Jihai Shao

Modifying Fe3O4 nanoparticles with humic acid for removal of Rhodamine B in water

Humic acid (HA) modifying Fe(3)O(4) nanoparticles (Fe(3)O(4)/HA) was developed for removal of Rhodamine B from water. Fe(3)O(4)/HA was prepared by a coprecipitation procedure with cheap and environmentally friendly iron salts and HA. TEM images revealed the Fe(3)O(4)/HA (with ≈ 10 nm Fe(3)O(4) cores) were aggregated as aqueous suspensions. With a saturation magnetization of 61.2 emu/g, the Fe(3)O(4)/HA could be simply recovered from water with magnetic separations at low magnetic field gradients within a few minutes. Sorption of the Rhodamine B to Fe(3)O(4)/HA reached equilibrium in less than 15 min, and agreed well to the Langmuir adsorption model with maximum adsorption capacities of 161.8 mg/g. The Fe(3)O(4)/HA was able to remove over 98.5% of Rhodamin B in water at optimized pH.

Allelopathic mechanism of pyrogallol to Microcystis aeruginosa PCC7806 (Cyanobacteria): From views of gene expression and antioxidant system

Pyrogallol is a potent allelochemical on Microcystis aeruginosa, but its allelopathic mechanism is not fully known. In order to explore this mechanism, gene expressions for prx, mcyB, psbA, recA, grpE, fabZ under pyrogallol stress were studied, and activities of the main antioxidant enzymes were also measured. The results showed that expression of grpE and recA showed no significant change under pyrogallol stress, while psbA and mcyB were up-regulated at 4 mg L(-1). Both prx and fabZ were up-regulated even under exposure to 1 mg L(-1) pyrogallol concentration. The activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced under pyrogallol stress. Levels of malodialdehyde (MDA) at 2 and 4 mg L(-1) pyrogallol were significantly higher than those of the controls. It was concluded that oxidant damage is an important mechanism for the allelopathic effect of pyrogallol on M. aeruginosa.

Potential for control of harmful cyanobacterial blooms using biologically derived substances: Problems and prospects

Water blooms of cyanobacteria have posed a worldwide environmental threat and a human health hazard in recent decades. Many biologically derived (but non-antibiotic) bioactive substances are known to inhibit the growth of aquatic bloom-forming cyanobacteria. Some of these biologically derived substances (BDSs) have no or low toxicity to aquatic animals and humans. Most BDSs are easily biodegradable in aquatic environments. These characteristics indicate that they may have potential for control and removal of harmful algae. However, BDSs also have the disadvantages of high cost of preparation, and possible damage to non-target aquatic organisms, and sometimes, low efficiency of algae removal. The ecological risks of most BDSs are still unknown. Here, we review recent research progress relative to the inhibitory effects of BDSs on cyanobacteria, and critically analyze the potential of BDSs as algicides with an emphasis on possible problems during the process of controlling harmful cyanobacteria. We suggest avenues of study to enhance effective use of BDSs in controlling of cyanobacterial blooms; these include guidelines for isolation and characterization of new effective BDSs, exploiting the synergistic effects of BDSs, the merits of controlling harmful cyanobacteria at the early stages of proliferation and evaluation of ecological risks of BDSs.

Elucidating the toxicity targets of β-ionone on photosynthetic system of Microcystis aeruginosa NIES-843 (Cyanobacteria)

In order to explore the potential targets of toxicity of β-ionone on the photosynthetic system of Microcystis aeruginosa, the polyphasic rise in chlorophyll a (Chl a) fluorescence transient and transcript expression for key genes in photosystem II (PSII) of M. aeruginosa NIES-843 were studied. The EC₅₀ value of β-ionone on M. aeruginosa NIES-843 was found to be 21.23±1.87 mg/L. It was shown that β-Ionone stress can lead to a decrease in pigment content of M. aeruginosa NIES-843 cells, and that carotenoids were more sensitive to β-ionone stress than Chl a. The normalized Chl a fluorescence transients were slightly decreased at 6.67 and 10 mg/L β-ionone, but significantly increased at 15, 22.5 and 33.75 mg/L. There was no significant variation on transcript expression of psbA and psbO at a concentration of 6.67 mg/L β-ionone, but they were down-regulated at 22.5 mg/L. Ultrastructural examination by transmission electron microscopy indicated that the thylakoids were distorted, and the thylakoid membrane stacks began to collapse when M. aeruginosa NIES-843 was exposed to β-ionone at a concentration of 22.5 and 33.75 mg/L. Our results indicate that the reaction centre of PS II and the electron transport at the acceptor side of PS II are the targets responsible for the toxicity of β-ionone on the PS II of M. aeruginosa NIES-843.

