Phylogenomics Uncovers Evolutionary Trajectory of Nitrogen Fixation in Cyanobacteria.

Biological nitrogen fixation (BNF) by cyanobacteria is of significant importance for the Earth's biogeochemical nitrogen cycle but is restricted to a few genera that do not form monophyletic group. To explore the evolutionary trajectory of BNF and investigate the driving forces of its evolution, we analyze 650 cyanobacterial genomes and compile the database of diazotrophic cyanobacteria based on the presence of nitrogen fixation gene clusters (NFGCs). We report that 266 of 650 examined genomes are NFGC-carrying members, and these potentially diazotrophic cyanobacteria are unevenly distributed across the phylogeny of Cyanobacteria, that multiple independent losses shaped the scattered distribution. Among the diazotrophic cyanobacteria, two types of NFGC exist, with one being ancestral and abundant, which have descended from diazotrophic ancestors, and the other being anaerobe-like and sparse, possibly being acquired from anaerobic microbes through horizontal gene transfer. Interestingly, we illustrate that the origin of BNF in Cyanobacteria coincide with two major evolutionary events. One is the origin of multicellularity of cyanobacteria, and the other is concurrent genetic innovations with massive gene gains and expansions, implicating their key roles in triggering the evolutionary transition from nondiazotrophic to diazotrophic cyanobacteria. Additionally, we reveal that genes involved in accelerating respiratory electron transport (coxABC), anoxygenic photosynthetic electron transport (sqr), as well as anaerobic metabolisms (pfor, hemN, nrdG, adhE) are enriched in diazotrophic cyanobacteria, representing adaptive genetic signatures that underpin the diazotrophic lifestyle. Collectively, our study suggests that multicellularity, together with concurrent genetic adaptations contribute to the evolution of diazotrophic cyanobacteria.

Urbanization shifts long-term phenology and severity of phytoplankton blooms in an urban lake through different pathways.

Climate change can induce phytoplankton blooms (PBs) in eutrophic lakes worldwide, and these blooms severely threaten lake ecosystems and human health. However, it is unclear how urbanization and its interaction with climate impact PBs, which has implications for the management of lakes. Here, we used multi-source remote sensing data and integrated the Virtual-Baseline Floating macroAlgae Height (VB-FAH) index and OTSU threshold automatic segmentation algorithm to extract the area of PBs in Lake Dianchi, China, which has been subjected to frequent PBs and rapid urbanization in its vicinity. We further explored long-term (2000-2021) trends in the phenological and severity metrics of PBs and quantified the contributions from urbanization, climate change, and also nutrient levels to these trends. When comparing data from 2011-2021 to 2000-2010, we found significantly advanced initiation of PBs (28.6 days) and noticeably longer duration (51.9 days) but an insignificant trend in time of disappearance. The enhancement of algal nutrient use efficiency, likely induced by increased water temperature and reduced nutrient concentrations, presumably contributed to an earlier initiation and longer duration of PBs, while there was a negative correlation between spring wind speed and the initiation of PBs. Fortunately, we found that both the area of the PBs and the frequency of severe blooms (covering more than 19.8 km2 ) demonstrated downward trends, which could be attributed to increased wind speed and/or reduced nutrient levels. Moreover, the enhanced land surface temperature caused by urbanization altered the thermodynamic characteristics between the land and the lake, which, in turn, possibly caused an increase in local wind speed and water temperature, suggesting that urbanization can differently regulate the phenology and severity of PBs. Our findings have significant implications for the understanding of the impacts of urbanization on PB dynamics and for improving lake management practices to promote sustainable urban development under global change.

Paraquat induces different programmed cell death patterns in Microcystis aeruginosa and Chlorella luteoviridis.

