The intestinal microbe Escherichia coli is subject to fecal deposition in secondary habitats, where it persists transiently, allowing for the opportunity to colonize new hosts. Selection in the secondary habitat can be postulated, but its impact on the genomic diversity of E. coli is unknown. Environmental selective pressure on extrahost E. coli can be revealed by landscape genetic analysis, which examines the influences of dispersal processes, landscape features, and the environment on the spatiotemporal distribution of genes in natural populations. We conducted multilocus sequence analysis of 353 E. coli isolates from soil and fecal samples obtained in a recreational meadow to examine the ecological processes controlling their distributions. Soil isolates, as a group, were not genetically distinct from fecal isolates, with only 0.8% of genetic variation and no fixed mutations attributed to the isolate source. Analysis of the landscape genetic structure of E. coli populations showed a patchy spatial structure consistent with patterns of fecal deposition. Controlling for the spatial pattern made it possible to detect environmental gradients of pH, moisture, and organic matter corresponding to the genetic structure of E. coli in soil. Ecological distinctions among E. coli subpopulations (i.e., E. coli reference collection [ECOR] groups) contributed to variation in subpopulation distributions. Therefore, while fecal deposition is the major predictor of E. coli distributions on the field scale, selection imposed by the soil environment has a significant impact on E. coli population structure and potentially amplifies the occasional introduction of stress-tolerant strains to new host individuals by transmission through water or food.

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Azotobacter vinelandii has been studied for over 100 years since its discovery as an aerobic nitrogen-fixing organism. This species has proved useful for the study of many different biological systems, including enzyme kinetics and the genetic code. It has been especially useful in working out the structures and mechanisms of different nitrogenase enzymes, how they can function in oxic environments and the interactions of nitrogen fixation with other aspects of metabolism. Interest in studying A. vinelandii has waned in recent decades, but this bacterium still possesses great potential for new discoveries in many fields and commercial applications. The species is of interest for research because of its genetic pliability and natural competence. Its features of particular interest to industry are its ability to produce multiple valuable polymers - bioplastic and alginate in particular; its nitrogen-fixing prowess, which could reduce the need for synthetic fertilizer in agriculture and industrial fermentations, via coculture; its production of potentially useful enzymes and metabolic pathways; and even its biofuel production abilities. This review summarizes the history and potential for future research using this versatile microbe.

The diazotroph Azotobacter vinelandii possesses three distinct nitrogenase isoenzymes, all of which produce molecular hydrogen as a by-product. In batch cultures, A. vinelandii strain CA6, a mutant of strain CA, displays multiple phenotypes distinct from its parent: tolerance to tungstate, impaired growth and molybdate transport, and increased hydrogen evolution. Determining and comparing the genomic sequences of strains CA and CA6 revealed a large deletion in CA6's genome, encompassing genes related to molybdate and iron transport and hydrogen reoxidation. A series of iron uptake analyses and chemostat culture experiments confirmed iron transport impairment and showed that the addition of fixed nitrogen (ammonia) resulted in cessation of hydrogen production. Additional chemostat experiments compared the hydrogen-producing parameters of different strains: in iron-sufficient, tungstate-free conditions, strain CA6's yields were identical to those of a strain lacking only a single hydrogenase gene. However, in the presence of tungstate, CA6 produced several times more hydrogen. A. vinelandii may hold promise for developing a novel strategy for production of hydrogen as an energy compound.

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Electrospun chitosan nanofibers were deposited onto atmospheric plasma treated cotton gauze to create a novel composite bandage with higher adhesion, better handling properties, enhanced bioactivity, and moisture management. Plasma treatment of the gauze substrate was performed to improve the durability of the nanofiber/gauze interface. The chitosan nanofibers were electrospun at 3–7% concentration in trifluoroacetic acid. The composite bandages were analyzed using peel, gelbo flex, antimicrobial assay, moisture vapor transmission rate, X‐ray photoelectron spectroscopy (XPS), absorbency, and air permeability tests. The peel test showed that plasma treatment of the substrate increased the adhesion between nanofiber layers and gauze substrate by up to four times. Atmospheric plasma pretreatment of the gauze fabric prior to electrospinning significantly reduced degradation of the nanofiber layer due to repetitive flexing. The chitosan nanofiber layer contributes significantly to the antimicrobial properties of the bandage. Air permeability and moisture vapor transport were reduced due to the presence of a nanofiber layer upon the substrate. XPS of the plasma treated cotton substrate showed formation of active sites on the surface, decrease in carbon content, and increase in oxygen content as compared to the untreated gauze. Deposition of chitosan nanofibers also increased the absorbency of gauze substrate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

selectively utilizes three types of nitrogenase (molybdenum, vanadium, and iron only) to fix N, with their expression regulated by the presence or absence of different metal cofactors in its environment. Each alternative nitrogenase isoenzyme is predicted to have different electron flux requirements based on measurements, with the molybdenum nitrogenase requiring the lowest flux and the iron-only nitrogenase requiring the highest. Here, prior characterized strains, derepressed in nitrogenase synthesis and also deficient in uptake hydrogenase, were further modified to generate new mutants lacking the ability to produce poly-β-hydroxybutyrate (PHB). PHB is a storage polymer generated under oxygen-limiting conditions and can represent up to 70% of the cells' dry weight. The absence of such granules facilitated the study of relationships between catalytic biomass and product molar yields across different adaptive respiration conditions. The released hydrogen gas observed during growth, due to the inability of the mutants to recapture hydrogen, allowed for direct monitoring of nitrogenase activity for each isoenzyme. The data presented here show that increasing oxygen exposure limits equally the activities of all nitrogenase isoenzymes, while under comparative conditions, the Mo nitrogenase enzyme evolves more hydrogen per unit of biomass than the alternative isoenzymes. has been a focus of intense research for over 100 years. It has been investigated for a variety of functions, including agricultural fertilization and hydrogen production. All of these endeavors are centered around 's ability to fix nitrogen aerobically using three nitrogenase isoenzymes. The majority of research up to this point has targeted measurements of the molybdenum nitrogenase, and robust data contrasting how oxygen impacts the activity of each nitrogenase isoenzyme are lacking. This article aims to provide nitrogenase activity data using a real-time evaluation of hydrogen gas released by derepressed nitrogenase mutants lacking an uptake hydrogenase and PHB accumulation.

We report the complete genome sequences of Azotobacter vinelandii mutant strain CA6 and its parent wild-type strain, CA. When fixing nitrogen, strain CA6 displays slow growth and impaired molybdate uptake, tolerance to tungstates, and production of hydrogen gas, compared to results for strain CA. Comparing these genome sequences may provide a genetic basis for these mutant phenotypes.