Summary: On the basis of a comparative study of 178 strains of cyanobacteria, representative of this group of prokaryotes, revised definitions of many genera are proposed. Revisions are designed to permit the generic identification of cultures, often difficult through use of the field-based system of phycological classification. The differential characters proposed are both constant and readily determinable in cultured material. The 22 genera recognized are placed in five sections, each distinguished by a particular pattern of structure and development. Generic descriptions are accompanied by strain histories, brief accounts of strain properties, and illustrations; one or more reference strains are proposed for each genus. The collection on which this analysis was based has been deposited in the American Type Culture Collection, where strains will be listed under the generic designations proposed here.

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Generic assignments, strain histories, and properties of pure cultures of cyanobacteria

https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.

/pdf/nitrogen-cycles-past-present-and-future-1zdbw0976r.pdf

Nitrogen cycles: past, present, and future

We have applied “whole-genome shotgun sequencing” to microbial populations collected en masse on tangential flow and impact filters from seawater samples collected from the Sargasso Sea near Bermuda. A total of 1.045 billion base pairs of nonredundant sequence was generated, annotated, and analyzed to elucidate the gene content, diversity, and relative abundance of the organisms within these environmental samples. These data are estimated to derive from at least 1800 genomic species based on sequence relatedness, including 148 previously unknown bacterial phylotypes. We have identified over 1.2 million previously unknown genes represented in these samples, including more than 782 new rhodopsin-like photoreceptors. Variation in species present and stoichiometry suggests substantial oceanic microbial diversity. Microorganisms are responsible for most of the biogeochemical cycles that shape the environment of Earth and its oceans. Yet, these organisms are the least well understood on Earth, as the ability to study and understand the metabolic potential of microorganisms has been hampered by the inability to generate pure cultures. Recent studies have begun to explore environ

/pdf/environmental-genome-shotgun-sequencing-of-the-sargasso-sea-43wxijxylr.pdf

Environmental Genome Shotgun Sequencing of the Sargasso Sea

Fluorescent oligonucleotide hybridization probes were used to label bacterial cells for analysis by flow cytometry. The probes, complementary to short sequence elements within the 16S rRNA common to phylogenetically coherent assemblages of microorganisms, were labeled with tetramethylrhodamine and hybridized to suspensions of fixed cells. Flow cytometry was used to resolve individual target and nontarget bacteria (1 to 5 microns) via probe-conferred fluorescence. Target cells were quantified in an excess of nontarget cells. The intensity of fluorescence was increased additively by the combined use of two or three fluorescent probes complementary to different regions of the same 16S rRNA. Images

Combination of 16S rRNA-targeted oligonucleotide probes with flow cytometry for analyzing mixed microbial populations.

The synthesis of nitrogenase by non-heterocystous cyanobacteria

The biological oxidations of ammonia to nitrite and nitrite to nitrate, collectively referred to as nitrification, are carried out in nature by two physiological groups of Gram-negative, chemolithotrophic bacteria. The organisms in both groups fix carbon dioxide via the Calvin cycle (Campbell, Hellebust, and Watson, 1966) for their major source of cell carbon and derive their energy and reducing power either from the oxidation of ammonia (ammonia-oxidizing bacteria) or nitrite (nitrite-oxidizing bacteria). With the exception of a few strains of Nitrobacter winogradskyi, which can be grown chemoheterotro-phically, the nitrifying bacteria are obligate chemo-lithotrophs.

The Family Nitrobacteraceae

Oxygenic photosynthesis is the dominant mode of nutrition of cyanobacteria. Despite this seeming metabolic uniformity, their ecological diversity is remarkable; they occupy a very wide range of illuminated ecological niches in terrestrial, marine, and freshwater environments.

Isolation and Purification of Cyanobacteria: Some General Principles

Publisher Summary This chapter focuses on the isolation and growth of marine planktonic cyanobacteria. Cyanobacteria are widespread in marine habitats, especially in the warmer temperate and tropical regions, where they are important both as primary producers and nitrogen fixers. The overall taxonomic diversity of marine forms is comparable to that found in freshwater and terrestrial habitats. A variety of media has been used for the culture of marine cyanobacteria. Two in particular, one having a natural seawater base and the other having an artificial seawater base, have been used successfully for the isolation and maintenance of pure cultures of a variety of marine cyanobacteria, mostly of coastal origin (e.g., intertidal and salt marsh isolates). Neither of these media has been successful for the isolation and maintenance of the open ocean planktonic forms, necessitating the development of two new media, designated SN for the natural seawater medium and AN for the artificial seawater medium.

[6] Isolation and growth of marine planktonic cyanobacteria

The cell wall structure, arrangement of photosynthetic membranes, and the attachment of flagella of Ectothiorhodospira mobilis strain 8112 were examined by using freeze-etching and conventional electron microscopic techniques. The outer coat of the multilayered cell wall is comprised of 50 A repeating subunits, arranged in a regular array. The photosynthetic membranes, which originate from and are attached to the plasma membrane, are arranged in a more complex pattern than previously seen in other bacteria. The tuft of flagella in E. mobilis is inserted into a polar organelle. The relationship of this organelle to the polar membrane and the mechanism of attachment of the flagella to the polar organelle is discussed.

John B. Waterbury

Papers

The synthesis of nitrogenase by non-heterocystous cyanobacteria

The Family Nitrobacteraceae

Isolation and Purification of Cyanobacteria: Some General Principles

[6] Isolation and growth of marine planktonic cyanobacteria

Fine Structure of Ectothiorhodospira mobilis Pelsh