Conditions Of Low Oxygen Tension Research Articles

Klebsiella pneumoniae nifA product activates the Rhizobium meliloti nitrogenase promoter.

Bacteria in the genus Rhizobium normally fix nitrogen only when they interact with leguminous plants to produce on the roots a highly differentiated structure, the nodule, within which the bacteria differentiate into nitrogen-fixing bacteroids. By contrast, the enteric bacterium Klebsiella pneumoniae reduces nitrogen in a free-living state in conditions of low oxygen tension and deficiency of fixed nitrogen. In K. pneumoniae, the overall circuitry by which nitrogen-fixation (nif) genes are regulated has been elucidated. In response to ammonia starvation, the product of the glnG gene activates transcription of the nifLA operon; this activation is dependent on the product of glnF (ref. 4). The nifA gene product is in turn required for transcription of all the other nif genes, including the nifHDK operon which codes for the subunits of nitrogenase. In contrast, very little is known about the sequence of events involved in the regulated change in rhizobial nif gene expression associated with bacteroid differentiation. In the work described here, we identify the K. pneumoniae and Rhizobium meliloti nifHDK promoters by mapping the in vivo start points of transcription. By defining and comparing the DNA sequences of these two promoters, we find that they share an unexpected degree of homology. Further, by constructing fusions of each of the two promoters to the lacZ gene from Escherichia coli, we show that both promoters are activated by the product of the K. pneumoniae nifA gene.

Conversion of fensulfothion by Klebsiella pneumoniae to fensulfothion sulfide and its accumulation.

In a detailed study it was shown that washed cell suspensions of K. pneumoniae reduced the organophosphorus pesticide fensulfothion to fensulfothion sulfide. Temperature and pH optima for this conversion plus sensitivity to sulfhydryl-reacting agents strongly suggested enzyme involvement. The reaction was also quite sensitive to molecular oxygen, only proceeding under conditions of low oxygen tension. Once formed, the fensulfothion sulfide was rapidly bound by living and heat-killed cells. A combination of lysozyme treatment and differential centrifugation showed 90% of the sulfide to be concentrated in the cell membrane fraction of exposed cells.

Respiratory responses of the pea crab, Pinnotheres hickmani (Guiler)

The respiration rates for various developmental stages of the Australian pea crab, P. hickmani, were obtained at three temperatures, representing the normal environmental range, and in light and dark conditions. The free-living hard stages of both the males and the females, show marked variation in oxygen uptake compared with the pre- and post-hard commensal stages. Oxygen requirements increase as the female matures to the stage-V form. Results obtained indicate that, under normal conditions, the presence of P. hickmani within a host mussel, Mytilus edulis planulatus, would present no undue burden on the host's available oxygen. Under conditions of low oxygen tension, P. hickmani shows the ability to build up an oxygen debt, again providing no undue burden on its host. It is proposed that P. hickmani is an obligatory commensal within M. e. planulatus.

Fermentation of a pentose by yeasts

Summary Several yeasts have been found to be able to ferment D-xylulose, a catabolite of D-xylose, and to produce ethanol thereby. The fermentation is carried out by several species which can utilise D-xylose oxidatively as well as by several which cannot do so. Xylose itself, and the other aldopentoses, are not utilised anaerobically by yeasts. Fermentation of D-xylulose by D-xylose oxidising species indicates that a control operates under conditions of low oxygen tension which prevents the catabolism of D-xylose to D-xylulose. The results are pertinent in efforts to obtain yeasts which can ferment biomass pentoses, a problem of interest in attempts to obtain a liquid fuel from a renewable resource.

Determinate development of nodule roots in actinomycete-induced root nodules of Myrica gale

Young seedlings of Myrica gale L. grown in water culture were inoculated with a nodule suspension containing the effective actinomycete which induced root nodule formation. Nodule development was followed from initiation to nodule lobe formation and nodule root development using living materials and fixed nodules sectioned for light microscopy. After root hair infection and prenodule formation, three stages were observed: nodule lobe formation, a transition or arrested state, and nodule root development. The primary nodule lobe meristem originates endogenously and its formation involves pericycle, endodermis, and cortical cell derivatives. The lobe develops slowly to about 2 mm in length while the cortical cells are invaded by the actinomycete endophyte. After a period of arrest of variable duration, from a few days to several weeks, the nodule lobe meristem begins altered development, forming the elongate nodule root which undergoes slow but continuous growth to about 3- to 4-cm final length. New nodule lobe primordia are initiated endogenously at the base of existing nodules lobes, ultimately forming a cluster of nodule roots. Each nodule root, which elongates at about 0.1–1.0 mm per day, has a terminal apical meristem with reduced root cap formation and produces a modified root structure possessing an elaborate cortical intercellular space system and a reduced central cylinder. Nodule root growth is distinctive in that it shows strong negative geotropism. The endophyte is restricted to cortical cells of the nodule lobe and is totally absent from tissues of the nodule root. A probable role for nodule roots is to facilitate gas diffusion to the nitrogen-fixing endophyte site in the nodule lobe when nodules occur under conditions of low oxygen tension.

N2 : Ar, nitrification and denitrification in southern California borderland basin sediments1

The first quantitative observations of dissolved molecular nitrogen (N2) in deep‐sea sedimentary pore waters show increases of up to 17% above adjacent bottom water values. The N2 : Ar concentration ratio similarly increases. This increase is greater than expected from reduction of seawater nitrate in the sediment. A mechanism is suggested in which ammonia, derived from nitrogen‐containing organic matter, is converted to N2 through a nitrite intermediate under conditions of low oxygen tension. Ammonia is not converted to N2 in anoxic sediments that are undergoing sulfate reduction even though N2 is the thermodynamically stable species.

