Morphological and metabolic shifts of Yarrowia lipolytica induced by alteration of the dissolved oxygen concentration in the growth environment.

Yarrowia lipolytica, an ascomycete with biotechnological potential, is able to form either yeast cells or hyphae and pseudohyphae in response to environmental conditions. This study shows that the morphology of Y. lipolytica, cultivated in batch cultures on hydrophilic (glucose and glycerol) and hydrophobic (olive oil) media, was not affected by the nature of the carbon source, nor by the nature or the concentration of the nitrogen source. By contrast, dissolved oxygen concentration (DOC) should be considered as the major factor affecting yeast morphology. Specifically, when growth occurred at low or zero DOC the mycelial and/or pseudomycelial forms predominated over the yeast form independently of the carbon and nitrogen sources used. Experimental data obtained from a continuous culture of Y. lipolytica on glycerol, being used as carbon and energy source, demonstrated that the mycelium-to-yeast form transition occurs when DOC increases from 0.1 to 1.5 mg l(-1). DOC also affected the yeast physiology, as the activity of enzymes implicated in lipid biosynthesis (i.e. ATP-citrate lyase, malic enzyme) was upregulated at high DOC whereas the activity of enzymes implicated in glycerol assimilation (such as glycerol dehydrogenase and kinase) remained fundamentally unaffected in the cell-free extract.

The olive mill wastewater as substrate for single cell oil production by Zygomycetes.

The conversion of olive mill wastewater (OMW) into high added value lipids containing polyunsaturated fatty acids (PUFA), in parallel with a significant phenolic removal by selected strains of Zygomycetes, is reported here for the first time. The growth of Mortierella isabellina, Mortierella ramanniana, Cunninghamella echinulata, Mucor sp., Thamnidium elegans and Zygorhynchus moelleri on solidified media was not significantly affected by the presence of OMW used in the growth medium up to 50% (v/v). Kinetic parameter values and conversion yields, estimated using a mathematical model which was fitted on the experimental data originated from submerged cultures, shows the ability of some Zygomycetes (i.e. T. elegans and Z. moelleri) to grow on OMW and accumulate storage material, i.e. lipids rich in PUFA, and these findings open new perspectives in OMW management and valorization. In liquid media containing OMW as sole carbon source, T. elegans and Z. moelleri produced 4.4 and 3.5g/L cell mass in surface (SC) and submerged (SMC) cultures, respectively, containing around 60% (w/w) of lipids. Oleic and palmitic acids were the predominant fatty acids. Gamma-linolenic acid was found in high percentages (up to 17.7%, w/w) in the lipid of Z. moelleri, in SMC with OMW as sole carbon source, while PUFA biosynthesis was not favored in SC.

Lipids containing polyunsaturated fatty acids synthesized by zygomycetes grown on glycerol.

Several strains of Zygomycetes cultivated on glycerol produced mycelia rich in lipids containing higher amounts of neutral lipids (NL) than glycolipids plus sphingolipids and phospholipids (P), while biosynthesis of P in Mortierella ramanniana, Mucor sp., and Cunninghamella echinulata occurred though NL accumulation process was in progress. Polyunsaturated fatty acids (PUFA) concentration gradually decreased in all lipid fractions of M. ramanniana during growth. In contrast, in C. echinulata concentration of both linoleic and γ-linolenic acids increased with time, especially in P. Taking for granted that the main function of PUFA is associated to their participation in mycelial membranes, we could suppose that biosynthesis of these fatty acids is associated to mycelial growth. However, this is accurate only for some Zygomycetes, e.g., M. ramanniana. On the contrary, PUFA biosynthesis in C. echinulata persists after growth cessation, suggesting that in this species biosynthetic ability is not a strictly growth-associated process. Phosphatidyl-inositol and phosphatidyl-choline were the major P classes in C. echinulata and M. ramanniana, respectively. In M. ramanniana, a decrease of PUFA concentration was noticed even when mycelia were incubated in low temperature (conditions that normally favor PUFA biosynthesis), indicating that PUFA biosynthesis in this fungus is associated to primary metabolism.

Metabolic activities of biotechnological interest in Yarrowia lipolytica grown on glycerol in repeated batch cultures.

The growth of Yarrowia lipolytica on glycerol was studied in bioreactor repeated batch cultures and three distinct phases, namely biomass production phase, lipogenic phase and citric acid production phase were identified during growth cycle. In each phase, yeast cells were characterised by specific morphological and biochemical features. Though high activity of NAD(+) dependent iso-citric dehydrogenase (NAD(+)-ICDH) was detected during biomass production phase, this activity was significantly decreased afterwards inducing lipogenesis. A further drop in NAD(+)-ICDH activity to minimal levels and a decrease in glycerol kinase activity were observed during the citric acid production phase. Surprisingly, citric acid production was accompanied by storage (neutral) lipid turnover, along with remarkable biosynthesis of glycolipids, sphingolipids and phospholipids. Oleic acid was the major fatty acid in all lipid fractions and phosphatidylcholine was the main phospholipid. This study allows concluding that Y. lipolytica successfully converts glycerol via phosphorylation pathway into valuable biotechnological products, such as single cell oil and citric acid.

Fatty acid composition in lipid fractions lengthwise the mycelium of Mortierella isabellina and lipid production by solid state fermentation.

