High Aeration Levels Research Articles

Root-zone aeration improves fruit yield and quality of tomato by enhancement of leaf photosynthetic performance

Heavy irrigation and soil compaction cause hypoxic stress in plant roots, which limits crop growth. This issue can be solved by root-zone aeration, but the photophysiological responses of crop plants to the dissolved oxygen (DO) concentration in irrigation water remain unclear. Here, a greenhouse plot experiment was conducted to investigate the changes in leaf photosynthesis and plant growth of tomato (Solanum lycopersicum L. cv. ‘Omanda 3′) under aerated irrigation with various DO concentrations. Plants were treated with three different levels of aeration: 5 mg L–1 DO (conventional subsurface irrigation as a non-aeration control), 15 mg L–1 DO (low aeration treatment), and 30 mg L–1 DO (high aeration treatment). Compared with the control, the aeration treatments promoted electron transport from the primary to secondary plastoquinone acceptors (QA to QB) of photosystem II (PSII) and increased leaf net photosynthetic rate in plants at the seedling, fruit expansion, and maturation stages. The opposite effects of aeration treatments were observed at the flowering and fruit-setting stage. The enhancement of leaf photosynthetic performance contributed to improved plant growth, fruit yield, and quality of tomato as a result of increased oxygen supply in the root zone. The aeration treatments additionally facilitated the biosynthesis and transport of photosynthetic carbon assimilates in plant tissues, as evidenced by increased starch and sucrose contents in the leaves and sucrose content in the roots. However, under the high aeration level, excessive transport of sucrose from leaves to roots hindered further improvements in tomato yield and biomass at the maturation stage. Based on plant photophysiological and yield performance, aerated irrigation with a low concentration of DO (15 mg L–1) is recommended for greenhouse tomato crops during the seedling, fruit expansion, and maturation stages, and there is no need of root-zone aeration at the flowering and fruit-setting stage.

Competitive Biosynthesis of Bacterial Alginate Using Azotobacter vinelandii 12 for Tissue Engineering Applications.

This study investigated the effect of various cultivation conditions (sucrose/phosphate concentrations, aeration level) on alginate biosynthesis using the bacterial producing strain Azotobacter vinelandii 12 by the full factorial design (FFD) method and physicochemical properties (e.g., rheological properties) of the produced bacterial alginate. We demonstrated experimentally the applicability of bacterial alginate for tissue engineering (the cytotoxicity testing using mesenchymal stem cells (MSCs)). The isolated synthesis of high molecular weight (Mw) capsular alginate with a high level of acetylation (25%) was achieved by FFD method under a low sucrose concentration, an increased phosphate concentration, and a high aeration level. Testing the viscoelastic properties and cytotoxicity showed that bacterial alginate with a maximal Mw (574 kDa) formed the densest hydrogels (which demonstrated relatively low cytotoxicity for MSCs in contrast to bacterial alginate with low Mw). The obtained data have shown promising prospects in controlled biosynthesis of bacterial alginate with different physicochemical characteristics for various biomedical applications including tissue engineering.

Production of Lignocellulolytic Enzymes and Biomass of Trametes versicolor from Agro-Industrial Residues in a Novel Fixed-Bed Bioreactor with Natural Convection and Forced Aeration at Pilot Scale

Solid-state fermentation requires the development of more efficient cultivation systems for its industrial application. The objective of this work was to evaluate the effect of aeration regime on the production of biomass and several lignocellulolytic enzymes (laccase, manganese peroxidase, endoxylanase, β-glucosidase, and total cellulases) by Trametes versicolor in a novel fixed-bed solid-state pilot-scale bioreactor. Three regimes were assessed: natural convection, low aeration level (10 min every 6 h at 10 L/h air flowrate), and high aeration level (1 h every 6 h at 10 L/h air flowrate). The mushroom was grown on a medium based on lignocellulosic residues. The design of the bioreactor, as well as the control of aeration, humidity, and temperature of the beds, allowed T. versicolor to grow properly on the medium, reaching a maximum biomass production of 204.7 mg/g dry solid (ds). The influence that aeration regime had on the production of lignocellulolytic enzymes was determined. Low level of forced aeration favored obtaining the highest titers of laccase (6.37 U/g ds) compared to natural convection and high aeration level. The greatest lignin degradation was also verified for low aeration regime. For the first time, pilot scale cultivation of T. versicolor was reported in a fixed-bed bioreactor.

