The development and vertical distribution of populations of gas-vacuolate bacteria in a eutrophic,monomictic lake

The role of gas vacuoles in the vertical stratification of planktonic bacteria is analysed. Measurements made with certain gas-vacuolate bacteria in laboratory culture suggest that only colonial forms could sink or float fast enough to form population maxima in lakes by vertical migration from other depths. It is suggested that in the case of individual cells the importance of the buoyancy provided by gas vacuoles is to minimise sinking rates and thereby to increase residence times of the organisms at depths where conditions support their growth.Changes in the vertical distribution of a number of gas-vacuolate bacteria were followed throughout the year in a monomictic, eutrophic lake (Crose Mere, Shropshire). All were restricted to the anaerobic hypolimnion which developed in summer. The various species formed maxima at different depths and times. With some of them (e.g. species of Thiopedia, Pelonema and Brachyarcus) growth was necessary to explain their development. In others (e. g. species of Pelodictyon and two colourless bacteria) vertical migrations might also have contributed to their development.     

Crystalline structure of the gas vesicle wall from Anabaena flos-aquae.

The gas vesicles isolated from Anabaena flos-aquae have been studied by X-ray diffraction. Electron microscopy has previously shown that the gas vesicles are elongated shapes, with a thin wall having regular striations (ribs) at right-angles to the long axis. The X-ray diffraction pattern from a specimen of oriented, intact vesicles includes a number of sharp reflections which are attributed to regular structure in the plane of the wall. After correcting for the imperfect alignment of the long axes of the vesicles, the in-plane reflections are all seen to lie on a few, regularly spaced lines parallel to the long axis. This result shows for the first time that there are subunits regularly spaced along each rib, one subunit every 11 Å. The spacing of the in-plane reflections along each line is consistent with a rib periodicity of 46 Å. The 11 Å repeat, together with the 46 Å repeating distance from rib to rib and the average wall thickness of about 20 Å, define a volume for the subunit. Assuming a reasonable value for the density of the protein making up the wall, the molecular weight of the subunit indicated is about 8000 g/mol.The X-ray data also indicate that a large part of the protein is in the β-sheet conformation. In this structure there are parallel, or anti-parallel, polypeptide chains which are hydrogen-bonded to one another in a regular way to form a thin sheet. Assuming the wall contains β-sheet in two layers, one on top of the other and with the chains in each layer tilted at 35 ° to the long axis of the vesicle, we can explain a number of the X-ray observations: (1) oriented arcs with a Bragg spacing of 4.7 Å, which is the distance between the axes of neighbouring chains in each layer; (2) diffraction oriented in the direction of the chains at a spacing of 6 to 7 Å, which is the repeating distance of the dipeptide unit along the chain; (3) the 11 Å repeat, which is the repeating distance of pairs of chains along each rib; and (4) a broad band of diffraction at right-angles to the plane of the wall and centred at a spacing of 10 Å, which is a reasonable value for the distance between the mid-planes of the two sheets. Moreover, we can also find the remaining lattice parameter, the angle relating the centres of the subunits in neighbouring ribs. Thus the shortest line joining the centres makes an angle of 86 ° with the direction of the ribs.     

The extracellular products of Anabaena cylindrica Lemm. I. Isolation of a macromolecular pigment-peptide complex and other components

The extracellular products of Anabaena cylindrica Lemm. comprise a large variety of compounds including peptides, brownish pigments and substances fluorescing white and blue in ultraviolet light. A number were separated or isolated using techniques of gel filtration, ion exchange and paper chromatography. Serine and threonine comprised over 90% of the amino acids in a group of complex pigmented and fluorescent compounds. One of these accounted for a large proportion of the peptide and pigment present. It contained a large pigment moiety of molecular weight > 5 000 which formed a firm complex with more than 10% of the iron supplied in the culture medium. The anti-polymyxin activity described by Whitton was not associated with any of the major pigments or peptides present.     