Although programmed cell death (PCD) has been reported in phytoplankton, knowledge of the characterization of the PCD pathway and cascade process in different phytoplankton species is still limited. In this study, PCD progression in cyanobacterium Microcystis aeruginosa and green algae Chlorella luteoviridis by paraquat-induced oxidative stress was monitored. The results showed that paraquat-induced PCD in the two species belonged to the caspase-dependent pathway. Dose- and time-dependent PCD characteristics in the two strains under paraquat included the increase in caspase-like activity, DNA fragmentation, and chromatin condensation. However, the signaling pathway and cascade events of PCD in M. aeruginosa and C. luteoviridis differed. In M. aeruginosa, the free Ca2+ concentration was rapidly increased at 8 h, followed by a significant elevation of the reactive oxygen species (ROS) level at 24 h, and eventual cell death. In C. luteoviridis, the mitochondrial apoptosis pathway, revealed by the depolarization of the mitochondrial membrane potential at 1 h and increase in the ROS level and caspase-like activity at 8 h, might contribute to cell death. In addition, the dynamics of ROS levels and metacaspase activity were synchronized, suggesting that paraquat-triggered PCD was ROS-mediated in both M. aeruginosa and C. luteoviridis. These results provide insights into PCD patterns in prokaryotic cyanobacteria and eukaryotic green algae under similar stress.

Dynamic Lone Pair Expression as Chemical Bonding Origin of Giant Phonon Anharmonicity in Thermoelectric InTe.

Loosely bonded ("rattling") atoms with s2 lone pair electrons are usually associated with strong anharmonicity and unexpectedly low thermal conductivity, yet their detailed correlation remains largely unknown. Here we resolve this correlation in thermoelectric InTe by combining chemical bonding analysis, inelastic X-ray and neutron scattering, and first principles phonon calculations. We successfully probe soft low-lying transverse phonons dominated by large In1+ z-axis motions, and their giant anharmonicity. We show that the highly anharmonic phonons arise from the dynamic lone pair expression with unstable occupied antibonding states induced by the covalency between delocalized In1+ 5s2 lone pair electrons and Te 5p states. This work pinpoints the microscopic origin of strong anharmonicity driven by rattling atoms with stereochemical lone pair activity, important for designing efficient materials for thermoelectric energy conversion.

The involvement of α-proteobacteria Phenylobacterium in maintaining the dominance of toxic Microcystis blooms in Lake Taihu, China.

Lake Taihu in China has suffered serious harmful cyanobacterial blooms for decades. The algal blooms threaten the ecological sustainability, drinking water safety, and human health. Although the roles of abiotic factors (such as water temperature and nutrient loading) in promoting Microcystis blooms have been well studied, the importance of biotic factors (e.g. bacterial community) in promoting and meditating Microcystis blooms remains unclear. In this study, we investigated the ecological dynamics of bacterial community, the ratio of toxic Microcystis, as well as microcystin in Lake Taihu. High-throughput 16S rRNA sequencing and principal component analysis (PCA) revealed that the bacteria community compositions (BCCs) clustered into three groups, the partitioning of which corresponded to that of groups according to the toxic profiles (the ratio of toxic Microcystis to total Microcystis, and the microcystin concentrations) of the samples. Further Spearman's correlation network showed that the α-proteobacteria Phenylobacterium strongly positively correlated with the toxic profiles. Subsequent laboratory chemostats experiments demonstrated that three Phenylobacterium strains promoted the dominance of the toxic Microcystis aeruginosa PCC7806 when co-culturing with the non-toxic PCC7806 mcyB- mutant. Taken together, our data suggested that the α-proteobacteria Phenylobacterium may play a vital role in the maintenance of toxic Microcystis dominance in Lake Taihu.

Long noncoding RNA lncRNA354 functions as a competing endogenous RNA of miR160b to regulate ARF genes in response to salt stress in upland cotton.

