The effects of two ammonium propionate formulations on growth in vitro of Aspergillus species isolated from hay

The efficacy of fully neutralized (AP) and half-neutralized ammonium propionate (H-AP) against growth of a number of Aspergillus spp. was determined in vitro on malt extract at different levels of water availability in the range 0.995–0.85 a_w (water activity) (= 40–25% water content of hay). In general, Aspergillus flavus, A. fumigatus, A. nidulans, A. niger and A. versicolor were more sensitive to the H-AP in the range 0.995–0.95 a_w than to AP. At 0.90 and 0.85 a_w growth of most species occurred in the absence of chemicals but only of a few species in 27 mmol/l AP. All three members of the A. glaucus group tested, A. amstelodami, A. repens and A. sejunctus , were similarly more sensitive to H-AP over the a_w range 0.95–0.85 than to AP. Aspergillus sejunctus was most tolerant, growing in 27 mmol/l H-AP and 54 mmol/l AP at 0.85 a_w. The number of days for growth initiation in 27 mmol/l H-AP was greater than with AP at different levels of water availability and reflected the different effects of the two chemicals on growth rate.     

Regulation of lipid metabolism: a tale of two yeasts

Eukaryotic cells synthesize multiple classes of lipids by distinct metabolic pathways in order to generate membranes with optimal physical and chemical properties. As a result, complex regulatory networks are required in all organisms to maintain lipid and membrane homeostasis as well as to rapidly and efficiently respond to cellular stress. The unicellular nature of yeast makes it particularly vulnerable to environmental stress and yeast has evolved elaborate signaling pathways to maintain lipid homeostasis. In this article we highlight the recent advances that have been made using the budding and fission yeasts and we discuss potential roles for the unfolded protein response (UPR) and the SREBP-Scap pathways in coordinate regulation of multiple lipid classes.     

Comparative aspects of propionate metabolism

1. The catabolism of propionate has been studied extensively in vertebrates and the major pathway has been shown to be its derivatization to propionyl-CoA, carboxylation to D-methylmalonyl-CoA, isomerization to L-methylmalonyl-CoA and then conversion to succinyl-CoA via a vitamin B12 dependent methylmalonyl-CoA mutase. 2. By contrast, in all insect species studied to date, many of which do not contain detectable levels of vitamin B12, the major metabolic pathway of propionate is its conversion to 3-hydroxypropionate and then to acetate. Carbon-3 of propionate becomes the carboxyl carbon of acetate and carbon-2 of propionate becomes the methyl carbon of acetate. 3. A number of species of non-insect arthropods and other invertebrates contain relatively high levels of vitamin B12 and catabolize propionate by the same pathway as that of vertebrates. Under anoxic conditions, some invertebrates, including bivalves, convert succinate to propionate. 4. In plants, evidence has been presented for the metabolism of propionate to both acetate and succinate. Micro-organisms possess a myriad of pathways by which they produce and catabolize propionate.     

Extent of propionate metabolism during absorption from the bovine ruminoreticulum

1. Solutions containing acetate, [2-(14)C]propionate and butyrate were placed into the ruminoreticulum of calves to measure the extent to which propionate is metabolized by ruminoreticulum epithelium. In response to five different combinations of pH and total volatile fatty acid concentrations, propionate absorption rates ranged from 89 to 341mmol/h. 2. The extent of propionate conversion into lactate, calculated from both concentration and specific radioactivity in portal and arterial blood, averaged 4.9 (range 2.5-9.1)%. 3. Circulating glucose synthesized from propionate had a higher specific radioactivity than arterial lactate and was converted into lactate by gastrointestinal tissues. Thus conversion of propionate into lactate was overestimated but was corrected to average 2.3 (1.0-4.6)%. 4. The estimates of propionate conversion into lactate were negatively correlated with its rate of absorption.     

Photosynthetic metabolism of propionate in Rhodospirillum rubrum

Summary As in the case of oxidative metabolism, the photosynthetic metabolism of propionate in Rhodospirillum rubrum begins with a carboxylation yielding succinate. This conclusion is based on experiments in which radioactive propionate (1-C¹⁴ and 2-C¹⁴) is administered in the presence of carrier lactate, pyruvate, succinate, and acrylate, and on studies of the inhibitory action of malonate.     