Biosynthesis of Alginate and Poly(3-Hydroxybutyrate) by the Bacterial Strain Azotobacter agile 12

The ability of Azotobacter agile 12 to produce the polymers alginate (ALG) and poly(3-hydroxybutyrate) (PHB) and their physicochemical properties is studied in the work. It was shown that the strain A. agile 12 produces ALG and PHB simultaneously, thought predominantly ALG, under the conditions of high aeration levels. Infrared spectroscopy of bacterial ALG showed a prevalence of mannuronic over guluronic residues (M/G = 70/30) in the polymer chain and the presence of acetyl groups on the mannuronic monomers. No acetyl groups were found in seaweed ALG. Infrared spectroscopy showed that PHB is characterized by an absorption band in the region 1760 cm–1. The chemical nature of PHB as a homopolymer consisting of resides of 3-hydroxybutyric acid was confirmed by 1H-NMR analysis. The thermal behavior of bacterial ALG by thermogravimetric analysis is characterized by three stages (dehydration, first decomposition, and second decomposition). In contrast to ALG, PHB had only one stage of decomposition with a prior very low mass loss (1.25%) at the dehydration stage. The water absorption test showed that bacterial ALG has a higher capacity for water absorption in comparison with seaweed ALG, whereas PHB is a hydrophobic polymer. Thus, PHB and ALG synthesized simultaneously by A. agile 12 differ in their physicochemical properties: PHB is a hydrophobic, thermoplastic, mechanically strong polyester, while alginate is hydrophilic, hydrogel-forming, temperature unstable, elastic and mechanically destructible polysaccharide.

Influence of controllable variables on the composting process, kinetic, and maturity of Stevia rebaudiana residues

PurposeStevia rebaudiana residues composting is studied and optimized using a central composite experimental designMethodsThe influence of controllable composting variables [moisture (40–70%), aeration (0.05–0.30 Lair min−1 kg−1), and time (0–50 days)] on the temperature history and the properties of the compost (pH, organic matter) produced to determine suitable composting conditions. Mass balance and emitted gases of all the composting reactors have been done.ResultsCompost with high degradation entails operating at 50 days of composting under high moisture content (70%) and aeration level with values close to 0.05 Lair min−1 kg−1. Moreover, the composting process kinetic for Stevia rebaudiana residues has been studied. The magnitude of the kinetic parameters on the studied conditions varies among 1/42 and 1/46 for 1/K1 and 0.15 and 1.6 for K2. Where 1/K1 is a value that measures the affinity between microorganisms and substrate and K2 depends on the composting variable optimization.ConclusionsBoth moisture and aeration affects positively and negatively the composting process. Moreover, low effect of aeration has been found. The values of 1/K1 and K2 obtained showed higher values (higher degradation kinetic) under 55% moisture content and 0.30 Lair min−1 kg−1.

Impact pressure and void fraction due to plunging breaking wave impact on a 2D TLP structure

Violent impacts due to the plunging breaking wave impingement on a 2D tension-leg platform (TLP) structure were experimentally investigated in a laboratory. Simultaneous pressure, void fraction, fluid velocity, and structure motion measurements were performed on the multiphase, turbulent flow. The maximum mean impact pressure is 2.3ρC 2 with C being the wave phase speed. The pressure maximum and its rise time are negatively correlated, and the rise time for impulsive-type impacts is less than 15 ms or 0.18H/C with H being the wave height. Different approaches show that impact coefficients vary from 0.6 to 9.7, including relating the impact pressure maxima to the wave phase speed, local velocity, and void fraction. By modeling the plunging breaking wave impact as a filling flow, a pressure–aeration relationship was investigated and compared with the approximate solution derived by Peregrine and Thais (J Fluid Mech 325:377–397, 1996). The measured data show that a high aeration level tends to reduce the impact pressure maximum so the cushioning effect is significant for breaking wave impacts on a moving vertical wall.

Lipid content and fatty acid composition of Porosira glacialis and Attheya longicornis in response to carbon dioxide (CO2) aeration.