Long non-coding RNAs (lncRNAs) play important roles in response to biotic and abiotic stress through acting as competing endogenous RNAs (ceRNAs) to decoy mature miRNAs. However, whether this mechanism is involved in cotton salt stress response remains unknown. We report the characterization of an endogenous lncRNA, lncRNA354, whose expression was reduced in salt-treated cotton and was localized at the nucleus and cytoplasm. Using endogenous target mimic (eTM) analysis, we predicted that lncRNA354 had a potential binding site for miR160b. Transient expression in tobacco demonstrated that lncRNA354 was a miR160b eTM and attenuated miR160b suppression of its target genes, including auxin response factors (ARFs). Silencing or overexpressing lncRNA354 affected the expression of miR160b and target ARFs. Silencing lncRNA354 and targets GhARF17/18 resulted in taller cotton plants and enhanced the resistant to salt stress. Overexpression of lncRNA354 and targets GhARF17/18 in Arabidopsis led to dwarf plants, decreased root dry weight and reduced salt tolerance. Our results show that the lncRNA354-miR160b effect on GhARF17/18 expression may modulate auxin signalling and thus affect growth. These results also shed new light on a mechanism of lncRNA-associated responses to salt stress.

Intratumoral and Peritumoral Radiomics Based on Functional Parametric Maps from Breast DCE-MRI for Prediction of HER-2 and Ki-67 Status.

BACKGROUND: Radiomics has been applied to breast magnetic resonance imaging (MRI) for gene status prediction. However, the features of peritumoral regions were not thoroughly investigated. PURPOSE: To evaluate the use of intratumoral and peritumoral regions from functional parametric maps based on breast dynamic contrast-enhanced MRI (DCE-MRI) for prediction of HER-2 and Ki-67 status. STUDY TYPE: Retrospective. POPULATION: A total of 351 female patients (average age, 51 years) with pathologically confirmed breast cancer were assigned to the training (n = 243) and validation (n = 108) cohorts. FIELD STRENGTH/SEQUENCE: 3.0T, T1 gradient echo. ASSESSMENT: Radiomic features were extracted from intratumoral and peritumoral regions on six functional parametric maps calculated using time-intensity curves of DCE-MRI. The intraclass correlation coefficients (ICCs) were used to determine the reproducibility of feature extraction. Based on the intratumoral, peritumoral, and combined intra- and peritumoral regions, three radiomics signatures (RSs) were built using the least absolute shrinkage and selection operator (LASSO) logistic regression model, respectively. STATISTICAL TESTS: Wilcoxon rank-sum test, minimum redundancy maximum relevance, LASSO, receiver operating characteristic curve (ROC) analysis, and DeLong test. RESULTS: The intratumoral and peritumoral RSs for prediction of HER-2 and Ki-67 status achieved areas under the ROC (AUCs) of 0.683 (95% confidence interval [CI], 0.574-0.793) and 0.690 (95% CI, 0.577-0.804), and 0.714 (95% CI, 0.616-0.812) and 0.692 (95% CI, 0.590-0.794) in the validation cohort, respectively. The combined RSs yielded AUCs of 0.713 (95% CI, 0.604-0.823) and 0.749 (95% CI, 0.656-0.841), respectively. There were no significant differences in prediction performance among intratumoral, peritumoral, and combined RSs. Most (69.7%) of the features had good agreement (ICCs >0.8). DATA CONCLUSION: Radiomic features of intratumoral and peritumoral regions on functional parametric maps based on breast DCE-MRI had the potential to identify HER-2 and Ki-67 status. LEVEL OF EVIDENCE: 3 Technical Efficacy Stage: 2.

Mitigation of salt stress response in upland cotton (Gossypium hirsutum) by exogenous melatonin.

