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The glbN gene of Nostoc commune UTEX 584 is juxtaposed to nifU and nifH, and it encodes a 12-kDa monomeric hemoglobin that binds oxygen with high affinity. In N. commune UTEX 584, maximum accumulation of GlbN occurred in both the heterocysts and vegetative cells of nitrogen-fixing cultures when the rate of oxygen evolution was repressed to less than 25 mol of O 2 mg of chlorophyll a ؊1 h ؊1 . Accumulation of GlbN coincided with maximum synthesis of NifH and ferredoxin NADP ؉ oxidoreductase (PetH or FNR). A total of 41 strains of cyanobacteria, including 40 nitrogen fixers and representing 16 genera within all five sections of the cyanobacteria were screened for the presence of glbN or GlbN. glbN was present in five Nostoc strains in a single copy. Genomic DNAs from 11 other Nostoc and Anabaena strains, including Anabaena sp. strain PCC 7120, provided no hybridization signals with a glbN probe. A constitutively expressed, 18-kDa protein which cross-reacted strongly with GlbN antibodies was detected in four Anabaena and Nostoc strains and in Trichodesmium thiebautii. The nifU-nifH intergenic region of Nostoc sp. strain MUN 8820 was sequenced (1,229 bp) and was approximately 95% identical to the equivalent region in N. commune UTEX 584. Each strand of the DNA from the nifU-nifH intergenic regions of both strains has the potential to fold into secondary structures in which more than 50% of the bases are internally paired. Mobility shift assays confirmed that NtcA (BifA) bound a site in the nifU-glbN intergenic region of N. commune UTEX 584 approximately 100 bases upstream from the translation initiation site of glbN. This site showed extensive sequence similarity with the promoter region of glnA from Synechococcus sp. strain PCC 7942. In vivo, GlbN had a specific and prominent subcellular location around the periphery of the cytosolic face of the cell membrane, and the protein was found solely in the soluble fraction of cell extracts. Our hypothesis is that GlbN scavenges oxygen for and is a component of a membrane-associated microaerobically induced terminal cytochrome oxidase.

Previous in vitro and in vivo animal studies showed that O(2) and CO(2) concentrations can affect virulence of pathogenic bacteria such as Staphylococcus aureus. The objective of this work was to measure O(2) and CO(2) levels in the vaginal environment during tampon wear using newly available sensor technology. Measurements by two vaginal sensors showed a decrease in vaginal O(2) levels after tampon insertion. These decreases were independent of the type of tampons used and the time of measurement (mid-cycle or during menstruation). These results are not in agreement with a previous study that concluded that oxygenation of the vaginal environment during tampon use occurred via delivery of a bolus of O(2) during the insertion process. Our measurements of gas levels in menses showed the presence of both O(2) and CO(2) in menses. The tampons inserted into the vagina contained O(2) and CO(2) levels consistent with atmospheric conditions. Over time during tampon use, levels of O(2) in the tampon decreased and levels of CO(2) increased. Tampon absorbent capacity, menses loading, and wear time influenced the kinetics of these changes. Colonization with S. aureus had no effect on the gas profiles during menstruation. Taken collectively, these findings have important implications on the current understanding of gaseous changes in the vaginal environment during menstruation and the potential role(s) they may play in affecting bacterial virulence factor production.

The speed of water uptake by desiccated Nostoc commune was found to depend upon the duration of desiccation. The rehydration of desiccated colonies led to marked, time-dependent changes in structure and ultrastructure and fluctuations in the composition of the transcriptome. Physical evaporative water loss is an active process that was influenced by inhibitors of transcription and translation.Certain cells can survive in a dry, metabolically inactive state, sometimes for long periods (8, 10). Such aged and desiccated cells rapidly recover their physiological capacities following the addition of water and then resume active growth. There is some understanding of the mechanisms that permit cells to withstand extreme fluctuations in water availability, including a knowledge of factors that lead to the damaging of cell components, as well as a knowledge of repair processes (1-4, 6, 13). Despite much study of the different strategies used to overcome acute water deficit, it is still unclear how physiological responses to drying and rehydration are controlled at the whole-cell level or how a complement of gene products could interact synergistically, through four dimensions, to provide desiccation tolerance.Nostoc commune is an important source of fixed nitrogen in nutrient-depleted soils from the tropics to the polar regions (10). In these habitats, N. commune is subject to repeated cycles of desiccation and rewetting, with water availability being the critical modulator of the function and success of this microorganism. In order to match key physiological processes with the availability of water, we first measured rates of water uptake and evaporation from sample colonies. Desiccated colonies of N. commune were collected from Topsail Island, N.C. (N. commune TOP/1993), and were stored dry in sealed glass bottles in the dark until analysis (16). The colonies form thin, irregular, flattened, brittle fragments of thallus, which consist of filaments embedded within a complex extracellular polysaccharide (6, 10). When submerged in water, the colonies swell rapidly and assume a consistency comparable to that of an approximately 4-mm-thick, 10% (wt/vol) polyacrylamide gel. The rates of rewetting and drying of these colonies were evaluated with an automated analytical balance system consisting of a Mettler Toledo AB 2045 analytical balance connected through a serial interface to a personal computer operating Balance Talk version 4.0 software (Labtronics Inc.). The results were compared with those obtained with synthetic colonies (inanimate controls) made of cellulose and molded and compressed into the shape of Nostoc colonies.Twenty-seven N. commune TOP/1993 colonies of different shapes and weights were used to measure the kinetics of water uptake and loss. In one rehydration experiment, six desiccated colonies with dry weights between 0.072 and 0.194 g were used.At the time of the first rehydration, the colonies had been in desiccation storage for 8 years. Desiccated colonies were rehydrated in petri dishes, through the ad...

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