Anabaena Circinalis Research Articles

PHYTOPLANKTON COMMUNITY DYNAMICS RELATED TO CERTAIN PHYSICAL AND CHEMICAL VARIABLES IN ARDIÇTEPE RESERVOIR (BALIKESIR, TURKEY)

Ardıçtepe Reservoir (Balıkesir, Turkey) was sampled seasonally at three stations between October 2018 and August 2019 to determine the phytoplankton community dynamics in relation to water temperature, speciffic conductance (SC), total dissolved solids (TDS), pH, oxidation-reduction potential (ORP) and Secchi disk depth. A total of 43 phytoplankton species were identified, 27 from Bacillariophyta, 4 from Charophyta, 6 from Chlorophyta, 5 from Cyanobacteria and 1 from Euglenozoa. Bacillariophyta made 76% total number of species, Cyanobacteria 11%, Chlorophyta 6%, Charophyta 4% and Euglenozoa 3%. Aulacoseria granulata, Aulacoseira granulata var. angustissima, Cyclotella meneghiniana and Ulnaria ulna from Bacillariophyta and Anabaena circinalis from Cyanobacteria dominanted phytoplankton during the study. The CCA explained 90.8% of the cumulative variance in the relationships of dominant species-environment. The CCA also showed that water temperature, TDS, ORP and pH had significant effects on the phytoplankton community of Ardıçtepe Reservoir (Monte Carlo test, p 0.05)

The antagonistic effect of Anabaena circinalis on some dermatophytes

Introduction and Aim: Anabaena circinalis, a photosynthetic cyanobacterium belonging to the Gram-negative group, is widely distributed in freshwater ecosystems across the world. The scientific focus on A. circinalis primarily stems from its ability to produce numerous cyanotoxins, which have the potential to be hazardous. The objective of this study was to assess the antifungal efficacy of A. circinalis against the dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes, with the aim of discovering a new antifungal agent. Methodology: The identification of Anabaena circinalis in this study was conducted through the observation of its morphological characteristics. Molecular identification and confirmation of the algae was done using the polymerase chain reaction (PCR) method, employing a specific set of primers targeting the PCbetaand PCalpha genes. Gas chromatography-mass spectrometry was employed in identifying A. circinalis antifungal compounds. The ability of 70% ethanolic and methanolic extracts produced from A. circinalis to inhibit the dermatophyte fungi Trichophyton rubrum and Trichophyton mentagrophytes was tested by in vitro tests. Results: The findings indicate that the hot ethanolic extract of Anabaena circinalis exhibited a significant inhibitory effect (100% inhibition) on the growth of dermatophyte fungi tested. Gas chromatography-mass spectrometry studies identified several antifungal compounds in A. circinalis extracts, which included Hexadecen-1-ol, Phthalic acid, Octadecenoic acid, Octadecynoic acid, Hexadecanoic acid, Pentadecadien, Tetradecenal, and Octadecadien-1-ol. Conclusion: Overall finding suggests hot ethanolic or methanolic extracts of Anabaena circinalis contain phyto components, which could be used as an antifungal agent in treating dermatophyte fungi-related infections.

Impact of sonication on the algal organic matter characteristics of Anabaena circinalis, Microcystis aeruginosa, and Chlorella vulgaris

The frequent occurrence of harmful algal blooms (HABs) in drinking water reservoirs causes water treatment and supply problems. Ultrasonication is a physicochemical treatment method used to treat HABs. During the ultrasonication of HABs, algal organic matter (AOM), including both extracellular organic matter (EOM) and intracellular organic matter (IOM), is released and changes the dissolved organic matter characteristics. In this study, Anabaena circinalis (A. circinalis), Microcystis aeruginosa (M. aeruginosa), and Chlorella vulgaris (C. vulgaris) were used to investigate changes in AOM characteristics during ultrasonication using a fluorescence excitation-emission matrix and assimilable organic carbon. We found that ultrasonication increased the dissolved AOM content, resulting in increased dissolved organic carbon from IOM released from algal cells. A. circinalis, M. aeruginosa, and C. vulgaris had dissolved organic carbon concentrations of 22.5, 3.8, and 6.7 mg/L before sonication, which increased to 29.1, 10.8, and 7.7 mg/L after ultrasonication, respectively. Additionally, the IOM released during ultrasonication held more protein-like substances and was mostly associated with biodegradable organic matter.