Anachelin, the siderophore of the cyanobacterium Anabaena cylindrica CCAP 1403/2A

A catecholate siderophore - anachelin - has been isolated from the cyanobacterium Anabaena cylindrica CCAP 1403/2A. The central part of the siderophore is a tripeptide consisting of L-Thr, D-Ser and L-Ser. Its C-terminus is linked amidically to a 1,1-dimethyl-3-amino-1,2,3,4-tetrahydro-7,8-dihydroxyquinolinium system and its N-terminus to 6-amino-3,5,7-trihydroxyheptanoic acid. The 7-hydroxyl group of the latter is esterified with salicylic acid whose carboxyl group is condensed with the 6-amino group to an oxazoline ring. Anachelin is the first genuine siderophore of a cyanobacterium whose structure has been elucidated.     

Calculation of z-coordinates and orientational restraints using a metal binding tag

We introduce a new simple methodology allowing the measurement of (1)H-(15)N residual dipolar couplings, dipolar shifts, and unpaired electron-amide proton distances. This method utilizes a zinc finger tag fused at either the N- or the C-terminus of a protein. We have demonstrated this fusion strategy by incorporating the zinc finger of the retroviral gag protein onto the C-terminus of barnase, a ribonuclease produced by Bacillus amiloliquifaciance. We show that this tag can be substituted with cobalt and manganese. Binding of cobalt to the gag zinc finger-barnase fusion protein introduced sufficient anisotropic paramagnetic susceptibility for orientation of the molecule in the magnetic field. Partial alignment permitted measurement of (1)J(HN) scalar couplings along with dipolar couplings. Replacement of bound cobalt with diamagnetic zinc removes the paramagnetic-induced orientation of barnase, permitting the measurement of only (1)J(HN) scalar couplings. Dipolar couplings, ranging from -0.9 to 0.6 Hz, were easily measured from the difference in splitting frequencies in the presence of cobalt and zinc. The observed paramagnetic anisotropy induced by cobalt binding to the metal binding tag also permitted measurement of dipolar shifts. Substitution of manganese into the metal binding tag permitted the measurement of unpaired electron-amide proton distances using paramagnetic relaxation enhancement methodology. The availability of both amide proton dipolar shifts and unpaired electron to amide proton distances permitted the direct calculation of z-coordinates for individual amide protons. This approach is robust and will prove powerful for global fold determination of proteins identified in genome initiatives.     

The uptake of amino acids by the cyanobacterium Planktothrix rubescens is stimulated by light at low irradiances

The rates of uptake of five amino acids--alanine, glutamate, glycine, leucine and serine--by axenic cultures of the cyanobacterium Planktothrix rubescens were measured over a range of irradiances using the (14)C-labelled amino acids at the nanomolar concentrations observed in Lake Zürich. The rates in the light exceeded the dark rates by as much as two- to ninefold. The light-affinity constants for stimulation were similar, indicating a similar process for each of the five amino acids. The E(k) (light saturation irradiance) for light stimulation was only 1 micromol m(-2) s(-1), less than the compensation point for photosynthesis and autotrophic growth, and much lower than the E(k) for either process. The E(k) for amino acid uptake was also less than the irradiance at which filaments obtain neutral buoyancy, which determines the depth at which they stratify and the irradiance they receive. This indicates that stimulation of amino acid uptake by light of low irradiances provides a mechanism for supplementing growth of filaments stratifying deep in the metalimnion, which, while able to grow at low irradiances, are often left with insufficient light to sustain them. Acetate uptake was also stimulated by light, but the kinetics differed.     

GAS VACUOLE COLLAPSE IN MARINE OSCILLATORIA (TRICHODESMIUM) THIEBAUTII (CYANOPHYTA) AND THE EFFECT ON NITROGENASE ACTIVITY AND PHOTOSYNTHESIS1

Photosynthesis and nitrogenase activity (acetylene reduction) in Oscillatoria (Trichodesmium) thiebautii were significantly reduced after its gas vesicles were collapsed by pressurizing to 6·2 MPa (62 bars). The reduction in nitrogenase activity was observed with both intact and disrupted colonies, and under both aerobic and microaerobic conditions. It is unlikely, therefore, that the reduction in either process results solely from loss of gas diffusion pathways, and may simply originate from disturbance of the cellular architecture as gas vesicles are destroyed. Since nitrogenase activity of the samples was affected by gas vesicle collapse, the process presumably resides in the gas vacuolate organism (Oscillatoria) rather than in any associated bacteria which might be present.