A 4 year series of field, light-microscope and ultrastructural observations is presented to illustrate biological aspects of the annual cycle of natural Microcystis populations enclosed in Lund tubes. Nine morphological stati, all referable to M. aeruginosa f. aeruginosa , feature at various stages of the cycle. Summer bloom-forming populations originate from vegetative colonial stock that overwinters on the bottom sediment each year, but there is no mass transfer of these colonies to the water column: intensive growth from individual cells in the old colonies leads to the formation of new infective colonies, being stimulated when the bottom water approaches anoxia and light penetrates to the bottom sediments. Growth is slow but the developing populations sustain only minor losses through grazing and settling out, eventually becoming dominant over other species. Allelopathy possibly contributes to this effect. In postmaximal populations, several mechanisms can contribute to net buoyancy loss and a (usually) rapid recruitment of vegetative colonies to the sediments is observed. Hypotheses are advanced to account for the observed behaviour, and some of these have been tested in the laboratory. The apparent physiological flexibility of Microcystis seems well suited to growth and survival in the microenvironments encountered in eutrophic lakes.

On the Annual Cycle of the Blue-Green Alga Microcystis Aeruginosa Kutz. Emend. Elenkin

Ultrasound is among the most widely used non-invasive imaging modalities in biomedicine, but plays a surprisingly small role in molecular imaging due to a lack of suitable molecular reporters on the nanoscale. Here, we introduce a new class of reporters for ultrasound based on genetically encoded gas nanostructures from microorganisms, including bacteria and archaea. Gas vesicles are gas-filled protein-shelled compartments with typical widths of 45-250 nm and lengths of 100-600 nm that exclude water and are permeable to gas. We show that gas vesicles produce stable ultrasound contrast that is readily detected in vitro and in vivo, that their genetically encoded physical properties enable multiple modes of imaging, and that contrast enhancement through aggregation permits their use as molecular biosensors.

/pdf/biogenic-gas-nanostructures-as-ultrasonic-molecular-1odhzs8uy2.pdf

Biogenic gas nanostructures as ultrasonic molecular reporters

Publisher Summary Besides the many species representative of the major eukaryotic algal phyla, the freshwater phytoplankton comprises a number of cyanobacteria (or blue-green algae) These aggregations have earned recognition in their own collective term, “water blooms” This chapter reviews the aspects of ecology of planktonic cyanobacreria in relation to the factors governing their buoyancy, population dynamics, and perennation in natural limnetic environments The buoyant properties of cyanobacteria are assessed in relation to the Stokes equation, drawing distinctions between the differential contributions of size, density, and form resistance among individual genera Density is altered through the erection or collapse of gas vesicles, their dilution by growth and through the maintenance of glycogen ballast The outcome of buoyancy-controlled movements in natural fields of turbulent mixing is described in empirical terms The chapter also reviews the growth requirements of cyanobacteria with respect to temperature, light, and nutrients together with their responses to deficiencies of supply The outcome of interactions between buoyancy regulation and limiting resources are proposed in a series of hypothetical model environments The circumstances under which excess buoyancy is acquired and expressed in surface bloom formation are re-examined Adaptations for perennation and re-establishment of populations after bloom formation or other adverse conditions are reviewed The evolutionary strategies of planktonic cyanobacteria are deduced

Cyanobacterial Water-Blooms

Floating and sinking in gas‐vacuolate cyanobacteria1

The carboxysomes of Thiobacillus neapolitanus are shown, by electron microscopy, to consist of a paracrystalline array of 10-nm particles surrounded by a “membrane.” The 10-nm particles have a center hole or depression and have been previously identified as ribulose diphosphate carboxylase. The membrane is a monolayer approximately 3.5-nm thick.

Electron Microscopy of the Carboxysomes (Polyhedral Bodies) of Thiobacillus neapolitanus

A method involving penicillin treatment was developed to osmotically lyse the cells of the blue-green alga,Microcystis aeruginosa Kuetz. emend. Elenkin, and release the pressure-sensitive gas vacuoles intact. The gas vacuoles were purified by liquid-polymer partitioning or by macromolecular sieving and centrifugation. The degree of purification of the gas vacuoles was followed by observation in the electron microscope and by the use of C14-labeled vacuolated and nonvacuolated strains ofM. aeruginosa. The gas-vacuole membrane is composed of only protein consisting of 10% basic, 18% acidic and 52% non-polar amino acids.

Isolation and chemical characterization of gas-vacuole membranes from Microcystis aeruginosa Kuetz. emend. Elenkin.

The morphological parameters of the cylindrical gas vacuoles in the blue-green alga, Microcystis aeruginosa, were investigated by quantitative electron microscopy. The gas vacuoles are made up of a...

Morphological parameters and macromolecular organization of gas vacuole membranes of Microcystis aeruginosa Kuetz. emend. Elenkin.

A microdroplet spray method is described to determine quantitatively the number of gas vacuoles in purified fractions and in total lysates of the blue-green alga,Microcystis aeruginosa. It is found that 6.45×1012 gas vacuoles of 370 nm length make up one mg of protein. This supports the idea that the entire organelle is made up by a single layer of protein only. The gas vacuole number per cell varies with the stage of growth between 3,700 and 11,000.

Counting of gas vacuoles by electron microscopy in lysates and purified fractions of Microcystis aeruginosa.

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Isolation and chemical characterization of gas-vacuole membranes from Microcystis aeruginosa Kuetz. emend. Elenkin.

Morphological parameters and macromolecular organization of gas vacuole membranes of Microcystis aeruginosa Kuetz. emend. Elenkin.

Counting of gas vacuoles by electron microscopy in lysates and purified fractions of Microcystis aeruginosa.