Biodegradation of phenol by alginate immobilized Chlamydomonas reinhardtii cells.

In the present work, the biodegradation of phenol by alginate immobilized Chlamydomonas reinhardtii cells was investigated. Immobilized Chlamydomonas reinhardtii could remove up to 1300 µmol/L of phenol within 10 days of cultivation. Metabolic activity was demonstrated by the extracellular release of catechol. Beads prepared at high concentrations of alginate (5-6% w/v) were found to protect microalgae against the strong inhibitory effects of phenol on the photosynthetic apparatus. Cells immobilized in beads of higher concentrations of alginate exhibited higher metabolic efficiencies compared to those prepared by lower alginate concentrations. Lower alginate concentrations (3-4% w/v) led to increased cell leakage, while the presence of phenol in the medium had the opposite effect in all alginate concentrations. Resuspension of immobilized microalgae in a medium containing a growth-promoting substrate, led to colony formation only on the external surface of alginate beads, indicating that acetic acid and consequently phenol, could not penetrate the internal of alginate beads. The significance of the work is that alginate immobilized Chlamydomonas substantially minimize the required volume of the aqueous medium and improve the economics and commercial application prospects of the process.

Production of Biohydrogen and/or Poly-ß-hydroxybutyrate by Rhodopseudomonas sp. Using Various Carbon Sources as Substrate.

The polyhydroxyalkanoates (PHA) are family of biopolyesters synthesized by numerous bacteria which are attracting a great attention due to their thermoplastic properties. Polyhydroxybutyrate (PHB) is the most common type of PHA which presents thermoplastic and biodegradable properties. It is synthesized under stressful conditions by heterotrophic bacteria and many photosynthetic microorganisms such as purple non-sulfur bacteria and cyanobacteria. Biological hydrogen (H2) production is being evaluated for use as a fuel since it is a promising substitute for carbonaceous fuels owing to its high conversion efficiency and high specific content. In the present work, the purple non-sulfur photosynthetic bacterium Rhodopseudomonas sp. for the simultaneous H2 photo-evolution and poly-ß-hydroxybutyrate (PHB) production has been investigated. Three different types of carbon sources were tested in the presence of glutamate as a nitrogen source in a batch cultivation system, under continuous irradiance. The results indicated the fact that the type of carbon source in the culture broth affects in various ways the metabolic activity of the bacterial biomass, as evidenced by the production of PHB and/or H2 and biomass. The best carbon source for PHB accumulation and H2 production by Rhodopseudomonas sp. turned out to be the acetate, having the highest H2 production (2286 mL/L) and PHB accumulation (68.99 mg/L, 18.28% of cell dry weight).

Biodegradation of phenol by Chlamydomonas reinhardtii.

The data presented in this particular study demonstrate that the biodegradation of phenol by Chlamydomonas reinhardtii is a dynamic bioenergetic process mainly affected by the production of catechol and the presence of a growth-promoting substrate in the culture medium. The study focused on the regulation of the bioenergetic equilibrium resulting from production of catechol after phenol oxidation. Catechol was identified by HPLC-UV and HPLC-ESI-MS/MS. Growth measurements revealed that phenol is a growth-limiting substrate for microalgal cultures. The Chlamydomonas cells proceed to phenol biodegradation because they require carbon reserves for maintenance of homeostasis. In the presence of acetic acid (a growth-promoting carbon source), the amount of catechol detected in the culture medium was negligible; apparently, acetic acid provides microalgae with sufficient energy reserves to further biodegrade catechol. It has been shown that when microalgae do not have sufficient energy reserves, a significant amount of catechol is released into the culture medium. Chlamydomonas reinhardtii acts as a versatile bioenergetic machine by regulating its metabolism under each particular set of growth conditions, in order to achieve an optimal balance between growth, homeostasis maintenance and biodegradation of phenol. The novel findings of this study reveal a paradigm showing how microalgal metabolic versatility can be used in the bioremediation of the environment and in potential large-scale applications.

Characterization of a novel herbicide and antibiotic-resistant Chlorella sp. with an extensive extracellular matrix.

A herbicide and antibiotic-resistant microalgal strain, isolated from a eutrophic site at Giofyros river (Heraklion, Crete, Greece) was extensively characterized. In the presence of relatively high concentrations of common photosynthesis inhibitors (DCMU and atrazine), as well as various antibiotics (spectinomycin, kanamycin, and chloramphenicol), the green microalga was able to increase its biomass in approximately equal levels compared to the control. Despite the high concentrations of the inhibitors, photosynthetic efficiency and chlorophyll a amount per dry cell biomass were comparable to those of control cultures in almost all cases. 18S rDNA analysis showed that this microalga belongs to the Chlorella genus. Optical and electron microscopy studies revealed the presence of an extensive extracellular matrix (EM) that surrounds the cells and plays an important role in colony formation and cell-cell interactions. Fourier transform infrared spectroscopy provided evidence that the EM consists of a polysaccharide. This matrix could be separated from the cells with a simple centrifugation. Depending on growth conditions, the dry cell biomass of this Chlorella strain was found to contain 35-39% proteins and 27-42% carbohydrates. The results of this study have demonstrated that the EM plays a protective role for cell homeostasis maintenance against the various chemical agents. This green microalga is a suitable candidate for further studies regarding sustainable biomass production in waste waters for a series of applications.