Active and silent members in the mlr gene cluster of a microcystin-degrading bacterium isolated from Lake Taihu, China

The microcystin-degrading genes, mlr, are important participants in the degradation process of hepatotoxic microcystins for several bacterial species. However, their expression status during degrading microcystins is still unknown. In order to study this expression process, we isolated a novel microcystin-degrading bacterial strain, sequenced its mlr gene cluster and examined the expression of the mlrA gene at different concentrations of microcystin LR. The expression of mlrA increased slightly at 0.4 mg L⁻¹, and was significantly upregulated at 2.0 mg L⁻¹. Frameshift mutations were found in the mlrB* gene, and the mRNA of mlrB* could not be detected in the total RNA extracts of Novosphingobium sp. THN1. We conclude that mlrA is actively involved in the microcystin-degrading process, but mlrB* has lost its activity in this bacterial strain.

Synthesis of nanoscale zero-valent iron immobilized in alginate microcapsules for removal of Pb(II) from aqueous solution

Alginate microcapsules immobilized nanoscale zero-valent iron (M-NZVI), with diameters from several hundreds nanometers to several micrometers, were synthesized using ferric and calcium ions as the cross-linking cations, and then tested for removal of Pb(II) from aqueous solution. The size of NZVI particles was only a few nanometers according to transmission electron microscopy (TEM) observation. The synthesized alginate microcapsules were stable in air for as long as they were dried and contained 9.97% of iron by weight. When 0.5 g L−1 of M-NZVI were introduced into an aqueous solution containing 300.0 mg L−1 of Pb(II), 88% of Pb(II), 581.7 mg g−1 of Pb(II) uptake amount were removed from the system in 15 min. The kinetics of the removal reactions, including an initial adsorption phase and a subsequent reduction, is complicated. In addition, the synthesized M-NZVI showed a higher removal capability of Pb compared to NZVI and Ca-alginate particles. This newly synthesized material could be regenerated and reused at least 4 times when the initial concentrations of Pb(II) were ≤200.0 mg L−1. The higher reaction rates and greater removal capacity suggest that M-NZVI may be a potential material for in situ remediation of metal contaminated water and sediments.

Genes Associated with 2-Methylisoborneol Biosynthesis in Cyanobacteria: Isolation, Characterization, and Expression in Response to Light

The volatile microbial metabolite 2-methylisoborneol (2-MIB) is a root cause of taste and odor issues in freshwater. Although current evidence suggests that 2-MIB is not toxic, this compound degrades water quality and presents problems for water treatment. To address these issues, cyanobacteria and actinomycetes, the major producers of 2-MIB, have been investigated extensively. In this study, two 2-MIB producing strains, coded as Pseudanabaena sp. and Planktothricoids raciborskii, were used in order to elucidate the genetic background, light regulation, and biochemical mechanisms of 2-MIB biosynthesis in cyanobacteria. Genome walking and PCR methods revealed that two adjacent genes, SAM-dependent methyltransferanse gene and monoterpene cyclase gene, are responsible for GPP methylation and subsequent cyclization to 2-MIB in cyanobacteria. These two genes are located in between two homologous cyclic nucleotide-binding protein genes that may be members of the Crp-Fnr regulator family. Together, this sequence of genes forms a putative operon. The synthesis of 2-MIB is similar in cyanobacteria and actinomycetes. Comparison of the gene arrangement and functional sites between cyanobacteria and other organisms revealed that gene recombination and gene transfer probably occurred during the evolution of 2-MIB-associated genes. All the microorganisms examined have a common origin of 2-MIB biosynthesis capacity, but cyanobacteria represent a unique evolutionary lineage. Gene expression analysis suggested that light is a crucial, but not the only, active regulatory factor for the transcription of 2-MIB synthesis genes. This light-regulated process is immediate and transient. This study is the first to identify the genetic background and evolution of 2-MIB biosynthesis in cyanobacteria, thus enhancing current knowledge on 2-MIB contamination of freshwater.