RESPIRATORY VARIATION AND ACCLIMATION IN THE FRESHWATER LIMPET,LAEVAPEX FUSCUS

1. From three populations of Laevapex fuscus samples were collected bi-weekly through 1970 to 1972. Oxygen consumption rates at ambient temperature and at 10° C and at 20° C were determined. Other respiration experiments involved decreasing O2 tension at 20° C and the consequences of low oxygen stress.2. At ambient temperatures, respiration during the summer is normally 26 to 36 times the winter respiratory rate.3. After treatment with low oxygen stress there is no overt payment of an oxygen debt in Laevapex, instead there is a general increase in respiratory rate at all oxygen tensions. These rates are maintained for up to 135 hours after return to fully saturated conditions and appear to be in part a short-term acclimation of respiratory rates to low oxygen tensions.4. Measured at 100% oxygen tension at 10° and 20° C, respiration rates are higher in the summer than in the winter for all three populations. Such a respiratory response to temperature has been called reverse acclimation. Laevapex lives in conditions of low oxygen tension during the winter. The respiration experiments with decreasing oxygen tension show that at low oxygen tensions winter-conditioned specimens have a higher respiratory rate than summer-conditioned individuals. Such a response to low oxygen tensions may be interpreted as a positive rather than reverse acclimation.5. A hypothesis is advanced regarding "reverse" acclimation in this species. Reverse acclimation appears to be merely one manifestation of a more general acclimatory change in winter-conditioned Laevapex. These limpets, when winter-conditioned, have a higher respiratory rate at low oxygen tension than do summer-conditioned limpets. Although this acclimatory process appears to be triggered by decreasing temperature, its adaptational significance involves the survival of the inactive overwintering limpet in contact with reducing mud.

Heterofermentative carbohydrate metabolism of lactose-impaired mutants of Streptococcus lactis.

Two mutants of Streptococcus lactis ATCC 11454 have been isolated which possess an impaired lactose-fermenting capacity; galactose utilization is also affected, but to a lesser extent. Although the Embden-Meyerhof-Parnas pathway is the major, if not the sole, pathway of carbohydrate metabolism in the three strains, the fermentation end products of the mutants are dramatically different from the typical homolactic pattern of the wild type. Under conditions of low oxygen tension and growth-limiting lactose concentrations, mutant strain T-1 produces largely formic acid, acetic acid (2:1), and ethanol rather than lactic acid. Aerated cultures produce acetic acid, CO(2) (1:1), acetyl-methylcarbinol, and diacetyl. When the mutants use galactose as an energy source, lactic acid is the major end product, but significant heterofermentative activity is observed. The aberrations responsible for the mutant phenotypes reside in the proteins which catalyze the transport and hydrolysis of galactosides. It is hypothesized that the impaired transport system of the mutants reduces the intracellular pool of glycolytic intermediates below that of the wild type. Since fructose-1, 6-diphosphate is an activator of lactic dehydrogenase in S. lactis, lactic acid production is reduced, and pathways leading to the formation of other products are expressed.

The effect of conditions of low oxygen tension on the assay of nitrogenase in moulds and yeasts using the acetylene reduction technique.

15 strains of Pullularia, Rhodotorula, Bullera and Torulopsis were tested for acetylene reduction under anaerobic and low pO2 (0.05) conditions. No production of ethylene was observed and it is concluded that nitrogenase activity is absent.

THE EFFECT OF HALOTHANE ON THE ISOLATED CAT HEART

SUMMARY The effect of The effect of halothane on the electrocardiogram recorded from the isolated perfused cat heart is described. A halothane tension of between 7 and 14 mm Hg produced bradycardia, atrioventricular dissociation, nodal rhythm and finally asystole. Conditions of low oxygen tension and high carbon dioxide tension produced ventricular extrasystoles in isolated hearts exposed to halothane. It is suggested that this provides corroborative evidence for the contention that the ventricular extrasystoles produced by halothane in cats can occur independently of sympatho-adrenal activity.

Oxygen Requirements and the Physiological Suppression of Supernumerary Insect Parasitoids

ABSTRACT The oxygen content of the haemolymph of mature larvae of Ephestia kühniella has been measured in healthy individuals and in those parasitized by the ichneumonid Nemeritis canescens. In the latter the oxygen content decreases with the progress of parasitism. The respiratory rate of first, second- and third-instar larvae of Nemeritis has been measured and found to increase rapidly at the end of the first instar, at about the time at which the phenomenon of physiological suppression appears. The partial pressure of oxygen in the gas mixture surrounding the Ephestia larva affects the oxygen content of its haemolymph proportionally and so was used to alter the availability of oxygen to the parasite in vivo. The survival of Nemeritis larvae increases with the availability of oxygen in the haemolymph of its host. The capacity for survival under conditions of low oxygen tension is minimal for eggs and newly hatched larvae of Nemeritis, but rapidly increases with age. The hypothesis of physiological suppression of supernumerary parasitoid larvae by asphyxiation is discussed with respect to these observations and is held to be supported by them.

Oxygen deficiency and radiation damage in the insect Rhodnius.

REDUCTION in radiation damage under conditions of low oxygen tension during the exposure has been demonstrated in a number of plant and animal tissues1. This report deals with similar effects in the insect Rhodnius prolixus. Latent radiation damage in ‘resting’ cells of the epidermis of Rhodnius is expressed as a burn at delayed moulting following a blood meal2. In these studies, the delay in moulting and the size of the burns have been utilized as convenient indices of the oxygen effect during X-irradiation.