Biostimulation by methanol enables the methylotrophic yeasts Hansenula polymorpha and Trichosporon sp. to reveal high formaldehyde biodegradation potential as well as to adapt to this toxic pollutant

Three chlorotoluene-degrading bacterial strains: Differences in biodegradation potential and cell surface properties

Pollution of the environment with chlorinated aromatic compounds is a problem of increasing importance, which has stimulated the search for efficient methods for the remediation of contaminated soil and water. Additionally, for better understanding of the significance of bioavailability to biodegradation, investigation of the cell surface properties is necessary. Hence, this study concerns the properties and possible application, in chlorotoluene removal, of three newly isolated environmental bacterial strains from the genera Pseudomonas, Raoultella and Rahnella. The results show the differences in the biochemical profiles of the isolated strains, their cellular fatty acid composition and their hemolytic properties. However, all three strains exhibit high biodegradation potential, degrading not less than 60% of each monochlorotoluene isomer in 21-day experiments. What is more, observations of changes in the cell surface properties indicate the possible adaptation mechanisms of the strains that enable efficient biodegradation of hydrophobic pollutants such as monochlorotoluenes.

Effects of limonene, n-decane and n-decanol on growth and membrane fatty acid composition of the microalga Botryococcus braunii

Botryococcus braunii is a promising microalga for the production of biofuels and other chemicals because of its high content of internal lipids and external hydrocarbons. However, due to the very thick cell wall of B. braunii, traditional chemical/physical downstream processing very often is not as effective as expected and requires high amounts of energy. In this cases, the application of two-phase aqueous-organic solvent systems could be an alternative to cultivate microalgae allowing for a simultaneous extraction of the valuable compounds without significant negative effects on cell growth. Two-phase systems have been applied before, however, there are no studies so far on the mechanisms used by microalgae to survive in contact with solvents present as a second-phase. In this study, the effects of the solvents limonene, n-decane and n-decanol on growth of the microalga B. braunii as well as the adaptive cell response in terms of their phospholipid fatty acid contents were analized. A concentration-dependent negative effect of all three solvents on cell growth was observed. Effects were accompanied by changes of the membrane fatty acid composition of the alga as manifested by a decrease of the unsaturation . In addition, an association was found between the solvent hydrophobicity (given as log octanol–water partition coefficient (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {P}_{O-W}$$\end{document}PO-W) values) and their toxic effects, whereby n-decanol and n-decane emerged as the most and least toxic solvent respectively. Among the tested solvents, the latter promises to be the most suitable for a two-phase extraction system.

A Novel Mitochondrial Serine O-Acetyltransferase, OpSAT1, Plays a Critical Role in Sulfur Metabolism in the Thermotolerant Methylotrophic Yeast Ogataea parapolymorpha

In most bacteria and plants, direct biosynthesis of cysteine from sulfide via O-acetylserine (OAS) is essential to produce sulfur amino acids from inorganic sulfur. Here, we report the functional analysis of a novel mitochondrial serine O-acetyltransferase (SAT), responsible for converting serine into OAS, in the thermotolerant methylotrophic yeast Ogataea parapolymorpha. Domain analysis of O. parapolymorpha SAT (OpSat1p) and other fungal SATs revealed that these proteins possess a mitochondrial targeting sequence (MTS) at the N-terminus and an α/β hydrolase 1 domain at the C-terminal region, which is quite different from the classical SATs of bacteria and plants. Noticeably, OpSat1p is functionally interchangeable with Escherichia coli SAT, CysE, despite that it displays much less enzymatic activity, with marginal feedback inhibition by cysteine, compared to CysE. The Opsat1Δ-null mutant showed remarkably reduced intracellular levels of cysteine and glutathione, implying OAS generation defect. The MTS of OpSat1p directs the mitochondrial targeting of a reporter protein, thus, supporting the localization of OpSat1p in the mitochondria. Intriguingly, the OpSat1p variant lacking MTS restores the OAS auxotrophy, but not the cysteine auxotrophy of the Opsat1Δ mutant strain. This is the first study on a mitochondrial SAT with critical function in sulfur assimilatory metabolism in fungal species.

Effects of ammonium-based ionic liquids and 2,4-dichlorophenol on the phospholipid fatty acid composition of zebrafish embryos

Ionic liquids consisting of a combination of herbicidal anions with a quaternary ammonium cation act as efficient herbicides, which are under consideration to be used in the agriculture. In the present study, we used embryos of the zebrafish (Danio rerio) as a model to assess the toxic potential of ammonium-based ionic liquids for aquatic organisms. As we assumed interference of the partially hydrophobic ionic liquid cation with lipids, we investigated the adaptation response in the lipid composition of the zebrafish embryos, triggered by the ionic compound. Therefore, the impact of ammonium-based ionic liquids with different lengths of the alkyl chain ([C6,C6,C1,C1N][Br], [C8,C8,C1,C1N][Br]) on the phospholipid fatty acid (PLFA) profile of zebrafish embryos up to 72 hours post fertilization (hpf) was examined. Furthermore, the changes in the unsaturation index (UI) of PLFAs, as the sum parameter of membrane fluidity in eukaryotic cells, were presented. The PLFA's UI in the zebrafish embryos upon exposure to quaternary ammonium salts was compared to the UI of the embryos upon exposure to nonionic 2,4-dichlorophenol, which has a similar hydrophobicity but is structurally different to [C8,C8,C1,C1N][Br]. It was shown that for ammonium-based ionic liquid precursors non-specific mode of action occurs and the toxic effect on lipid composition of zebrafish embryos can be well predicted based on chemical properties, like hydrophobicity. Furthermore, the changes in PLFAs, expressed by the UI, can be useful to study toxic effects of organic contamination. However, for zebrafish embryos, after ionic liquids and 2,4-DCP exposure, the changes were observed at high lethal concentrations, which caused the incidence of lethality of 30 and 50% of a group of test animals.

