. In this work, we focus on the small-scale dynamics of jellyfish and offer a novel method to accurately track the trajectory of individual jellyfish with respect to the water current. The existing approaches for similar tasks usually involve a surface float tied to the jellyfish for location reference. This operation may induce drag on the jellyfish, thereby affecting its motion. Instead, we propose to attach an acoustic tag to the jellyfish’s bell and then track its geographical location using acoustic beacons, which detect the tag’s emissions, decode its ID and depth, and calculate the tag’s position via time-difference-of-arrival acoustic localization. To observe the jellyfish’s motion relative to the water current, we use a submerged floater that is deployed together with the released tagged jellyfish. Being Lagrangian on the horizontal plane while maintaining an on-demand depth, the floater drifts with the water current; thus, its trajectory serves as a reference for the current’s velocity field. Using an acoustic modem and a hydrophone mounted to the floater, the operator from the deploying boat remotely changes the depth of the floater on-the-fly, to align it with that of the tagged jellyfish (as reported by the jellyfish’s acoustic tag), thereby serving as a reference for the jellyfish’s 3D motion with respect to the water current. We performed a proof-of-concept to demonstrate our approach over three jellyfish caught and tagged in Haifa Bay, and three corresponding floaters. The results present different dynamics for the three jellyfish, and show how they can move with, and even against, the water current

Direct fluorescence detection of VirE2 secretion by Agrobacterium tumefaciens.

VirE2 is a ssDNA binding protein essential for virulence in Agrobacterium tumefaciens. A tetracysteine mutant (VirE2-TC) was prepared for in vitro and in vivo fluorescence imaging based on the ReAsH reagent. VirE2-TC was found to be biochemically active as it binds both ssDNA and the acidic secretion chaperone VirE1. It was also biologically functional in complementing virE2 null strains transforming Arabidopsis thaliana roots and Nicotiana tabacum leaves. In vitro experiments demonstrated a two-color fluorescent complex using VirE2-TC/ReAsH and Alexa Fluor 488 labeled ssDNA. In vivo, fluorescent VirE2-TC/ReAsH was detected in bacteria and in plant cells at time frames relevant to transformation

GUS expression in <i>Arabidopsis</i> roots.

<p>(A) Infection by VirE2-null strain with both wild-type VirE2 expression and GUS gene transfer from binary plasmid pCAMBIA2301. (B) Infection by VirE2-null strain with both VirE2-TC expression and GUS gene transfer from binary plasmid pCAMBIA2301. (C) Positive control: GUS expression in roots infected by wild type strain transferring GUS gene from pCAMBIA2301 vector. (D) Negative control: roots infected by VirE2-null strain carrying the same GUS gene on pCAMBIA2301 vector.</p

Differences in Membrane Fluidity and Fatty Acid Composition between Phenotypic Variants of Streptococcus pneumoniae

Phase variation in the colonial opacity of Streptococcus pneumoniae has been implicated as a factor in the pathogenesis of pneumococcal disease. This study examined the relationship between membrane characteristics and colony morphology in a few selected opaque-transparent couples of S. pneumoniae strains carrying different capsular types. Membrane fluidity was determined on the basis of intermolecular excimerization of pyrene and fluorescence polarization of 1,6-diphenyl 1,3,5-hexatriene (DPH). A significant decrease, 16 to 26% (P ≤ 0.05), in the excimerization rate constant of the opaque variants compared with that of the transparent variants was observed, indicating higher microviscosity of the membrane of bacterial cells in the opaque variants. Liposomes prepared from phospholipids of the opaque phenotype showed an even greater decrease, 27 to 38% (P ≤ 0.05), in the pyrene excimerization rate constant compared with that of liposomes prepared from phospholipids of bacteria with the transparent phenotype. These findings agree with the results obtained with DPH fluorescence anisotropy, which showed a 9 to 21% increase (P ≤ 0.001) in the opaque variants compared with the transparent variants. Membrane fatty acid composition, determined by gas chromatography, revealed that the two variants carry the same types of fatty acids but in different proportions. The trend of modification points to the presence of a lower degree of unsaturated fatty acids in the opaque variants compared with their transparent counterparts. The data presented here show a distinct correlation between phase variation and membrane fluidity in S. pneumoniae. The changes in membrane fluidity most probably stem from the observed differences in fatty acid composition

Electrophoretic Mobility Shift Analysis (EMSA) confirms binding of VirE2 to M13 ssDNA substrate.

<p>M13 ssDNA concentration was held constant, while relative protein concentration increased. Lanes: (A) M13 alone, B-E) wtVirE2 at 1:1, 1:5, 1:10, 1:15 ratios wt:wt, (F-I) VirE2-TC at equal ratios. VirE2-TC binds M13 ssDNA less avidly than the wild-type, but leaves no evidence of completely unbound ssDNA.</p

A <i>virB</i> mutant strain does not secrete fluorescent puncta.

<p>(A) Large, motile fluorescent spots, visible also in the bright field images (B, lower panels), indicate bacteria. Smaller spots representing secreted VirE2 in the host cells were not observed. Scale bar 10 μm.</p

<i>In vivo</i> labeling of VirE2-TC.

<p>ReAsH labeling of virulence activated bacteria expressing VirE2-TC. Inset: zoom of a single fluorescent bacterium (white arrow) shows polar accumulation of the fluorescent label. Scale bar 10 μm.</p