AN INVESTIGATION OF PHYSICOCHEMICAL PARAMETERS AND PHYTOPLANKTON COMMUNITY STRUCTURE OF EKO-NDE RESERVOIR IN OSUN STATE, NIGERIA

This research was carried out to determine the relationship between physicochemical variables and phytoplankton community of the Eko-Nde reservoir. Changes in physicochemical parameters of aquatic ecosystems have significant impact on the species that live therein. Eko-Nde reservoir is of socio-economic significance to communities that surround it, which necessitates a proper study of the phytoplankton composition and environmental status of the reservoir. Water samples were collected from two stations in the reservoir from January 2019 to August 2019. The physicochemical parameters that were determined include but not limited to temperature, total hardness, pH and biochemical oxygen demand. The composition and diversity of phytoplankton were analyzed. A total of 2039 cells ml-1 belonging to four (4) major divisions were dominant in the order; Bacillariophyta (898 cells ml-1) > Charophyta (788 cells ml-1) > Chlorophyta (302 cells ml-1) > Cyanophyta (51 cells ml-1). Principal Component Analysis and Canonical Corresponding Analysis showed that certain physicochemical variables such as temperature, pH and total hardness were key drivers of the phytoplankton community structure of the reservoir. Diversity indices showed moderate abundance and distribution of phytoplankton species, with the highest diversity of species in the months associated with the rainy season. The appearance of pollution tolerant species such as Anabaena circinalis, Oscillatoria limosa, Nitzschia gracilis, Cymbella mexicana, Pediastrum boryanum, Synedra ulna, Cyclotella meneghiniana and Gomphonema spp. suggest that the reservoir was on the verge of pollution. Anthropogenic activities around the reservoir should be closely monitored to avoid health risks to humans and endangerment of aquatic organisms.

Spatial and seasonal dynamics of phytoplankton groups and its relationship with environmental variables in Lake Okeechobee, USA

The concept of phytoplankton functional groups was used to assess phytoplankton community structure in an attempt to better understand their spatial and seasonal variation in Lake Okeechobee, USA. Samples were collected for analyses during summer and winter. 23 phytoplankton functional groups were identified among 102 species, of which 9 groups (H1, M, C, MP, Y, S1, J, X1 and X2) were categorized as dominant. Y represented by Cryptomonas ovate and H1, represented by Anabaena circinalis and Anabaena variabilis, were dominant in some sites in summer corresponding to higher temperatures. In winter, the biomass of the functional groups was dominated by chlorophyta group X2 corresponding to lower temperatures, and relatively high nutrients. Redundancy analysis (RDA) with Monte Carlo test revealed that water temperature (WT), TP, and TN were the most dominant environmental variables which influenced phytoplankton functional group distribution in Lake Okeechobee. Functional group H1 was associated with TN, pH, TP and WT. Similarly, functional group Y was significantly positively correlated with TN, TP and WT but negatively correlated with TN/TP ratios. This study reveals the importance of physical–chemical variables across a spatial and seasonal gradient, in structuring phytoplankton functional groups, and consequently in the assessment of environmental status of the lake.