Effects of pH, temperature and salinity on P3HB synthesis culturing the marine Rhodovulum sulfidophilum DSM-1374.

Rhodovulum sulfidophilum DSM-1374 is a potential producer of polyester when growing in phototrophic conditions. The present study investigated on a polyester product (P3HB) by culturing Rhodovulum sulfidophilum DSM-1374 in two different photobioreactors (PBR-1 and PBR-2) both with 4-L working volumes. PBR-1 is equipped with an internal rotor having 4 paddles to mix the bacterial culture while PBR-2 has an internal coil-shaped rotor. After selecting PBR-1, which best performed in the preliminary experiment, the effect of different stressing growth conditions as pH (7.0, 8.0, and 9.0), temperature (25, 30, and 35 °C), and medium salinity (1.5, 2.5, 3.5, and 4.5%) were tested. When the pH of the culture was set to 8.0, the capability of the bacterium to synthetize the polyester increased significantly reaching a concentration of 412 mg (P3HB)/L; the increase of the pH at 9.0 caused a reduction of the P3HB concentration in the culture. The medium salinity of 4.5% was the best stress-growth condition to reach the highest concentration of polyester in the culture (820 ± 50 mg (P3HB)/L) with a P3HB mass fraction in the dry biomass of 33 ± 1.5%. Stresses caused by culture temperature are another potential parameter that could increase the synthesis of P3HB.

The effect of nitrogen starvation on membrane lipids of Synechocystis sp. PCC 6803 investigated by using easy ambient sonic-spray ionization mass spectrometry.

BACKGROUND: Glycerolipids are important components of membranes in cyanobacteria that possess vital roles in biological processes. The effect of nitrogen deprivation on membrane lipids of Synechocystis sp. PCC 6803 lipids has not been previously examined. METHODS: Easy ambient sonic-spray ionization mass spectrometry (EASI-MS) was used for the analysis of Synechocystis 6803 cells with minimal sample preparation, providing rapid qualitative and relative quantitative information on the lipid content of their membranes. RESULTS: Changes in the degree of unsaturation of membrane lipids were observed for cells grown under normal conditions during different growth phases. This physiological remodeling was disrupted when nitrogen was withdrawn from the cultivation medium. However, this disruption was reversed when the cells were resuspended in normal N-containing medium. Mass spectrometric data were supported by examination of cells by electron microscopy. CONCLUSIONS: EASI-MS was applied for the first time in the analysis of Synechocystis 6803 cells grown under nitrogen deprived conditions and was found to be a powerful technique operating in a high-throughput manner for the rapid lipid profiling of cells at different growth stages and under different growth conditions. GENERAL SIGNIFICANCE: The effect of nitrogen deprivation on membrane lipids of Synechocystis 6803 cells was revealed using an ambient ionization technique which enabled high-throughput cell analysis with minimal sample preparation. The results obtained have the potential to be used in future studies to decipher the involvement of enzymes in the observed lipid profile changes.

Metabolism of xenobiotics by Chlamydomonas reinhardtii: Phenol degradation under conditions affecting photosynthesis.

In the present work, the biodegradation of phenol by axenic cultures of the unicellular microalga Chlamydomonas reinhardtii was investigated. Biodegradation proved to be a dynamic bioenergetic process, affected by changes in the culture conditions. Microalgae biodegraded defined amounts of phenol, as a result of the induced stress caused at high concentrations, despite the fact that this process proved to be energy demanding and thus affected growth of the culture. High levels of biodegradation were observed both in the absence of an alternative carbon source and in the presence of acetate as a carbon source. Biodegradation of phenol by Chlamydomonas proved to be an aerobic, photoregulated process. This is the first time that Chlamydomonas reinhardtii has been used for bioremediation purposes. This study has demonstrated that the most important factor in the biodegradation of phenol is the selection of the appropriate culture conditions (presence or absence of alternative carbon source, light intensity, and oxygen availability) that provide the best bioenergetic balance among growth, induced stress, and biodegradation of phenol.

Intercalation of the herbicide atrazine in layered double hydroxides for controlled-release applications.