As a pleiotropic signal molecule, melatonin is ubiquitous throughout the animal and plant kingdoms and plays important roles in the regulation of plant growth, development, and responses to environmental stresses. In this study, we quantified the endogenous melatonin levels in upland cotton (Gossypium hirsutum L.), using high-performance liquid chromatography-tandem mass spectrometry. The melatonin concentrations in root, stem, and leaf were 150.60, 37.92, and 40.58 ng g fresh weight- 1, respectively. The effects of exogenous melatonin (1 µM) on plant growth, photosynthesis, antioxidant enzyme activity, and ion homeostasis in upland cotton seedlings exposed to 100 mM NaCl treatment were determined. Pretreatment (prior to exposure to salt stress) of seedlings with exogenous melatonin significantly alleviated plant growth inhibition by salt stress and maintained an improved photosynthetic capacity. The application of melatonin also significantly reduced the salt-induced oxidative damage, possibly through the accumulation of osmotic regulatory substances and the activation of antioxidant enzymes. We also showed that exogenous melatonin regulated the expression of stress-responsive and ion-channel genes under salinity, which could contribute to improved salt tolerance in cotton. Taken together, our study provides evidence that cotton contains endogenous melatonin, and it may have unraveled crucial evidence of the role of melatonin in cotton against salt stress.

Comprehensive analysis of the Gossypium hirsutum L. respiratory burst oxidase homolog (Ghrboh) gene family.

BACKGROUND: Plant NADPH oxidase (NOX), also known as respiratory burst oxidase homolog (rboh), encoded by the rboh gene, is a key enzyme in the reactive oxygen species (ROS) metabolic network. It catalyzes the formation of the superoxide anion (O2•-), a type of ROS. In recent years, various studies had shown that members of the plant rboh gene family were involved in plant growth and developmental processes as well as in biotic and abiotic stress responses, but little is known about its functional role in upland cotton. RESULTS: In the present study, 26 putative Ghrboh genes were identified and characterized. They were phylogenetically classified into six subfamilies and distributed at different densities across 18 of the 26 chromosomes or scaffolds. Their exon-intron structures, conserved domains, synteny and collinearity, gene family evolution, regulation mediated by cis-acting elements and microRNAs (miRNAs) were predicted and analyzed. Additionally, expression profiles of Ghrboh gene family were analyzed in different tissues/organs and at different developmental stages and under different abiotic stresses, using RNA-Seq data and real-time PCR. These profiling studies indicated that the Ghrboh genes exhibited temporal and spatial specificity with respect to expression, and might play important roles in cotton development and in stress tolerance through modulating NOX-dependent ROS induction and other signaling pathways. CONCLUSIONS: This comprehensive analysis of the characteristics of the Ghrboh gene family determined features such as sequence, synteny and collinearity, phylogenetic and evolutionary relationship, expression patterns, and cis-element- and miRNA-mediated regulation of gene expression. Our results will provide valuable information to help with further gene cloning, evolutionary analysis, and biological function analysis of cotton rbohs.

Isolation of axenic cyanobacterium and the promoting effect of associated bacterium on axenic cyanobacterium.

BACKGROUND: Harmful cyanobacterial blooms have attracted wide attention all over the world as they cause water quality deterioration and ecosystem health issues. Microcystis aeruginosa associated with a large number of bacteria is one of the most common and widespread bloom-forming cyanobacteria that secret toxins. These associated bacteria are considered to benefit from organic substrates released by the cyanobacterium. In order to avoid the influence of associated heterotrophic bacteria on the target cyanobacteria for physiological and molecular studies, it is urgent to obtain an axenic M. aeruginosa culture and further investigate the specific interaction between the heterotroph and the cyanobacterium. RESULTS: A traditional and reliable method based on solid-liquid alternate cultivation was carried out to purify the xenic cyanobacterium M. aeruginosa FACHB-905. On the basis of 16S rDNA gene sequences, two associated bacteria named strain B905-1 and strain B905-2, were identified as Pannonibacter sp. and Chryseobacterium sp. with a 99 and 97% similarity value, respectively. The axenic M. aeruginosa FACHB-905A (Microcystis 905A) was not able to form colonies on BG11 agar medium without the addition of strain B905-1, while it grew well in BG11 liquid medium. Although the presence of B905-1 was not indispensable for the growth of Microcystis 905A, B905-1 had a positive effect on promoting the growth of Microcystis 905A. CONCLUSIONS: The associated bacteria were eliminated by solid-liquid alternate cultivation method and the axenic Microcystis 905A was successfully purified. The associated bacterium B905-1 has the potentiality to promote the growth of Microcystis 905A. Moreover, the purification technique for cyanobacteria described in this study is potentially applicable to a wider range of unicellular cyanobacteria.