The Diversity of Phytoplankton in a Combined Rice-Shrimp Farming System in the Coastal Area of the Vietnamese Mekong Delta

An assessment of varying density, species composition and dynamics of phytoplankton in a combined rice-shrimp culture was carried out in My Xuyen district, Soc Trang province in the Vietnamese Mekong delta. Water was sampled six times at six separate locations within the culture system, on days 1, 20, 34, 57, 68, and day 81 of the rice-shrimp crop cycle. The results showed the abundance of 95 phytoplankton species belonging to five phyla including Cyanophyta, Chlorophyta, Bacillariophyta, Euglenophyta, and Pyrrophyta. The values of Shannon–Wiener index indicated high phytoplankton diversity, while the water quality ranged from medium to good. A Cluster Analysis showed that the phytoplankton density variation can be divided into three distinct periods. The initial phase of crop growth was dominated by Pandorina morum, Pediastrum simplex, Eudorina elegans, Oscillatoria limosa, and Anabaena circinalis. The midstage, reproductive phase of crop growth was dominated by Scenedesnus acuminatus, Pediastrum duplex, Closterinm setaceum, Scenedesnus quadricauda, and Actinastnum hantzschii. Whereas Scenedesnus acuminatus, Scenedesnus quadricauda, Closterinm closterioides, Staurastrum arcuatum, Euglena nhrenbergii, and Phacus lnsmorensis were dominant at the end of crop cycle. The findings provide useful information on phytoplankton assemblages in a typical rice-shrimp culture, which has recently gained popularity as an adaptive livelihood system.

Seasonal dynamics of phytoplankton and its relationship with environmental factors in Lake Hulun

为探究呼伦湖浮游植物群落的季节变化特征及其与环境因子的关系，本研究分别于2019年3、5—10月对呼伦湖浮游植物的种类、细胞密度和生物量及湖水水质进行调查.结果显示，共鉴定出120种浮游植物，隶属于7门72属.从浮游植物群落季节组成差异上来看，春季绿藻门种类数最多，其次是硅藻门、蓝藻门；夏秋季绿藻门种类数最多，蓝藻门次之；冬季硅藻门种类数最多，绿藻门次之.呼伦湖浮游植物优势种主要为硅藻门的梅尼小环藻（Cyclotella meneghiniana）、蓝藻门的卷曲长孢藻（Anabaena circinalis）和细小平裂藻（Merismopedia minima），种类数在春季最多，秋冬季最少.浮游植物细胞密度在春季（123.52×10⁴ cells/L）和冬季（16.41×10⁴ cells/L）较夏季（280.80×10⁴ cells/L）和秋季（380.63×10⁴ cells/L）低，春冬季绿藻门细胞密度最高，夏秋季蓝藻门细胞密度最高.就浮游植物生物量而言，夏季（0.38 mg/L）最大，其次是秋季（0.26 mg/L）和春季（0.24 mg/L），冬季（0.13 mg/L）最小.香农-威纳（Shannon-Wiener）多样性指数、均匀度指数和综合营养状态指数均表明呼伦湖水体处于中营养状态.冗余分析（RDA）表明：水温、叶绿素a、pH和营养盐浓度是影响呼伦湖浮游植物群落分布的主要环境因子.;To understand the phytoplankton community characteristics and its relationships with environmental factors, we investigated the species, abundance and biomass of phytoplankton and environmental factors at eight sampling sites in Lake Hulun during March and from May to October of 2019. The results showed that:A total of 120 phytoplankton species were identified, belonging to 7 plyla and 72 genera. In terms of the seasonal composition of the phytoplankton community, Chlorophyta was the dominant groups in spring, followed by Bacillariophyta and Cyanophyta. The number of Chlorophyta was the largest in summer and autumn, followed by Cyanophyta. Bacillariophyta was the dominant group in winter, followed by Chlorophyta. The dominant species of phytoplankton in Lake Hulun were Cyclotella meneghiniana of Bacillariophyta, Anabaena circinalis and Merismopedia minima of Cyanophyta. The number of the dominant species was the most in spring and the least in autumn and winter. The phytoplankton abundance in spring (123.52×10⁴ cells/L) and winter (16.41×10⁴ cells/L) was lower than that in summer (280.80×10⁴ cells/L) and autumn (380.63×10⁴ cells/L). The abundance of Chlorophyta was the highest in spring and winter, and the abundance of Cyanophyta was the highest in summer and autumn. In terms of phytoplankton biomass, summer (0.38 mg/L) had the largest, followed by autumn (0.26 mg/L) and spring (0.24 mg/L), and winter (0.13 mg/L) had the smallest. Shannon-Wiener diversity index, evenness index J and comprehensive trophic state index all indicated that Lake Hulun was in mesotrophic condition. Redundancy analysis of phytoplankton abundance and water environmental factors showed that water temperature, chlorophyll-a, pH and nitrogen and phosphorus nutrients were the main environmental factors that affected the distribution of the phytoplankton community in Lake Hulun.