BACKGROUND: The herbicide atrazine was intercalated in the interlayer region of Mg/Al layered double hydroxides in order to produce a nanohybrid that could be used in controlled-release applications. RESULTS: The hydrophobic herbicide was incorporated in artificial membranes formed in the interlayer of the inorganic host by using palmitic acid. The synthetic nanohybrid material was characterised by various techniques, and release studies were carried out. In addition, the photosynthetic alga Chlamydomonas reinhardtii Dang. was treated with the atrazine-containing nanohybrid, which exerted an herbicidal efficacy similar to that of the free herbicide. CONCLUSION: The herbicide containing nanohybrid could enable a controlled release of the herbicide. In addition, the herbicide would be delivered close to its site of uptake, enhancing efficiency and reducing the required doses.

Nutraceutical use of garlic sulfur-containing compounds.

Garlic is one of the world's oldest medicines that has been employed not only for flavouring but also as a medical herb for its prophylactic and therapeutic actions. Most garlics' beneficial effects are due to the presence of the organosulphate molecule allicin. Allicin is a highly unstable molecule and, during processing, is rapidly transformed into a variety of organosulfur components. The enzyme alliinase, which is responsible for the conversion of alliin to allicin, is irreversibly destroyed at the acidic environment of stomach. This is the reason why most garlic supplements contain garlic powder or granules, but do not contain allicin itself. Garlic alliinase could be encapsulated and coated with materials which would protect it in the harsh conditions of the stomach. The objective of this chapter is to summarize the most important garlic health benefits and to discuss promising encapsulation/stabilization approaches.

Development of a photosystem II-based optical microfluidic sensor for herbicide detection.

Herbicides are highly toxic for both human and animal health. The increased application of herbicides in agriculture during the last decades has resulted in the contamination of both soil and water. Herbicides, under illumination, can inhibit photosystem II electron transfer. Photosynthetic membranes isolated from higher plants and photosynthetic micro-organisms, immobilized and stabilized, can serve as a biorecognition element for a biosensor. The inhibition of photosystem II causes a reduced photoinduced production of hydrogen peroxide, which can be measured by a chemiluminescence reaction with luminol and the enzyme horseradish peroxidase. In the present work, a compact and portable sensing device that combines the production and detection of hydrogen peroxide in a single flow assay is proposed for herbicide detection.

Intercalation of hydrophilic and hydrophobic antibiotics in layered double hydroxides.

Four pharmaceutically active molecules, each representing a different class of antibiotic, were intercalated in layered double hydroxides. Two of them, gramicidin and amphotericin B, are hydrophobic, surface active drugs that were incorporated in artificial membranes formed in the interlayer of the inorganic host. The other two, ampicillin and nalidixic acid, are water soluble, commonly used antibiotics that were directly intercalated by using simple ion exchange reactions. The synthetic nanohybrid materials were characterized by various methods, as X-ray diffraction, infrared spectroscopy and ultraviolet-visible spectroscopy that verified the successful intercalation of the antibiotics and provided information regarding the interlayer structure of the nanohybrids. The reversible interaction of the antibiotic molecules with the inorganic host leads to release of the active drugs under the appropriate conditions. The release studies showed that the synthetic nanohybrids can successfully serve as controlled release systems for different kinds of antibiotics.

Isolation, characterization, sequencing and crystal structure of charybdin, a type 1 ribosome-inactivating protein from Charybdis maritima agg.

A novel, type 1 ribosome-inactivating protein designated charybdin was isolated from bulbs of Charybdis maritima agg. The protein, consisting of a single polypeptide chain with a molecular mass of 29 kDa, inhibited translation in rabbit reticulocytes with an IC50 of 27.2 nm. Plant genomic DNA extracted from the bulb was amplified by PCR between primers based on the N-terminal and C-terminal sequence of the protein from dissolved crystals. The complete mature protein sequence was derived by partial DNA sequencing and terminal protein sequencing, and was confirmed by high-resolution crystal structure analysis. The protein contains Val at position 79 instead of the conserved Tyr residue of the ribosome-inactivating proteins known to date. To our knowledge, this is the first observation of a natural substitution of a catalytic residue at the active site of a natural ribosome-inactivating protein. This substitution in the active site may be responsible for the relatively low in vitro translation inhibitory effect compared with other ribosome-inactivating proteins. Single crystals were grown in the cold room from PEG6000 solutions. Diffraction data collected to 1.6 A resolution were used to determine the protein structure by the molecular replacement method. The fold of the protein comprises two structural domains: an alpha + beta N-terminal domain (residues 4-190) and a mainly alpha-helical C-terminal domain (residues 191-257). The active site is located in the interface between the two domains and comprises residues Val79, Tyr117, Glu167 and Arg170.