Frederica W. Valois

Nitrospira marina gen. nov. sp. nov.: a chemolithotrophic nitrite-oxidizing bacterium

A new chemolithotrophic nitrite-oxidizing bacterium, for which the name Nitrospira marina is proposed, was isolated from the Gulf of Maine. N. marina is a Gramnegative curved rod which may form spirals with 1 to 12 turns. Cells have a unique periplasmic space and lack intracytoplasmic membranes and carboxysomes. N. marina is an obligate chemolithotroph, but best growth is obtained in a mixotrophic medium. N. marina may be one of the most prevalent nitrite-oxidizing bacteria in some oceanic environments. Type strain is field with American Type Culture Collection (ATCC 43039).

Iron conservation by reduction of metalloenzyme inventories in the marine diazotroph Crocosphaera watsonii

The marine nitrogen fixing microorganisms (diazotrophs) are a major source of nitrogen to open ocean ecosystems and are predicted to be limited by iron in most marine environments. Here we use global and targeted proteomic analyses on a key unicellular marine diazotroph Crocosphaera watsonii to reveal large scale diel changes in its proteome, including substantial variations in concentrations of iron metalloproteins involved in nitrogen fixation and photosynthesis, as well as nocturnal flavodoxin production. The daily synthesis and degradation of enzymes in coordination with their utilization results in a lowered cellular metalloenzyme inventory that requires ∼40% less iron than if these enzymes were maintained throughout the diel cycle. This strategy is energetically expensive, but appears to serve as an important adaptation for confronting the iron scarcity of the open oceans. A global numerical model of ocean circulation, biogeochemistry and ecosystems suggests that Crocosphaera’s ability to reduce its iron-metalloenzyme inventory provides two advantages: It allows Crocosphaera to inhabit regions lower in iron and allows the same iron supply to support higher Crocosphaera biomass and nitrogen fixation than if they did not have this reduced iron requirement.

A Cyanobacterium Capable of Swimming Motility

A novel cyanobacterium capable of swimming motility was isolated in pure culture from several locations in the Atlantic Ocean. It is a small unicellular form, assignable to the genus Synechococcus, that is capable of swimming through liquids at speeds of 25 micrometers per second. Light microscopy revealed that the motile cells display many features characteristic of bacterial flagellar motility. However, electron microscopy failed to reveal flagella and shearing did not arrest motility, indicating that the cyanobacterium may be propelled by a novel mechanism.

The Family Nitrobacteraceae

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.

Phenotypic and genotypic characterization of multiple strains of the diazotrophic cyanobacterium, Crocosphaera watsonii, isolated from the open ocean

Diazotrophic cyanobacteria have long been recognized as important sources of reduced nitrogen (N) and therefore are important ecosystem components. Until recently, species of the filamentous cyanobacterium Trichodesmium were thought to be the primary sources of fixed N to the open ocean euphotic zone. It is now recognized that unicellular cyanobacteria are also important contributors, with members of the oligotrophic genus Crocosphaera being the only cultured examples. Herein we genetically and phenotypically characterize 10 strains isolated from the tropical Atlantic and North Pacific Oceans, and show that although all of the strains are highly similar at the genetic level, with the internal transcribed sequence (ITS) region sequence varying by approximately 2 bp on average, there are many unexpected phenotypic differences between the isolates (e.g. cell size, temperature optima and range, extracellular material excretion and variability in rates of nitrogen fixation). However based on the observed sequence similarity, we propose that all of these isolates are members of the genus Crocosphaera (type strain Crocosphaera watsonii WH8501), and that the phenotypic diversity we see may reflect ecologically important variation relevant for modelling N(2) fixation in the oligotrophic ocean.

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.

Ammonia oxidation by cell-free extracts of Nitrosocystisoceanus

Abstract Cell-free extracts prepared by rupturing cells of Nitrosocystis oceanus in the presence of seawater, Tris, ATP, magnesium, and phosphate oxidize ammonia to nitrite.