Adaptive response of Rhodococcus opacus PWD4 to salt and phenolic stress on the level of mycolic acids

Mycolata form a group of Gram-positive bacteria with unique cell envelope structures that are known for their high tolerance against antibiotics and both aromatic and aliphatic hydrocarbons. An important part of the unique surface structure of the mycolata is the presence of long chain α-alkyl-β-hydroxy fatty acids, the mycolic acids. In order to investigate the adaptive changes in the mycolic acid composition, we investigated the composition of mycolic acids during the response both to osmotic stress caused by NaCl and to 4-chlorophenol in Rhodococcus opacus PWD4. This bacterium was chosen as it is known to adapt to different kinds of stresses. In addition, it is a potential biocatalyst in bioremediation as well as for biotechnological applications. In the present study, cells of R. opacus PWD4, grown in liquid cultures, responded to toxic concentrations of NaCl by increasing the ratio between mycolic acids and membrane phospholipid fatty acids (MA/PLFA-ratio). Cells reacted to both NaCl and 4-chlorophenol by decreasing both the average chain length and the unsaturation index of their mycolic acids. These changes in mycolic acid composition correlated with increases in cell surface hydrophobicity and saturation of membrane fatty acids, demonstrating the relation between mycolic acid and phospholipid synthesis and their contribution to cell surface properties of R. opacus PWD4.

Body Mass Parameters, Lipid Profiles and Protein Contents of Zebrafish Embryos and Effects of 2,4-Dinitrophenol Exposure

Morphology and physiology of fish embryos undergo dramatic changes during their development until the onset of feeding, supplied only by endogenous yolk reserves. For obtaining an insight how these restructuring processes are reflected by body mass related parameters, dry weights (dw), contents of the elements carbon and nitrogen and lipid and protein levels were quantified in different stages within the first four days of embryo development of the zebrafish (Danio rerio). The data show age dependent changes in tissue composition. Dry weights decreased significantly from 79μgdw/egg at 0hours post fertilization (hpf) to 61 μgdw/egg after 96 hpf. The amounts of total carbon fluctuated between 460 mg g^-1 and 540 mg g^-1 dw, nitrogen was at about 100 mg g^-1 dw and total fatty acids were between 48–73 mg g^-1 dw. In contrast to these parameters that remained relatively constant, the protein content, which was 240 mg g^-1 at 0 hpf, showed an overall increase of about 40%. Comparisons of intact eggs and dechorionated embryos at stages prior to hatching (24, 30, 48 hpf) showed that the differences seen for dry weight and for carbon and nitrogen contents became smaller at more advanced stages, consistent with transition of material from the chorion to embryo tissue. Further, we determined the effect of 2,4-dinitrophenol at a subacutely toxic concentration (14 μM, LC10) as a model chemical challenge on the examined body mass related parameters. The compound caused significant decreases in phospholipid and glycolipid fatty acid contents along with a decrease in the phospholipid fatty acid unsaturation index. No major changes were observed for the other examined parameters. Lipidomic studies as performed here may thus be useful for determining subacute effects of lipophilic organic compounds on lipid metabolism and on cellular membranes of zebrafish embryos.

Genome and physiology of the ascomycete filamentous fungus Xeromyces bisporus, the most xerophilic organism isolated to date

Xeromyces bisporus can grow on sugary substrates down to 0.61, an extremely low water activity. Its genome size is approximately 22 Mb. Gene clusters encoding for secondary metabolites were conspicuously absent; secondary metabolites were not detected experimentally. Thus, in its 'dry' but nutrient-rich environment, X. bisporus appears to have relinquished abilities for combative interactions. Elements to sense/signal osmotic stress, e.g. HogA pathway, were present in X. bisporus. However, transcriptomes at optimal (∼ 0.89) versus low aw (0.68) revealed differential expression of only a few stress-related genes; among these, certain (not all) steps for glycerol synthesis were upregulated. Xeromyces bisporus increased glycerol production during hypo- and hyper-osmotic stress, and much of its wet weight comprised water and rinsable solutes; leaked solutes may form a protective slime. Xeromyces bisporus and other food-borne moulds increased membrane fatty acid saturation as water activity decreased. Such modifications did not appear to be transcriptionally regulated in X. bisporus; however, genes modulating sterols, phospholipids and the cell wall were differentially expressed. Xeromyces bisporus was previously proposed to be a 'chaophile', preferring solutes that disorder biomolecular structures. Both X. bisporus and the closely related xerophile, Xerochrysium xerophilum, with low membrane unsaturation indices, could represent a phylogenetic cluster of 'chaophiles'.