Direct measurement of dissolved gases in microbiological systems using membrane inlet mass spectrometry

Membrane inlet mass spectrometry is a novel technique that has been used to measure concentrations of dissolved gases and volatile compounds of microbiological interest. This technique is compared with other methods of measuring dissolved gases. Applications to some microbiological processes (respiration, photosynthesis, fermentation, nitrogen fixation and methanogenesis) are discussed in greater detail. The advantages of the technique and possible future developments are presented; its major attraction is that a number of different gases can be simultaneously and continuously monitored directly and non-invasively in cell suspensions.     

Regulation of methanol oxidation and carbon dioxide fixation in Xanthobacter strain 25a grown in continuous culture

The regulation of C₁-metabolism in Xanthobacter strain 25a was studied during growth of the organism on acetate, formate and methanol in chemostat cultures. No activity of methanol dehydrogenase (MDH), formate dehydrogenase (FDS) or ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisC/O) could be detected in cells grown on acetate alone over a range of dilution rates tested. Addition of methanol or formate to the feed resulted in the immediate induction of MDH and FDH and complete utilization (D=0.10 h^-1) of acetate and the C ₁-substrates. The activities of these enzymes rapidly dropped at the higher growth rates, which suggests that their synthesis is further controlled via repression by heterotrophic substrates such as acetate. Synthesis of RuBisC/O already occurred at low methanol concentrations in the feed, resulting in additive growth yields on acetate/methanol mixtures. The energy generated in the oxidation of formate initially allowed an increased assimilation of acetate (and a decreased dissimilation), resulting in enhanced growth yields on the mixture. RuBisC/O activity could only be detected at the higher formate/acetate ratios in the feed. The data suggest that synthesis of RuBisC/O and CO₂ fixation via the Calvin cycle in Xanthobacter strain 25 a is controlled via a (de)repression mechanism, as is the case in other facultatively autotrophic bacteria. Autotrophic CO₂ fixation only occurs under conditions with a diminished supply of heterotrophic carbon sources and a sufficiently high availability of suitable energy sources. The latter point is further supported by the clearly more pronounced derepressing effect exerted by methanol compared to formate.Abbreviations FDH formate dehydrogenase - FBPase fructose-1,6-bisphosphatase - ICDH isocitrate dehydrogenase - MDH methanol dehydrogenase - PQQ pyrrolo quinoline quinone - PRK phosphoribulokinase - RuBisC/O ribulose-1,5-bisphosphate carboxylase/oxygenase - RuMP ribulose monophosphate - TCA tricarboxylic acid cycle     

Shigella dysenteriae 60R strain adheres to and invades tissue culture cells in the absence of virulence plasmid

The influence of various carbon and nitrogen sources on fusarin C synthesis was examined in submerged cultures of Fusarium moniliforme NRRL 13616. Using a zinc-deficient, synthetic medium, highest levels of fusarin C were produced by cultures grown with urea or ammonium sulfate as the nitrogen source and fructose, sucrose, or glucose as the carbon source. In media supplemented with various concentrations of glucose and ammonium sulfate, glucose concentrations which provided excess carbohydrate significantly increased fusarin C synthesis, regardless of the ammonium sulfate concentration.     

Effects of Relative Humidity on Carbon Isotope Fractionation in Plants

Four C₃ plants and a C₄ plant were grown from seeds at four levels (30, 45, 60, and 75 %) of relative humidity. All plants were subjected to a 16 h day, at 500 μE/m².s^?1 photon flux density. Mature leaves were analyzed for their carbon isotopic composition. Isotope fractionation decreased by up to 3 ‰ with decreasing relative humidity in all C₃ plants, while the opposite trend was observed in the C₄ plant. The observed shifts in both C₃ and C₄ plants are attributed to decreased stomatal conductance at low relative humidity, resulting in a smaller P_i.     

Nitrogen dynamics and growth of seedlings of an N-fixing tree (Gliricidia sepium (Jacq.) Walp.) exposed to elevated atmospheric carbon dioxide

