Charles C. Remsen

Effects of PCB on interspecific competition in natural and gnotobiotic phytoplankton communities in continuous and batch cultures

The toxicity of polychlorinated biphenyls (PCB) to the diatomThalassiosira pseudonana (formerlyCyclotella nana), grown in pure and mixed cultures, was greatest when in competition with other species. Continuous cultures were superior to batch cultures for studying competitive interactions, and PCB caused greater alteration of species composition in continuous cultures than it did in batch cultures. Natural phytoplankton communities from Vineyard Sound, maintained in continuous culture, responded to PCB stress the same as did gnotobiotic communities, withT. pseudonana showing similar responses in both communities.A PCB concentration of 0.1 μg/liter (0.1 part per billion), a level not uncommon in natural waters, did not affect algal growth in pure cultures but caused substantial disruption of continuous culture communities. The possible impact of PCB pollution on natural phytoplankton communities is discussed.

Competition for Urea among Estuarine Microorganisms

Phytoplankton were responsible for the major part of the urea decomposition in the Savannah—Wilmington—Ogeechee estuaries and adjacent coastal waters in Georgia. This is an exception to the general rule that bacteria are favored of algae in the competition for dissolved organic compounds. Filtration of estuary water through a 20—μ mesh filter did not significantly change the concentration of urea—decomposing bacteria; there was, however, a significant change in phytoplankton cell concentrations, chlorophyll a, and urea decomposition rates. Thus, any differences in the decomposition of urea in filtered and unfiltered aliquots could be attributed to the phytoplankters removed by filtration. Average cell concentrations and chlorophyll a removed by filtration was 15% and 39% of the totals, respectively. However, the removal of urea—decomposing activity average 53% of the total. This indicates that the phytoplankters removed by filtration, mainly diatoms with large cross—sectional areas such as Rhizosolenia, C...

Freeze-Etching of Bacteria

Publisher Summary The first electron micrographs of bacterial cells were published about 20 years ago. These early studies suggested the presence of definite intracellular structures. Sectioning techniques, originally developed for eucaryotic cells, were gradually modified so that thin sections of bacteria could be obtained. These first thin sections of procaryotic cells revealed an unsuspected level of intracellular complexity. While electron microscopes have advanced technically, preparative techniques for biological material have not kept pace. The newest models have a potential resolution of 0.2-0.3 nm but less refined preparative techniques have denied biologists the use of this degree of sophistication. Some difficulties encountered in the preparation of biological material for electron microscope examination are intrinsic and unavoidable. Live bacteria cannot be examined in thin section and the process of fixation and dehydration frequently alters or even extracts cellular components, leaving the degree of preservation of structural integrity open to question. About 10 years ago, a new technique permitting the replication of freeze-fractured live biological specimens was developed. This method allowed the internal morphology of cells that had neither been dried nor chemically fixed to be seen, thereby eliminating or minimizing many of the artifacts typically introduced. This chapter discusses the technique of freeze-etching; its application in bacterial cytology, morphology, and related fields; and its possible future development in microbiology.

A lobular, ammonia-oxidizing bacterium, Nitrosolobus multiformis nov.gen.nov.sp.

SummaryNitrosolobus multiformis is a lobular shaped, previously undescribed ammonia-oxidizing bacterium. The organism is ubiquitous and was isolated from soil samples obtained in various parts of the world. Its lobular nature and its internal, partially compartmentalized cytoplasm makes it morphologically unique and easily distinguishable from all other microorganisms. Physiological compartmentalization also occurs and is characterized by glycogen deposition in the peripheral compartments of the cell. The cells are obligate chemoautotrophs using CO2 and ammonia as primary carbon and energy sources. Its obligate chemoautotrophic nature stems primarily from a metabolic deficiency. Even though the cells cannot be grown on an organic medium the cells still have a slight heterotrophic potential and are able to oxidize and assimilate minute amounts of acetate in the absence of an inorganic energy source.

Cell envelope of Nitrosocystis oceanus

The cell envelope of Nitrosocystis oceanus , a marine nitrifying bacterium, has been shown to be composed of seven distinct layers including an outer fibrous slime layer, a hexagonal layer comprised of 50 A subunits, a double-tracked layer consisting of 40 A subunits, two globular layers which are separated by a mucopeptide layer, and a plasma membrane. These studies show that N. oceanus cell envelopes differ from those found in Escherichia coli and other Gramnegative bacteria and illustrate the value of combining freeze-etching with other electron microscopic techniques for the study of bacterial cell envelopes.