Seasonal variation of microcystins and their accumulation in fish in two large shallow lakes of China.

Bioaccumulation of microcystins (MCs) has been widely observed in aquatic vertebrates and invertebrates, but its seasonal and specific variations remain unclear. In the present study, dissolved MCs in water, algal cell-bound MCs and muscle tissue MCs of nine fish species were investigated monthly in two of the largest shallow lakes in China: Lake Taihu and Lake Chaohu. The fish species were grouped as carnivorous, planktivorous, and omnivorous fish. Seasonal variations in dissolved and algal cell-bound MCs in water and MCs contents of fish hepatopancreas and muscle were investigated in the two lakes from 2009 to 2010. Dissolved MCs in water ranged from 0.35 to 2.56 µg l-1 in Lake Taihu and 0.16 to 2.45 µg l-1 in Lake Chaohu, and showed seasonally a unimodal distribution. Algal cell-bound MCs also showed a similar seasonal variation in both lakes, but dissolved MCs in water peaked about one month later than algal cell-bound MCs. The MCs content in the Fish muscle was higher MCs from October to December than in the other months. For most of the fish species, it exceeded the tolerable daily intake value established by the WHO. The averaged MCs content in the muscle of carnivorous, planktivorous, omnivorous fish was 48.2, 28.7 and 37.8 µg kg-1 in Lake Taihu, respectively, and 27.8, 18.6 and 20.4 µg kg-1 in Lake Chaohu. It was significantly higher in carnivorous fish than in planktivorous and omnivorous fish, indicating that carnivorous fish has a higher exposure risk to the local people when consuming the harvested fish. The average ratio of hepatopancreas to muscle MCs contents was 13.0, 25.2, 13.8 for carnivorous, planktivorous, omnivorous fishes in Lake Taihu, respectively, and 18.0, 24.9, 14.8 in Lake Chaohu. These ratio for planktivorous fish almost doubled that for carnivorous and omnivorous fish. High correlation of MC content in carnivorous, omnivorous and planktivorous fish indicates that MCs can be delivered along trophic levels in the food chains.

Rapid One-Step Synthesis and Compaction of High-Performance n-Type Mg3 Sb2 Thermoelectrics.

n-type Mg3 Sb2 -based compounds have emerged as a promising class of low-cost thermoelectric materials due to their extraordinary performance at low and intermediate temperatures. However, so far, high thermoelectric performance has merely been reported in n-type Mg3 Sb2 -Mg3 Bi2 alloys with a large amount of Bi. Moreover, current synthesis methods of n-type Mg3 Sb2 bulk thermoelectrics involve multi-step processes that are time- and energy-consuming. Herein, we report a fast and straightforward approach to fabricate n-type Mg3 Sb2 thermoelectrics using spark plasma sintering, which combines the synthesis and compaction in one step. Using this method, we achieve a high thermoelectric figure of merit zT of about 0.4-1.5 at 300-725 K in n-type (Sc, Te)-co-doped Mg3 Sb2 without alloying with Mg3 Bi2 . In comparison with the currently reported synthesis methods, the complexity, process time, and cost of our method are significantly reduced. This work demonstrates a simple, low-cost route for the potential large-scale production of n-type Mg3 Sb2 thermoelectrics.

The long non-coding RNA lncRNA973 is involved in cotton response to salt stress.