Carbohydrate and energy-yielding metabolism in non-conventional yeasts

Sugars are excellent carbon sources for all yeasts. Since a vast amount of information is available on the components of the pathways of sugar utilization in Saccharomyces cerevisiae it has been tacitly assumed that other yeasts use sugars in the same way. However, although the pathways of sugar utilization follow the same theme in all yeasts, important biochemical and genetic variations on it exist. Basically, in most non-conventional yeasts, in contrast to S. cerevisiae, respiration in the presence of oxygen is prominent for the use of sugars. This review provides comparative information on the different steps of the fundamental pathways of sugar utilization in non-conventional yeasts: glycolysis, fermentation, tricarboxylic acid cycle, pentose phosphate pathway and respiration. We consider also gluconeogenesis and, briefly, catabolite repression. We have centered our attention in the genera Kluyveromyces, Candida, Pichia, Yarrowia and Schizosaccharomyces, although occasional reference to other genera is made. The review shows that basic knowledge is missing on many components of these pathways and also that studies on regulation of critical steps are scarce. Information on these points would be important to generate genetically engineered yeast strains for certain industrial uses.     

Oxidative metabolism of propionate in Rhodospirillum rubrum

Summary Studies were conducted of the oxidative metabolism of propionate in Rhodospirillum rubrum, using C¹⁴-labeled compounds. The results, taken in conjunction with a carbon dioxide requirement described previously (Clayton et al., 1957), reveal that the first step is a carboxylation of propionic acid, yielding succinic acid. This result is confirmed through manometric studies of inhibition by malonate.     

Biodiversity in sulfur metabolism in hemiascomycetous yeasts

The evolution of the metabolism of sulfur compounds among yeast species was investigated. Differences between species were observed in the cysteine biosynthesis pathway. Most yeast species possess two pathways leading to cysteine production, the transsulfuration pathway and the O-acetyl-serine (OAS) pathway, with the exception of Saccharomyces cerevisiae and Candida glabrata, which only display the transsulfuration pathway, and Schizosaccharomyces pombe, which only have the OAS pathway. An examination of the components of the regulatory network in the different species shows that it is conserved in all the species analyzed, as its central component Met4p was shown to keep its functional domains and its partners were present. The analysis of the presence of genes involved in the catabolic pathway shows that it is evolutionarily conserved in the sulfur metabolism and leads us to propose a role for two gene families which appeared to be highly conserved. This survey has provided ways to understand the diversity of sulfur metabolism products among yeast species through the reconstruction of these pathways. This diversity could account for the difference in metabolic potentialities of the species with a biotechnological interest.     

Metabolism of propionate by sheep liver: Pathway of propionate metabolism in aged homogenate and mitochondria

Experiments were conducted with aged nuclear-free homogenate of sheep liver and aged mitochondria in an attempt to measure both the extent of oxidation of propionate and the distribution of label from [2-¹⁴C]propionate in the products. With nuclear-free homogenate, propionate was 44% oxidized with the accumulation of succinate, fumarate, malate and some citrate. Recovery of ¹⁴C in these intermediates and respiratory carbon dioxide was only 33%, but additional label was detected in endogenous glutamate and aspartate. With washed mitochondria 30% oxidation of metabolized propionate occurred, and proportionately more citrate and malate accumulated. Recovery of ¹⁴C in dicarboxylic acids, citrate, α-oxoglutarate, glutamate, aspartate and respiratory carbon dioxide was 91%. The specific activities of the products and the distribution of label in the carbon atoms of the dicarboxylic acids were consistent with the operation solely of the methylmalonate pathway together with limited oxidation of the succinate formed by the tricarboxylic acid cycle via pyruvate. In a final experiment with mitochondria the label consumed from [2-¹⁴C]propionate was entirely recovered in the intermediates of the tricarboxylic acid cycle, glutamate, aspartate, methylmalonate and respiratory carbon dioxide.     