In the current study two novel psychrophilic diatoms Porosira glacialis and Attheya longicornis were tested for suitability to CO2 mitigation coupled with production of the physiologically requisite omega– 3 fatty acids. This study is in line with the worldwide conducted research aimed at applying biorefinery concept to heavy polluting industries. Since the production of algal high value compounds, i.e. essential fatty acids, relies on utilization of residual CO2 emissions coming from industry, the costs of such production maybe substantially reduced. Besides, the ecological benefits of the biorefinery concept being implemented are obvious, since CO2 is one of the major greenhouse gases. The current research has shown that one of the tested microalgal species, the diatom P. glacialis showed good tolerance to high (20–25%) levels of CO2 and maintained growth rates comparable to controls. The total lipid content in the CO2 aerated culture increased from 8.91 to 10.57% in cell dry mass. Additionally, the content of docosahexaenoic acid (DHA) increased from 3.90 to 5.75%, while the concentration of eicosapentaenoic acid (EPA) decreased from 26.59 to 23.66%. In contrast, A. longicornis did not demonstrate any significant increase in total lipid content. Besides, its growth was hampered by high levels of CO2 aeration.

Economics of Intensively Aerated Catfish Ponds

AbstractTheUScatfish industry is evolving by adopting production‐intensifying practices that enhance productivity. Catfish producers have increased aeration rates over time, and some now use intensive rates of aeration (>9.33kW/ha). Costs and production performance were monitored at commercial catfish farms using high levels of aeration (11.2–18.7 kW/ha) in Alabama, Arkansas, and Mississippi. A multivariate‐cluster analysis was used to identify four different management clusters of intensively aerated commercial catfish farms based on stocking density, size of fingerlings at stocking, and feed conversion ratios (FCR). Breakeven prices of hybrid catfish raised in intensively aerated pond systems were estimated to range from $1.86/kg to $2.17/kg, with the lowest costs associated with the second greatest level of production intensity. The two medium‐intensity clusters generated sufficiently high revenues for long‐term profitability. However, the least‐intensive and the most‐intensive clusters were economically feasible only when catfish and feed prices were closer to less probable market prices. Feed price,FCR, and yield contributed the most to downside risk. Intensive aeration in catfish ponds, up to the levels analyzed in this study, appears to be economically feasible under the medium‐intensity management strategies identified in this analysis.

Environmental factors influencing the efficacy of different yeast strains for alcohol level reduction in wine by respiration

We have recently shown that ethanol yields in winemaking can be reduced by taking advantage of the respiratory metabolism of some non-Saccharomyces yeast species. Using an orthogonal design we have now addressed the impact of three environmental factors (temperature, nitrogen source, and oxygen supply level) on the aerobic metabolism in synthetic must of Saccharomyces cerevisiae, Metschnikowia pulcherrima, Kluyveromyces lactis, and Candida sake. An integrative parameter, Efficacy (efficacy for alcohol level reduction) was designed to simplify comparisons between strains or growth conditions. It integrates sugar consumption, ethanol yield, and acetic acid production data. We found a high relative impact of nitrogen source availability and temperature, as compared to aeration conditions, for several fermentation parameters, including ethanol yield. However, increasing oxygen supply showed a positive impact in terms of alcohol reduction and Efficacy for all the strains tested. The best results across assays were obtained for C. sake CBS 5093, with high sugar consumption rates, associated to low ethanol yields, and very low acetic acid production. Processes involving this yeast strain would benefit from high aeration levels and low nitrogen source availability; while fermentation temperatures would have little impact on its Efficacy for alcohol level reduction.

Research Verification of Production Practices Using Intensive Aeration at a Hybrid Catfish Operation

AbstractAquaculture research verification programs are designed to demonstrate and test research‐based practices recommended by extension services on commercial‐scale operations. From 2010 to 2013, in western Alabama, three management protocols were followed over three crop cycles on a farm producing hybrid catfish (female Channel Catfish Ictalurus punctatus × male Blue Catfish I. furcatus) using high levels of aeration. The protocols were an owner‐defined, multiple‐batch treatment and single‐batch and multiple‐batch treatments defined by the Alabama Cooperative Extension System (ACES). Results from nine production cycles were analyzed to calculate yields, feed conversion ratios (FCRs), cost of production, and net returns. Over three production cycles the owner‐defined, multiple‐batch treatment outperformed the two ACES‐recommended treatments in terms of yield, survival, FCR, and net returns. The owner‐defined treatment could vary, and the producer chose to feed above the recommended daily maximum and observed no low dissolved oxygen levels. High losses owing to disease in the ACES multiple‐batch treatment led to poor results. The owner‐defined multiple‐batch system completed three crops in 2.8 years compared with 3.6–3.7 years for the other two treatments. Thus, this study highlights the importance of research‐based recommendations being verified under commercial catfish production conditions and the value of research verification programs.

