Responses of Synechocystis sp. PCC 6803 (cyanobacterium) photosystem II to pyrene stress

Effects of polycyclic aromatic hydrocarbons on marine and freshwater microalgae - A review

The first synthetic review of the PAHs effects on microalgae in experimental studies and aquatic ecosystems is provided. Phytoplankton and phytobenthos from marine and freshwaters show a wide range of sensitivities to PAHs, and can accumulate, transfer and degrade PAHs. Different toxicological endpoints including growth, chlorophyll a, in vivo fluorescence yield, membrane integrity, lipid content, anti-oxidant responses and gene expression are reported for both freshwater and marine microalgal species exposed to PAHs in culture and in natural assemblages. Photosynthesis, the key process carried out by microalgae appears to be the most impacted by PAH exposure. The effect of PAHs is both dose- and species-dependent and influenced by environmental factors such as UV radiation, temperature, and salinity. Under natural conditions, PAHs are typically present in mixtures and the toxic effects induced by single PAHs are not necessarily extrapolated to mixtures. Natural microalgal communities appear more sensitive to PAH contamination than microalgae in monospecific culture. To further refine the ecological risks linked to PAH exposure, species-sensitivity distributions (SSD) were analyzed based on published EC₅₀s (half-maximal effective concentrations during exposure). HC₅ (harmful concentration for 5% of the species assessed) was derived from SSD to provide a toxicity ranking for each of nine PAHs. The most water-soluble PAHs naphthalene (HC₅ = 650 µg/L), acenaphthene (HC₅ = 274 µg/L), and fluorene (HC₅ = 76.8 µg/L) are the least toxic to microalgae, whereas benzo[a]pyrene (HC₅ = 0.834 µg/L) appeared as the more toxic. No relationship between EC₅₀ and cell biovolume was established, which does not support assumptions that larger microalgal cells are less sensitive to PAHs, and calls for further experimental evidence. The global PAHs HC₅ for marine species was on average higher than for freshwater species (26.3 and 1.09 µg/L, respectively), suggesting a greater tolerance of marine phytoplankton towards PAHs. Nevertheless, an important number of experimental exposure concentrations and reported toxicity thresholds are above known PAHs solubility in water. The precise and accurate assessment of PAHs toxicity to microalgae will continue to benefit from more rigorously designed experimental studies, including control of exposure duration and biometric data on test microalgae.

Willow can be recommended as a strong candidate for the phytoremediation of cadmium and pyrene co-polluted soil under flooding condition

Soil cadmium (Cd) and pyrene (PYR) pollutions have gained worldwide attention due to their negative effects on the environment. Intermittent flooding in rain-rich areas may affect phytoremediation of Cd and PYR in soil. Therefore, a pot-culture experiment, with and without flooding, was conducted to study the effects of flooding on soil Cd and PYR phytoremediation. Concentrations of Cd, PYR, and nutrients in soils and plants, as well as plant physiological and biochemical responses, were examined. Under both flooding and non-flooding conditions, willow (Salix × aureo-pendula CL 'J1011') demonstrated a better ability to remove soil Cd and PYR. Flooding led to higher Cd accumulation in roots than that in shoots. Conversely, non-flooding resulted in higher Cd accumulation in shoots than that in roots. The maximum concentrations of Cd in shoots were 11.02 and 14.07 mg kg^-1 with and without flooding, respectively. The maximum dissipation rates of PYR in soil were 47.35% and 88.61% under flooding and non-flooding conditions, respectively. In addition, flooding significantly increased the photosynthetic pigment, photosynthetic fluorescence, and chlorophyll fluorescence parameters in leaves, compared with non-flooding treatment. Flooding also increased the concentrations of Mg, Mn, P, Fe, and K in roots and shoots. This study outlines an effective insight for the phytoremediation of Cd- and PYR-contaminated soil under flooding condition.

Selective Complex Precipitation for Ferro-Chrome Separation From Electroplating Sludge Leaching Solution

In this paper, aiming at the problem of chrome-iron separation in electroplating sludge, the separation of ferrochrome by complexation and precipitation with benzoic acid as complexing agent is achieved. The optimal conditions consisted of a 1: 3 molar ratio of Fe³⁺: C₆H₅COOH, a reaction temperature of 30°C, a final pH of 2.5 and a reaction time of 2 min. The separation rate of the iron was 97.38% and the rate of loss of chromium was only 3.59%. The ferrochromium separation products were analyzed by XRD, fluorescence spectroscopy, infrared spectroscopy and H NMR Spectroscopy in order to study the mechanism of precipitation. The results showed that benzoic acid preferentially forms a complex with iron and iron benzoate precipitates with an increase pH. The iron benzoate crystals have a fine particle size, settle rapidly and are easy to filter. The separation of Cr ³⁺/Fe³⁺ was successful using our methodology.