BACKGROUND: Long non-coding (lnc) RNAs are a class of functional RNA molecules greater than 200 nucleotides in length, and lncRNAs play important roles in various biological regulatory processes and response to the biotic and abiotic stresses. LncRNAs associated with salt stress in cotton have been identified through RNA sequencing, but the function of lncRNAs has not been reported. We previously identified salt stress-related lncRNAs in cotton (Gossypium spp.), and discovered the salt-related lncRNA-lncRNA973. RESULTS: In this study, we identified the expression level, localization, function, and preliminary mechanism of action of lncRNA973. LncRNA973, which was localized in the nucleus, was expressed at a low level under nonstress conditions but can be significantly increased by salt treatments. Here lncRNA973 was transformed into Arabidopsis and overexpressed. Along with the increased expression compared with wild type under salt stress conditions in transgenic plants, the seed germination rate, fresh weights and root lengths of the transgenic plants increased. We also knocked down the expression of lncRNA973 using virus-induced gene silencing technology. The lncRNA973 knockdown plants wilted, and the leaves became yellowed and dropped under salt-stress conditions, indicating that the tolerance to salt stress had decreased compared with wild type. LncRNA973 may be involved in the regulation of reactive oxygen species-scavenging genes, transcription factors and genes involved in salt stress-related processes in response to cotton salt stress. CONCLUSIONS: LncRNA973 was localized in the nucleus and its expression was increased by salt treatment. The lncRNA973-overexpression lines had increased salt tolerance compared with the wild type, while the lncRNA973 knockdown plants had reduced salt tolerance. LncRNA973 regulated cotton responses to salt stress by modulating the expression of a series of salt stress-related genes. The data provides a basis for further studies on the mechanisms of lncRNA973-associated responses to salt stress in cotton.

MicroRNA414c affects salt tolerance of cotton by regulating reactive oxygen species metabolism under salinity stress.

Salinity stress is a major abiotic stress affecting the productivity and fiber quality of cotton. Although reactive oxygen species (ROS) play critical roles in plant stress responses, their complex molecular regulatory mechanism under salinity stress is largely unknown in cotton, especially microRNA (miRNA)-mediated regulation of superoxide dismutase gene expression. Here, we report that a cotton iron superoxide dismutase gene GhFSD1 and the cotton miRNA ghr-miR414c work together in response to salinity stress. The miRNA ghr-miR414c targets the coding sequence region of GhFSD1, inhibiting expression of transcripts of this antioxidase gene, which represents the first line of defense against stress-induced ROS. Expression of GhFSD1 was induced by salinity stress. Under salinity stress, ghr-miR414c showed expression patterns opposite to those of GhFSD1. Ectopic expression of GhFSD1 in Arabidopsis conferred salinity stress tolerance by improving primary root growth and biomass, whereas Arabidopsis constitutively expressing ghr-miR414c showed hypersensitivity to salinity stress. Silencing GhFSD1 in cotton caused an excessive hypersensitive phenotype to salinity stress, whereas overexpressing miR414c decreased the expression of GhFSD1 and increased sensitivity to salinity stress, yielding a phenotype similar to that of GhFSD1-silenced cotton. Taken together, our results demonstrated that ghr-miR414c was involved in regulation of plant response to salinity stress by targeting GhFSD1 transcripts. This study provides a new strategy and method for plant breeding in order to improve plant salinity tolerance.

Thermal stability of p-type Ag-doped Mg3Sb2 thermoelectric materials investigated by powder X-ray diffraction.

