PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-4 (4)
 

Clipboard (0)
None

Select a Filter Below

Journals
Authors
more »
Year of Publication
Document Types
1.  Organic Acid Excretion in Penicillium ochrochloron Increases with Ambient pH 
Despite being of high biotechnological relevance, many aspects of organic acid excretion in filamentous fungi like the influence of ambient pH are still insufficiently understood. While the excretion of an individual organic acid may peak at a certain pH value, the few available studies investigating a broader range of organic acids indicate that total organic acid excretion rises with increasing external pH. We hypothesized that this phenomenon might be a general response of filamentous fungi to increased ambient pH. If this is the case, the observation should be widely independent of the organism, growth conditions, or experimental design and might therefore be a crucial key point in understanding the function and mechanisms of organic acid excretion in filamentous fungi. In this study we explored this hypothesis using ammonium-limited chemostat cultivations (pH 2–7), and ammonium or phosphate-limited bioreactor batch cultivations (pH 5 and 7). Two strains of Penicillium ochrochloron were investigated differing in the spectrum of excreted organic acids. Confirming our hypothesis, the main result demonstrated that organic acid excretion in P. ochrochloron was enhanced at high external pH levels compared to low pH levels independent of the tested strain, nutrient limitation, and cultivation method. We discuss these findings against the background of three hypotheses explaining organic acid excretion in filamentous fungi, i.e., overflow metabolism, charge balance, and aggressive acidification hypothesis.
doi:10.3389/fmicb.2012.00121
PMCID: PMC3318189  PMID: 22493592
ambient pH; organic acids; chemostat; bioreactor batch culture; Neurospora crassa; overflow metabolism; charge balance; aggressive acidification
2.  Interaction of 5-hydroxytryptamine (serotonin) against Aspergillus spp. in vitro 
This study examined the direct interaction of serotonin (5-hydroxytryptamine (5-HT)) with Aspergillus species. Accumulation of 5-HT in aspergilli was investigated by immunofluorescence staining and laser confocal scanning microscopy. The influence of 5-HT on fungal ergosterol content, cell membrane integrity, fungal growth and hyphal elongation was determined. 5-HT was localised in the cytoplasm of Aspergillus spp., as 5-HT fluorescent signals appeared after 30 min at 4°C and in the presence of inhibitors of oxidative phosphorylation. 5-HT treatment of Aspergillus spp. significantly affected ergosterol synthesis, fungal cell membrane integrity and hyphal elongation (P < 0.05). 5-HT treatment for 4 h resulted in a lag of re-growth (post-antifungal effect). In conclusion, our findings suggest that 5-HT affects hyphal growth and diminishes fungal cell membrane integrity.
doi:10.1016/j.ijantimicag.2006.12.003
PMCID: PMC3010239  PMID: 17276041
Serotonin; Aspergillus spp.; Ergosterol; Platelets
3.  Leaching with Penicillium simplicissimum: Influence of Metals and Buffers on Proton Extrusion and Citric Acid Production 
In the presence of insoluble metal oxides (industrial filter dust, zinc oxide, synthetic mixture of metal oxides), Penicillium simplicissimum developed the ability to excrete considerable amounts of citric acid (>100 mM). Parallel with the increase of citric acid concentration in the culture broth, zinc was solubilized from zinc oxide. The adsorption of filter dust onto the mycelium (the pellets formed were less than 1 mm in diameter) was required for not only the citric acid excretion but also the leaching of zinc. When the filter dust was replaced with a synthetic mixture of metal oxides or with zinc oxide in combination with trace elements, levels of adsorption and citric acid production were observed to be similar to those in experiments where industrial filter dust was used. The two most important properties of the filter dust were its heavy-metal content and its buffering capacity. These properties were simulated by adding heavy metals in soluble form (as chlorides, sulfates, or nitrates) or soluble buffers to the medium. Both heavy metals and buffers were not able to induce a citric acid efflux. As with citric acid production by Aspergillus niger, the addition of manganese lowered citric acid excretion (by 40% with metal oxide-induced citric acid efflux and by 100% with urea-induced citric acid efflux). Copper antagonized the effect of manganese. The mechanism for the bulk of citric acid excretion by P. simplicissimum, however, seemed to be different from that described for citric acid accumulation by A. niger. Because of the inefficiency of metals in solubilized form and of soluble buffers to induce a strong citric acid efflux, adsorption of an insoluble metal compound (zinc oxide) turned out to be essential. Surface phenomena possibly involving the plasma membrane H+-ATPase are thought to participate in the induction of citric acid excretion by P. simplicissimum in the presence of industrial filter dust.
PMCID: PMC182793  PMID: 16348442
4.  Extraction of Zinc from Industrial Waste by a Penicillium sp 
Zinc was extracted from a filter residue of a copper works (58.6% zinc) by a Penicillium sp. isolated from a metal-containing location. By isotachophoresis citric acid was identified as the leaching agent. Citrate was only formed when the leaching substrate was present. This production of citrate was different in several ways from that achieved by Aspergillus niger: glucose was utilized before fructose; the initial concentration of zinc was 50 to 500 times higher than usual in citrate fermentations with A. niger; citrate production stopped when 80 to 90% of the zinc was leached, although sufficient sugar for further synthesis was still present; and in synthetic media citrate production by A. niger needs an acidic environment (pH 2), while the formation of citric acid by Penicillium sp. occurred in a pH range of 7 to 4. Tests with different concentrations of waste material (0.5, 2.5, and 5%) showed that the highest yield of solubilized zinc occurred with a 2.5% substrate (93% zinc extracted after 13 days).
PMCID: PMC184269  PMID: 16347908

Results 1-4 (4)