The Role of Selected Wavelengths of Light in the Activity of Photosystem II in Gloeobacter violaceus

Gloeobacter violaceus is a cyanobacteria species with a lack of thylakoids, while photosynthetic antennas, i.e., phycobilisomes (PBSs), photosystem II (PSII), and I (PSI), are located in the cytoplasmic membrane. We verified the hypothesis that blue–red (BR) light supplemented with a far-red (FR), ultraviolet A (UVA), and green (G) light can affect the photosynthetic electron transport chain in PSII and explain the differences in the growth of the G. violaceus culture. The cyanobacteria were cultured under different light conditions. The largest increase in G. violaceus biomass was observed only under BR + FR and BR + G light. Moreover, the shape of the G. violaceus cells was modified by the spectrum with the addition of G light. Furthermore, it was found that both the spectral composition of light and age of the cyanobacterial culture affect the different content of phycobiliproteins in the photosynthetic antennas (PBS). Most likely, in cells grown under light conditions with the addition of FR and G light, the average antenna size increased due to the inactivation of some reaction centers in PSII. Moreover, the role of PSI and gloeorhodopsin as supplementary sources of metabolic energy in the G. violaceus growth is discussed.

Cell-by-cell estimation of PAH sorption and subsequent toxicity in marine phytoplankton

Polycyclic Aromatic Hydrocarbons (PAHs) have elicited increasing concern due to their ubiquitous occurrence in coastal marine environments and resultant toxicity in organisms. Due to their lipophilic nature, PAHs tend to accumulate in phytoplankton cells and thus subsequently transfer to other compartments of the marine ecosystem. The intrinsic fluorescence properties of PAHs in the ultraviolet (UV)/blue spectral range have recently been exploited to investigate their uptake modes, localization, and aggregation in various biological tissues. Here, we quantitatively evaluate the sorption of two model PAHs (phenanthrene and pyrene) in three marine phytoplankton species (Chaetoceros tenuissimus, Thalassiosira sp. and Proteomonas sp.) using a combined approach of UV excitation flow cytometry and fluorescence microscopy. Over a 48-h exposure to a gradient of PAHs, Thalassiosira sp. showed the highest proportion of PAH-sorbed cells (29% and 97% of total abundance for phenanthrene and pyrene, respectively), which may be attributed to its relatively high total lipid content (33.87 percent dry weight). Moreover, cell-specific pulse amplitude modulation (PAM) microscope fluorometry revealed that PAH sorption significantly reduced the photosynthetic quantum efficiency (F_v/F_m) of individual phytoplankton cells. We describe a rapid and precise hybrid method for the detection of sorption of PAHs on phytoplankton cells. Our results emphasize the ecologically relevant sub-lethal effects of PAHs in phytoplankton at the cellular level, even at concentrations where no growth inhibition was apparent. This work is the first study to address the cell-specific impacts of fluorescent toxicants in a more relevant toxicant-sorbed subpopulation; these cell-specific impacts have to date been unidentified in traditional population-based phytoplankton toxicity assays.

Temperature-dependent growth and hypericin biosynthesis in Hypericum perforatum

Hypericum perforatum is a perennial herb that produces the anti-depression metabolite hypericin (Hyp). While several efforts to increase Hyp production have been made, the effects of temperatures on growth and Hyp biosynthesis are still limited. In this study, the growth morphophysiological traits, Hyp biosynthesis and their related genes expression, as well as major bioactive compounds accumulation and antioxidant capacity were assessed by exposing H. perforatum seedlings to three different temperatures (15, 22 and 30 °C). The results showed that aerial parts biomass was greater at 15 °C with 1.3 and 1.6-fold increase compared to at 22 and 30 °C, in large part because of greater increase in chlorophyll content, stem number and leaf area on a per plant basis. Hyp content in the aerial parts was greater 1.9 and 5.6-fold on a per plant basis compared to 22 and 30 °C treatments, and the contents of other bioactive compounds (flavonoids and phenolics) as well as antioxidant capacity in the aerial parts, on dry weight and per plant basis, also exhibited significant increases with the temperatures decrease. The mRNA expressions of eight genes (psbA, psbB, psbC, psbD, ycf3, ycf4, ycf5 and matK) related to photosynthesis and two genes (Polyketide synthase, PKS; Phenolic oxidative coupling protein, Hyp-1) involved in Hyp biosynthesis were also up-regulated at 15 °C. The findings are useful in guiding cultivation and regulating Hyp biosynthesis in H. perforatum.