Staphylococcus aureus transcriptomic response to inhibition by H2O2-producing Lactococcus garvieae

Growth of the foodborne pathogen Staphylococcus aureus can be inhibited in milk and in cheese by the hydrogen peroxide-producing Lactococcus garvieae N201 dairy strain. Transcriptomic responses of two S. aureus strains, the S. aureus SA15 dairy strain and the MW2 human pathogenic strain, to this growth inhibition were investigated in Brain-Heart Infusion broth under a high or a low aeration level. We demonstrated that S. aureus MW2 had a higher resistance to L. garvieae inhibition under the high aeration level: this correlated to a higher survival under hydrogen peroxide exposure. Conversely, the two strains were similarly inhibited under the low aeration level. Expression of S. aureus genes involved in response to H2O2 or other stresses as well as in cell division was generally repressed by L. garvieae. However, differential expressions between the two S. aureus strains were observed, especially under the high aeration level. Additionally, expression of virulence-related genes (enterotoxins, regulatory genes) was modulated by L. garvieae depending on the aeration level and on the S. aureus strain. This study led to new insights into potential molecular mechanisms of S. aureus inhibition by Lactic Acid Bacteria via H2O2 production.

Biomass, total lipid production, and fatty acid composition of the marine diatom Chaetoceros muelleri in response to different CO2 levels

The marine diatom Chaetoceros muelleri grown under air (0.03% CO2), 10%, 20%, and 30% CO2 conditions was evaluated to determine its potential for CO2 reduction coupled with biodiesel production. The results indicated that C. muelleri grows well with high CO2 aeration levels (10-20%) and is induced to accumulate lipids under 10-30% CO2. In particular, the highest values of the maximum biomass concentration (1.059gL(-1)), maximum specific growth rate (0.868d(-1)), maximum biomass productivity (0.272gL(-1)d(-1)), maximum CO2 biofixation (0.428gL(-1)d(-1)), and total lipid (43.40% dry weight) and neutral lipid contents were all obtained with 10% CO2 aeration. Moreover, the analysis of the fatty acid composition of C. muelleri revealed the predominance of C14-C18 fatty acids (>90%) and saturated and monounsaturated fatty acids (>80%) under all CO2 levels. The results suggest that C. muelleri has great potential to biodiesel production using flue gases.

Use of slow glucose feeding as supporting carbon source in lactose autoinduction medium improves the robustness of protein expression at different aeration conditions

Recombinant protein expression from lac derived promoters by the autoinduction regime is based on diauxic growth of Escherichia coli on glucose and lactose. Glycerol is used as a supporting carbon source during the lactose-induced expression. While this glycerol-based formulation usually provides high cell densities, successful protein expression by autoinduction is often very dependent on correct aeration level. This complicates the reproducibility and scalability of the cultures. In this study we investigate the use of an alternative autoinduction formulation, in which the supporting carbon source is provided by fed-batch-like slow glucose feed from a biocatalytically degraded polysaccharide. The glucose feed as supporting carbon source allowed for high level of autoinduced target protein expression from T7lac promoter in E. coli BL21(DE3) and from T5lac promoter in E. coli K-12 RB791(lacIq) with lactose concentrations of 0.5–2gl−1. Cell densities and protein yields per culture volume were similar to or higher than in the glycerol-based ZYM-5052 medium. In the glycerol-based medium, protein production was adversely influenced by high aeration level, resulting in 75–90% reduction in protein yield per cell compared to more moderately aerated conditions. The glucose fed-batch medium attenuated this oxygen-sensitivity and provided robust high-yield expression also under high aeration rates. It is concluded that the slow glucose feed as supporting carbon source mitigates aeration-related scale differences in autoinduced protein expression, and combined with the benefit of high product yields this makes the fed-batch autoinduction medium ideal for high-throughput screening and scale-up of the production process.