The thermal stability of the p-type Mg2.985Ag0.015Sb2 material with reported good thermoelectric performance is systematically investigated using powder X-ray diffraction (PXRD). Rietveld refinements were performed to extract the quantitative compositional and structural information from PXRD data. For both densified bulk samples and powdered samples of Mg2.985Ag0.015Sb2 studied under vacuum, a secondary phase, Sb, appears upon the first heating process at temperatures above 500 K, but the amount of the Sb phase stabilizes in subsequent thermal cycles. This is consistent with the good repeatability of the electrical resistivity data after the first cycle measurement, and it indicates that the appearance of the Sb phase does not result in structural decomposition or degradation of the thermoelectric properties. To investigate the effect of the Mg vacancy concentration on the formation of the secondary Sb phase, Mg3.5-xAgxSb2 (x = 0 and 0.015) samples with nominal excess Mg were synthesized and characterized. Compared with Mg2.985Ag0.015Sb2, it is found that Mg3.5-xAgxSb2 (x = 0.015) shows no Sb phase appearing for the bulk sample after heat treatment, and only a small amount of Sb emerges in the powdered sample. This reveals that decreasing the Mg deficiency is beneficial for reducing the amount of emerging Sb secondary phase. In addition, there is less Sb appearing in the Ag-doped powder sample of Mg3.5-xAgxSb2 (x = 0.015) than the undoped Mg3.5Sb2 powder sample, indicating that Ag doping at the Mg sites can inhibit the appearance of the Sb phase to some extent. Our work implies that the emergence of the Sb phase is unlikely due to the decomposition of the Mg3Sb2 structure and can be hindered by reducing the Mg deficiency or Ag doping on the Mg sites.

Hypoxia Remediation and Methane Emission Manipulation Using Surface Oxygen Nanobubbles.

Algal blooms in eutrophic waters often induce anoxia/hypoxia and enhance methane (CH4) emissions to the atmosphere, which may contribute to global warming. At present, there are very few strategies available to combat this problem. In this study, surface oxygen nanobubbles were tested as a novel approach for anoxia/hypoxia remediation and CH4 emission control. Incubation column experiments were conducted using sediment and water samples taken from Lake Taihu, China. The results indicated that algae-induced anoxia/hypoxia could be reduced or reversed after oxygen nanobubbles were loaded onto zeolite micropores and delivered to anoxic sediment. Cumulated CH4 emissions were also reduced by a factor of 3.2 compared to the control. This was mainly attributed to the manipulation of microbial processes using the surface oxygen nanobubbles, which potentially served as oxygen suppliers. The created oxygen-enriched environment simultaneously decreased methanogen but increased methanotroph abundances, making a greater fraction of organic carbon recycled as carbon dioxide (CO2) instead of CH4. The CH4/CO2 emission ratio decreased to 3.4 × 10-3 in the presence of oxygen nanobubbles, compared to 11 × 10-3 in the control, and therefore the global warming potential was reduced. This study proposes a possible strategy for anoxia/hypoxia remediation and CH4 emission control in algal bloom waters, which may benefit global warming mitigation.

A fluorescence ratio-based method to determine microalgal viability and its application to rapid optimization of cryopreservation.

The utility of microalgal biomass and bioproducts depends on long-term maintenance of certain physiological or biochemical features of the species. While unique characteristics may not be durably maintained with general subculture, cryopreservation methods better prevent alterations from desired characteristics. Post-thaw viability is critical to establishing microalgal cultures, and there is a critical need to effectively and rapidly evaluate microalgal viability after the post-thawing process. In the present study, we developed a rapid assay based on the change of fluorescence ratio to determine microalgal viability post-thaw. It was shown that the assessment of microalgal viability by the fluorescence ratio method correlated well with that of the FDA-staining (R2 = 0.978) and regrowth method (R2 = 0.976), demonstrating that the present method could be applied in the high-throughput detection of viability of microalgal strains. Subsequent to establishing this method, we aimed to find out optimal cryopreservation protocol for each strain from a group of 125 microalgal strains. The viability of these strains under different treatments was quickly evaluated by the fluorescence ratio method. Of these strains, 95 attained post-thaw viability over 60%. DMSO was a suitable cryoprotectant for most strains at a concentration ≤10%. Based on the dataset, the relative contribution of 3 variables-genus, cryoprotectants and concentration to post-viability was analyzed with the Random Forest (RF) classification method. All variables together could explain 97.8% of the viability, and type and concentration of cryoprotectant could explain 59.1% in Chlorophyta. This study provided a new approach for viability assay and demonstrated that this method can facilitate to find out the optimal protocols for cryopreservation of microalgal strains.