Water relations and chlorophyll fluorescence responses of two leguminous trees from the Caatinga to different watering regimes

Leguminous species, Piptadenia moniliformes (Benth.) and Trischidium molle (Benth.) H. E. Ireland, both prevalent in the Caatinga vegetation, were submitted to varying watering regimes under greenhouse conditions. In experiment I, 60-day-old P. moniliformes plants were maintained under suspended irrigation for 12 days. Assessment on day 12 of drought revealed that leaf relative water content decreased to 40% and stomatal conductance and transpiration were also strongly diminished. Apparent electron transport rate (ETR) and photochemical quenching (qP) values were reduced by water deficit treatment compared to controls, while non-photochemical quenching (NPQ) increased; however, the basal values were recovered in moisturized plants when analyzed after 48 h of rewatering. In experiment II, T. molle plants were watered once (1 ×), 3 (3 ×) or 5 times (5 ×) per week, up to day 65 after emergence. Chlorophyll a, chlorophyll b and carotenoid contents were reduced in the 3 × and 5 × watering treatments. Photosystem II maximum efficiency (F _v′/F _m′), ETR and qP values strongly decreased when drainage frequency and NPQ values were increased. Observation verified that chlorophyll fluorescence is a suitable tool for evaluating the developmental characteristics of the arboreal leguminous species studied. Analysis of the data obtained suggest that plant tolerance to the dry climate conditions of the Caatinga ecosystem is directly associated with fast physiological adaptation to water deficit, by accumulating biomass in the root system in detriment to the shoots. The data presented contribute to further understanding the developmental and physiological mechanisms that enable plant adaptation to dry climates and, particularly, to the unique dry environmental conditions of the Caatinga region.     

Fermentation and aerobic metabolism of cellodextrins by yeasts

The fermentation and aerobic metabolism of cellodextrins by 14 yeast species or strains was monitored. When grown aerobically, Candida wickerhamii, C. guilliermondii, and C. molischiana metabolized cellodextrins of degree of polymerization 3 to 6. C. wickerhamii and C. molischiana also fermented these substrates, while C. guilliermondii fermented only cellodextrins of degree of polymerization less than or equal to 3. Debaryomyces polymorphus, Pichia guilliermondii, Clavispora lusitaniae, and one of two strains of Kluyveromyces lactis metabolized glucose, cellobiose, and cellotriose when grown aerobically. These yeasts also fermented these substrates, except for K. lactis, which fermented only glucose and cellobiose. The remaining species/strains tested, K. lactis, Brettano-myces claussenii, B. anomalus, K. dobzhanskii, Rhodotorula minuta, and Dekkera intermedia, both fermented and aerobically metabolized glucose and cellobiose. Crude enzyme preparations from all 14 yeast species or strains were tested for ability to hydrolyze cellotriose and cellotretose. Most of the yeasts produced an enzyme(s) capable of hydrolyzing cellotriose. However, with two exceptions, R. minuta and P. guilliermondii, only the yeasts that metabolized cellodextrins of degree of polymerization greater than 3 produced an enzyme(s) that hydrolyzed cellotretose.     

Changes of glycogen metabolism in phosphorylcreatine-depleted muscles taken from rats fed with beta-guanidine propionate

Changes in glycogen metabolism were explored in fast and slow muscles taken from rats fed with a diet containing 1% beta-guanidine propionate (GPA), a synthetic analog that inhibits the entry of creatine into muscle cells competitively and causes phosphorylcreatine depletion. Feeding with the GPA-containing diet increased glycogen levels in the two types of muscles to a different extent and with different temporal patterns; it did not change significantly the rate of glycogen turnover both at rest and during exercise; it did not affect the net degradation of glycogen during exercise. Diet could affect the activity of several enzymes of sugar metabolism. These latter changes too were different in fast-twitch and in slow-twitch muscles.     

A direct pathway for the metabolism of propionate in cell extracts from Moraxella Iwoffi

1. Extracts from Moraxella lwoffi oxidize propionate, but at a low rate when compared with whole cells. 2. This oxidative activity requires the formation of propionyl-CoA. 3. Enzymes catalysing the formation of propionyl phosphate and propionyl-CoA are present. The presence of a propionyl-CoA hydrolase is considered to be an artifact, but partly responsible for the low rates of oxidation. 4. Enzymes catalysing the reduction of NAD(+) and the formation of pyruvate with propionyl-CoA as substrate are also present. 5. That the only pathway for the metabolism of propionate in extracts is a direct one to acetate via pyruvate was confirmed by the use of (14)C-labelled materials. 6. A possible sequence of enzyme-catalysed reactions that will account for the experimental observations is described.