This paper investigates the correlation between mycelial age and fatty acid biosynthesis. The correlation was investigated by analyzing the lipid composition lengthwise the mycelium of the oleaginous fungus Mortierella isabellina, a potential producer of gamma-linolenic acid (GLA). Young mycelia were rich in polar lipids (glycolipids plus sphingolipids and phospholipids), while neutral lipid content increased in aged mycelia. In young mycelia, each polar lipid fraction contained almost 40% (w/w) polyunsaturated fatty acids (PUFAs), but this content decreased to less than 30% (w/w) in aged mycelia. On the other hand, PUFA content in neutral lipids fluctuated slightly with age. These results indicate that PUFA biosynthesis is favored in young, fast growing mycelia, while it decreases significantly in aged mycelia. This trend was also observed when we grew M. isabellina on pear pomace, an agro-industrial waste. Pear pomace cultures yielded significant amounts of lipid, which reached 12% (w/w) in dry fermented mass. The produced lipid was rich in GLA and the maximum GLA content in dry fermented mass was 2.9 mg/g.

Vulnerability to air pollution health effects.

INTRODUCTION: Ambient air pollution can have adverse effects on the health of exposed populations, but individuals or groups are not equally vulnerable, and pollution reduction benefits are likely to be unevenly distributed within a population. While the use of total-population risks is a valid approach for public health protection, it is increasingly recognized that more attention on vulnerable groups is necessary. This paper describes population vulnerability to the health effects of air pollutants using risk analysis concepts and based on available evidence. METHODS: Publications reporting air pollution health risks for specific sub-populations, or more conceptual discussions of vulnerability, were selected following a literature search of the PubMed database. Only studies in the context of developed countries were included. Information on population characteristics and factors that can influence risk was assessed from the perspective of the vulnerability framework, and was used to outline interactions with biological susceptibility, exposure, and social coping. RESULTS: Population characteristics encompass several factors that interact and confer vulnerability. Age, for example, regarded as significant mostly in terms of physiology, also relates to exposure through behaviours and activities that can be more amenable to prevention. Children are recognized as a high-risk group but their vulnerability may differ by childhood stage, while pregnant women are not explicitly identified as a vulnerable group despite growing evidence for reproductive risks. Social-economic factors have received little attention, although they can affect coping capacity as well as interact with susceptibility and exposure to air pollution. CONCLUSIONS: Evidence for vulnerability components often lies in different fields of study and has not been evaluated in an integrated manner. Better understanding of population vulnerability can improve the scientific basis to assess risks and develop policies or other health protection initiatives to reduce the impacts of air pollution.

Children's susceptibility to chemicals: a review by developmental stage.

Concerns about adequate protection of children's health from chemicals in the environment have created a need for research to identify how children's risks differ from adults'. A systematic review of factors that affect child sensitivity throughout development may be useful for research and practice in this area. We summarized available literature and other peer-reviewed information on factors that affect pharmacokinetics and exposure in an age-based developmental framework. Biological processes related to chemical absorption (gastrointestinal, dermal, and pulmonary), distribution, metabolism, and excretion were considered, along with reference to behaviors and other factors associated with child-specific exposures. The available information was summarized in a timeline of maturation for biological processes. It indicates variability in the duration and timing of maturation for each biological function. Possible implications for understanding pediatric sensitivity to environmental chemicals are discussed in light of factors affecting exposure through development. Themes that emerge from the evidence are presented as hypothesis-generating conclusions. This approach may be useful for evaluating developmental trends of susceptibility, and for identifying time periods and/or chemical classes of particular concern and thus important to consider in risk assessment.

Defining susceptibility for microbial risk assessment: results of a workshop.

An interdisciplinary workshop was convened by the George Washington University in June 2001 to discuss how to incorporate new knowledge about susceptibility to microbial pathogens into risk assessment and management strategies. Experts from government, academic, and private sector organizations discussed definitions, methods, data needs, and issues related to susceptibility in microbial risk assessment. The participants agreed that modeling approaches need to account for the highly specific nature of host-pathogen relationships, and the wide variability of infectivity, immunity, disease transmission, and outcome rates within microbial species and strains. Concerns were raised about distinguishing between exposure and dose more clearly, interpreting experimental and outbreak data correctly, and using thresholds and possibly linearity at low doses. Recommendations were made to advance microbial risk assessment by defining specific terms and concepts more precisely, designing explicit conceptual frameworks to guide development of more complex models and data collection, addressing susceptibility in all steps of the model, measuring components of immunity to characterize susceptibility, reexamining underlying assumptions, applying default methods appropriately, obtaining more mechanistic data to improve default methods, and developing more biologically relevant and continuous risk estimators. The interrelated impacts of selecting specific subpopulations and health outcomes, and of increasing model complexity and data demands, were considered in the contexts of public policy goals and resources required. The participants stated that zero risk is unattainable, so targeted and effective risk reduction and communication strategies are essential not only to raise pubic awareness about water quality but also to protect the most susceptible members of the population.

Cryptosporidiosis susceptibility and risk: a case study.

Regional estimates of cryptosporidiosis risks from drinking water exposure were developed and validated, accounting for AIDS status and age. We constructed a model with probability distributions and point estimates representing Cryptosporidium in tap water, tap water consumed per day (exposure characterization); dose response, illness given infection, prolonged illness given illness; and three conditional probabilities describing the likelihood of case detection by active surveillance (health effects characterization). The model predictions were combined with population data to derive expected case numbers and incidence rates per 100,000 population, by age and AIDS status, borough specific and for New York City overall in 2000 (risk characterization). They were compared with same-year surveillance data to evaluate predictive ability, assumed to represent true incidence of waterborne cryptosporidiosis. The predicted mean risks, similar to previously published estimates for this region, overpredicted observed incidence-most extensively when accounting for AIDS status. The results suggest that overprediction may be due to conservative parameters applied to both non-AIDS and AIDS populations, and that biological differences for children need to be incorporated. Interpretations are limited by the unknown accuracy of available surveillance data, in addition to variability and uncertainty of model predictions. The model appears sensitive to geographical differences in AIDS prevalence. The use of surveillance data for validation and model parameters pertinent to susceptibility are discussed.