Simultaneous elimination of cyanotoxins and PCBs via mechanical collection of cyanobacterial blooms: An application of "green-bioadsorption concept".

In this study, the distribution, transfer and fate of both polychlorinated biphenyls (PCBs) and cyanotoxins via phytoplankton routes were systematically investigated in two Chinese lakes. Results indicated that PCB adsorption/bioaccumulation dynamics has significantly positive correlations with the biomass of green alga and diatoms. Total lipid content of phytoplankton is the major factor that influences PCB adsorption/bioaccumulation. Cyanobacterial blooms with relatively lower lipid content could also absorb high amount of PCBs due to their high cell density in the water columns, and this process was proposed as major route for the transfer of PCBs in Chinese eutrophic freshwater. According to these findings, a novel route on fates of PCBs via phytoplankton and a green bioadsorption concept were proposed and confirmed. In the practice of mechanical collections of bloom biomass from Lake Taihu, cyanotoxin/cyanobacteria and PCBs were found to be removed simultaneously very efficiently followed this theory.

Microcystin-degrading bacteria affect mcyD expression and microcystin synthesis in Microcystis spp.

Cyanobacterial blooms occur increasingly often and cause ecological, economic and human health problems worldwide. Microcystins (MCs) are the dominant toxins produced by cyanobacteria and are implicated in epidemic disease and environmental problems. Extensive research has been reported on the various regulating factors, e.g., light, temperature, nutrients such as nitrogen and phosphorus, pH, iron, xenobiotics, and predators, that influence microcystin (MC) synthesis, but little is known about the effects of cyanobacteria-associated bacteria on MC synthesis. A considerable number of studies have focused on interactions between Microcystis species and their associated bacteria. In this study, we evaluated the effects of MC-degrading bacteria (MCDB) on MC synthesis gene mcyD expression and MC synthesis in axenic strain PCC7806, non-axenic strain FACHB905, and colony strain FACHB1325 of Microcystis by quantitative real-time polymerase chain reaction (RT-PCR) assay and enzyme-linked immunosorbent assay (ELISA). We demonstrate for the first time that MCDB can induce and up-regulate the MC production and transcriptional response of the mcyD gene of toxic Microcystis. On day 4 of the culturing experiment, the intracellular MC concentration and transcriptional response of mcyD of FACHB1325 were up-regulated 1.9 and 5.3-fold over that of the control, and for FACHB905 were up-regulated 1.8 and 4.2-fold over that of the control, respectively. On day 10, the transcriptional response of mcyD was up-regulated 21.3-fold in PCC7806. These results indicate that there are interactions between toxic Microcystis and MCDB, and MCDB may play a role in regulating mcyD expression in toxic Microcystis.

Photocatalytic properties of hierarchical BiOXs obtained via an ethanol-assisted solvothermal process.

In this study, bismuth oxyhalide (BiOXs (XCl, Br, I)) semiconductors were prepared by a simple solvothermal method, with ethanol serving as solvent and a series of tetrabutylammonium halide surfactants as halogen sources. Under identical synthetic conditions, BiOBr was more readily constructed into regular flower-like hierarchical architectures. The photocatalytic properties of the materials were studied by monitoring the degradation of rhodamine B (RhB), with visible light absorption, and colorless salicylic acid (SA). It was found that both RhB and SA were rapidly degraded on the surface of BiOBr. BiOCl was rather active for the degradation of RhB, but ineffective toward the degradation of SA. However, neither RhB nor SA could be degraded effectively in the case of BiOI. Further experiments such as UV-visible spectroscopy and detection of OH and O2(-) radicals suggest that the electronic structure of the BiOX photocatalysts is responsible for the difference in their activities.