Macromolecular Subunits in the Walls of Marine Nitrifying Bacteria

The outteromost laver of the cell wall of all marine ammonia-oxidizing bacteria So far isolated is made up of protein subunits arranged in a regular manner and linked together through metal-oxygen bonds. This sculptured, outer wall layver appears to be uniique to the terrestrial ammonia-oxidizing bacteria.

THE CELL WALL OF PYROCYSTIS SPP. (DINOCOCCALES)1,2

The cell of Pyrocystis spp. is covered by an outer layer of material resistant to strong acids and bases. Internal to this layer much of the cell wall is composed of cellulose fibrils. The presence of cellulose fibrils was established by staining raw and ultra‐violet–peroxide‐cleaned cell walls and by combining X‐ray diffraction spectroscopy with electron microscope observation. Carbon replicas of freeze‐etched preparations and thin sections of P. lunula walls show outer layers, inside them ca. 24 layers of crossed parallel cellulose fibrils (4–5 nm thick, ca. 12 nm wide), then a region of smaller (ca. 6–12 nm diameter) fibrils in a disperse texture, and then the plasma membrane. Cellulose fibrils in the parallel texture are constructed of 3–5 elementary fibrils ca. 3 nm in diameter. Walls of P. fusiformis and P. pseudonctiluca also have cellulose fibrils in a crossed parallel texture similar to those of P. lunula.

Bacteriophage T2 as seen with the freeze-etching technique

Abstract Freeze-etching of bacteriophage T2 reveals new data on the phage ultrastructure which are discussed in relation to information obtained from negatively stained preparations. The polygonal head of the freeze-etched phage shows capsomeres of 10 nm (= 100 A) in diameter with central depressions. There are six neighbors around most of the capsomeres, and the repeat vector of the surface lattice measures about 10 nm. Individual capsomeres seem to be composed of smaller units. The sheath of the phage tail exhibits a surface lattice indicative of six right-handed helices. The helices reveal a beaded fine structure, the elements of which are interpreted as homologous to the subunits seen after negative staining. The neighboring helices are cross-linked by bridgelike elements. During sheath contraction the pitch angle of the helices increases from 50 ° to 66 °. In the contracted sheath twelve helices are visible, again composed of subunits and cross-linked to their neighbors. The surface structure of the “polysheath” resembles that of a contracted sheath. Polysheaths break down into right-handed helical structures.

Comparison of laboratory and in situ measurements of urea decomposition by a marine diatom

Abstract The rate of decomposition of urea in situ by a marine diatom has been compared with laboratory estimated rates, at in situ urea concentrations, using an isolate of the same diatom species. The in situ measurements were made at two stations off the coast of Georgia, U.S.A. At these stations, Stephanopyxis costata Hustedt ( Skeletonema costatum ), decomposed 7.76 and 4.40 nM urea l −1 h −1 . Using a clone of Stephanopyxis costata isolated near Marthas Vineyard, Massachusetts, we obtained a Michaelis-Menten curve for urea decomposition. At the urea concentrations of the two stations near Georgia (0.93 and 0.85 μM) we calculated urea decomposition of 0.27 and 0.13 nM urea l −1 h −1 . Thus, the laboratory-determined rates were 3.5 and 3.7% of the actual in situ rates. Measurements of in situ decomposition of an organic solute by one species are rare. The causes of these large differences in urea decomposition rates may possibly be related to temperature or genetic differences between races of S. costata . These data suggest a cautious approach to the application of laborator-determined kinetics to in situ conditions.

Fossil membranes and cell wall fragments from a 7000-year-old Black Sea sediment.

Lamellar and tubular membranes and orgacnic fragments resemnbling bacterial cell walls were abundant in Black Sea sediments deposited between 3000 and 7000 years ago. This time period was marked by a gradual transition from a freshwater to a seawater environment. The resulting salinity gradient in the interstitial solutions probably promoted natural chromatography and dissolution, redeposition, and preservation of organic molecules. The preservation of organic structures may have resulted from the lack of dissolved oxygen, high concentrations of metal ions, and structural reorganization during compaction.