Scaling-up the production of thermostable lipolytic enzymes from Thermus aquaticus YT1

The lipolytic enzymes synthesized by Thermusaquaticus YT1 present extremely interesting properties of thermostability (more than 70% of activity after 12 days at 80°C and a half-life time of 1 h at 95°C), which point out the interest of proposing efficient strategies to successfully tackle the scale-up of the production process. In this study,viable scaling-up of the production process was implemented,and relevant aspects affecting the enzyme synthesis, such as the mineral composition of the culture medium, the aeration and the agitation have been evaluated.A strategy combining the modification of the culture medium and the aeration degree was also approached by adding perfluorocarbons, compounds which improve the availability of oxygen in the culture medium. An opposite response of biomass and lipolytic activity to the aeration conditions was found between scales (about 600 U L(-1) at high aeration levels in flask vs. 150 U L(-1) at high aeration rates in reactor), which further demonstrates the important role of the hydrodynamic conditions on the suitable development of the biological process. In all cases, the cultures were kinetically characterized and the Luedeking and Piret model turned out to be a valuable tool to conclude that the produced lipolytic enzyme is a growth-associated metabolite, no matter the medium and the scale.

Influence of Aeration Rate on the Physio-Chemical Characteristics of Biodried Dairy Manure - Wheat Straw Mixture

Animal manure is a prime candidate for thermochemical conversion (co-firing, gasification, and pyrolysis) except for its high moisture content. Biodrying is a promising solution to reduce manure moisture with minimum energy input. This study investigated the effects of different aeration rates; low (0.05 L/min/kg VM), medium (0.80 L/min/kgVM), and high (1.50 L/min/kgVM), on the biodrying of dairy manure mixed with wheat straw. The moisture content dropped in 21 days from 56% to 28%, 34%, and 35% wb under high, medium, and low aeration rates, respectively. The heating value of the mixture decreased from 16.19 MJ/kgdry to 14.31, 13.79, and 13.83 MJ/kgdry under high, medium, and low aeration, respectively. Evaluation of energy consumption to remove a unit mass of moisture showed that high aeration levels required the least energy input, 7.84 MJ/kgH2O, followed by low aeration at 7.93 MJ/ kgH2O, while the medium aeration had a relatively high energy cost for water removal, 9.09 MJ/ kgH2O. The high aeration level was superior in terms of both drying energy and time requirements to the other rates considered. Comparison showed that high aeration level biodrying (1.50 L/min/kgVM) exceeded the range of conventional drying energy demand. However, the ratio of external fossil fuel demand was much lower in biodrying (due to the auto-thermal effect) than in conventional drying.

Evaluation of a novel Bacillus strain from a north‐western Spain hot spring as a source of extracellular thermostable lipase

AbstractBACKGROUND: Thermophilic microorganisms are receiving significant attention as a source of useful thermostable enzymes. However, the number of known strains is still limited, and very often their most interesting biocatalysts are intracellular or membrane‐bound and produced at low levels. Thus, the isolation and study of novel extracellular enzyme‐producing thermophilic microorganisms is very interesting. Moreover, the assessment of bioreactor performance is crucial, given the scarce information on the large‐scale culture of these strains.RESULTS: The production of a thermostable extracellular lipase in submerged cultures of a thermophilic microorganism, recently isolated in north‐west Spain, was investigated. The strain was identified by 16S rDNA sequencing as belonging to genus Bacillus. The influence of operating variables (i.e. pH, temperature, aeration) on lipase biosynthesis was analysed. Enzyme production at bioreactor scale was investigated, special attention being paid to the effect of aeration and agitation rates.CONCLUSION: The best conditions for the studied process were determined in shake flasks as pH 7.0, 55 °C and high aeration levels. Also, the non‐association between lipase production and cell growth was ascertained. The culture of this novel strain was successfully carried out in laboratory‐scale bioreactors, thus proving its potential for further applications. Copyright © 2009 Society of Chemical Industry

Preparation and sensory perception of fat‐free foams – effect of matrix properties and level of aeration

SummaryThe sensory perception of fat‐free model foams with a consistency between pourable (liquid; xanthan thickened) and spoonable (semi‐solid; gelled; carrageenan thickened) and varying level of aeration was studied. At low air contents (5, 10% v/v) perception is largely determined by the matrix properties; the presence of air is hardly experienced. On the other hand, at high levels of aeration (80% v/v) perception is determined by bubble characteristics and the matrix plays a negligible role in perception. Bubbles were better noticeable in a semi‐solid, i.e. carrageenan matrix, than in liquid, i.e. xanthan‐based foams. In semi‐solid sucrose–ester carrageenan foams, large bubbles were perceived as more airy and less creamy, compared with the same compositions with smaller bubbles.

