Carbon dioxide assimilation by Thiobacillus novellus under nutrient-limited mixotrophic conditions

The contribution of CO2 to cell material synthesis in Thiobacillus novellus under nutrient-limited conditions was estimated by comparing 14CO2 uptake rates of steady-state autotrophic cultures with that of heterotrophic and mixotrophic cultures at a given dilution rate. Under heterotrophic conditions, some 13% of the cell carbon was derived from CO2; this is similar to the usual anaplerotic CO2 fixation in batch cultures of heterotrophic bacteria. Under mixotrophic conditions, the contribution of CO2 to cell material synthesis increased with increasing S2O3 2- -to-glucose ratio in the medium inflow; at a ratio of 10, ca. 32% of the cell carbon was synthesized from CO2. We speculate that the use of CO2 as carbon source, even when the glucose provided is sufficient to fulfill the biosynthetic needs, may augment the growth rate of the bacterium under such nutrient-limited conditions and could therefore be of survival value in nature. Some of the CO2 assimilated was excreted into the medium as organic compounds under all growth conditions, but in large amounts only in autotrophic environments as very low dilution rates.     

Influence of wine-like conditions on arginine utilization by lactic acid bacteria

Wine can contain trace amounts of ethyl carbamate (EC), a carcinogen formed when ethanol reacts with carbamyl compounds such as citrulline. EC is produced from arginine by lactic acid bacteria (LAB), e.g., Lactobacillus and Pediococcus. Although the amounts of EC in wine are usually negligible, over the last few years there has been a slight but steady increase, as climate change has increased temperatures and alcohol levels have become proportionately higher, both of which favor EC formation. In this study, resting cells of LAB were used to evaluate the effects of ethanol, glucose, malic acid, and low pH on the ability of non-oenococcal strains of these bacteria to degrade arginine and excrete citrulline. Malic acid was found to clearly inhibit arginine consumption in all strains. The relation between citrulline produced and arginine consumed was clearly higher in the presence of ethanol (10-12%) and at low pH (3.0), which is consistent with both the decreased amount of ornithine produced from arginine and the reduction in arginine degradation. In L. brevis and L. buchneri strains isolated from wine and beer, respectively, the synthesis of citrulline from arginine was highest.     

Germination conditions that require mitochondrial function in Saccharomyces cerevisiae: utilization of acetate and galactose.

Ascospores of Saccharomyces cerevisiae inherited at least one functioning mitochondrion as shown by their ability to germinate on nonfermentable carbon sources. After transfer to germination medium, the optical density of the culture at 600 nm decreased (phase-dark), reaching a minimum within 60 min in the presence of glucose and within 180 min after transfer to acetate medium; thereafter, the optical density increased. Budding cells first appeared 90 min after transfer to glucose and 150 min after transfer to acetate. Augmentation of respiratory components, respiratory activity, and macromolecular synthesis (except for DNA synthesis) started at about the same time on glucose and on acetate, although the highest values for all these processes were reached in the presence of glucose. Mitochondrial inhibitors which affected germination on acetate did not arrest germination on glucose. However, mitochondrial activity was required for germination on galactose in a strain carrying the mutated allele imp1 of the nucleomitochondrion-connecting gene IMP1.     

Effect of trimethylamine on acetate utilization by Methanosarcina barkeri

During growth of Methanosarcina barkeri strain Fusaro on a mixture of trimethylamine and acetate, methane production and acetate consumption were biphasic. In the first phase trimethylamine (33 mmol x l^-1) was depleted and some acetate (11–14 from 50 mmol x l^-1) was metabolized simultaneously. In the second phase the remaining acetate was cleaved stoichiometrically into CH₄ and CO₂. Kinetic experiments with (2-¹⁴C)acetate revealed that only 2.5% of the methane produced in the first phase originated from acetate: 18% of the acetate metabolized was cleaved into CH₄ and CO₂, 23% of the acetate was oxidized, and 55% was assimilated. Methane produced from CD₃–COOH in the first phase consisted of CD₂H₂ and CD₃H in a ratio of 1:1.     

Studies on the mechanism of acetate oxidation by bacteria. VI. Comparative patterns of acetate oxidation by citrate-grown and acetate-grown Aerobacter aerogenes

The data presented in this paper indicate operation of different mechanisms for acetate oxidation by A. aerogenes, depending on the carbon source used for growth. The mechanism for citrate-grown cells appears to involve a conventional citric acid cycle, whereas acetate-grown cells appear to incorporate acetate carbon more readily via a dicarboxylic acid cycle.     

Carbon dioxide effects on stomatal responses to the environment and water use by crops under field conditions

The structural complexity of habitats has been espoused as an important factor influencing natural-enemy abundance and food-web dynamics in invertebrate-based communities, but a rigorous synthesis of published studies has not heretofore been conducted. We performed a meta-analytical synthesis of the density response of natural enemies (invertebrate predators and parasitoids) to experimental increases and decreases in the structural complexity of their habitats using data from 43 published studies, reporting 62 independent taxa. Studies varied in structural complexity at two spatial scales (habitat and within-plant architecture) and comprised a diverse array of natural-enemy taxa (natural-enemy assemblage at large, the entire spider assemblage, hunting spiders, web-building spiders, mites, hemipterans, coccinellid beetles, carabid beetles, ants, and parasitoids). For all taxa combined, increasing habitat structure resulted in a large and significant increase in natural enemy abundance. Similarly, decreasing habitat structure significantly diminished natural enemy abundance. Separate meta-analyses at two spatial scales (habitat and within-plant architecture) found that increasing habitat complexity resulted in significant increases in abundance. In particular, manipulating levels of detritus at the habitat spatial scale had the strongest effect on natural enemy abundance. In general, most guilds of natural enemies were significantly affected when the structural complexity of the habitat was altered. Seven of nine natural enemy guilds were more abundant under conditions of increased habitat complexity, with hunting spiders and web-building spiders showing the strongest response followed by hemipterans, mites, and parasitoids. Spiders in particular were negatively affected when habitat structure was simplified. The mechanisms underlying the accumulation of natural enemies in complex-structured habitats are poorly known. However, refuge from intraguild predation, more effective prey capture, and access to alternative resources (alternative prey, pollen, or nectar), are possible candidates. Our analysis was unable to confirm that predators aggregate in complex-structured habitats because prey (mostly herbivores) are more abundant there. The results of this meta-analysis support the view that basal resources mediate top-down impacts on herbivores, and provide encouragement that manipulations of habitat complexity can be made in agroecosystems that will enhance the effectiveness of the natural enemy complex for more effective pest suppression.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Effect of acetate on glucose utilization by isolated rat thymocytes

The effects of acetate and ammonium salts on glucose metabolism, aminoisobutyric acid influx, and radioiodinated insulin binding in isolated thymocytes were studied. Acetate in the concentration range, 0.1–30 mm, was found to inhibit basal and insulin-stimulated CO₂ production whereas ammonium chloride at concentrations greater than 0.3 mm was slightly stimulatory. Ammonium salts inhibited glucose incorporation into glycogen and aminoisobutyric acid influx only at high concentration (30 mm). Neither acetate nor ammonium salts had significant effects on glucose incorporation into glycogen or aminoisobutyric acid influx at lower concentrations. No effect on insulin binding was observed. The observation that very low concentrations of acetate can perturb these biological assay systems suggests that other biological functions may be affected by trace amounts of buffer salts carried over from protein isolation steps.