Evaluating glucose and xylose as cosubstrates for lipid accumulation and c-linolenic acid biosynthesis of Thamnidium elegans

Aims: To study the biotechnological production of lipids containing rich amounts of the medically and nutritionally important c-linolenic acid (GLA), during cultivation of the Zygomycetes Thamnidium elegans, on mixtures of glucose and xylose, abundant sugars of lignocellulosic biomass. Methods and Results: Glucose and xylose were utilized as carbon sources, solely or in mixtures, under nitrogen-limited conditions, in batch-flask or bioreactor cultures. On glucose, T. elegans produced 31.9 g/L of biomass containing 15.0 g/L lipid with significantly high GLA content (1014 mg/L). Xylose was proved to be an adequate substrate for growth and lipid production. Additionally, xylitol secretion occurred when xylose was utilized as carbon source, solely or in mixtures with glucose. Batch-bioreactor trials on glucose yielded satisfactory lipid production, with rapid substrate consumption rates. Analysis of intracellular lipids showed that the highest GLA content was observed in early stationary growth phase, while the phospholipid fraction was the most unsaturated fraction of T. elegans. Conclusions: Thamnidium elegans represents a promising fungus for the successful valorization of sugar-based lignocellulosic residues into microbial lipids of high nutritional and pharmaceutical interest.

Rhodosporidium toruloides cultivated in NaCl-enriched glucose-based media: adaptation dynamics and lipid production

In the present report and for the first time in the international literature, the impact of the addition of NaCl upon growth and lipid production on the oleaginous yeast Rhodosporidium toruloides was studied. Moreover, equally for first time, lipid production by R. toruloides was performed under non-aseptic conditions. Therefore, the potentiality of R. toruloides DSM 4444 to produce lipid in media containing several initial concentrations of NaCl with glucose employed as carbon source was studied. Preliminary batch-flask trials with increasing amounts of NaCl revealed the tolerance of the strain against NaCl content up to 6.0% (w/v). However, 4.0% (w/v) of NaCl stimulated lipid accumulation for this strain, by enhancing lipid production up to 71.3% (w/w) per dry cell weight. The same amount of NaCl was employed in pasteurized batch-flask cultures in order to investigate the role of the salt as bacterial inhibiting agent. The combination of NaCl and high glucose concentrations was found to satisfactorily suppress bacterial contamination of R. toruloides cultures under these conditions. Batch-bioreactor trials of the yeast in the same media with high glucose content (up to 150 g/L) resulted in satisfactory substrate assimilation, with almost linear kinetic profile for lipid production, regardless of the initial glucose concentration imposed. Finally, fed-batch bioreactor cultures led to the production of 37.2 g/L of biomass, accompanied by 64.5% (w/w) of lipid yield. Lipid yield per unit of glucose consumed received the very satisfactory value of 0.21 g/g, a value amongst the highest ones in the literature. The yeast lipid produced contained mainly oleic acid and to lesser extent palmitic and stearic acids, thus constituting a perfect starting material for “second generation” biodiesel

Isoform specificity for oestrogen receptor and thyroid hormone receptor genes and their interactions on the NR2D gene promoter

Oestrogens are critical for the display of lordosis behaviour and, in recent years, have also been shown to be involved in synaptic plasticity. In the brain, the regulation of ionotropic glutamate receptors has consequences for excitatory neurotransmission. Oestrogen regulation of the N-methyl-d-aspartate receptor subunit 2D (NR2D) has generated considerable interest as a possible molecular mechanism by which synaptic plasticity can be modulated. Since more than one isoform of the oestrogen receptor (ER) exists in mammals, it is possible that oestrogen regulation via the ERalpha and ERbeta isoforms on the NR2D oestrogen response element (ERE) is not equivalent. In the kidney fibroblast (CV1) cell line, we show that in response to 17beta-oestradiol, only ERalpha, not ERbeta, could upregulate transcription from the ERE which is in the 3' untranslated region of the NR2D gene. When this ERE is in the 5' position, neither ERalpha nor ERbeta showed transactivation capacity. Thyroid hormone receptor (TR) modulation of ER mediated induction has been shown for other ER target genes, such as the preproenkephalin and oxytocin receptor genes. Since the various TR isoforms exhibit distinct roles, we hypothesized that TR modulation of ER induction may also be isoform specific. This is indeed the case. The TRalpha1 isoform stimulated ERalpha mediated induction from the 3'-ERE whereas the TRbeta1 isoform inhibited this induction. This study shows that isoforms of both the ER and TR have different transactivation properties. Such flexible regulation and crosstalk by nuclear receptor isoforms leads to different transcriptional outcomes and the combinatorial logic may aid neuroendocrine integration.

Estrogen and thyroid hormone receptor interactions: physiological flexibility by molecular specificity

The influence of thyroid hormone on estrogen actions has been demonstrated both in vivo and in vitro. In transient transfection assays, the effects of liganded thyroid hormone receptors (TR) on transcriptional facilitation by estrogens bound to estrogen receptors (ER) display specificity according to the following: 1) ER isoform, 2) TR isoform, 3) the promoter through which transcriptional facilitation occurs, and 4) cell type. Some of these molecular phenomena may be related to thyroid hormone signaling of seasonal limitations upon reproduction. The various combinations of these molecular interactions provide multiple and flexible opportunities for relations between two major hormonal systems important for neuroendocrine feedbacks and reproductive behaviors.