Summary Seeds of Gliricidia sepium (Jacq.) Walp., a tree native to seasonal tropical forests of Central America, were inoculated with N-fixing Rhizobium bacteria and grown in growth chambers for 71 days to investigate interactive effects of atmospheric CO₂ and plant N status on early seedling growth, nodulation, and N accretion. Seedlings were grown with CO₂ partial pressures of 350 and 650 bar (current ambient and a predicted partial pressure of the mid-21st century) and with plus N or minus N nutrient solutions to control soil N status. Of particular interest was seedling response to CO₂ when grown without available soil N, a condition in which seedlings initially experienced severe N deficiency because bacterial N-fixation was the sole source of N. Biomass of leaves, stems, and roots increased significantly with CO₂ enrichment (by 32%, 15% and 26%, respectively) provided seedlings were supplied with N fertilizer. Leaf biomass of N-deficient seedlings was increased 50% by CO₂ enrichment but there was little indication that photosynthate translocation from leaves to roots or that plant N (fixed by Rhizobium) was altered by elevated CO₂. In seedlings supplied with soil N, elevated CO₂ increased average nodule weight, total nodule weight per plant, and the amount of leaf nitrogen provided by N-fixation (as indicated by leaf ¹⁵N). While CO₂ enrichment reduced the N concentration of some plant tissues, whole plant N accretion increased. Results support the contention that increasing atmospheric CO₂ partial pressures will enhance productivity and N-fixing activity of N-fixing tree seedlings, but that the magnitude of early seedling response to CO₂ will depend greatly on plant and soil nutrient status.     

Estimates of nitrogen fixation by trees on an aridity gradient in Namibia

Summary Nitrogen (N₂) fixation was estimated along an aridity gradient in Namibia from the natural abundance of ¹⁵N (¹⁵N value) in 11 woody species of the Mimosacease which were compared with the ¹⁵N values in 11 woody non-Mimosaceae. Averaging all species and habitats the calculated contribution of N₂ fixation (N _f ) to leaf nitrogen (N) concentration of Mimosaceae averaged about 30%, with large variation between and within species. While in Acacia albida N _f was only 2%, it was 49% in Acacia hereroensis and Dichrostachys cinerea, and reached 71% in Acacia melifera. In the majority of species N _f was 10–30%. There was a marked variation in background ¹⁵N values along the aridity gradient, with the highest ¹⁵N values in the lowland savanna. The difference between ¹⁵N values of Mimosaceae and non-Mimosaceae, which is assumed to result mainly from N₂ fixation, was also largest in the lowland savanna. Variations in ¹⁵N of Mimosaceae did not affect N concentrations, but higher ¹⁵N-values of Mimosaeae are associated with lower carbon isotope ratios (¹³C value). N₂ fixation was associated with reduced intrinsic water use efficiency. The opposite trends were found in non-Mimosaceae, in which N-concentration increased with ¹⁵N, but ¹³C was unaffected. The large variation among species and sites is discussed.This paper is prepared in memory of J. Visser, who took part in the collection of species, but died in 1990     

Plasticity in the degree of CAM-cycling and its relationship to drought stress in five species of Talinum (Portulacaceae)

Summary The degree of CAM-cycling was examined in plants from 23 populations representing five morphologically similar species of Talinum to determine how CAM-cycling correlates with site aridity and drought stress. In the field, CAM-cycling, as indicated by the amount of malic acid accumulated in plant tissues overnight, and stable carbon isotope ratio (¹³C) were positively correlated with an index of site aridity. The relative levels of CAM-cycling and ¹³C values among populations in the field reversed when plants were grown under less arid conditions in a growth chamber such that populations with the highest average CAM-cycling and ¹³C in the field had the lowest averages in the growth chamber. In both cases, plants from all populations showed significantly higher levels of CAM-cycling under drought-stressed conditions relative to conditions known or predicted to be less arid. CAM-cycling was also positively correlated with tissue water content in both well-watered and drought-stressed plants, possibly reflecting greater water conservation associated with reductions in stomatal conductance. Biomass accumulation in plants exhibiting the greatest degree of CAM-cycling in the growth chamber was suppressed by drought stress to a similar degree as in the other plants, yet reproductive biomass of these plants was inhibited to a smaller degree. Thus, the importance of CAM-cycling increases in these species of Talinum during drought stress, due to increased malic acid accumulation overnight, potentially enhancing their water status, survival, and reproduction.     

Crassulacean acid metabolism in Kalanchoë species collected in various climatic zones of Madagascar: a survey by δ13C analysis

Summary The carbon isotope compositions of samples of Kalanchoë species collected at the natural stands in Madagascar were determined. The results suggest that all species of the genus Kalanchoë are capable of crassulacean acid metabolism. The observed ¹³C values cover the whole range from –10 to –30. This high diversity of the ¹³C values was found among the species of the genus as well as, in certain cases, within a single species. This suggest that the CAM patterns in Kalanchoë are generally very flexible. The ¹³C values show a clear correlation with the climate of the habitats from where the samples derived. Values indicative of CO₂ fixation taking place exclusively during the night were found in the dry regions of Madagascar, whereas ¹³C values indicative of mixed CO₂ fixation during night and day or of CO₂ fixation entirely during the day are distributed in the humid zones.