Parental care in response to natural variation in nest predation pressure in six sunfish (Centrarchidae: Teleostei) species

Abstract – Parental care is an important, energetically costly component of the life history of many fishes. Despite this importance, little is known about how different species of fish vary parental care in response to natural nest predator burdens. In this study, underwater videography was used to quantify parental care activity of six species of syntopic nesting male centrarchid fishes in Lake Opinicon, Ontario, in response to natural predators. This approach was used to test the hypothesis that as offspring develop from eggs to wrigglers, parental care activity should decrease or remain static for fish guarding nests with low predator burden and increase for those with high predator burden, reflecting different external risks. Principal components analysis (PCA) was used to derive common aeration and nest defence variables. Aeration and predator defence activity of the fish varied extensively among species. Parental care behaviours indicative of defence and vigilance (e.g., turning, departures, time away from nest, displays) tended to be highest for species that had the most predation attempts, although this was not entirely consistent. There was also a positive relationship between the defence PCA metric and attempted predation. Defence did not vary with stage of offspring development, although interactions between defence and developmental stage were noted for several species. A trade‐off between aeration and defence was not observed. In fact, species that provide high levels of aeration also simultaneously provide high levels of defence. Stage‐specific patterns of defence in this study were less apparent than those documented by studies using responses to staged predator intrusions making it unclear as to the extent that fish were responding to the level of the risk to offspring than to the value of the brood. Therefore, combined use of observational and experimental assessments of parental care investment may be most appropriate for refining current theoretical paradigms.

Violent breaking wave impacts. Part 1: Results from large-scale regular wave tests on vertical and sloping walls

As part of an investigation into the detailed characteristics of wave impacts, experimental data are presented for the impact pressures and forces generated by waves up to 1.7 m high breaking onto a vertical wall and a wall inclined at 27° to the vertical. Particular attention is given to the influence of entrained and entrapped air and, by selecting regular wave conditions that produce impacts, trends are identified for highly variable phenomena that could easily be missed when masked by the even greater variability associated with irregular waves. The characteristics of the impacts are found to depend on the breaker conditions and four different types of impact are identified and discussed. The distinctive features of low-aeration and high-aeration impacts are considered in some detail and it is shown that a high level of aeration does not always reduce the peak pressure although it tends to increase both the rise time and duration. Consequently, high levels of aeration can increase both the force and impulse on the structure. Alternate compression and expansion of the air can also generate potentially detrimental sub-atmospheric pressures. The largest impact pressures tend to occur around still water level and distributions in terms of both the incident wave height and the peak pressure are presented in dimensionless terms for each type of impact. Although the highest pressures are associated with low- and high-aeration impacts, the results suggest that slightly-breaking and broken wave impacts should not be neglected and percentage exceedance curves are included to give an indication of the frequency of extreme values. Whilst nominally identical waves often produce very different spatial and temporal pressure distributions, the impulse on the structure during an impact is far less variable and is shown to be broadly proportional to the peak momentum flux of the incident waves. The pressures, forces and impulses associated with an impact on the sloping wall tend to be lower than those on the vertical wall in the same circumstances. However, the total impulse caused by a whole wave event (impact plus quasi-hydrostatic phases) is found to be independent of wall slope in accordance with basic principles. The paper concludes by demonstrating that, for the conditions investigated, the impact can account for up to ∼ 30% of the total impulse.

L-Arabinose metabolism in Candida arabinofermentans PYCC 5603T and Pichia guilliermondii PYCC 3012: influence of sugar and oxygen on product formation

L-Arabinose utilization by the yeasts Candida arabinofermentans PYCC 5603(T) and Pichia guilliermondii PYCC 3012 was investigated in aerobic batch cultures and compared, under similar conditions, to D-glucose and D-xylose metabolism. At high aeration levels, only biomass was formed from all the three sugars. When oxygen became limited, ethanol was produced from D-glucose, demonstrating a fermentative pathway in these yeasts. However, pentoses were essentially respired and, under oxygen limitation, the respective polyols accumulated--arabitol from L-arabinose and xylitol from D-xylose. Different L-arabinose concentrations and oxygen conditions were tested to better understand L-arabinose metabolism. P. guilliermondii PYCC 3012 excreted considerably more arabitol from L-arabinose (and also xylitol from D-xylose) than C. arabinofermentans PYCC 5603(T). In contrast to the latter, P. guilliermondii PYCC 3012 did not produce any traces of ethanol in complex L-arabinose (80 g/l) medium under oxygen-limited conditions. Neither sustained growth nor active metabolism was observed under anaerobiosis. This study demonstrates, for the first time, the oxygen dependence of metabolite and product formation in L-arabinose-assimilating yeasts.