Carbon disulfide-modified magnetic ion-imprinted chitosan-Fe(III): A novel adsorbent for simultaneous removal of tetracycline and cadmium

A novel composite of carbon disulfide-modified magnetic ion-imprinted chitosan-Fe(III), i.e., MMIC-Fe(III) composite, was prepared as an efficient adsorbent for the simultaneous removal of tetracycline (TC) and Cd(II). This adsorbent showed excellent performance in removing TC and Cd(II) due to its rapid kinetics, high adsorption capacity, good reusability, and was well suited for use with real water samples. Kinetics studies demonstrated that the adsorption proceeded according to a pseudo-second order model. The adsorption isotherms were well described by the Langmuir model, with maximum adsorption capacity for TC and Cd(II) being 516.29 and 194.31mg/g, respectively. The synergistic effect of TC and Cd(II) adsorption might be due to the formation of TC-Cd(II) complex bridging the adsorbate and adsorbent. These properties demonstrate the potential application of MMIC-Fe(III) for the simultaneous removal of TC and Cd(II), and may provide some information for the synergistic removal of antibiotics and heavy metals from aquatic environments.

Sporadic distribution and distinctive variations of cylindrospermopsin genes in cyanobacterial strains and environmental samples from Chinese freshwater bodies

ABSTRACT Increasing reports of cylindrospermopsins (CYNs) in freshwater ecosystems have promoted the demand for identifying all of the potential CYN-producing cyanobacterial species. The present study explored the phylogenetic distribution and evolution of cyr genes in cyanobacterial strains and water samples from China. Four Cylindrospermopsis strains and two Raphidiopsis strains were confirmed to produce CYNs. Mutant cyrI and cyrK genes were observed in these strains. Cloned cyr gene sequences from eight water bodies were clustered with cyr genes from Cylindrospermopsis and Raphidiopsis (C/R group) in the phylogenetic trees with high similarities (99%). Four cyrI sequence types and three cyrJ sequence types were observed to have different sequence insertions and repeats. Phylogenetic analysis of the rpoC1 sequences of the C/R group revealed four conserved clades, namely, clade I, clade II, clade III, and clade V. High sequence similarities (>97%) in each clade and a divergent clade IV were observed. Therefore, CYN producers were sporadically distributed in congeneric and paraphyletic C/R group species in Chinese freshwater ecosystems. In the evolution of cyr genes, intragenomic translocations and intergenomic transfer between local Cylindrospermopsis and Raphidiopsis were emphasized and probably mediated by transposases. This research confirms the existence of CYN-producing Cylindrospermopsis in China and reveals the distinctive variations of cyr genes.

First report on the allelopathic effect of Tychonema bourrellyi (Cyanobacteria) against Microcystis aeruginosa (Cyanobacteria)

The allelopathic effect of the cyanobacterium Tychonema bourrellyi against the cyanobacterium Microcystis aeruginosa is reported for the first time in this paper. The filtrate of T. bourrellyi CHAB663 culture showed strong inhibitory effect on M. aeruginosa NIES-843, but the inhibitory effect was weakened by shaking culture, and such results implied that the allelopathic effect was probably mediated by the volatile substances secreted by T. bourrellyi. β-Ionone was identified as a major ingredient in the volatile substances in the cultures of T. bourrellyi, and it may act as an important allelochemical responsible for this allelopathic activity. The filtrates of T. bourrellyi culture were shown to decrease the maximum electron transport rate (ETRmax) and elevate the reactive oxygen species (ROS) levels in the cells of M. aeruginosa NIES-843.