Impacts of Fe2+ on 5-aminolevulinic acid (ALA) biosynthesis of Rhodobacter sphaeroides in wastewater treatment by regulating nif gene expression

This study aimed to increase bacterial growth and 5-aminolevulinic acid (ALA) biosynthesis of Rhodobacter sphaeroides in wastewater treatment through adding ferrous ion (Fe2+). Results demonstrated that Fe2+ effectively enhanced the biomass production and ALA yield of R. sphaeroides. Moreover, the optimal Fe2+ dosage was found to be 400μmol/L, which was associated with the highest biomass of 4015.3mg/L and maximum ALA yield of 15.9mg/g-dry cell weight (mg/g-DCW). Mechanism analysis revealed that Fe2+ vastly improved Adenosine Triphosphate (ATP) production by up-regulating the nif gene expression, and increasing ATP enhanced the biomass and ALA yield by supplying energy for bacterial growth and ALA biosynthesis, respectively. Correlation analysis showed that the ALA and ATP yields had positive relation with nifA and nifU gene expression. In addition, the nifA and nifU gene expression displayed high consistency of co-transcription at the optimal Fe2+ dosage.

Effect of magnesium ion on crt gene expression in improving carotenoid yield of Rhodobacter sphaeroides

This study aimed at increasing carotenoid yield of Rhodobacter sphaeroides in wastewater treatment by adding magnesium ion (Mg(2+)). Results showed that Mg(2+) could improve R. sphaeroides biomass and carotenoid yield effectively. The highest carotenoid yield of 4.83 ± 0.14 mg/g biomass and biomass production of 3900 ± 180 mg/L were achieved at optimal Mg(2+) concentration of 15 mmol/L. Mechanism analysis revealed that Mg(2+) could promote carotenoid production by regulating the expressions of crt genes. Up-regulation of crtBDA genes improved carotenoid biosynthesis of R. sphaeroides.

Enhancement of Rhodobacter sphaeroides growth and carotenoid production through biostimulation

Bacillus thuringiensis/cereus L2 was added as a biostimulant to enhance the biomass accumulation and carotenoid yield of Rhodobacter sphaeroides using wastewater as the culturing medium. Results showed that biostimulation could significantly enhance the R. sphaeroides biomass production and carotenoid yield. The optimal biostimulant proportion was 40 μL (about 6.4×10(5) CFU). Through the use of biostimulation, chemical oxygen demand removal, R. sphaeroides biomass production, carotenoid concentration, and carotenoid yield were improved by 178%, 67%, 214%, and 70%, respectively. Theoretical analysis revealed that there were two possible reasons for such increases. One was that biostimulation enhanced the R. sphaeroides wastewater treatment efficiency. The other was that biostimulation significantly decreased the peroxidase activity in R. sphaeroides. The results showed that the highest peroxidase activity dropped by 87% and the induction ratio of the RSP_3419 gene was 3.1 with the addition of biostimulant. The enhanced carotenoid yield in R. sphaeroides could thus be explained by a decrease in peroxidase activity.

Divergent responses of functional gene expression to various nutrient conditions during microcystin-LR biodegradation by Novosphingobium sp. THN1 strain

To better understand the mechanisms for microcystin-LR (MCLR) biodegradation, the linkage between MCLR-biodegradation kinetics and functional gene expression dynamics was originally investigated with Novosphingobium sp. THN1 as inoculum under various nutrient conditions. Along biodegradation, mlrA gene expression, coupled with mlrD, presented similar trend but was regulated differentially among different conditions. Good positive correlation was observed between MCLR degraded and induction ratios of functional genes until 42h at respective condition. Compared to those under nutrient-free condition, the stimulated or decelerated biodegradation with dipotassium phosphate (DP) or ammonium chloride (AC) (both at 100mg L(-1)) was related to higher or lower up-regulation in mlr gene expression, suggesting that divergent mlr gene expression was one of the reasons for different effects of DP or AC on degradation. However, stimulated degradation with sodium nitrate (100mg L(-1)) might involve other mechanisms where mlr expression was not the decisive prerequisite to govern MCLR-biodegradation.