Molecular detection of some toxogenic cyanobacteria in Tigris River in Baghdad-Iraq.

Cyanobacteria and their pollution are being increasingly commonly reported worldwide that cause a serious hazard to environmental and human health. Cyanotoxin was the most algal toxin reported to be produced by several orders of cyanobacteria. This study aimed to provide a technique to detect cylindrosprmopsin and saxitoxin biosynthesis genes in the river. In November, December 2019, and January 2020. Cyanobacteria were isolated from freshwater of Tigris River and identified by compound microscope also conventional PCR. Five isolates of cyanobacteria that successfully amplified a gene fragment from the phycocyanin were found in all cyanobacteria (Microcystis flosaquae, Microcystis sp, anabaena circinalis, nostoc commune and westiellopsis prolifica) and all isolates successfully amplified aoaC gene to detecting the cylidrospemopsin and the saxitoxin. Our results concluded that PCR assay can be used for early detection of cylidrospemopsin and the saxitoxin producing cyanobacteria in river water that useful to stations responsible for the preparation of drinking water to public.

Food Web Responses to a Cyanobacterial Bloom in a Freshwater Eutrophic Lake

The microbial food web is an important part in aquatic ecosystem, but studies on the microbial food web in freshwater ecosystem, especially in freshwater eutrophic lakes, still need further investigation. In the present study, using eutrophic Lake Nanhu as model, the community changes of phytoplankton, zooplankton, and bacteria between the bloom and non-bloom period were analyzed, and microzooplankton grazing experiments were also conducted to measure the grazing pressure and selectivity of microzooplankton on phytoplankton community. Phytoplankton community in Lake Nanhu was mainly dominated by Cyanophyta (49.44%), especially Anabaena circinalis and Microcystis flos-aquae, during bloom period. Rotifers were the main components of zooplankton in Lake Nanhu (44.15%), Brachionus calyciflorus and Moina macrocopa were the most dominant zooplankton in the non-bloom and bloom period, respectively. Bacteroidetes showed significantly higher mean proportion in bloom period than that in non-bloom period (p < 0.001). The growth rates of phytoplankton ranged from −1.00 d−1 to 1.29 d−1, while grazing rates of microzooplankton ranged from −1.15 d−1 to 1.05 d−1. Results indicated that microzooplankton could respond quickly to the increase of phytoplankton during bloom period. Meanwhile, microzooplankton showed grazing preference on Cyanophyta and Cryptophyta during bloom period and non-bloom period, respectively. The microzooplankton grazing selectivity during bloom period might depend on phytoplankton community composition.

Effects of Some Cyanophyta Along with the Reduced Levels of Chemical Fertilizers on the Growth and Yield of Wheat

The present work was conducted in the fields of Al-Sewarah and Kurkok stations which belong to the State Board of Agricultural Researches, Ministry of Agriculture, Iraq during the growing season of 2018. The goal of the study was to test the effects of the application of cyanobacteria (Anabaena circinalis and Nostoc commune) alone or in combination with reducing the dose of chemical fertilizers (CFs), which consisted of diammonium phosphate (DAP) and urea (46% nitrogen), on growth, yield and yield components of wheat cv. IPA99. Application of 50% and 100% of CFs without cyanobacteria as well as control (without cyanobacteria and CFs) were also included in this study for comparison.
 The results indicated that the use of wheat grains coated with compost amended with cyanobacteria, grains coated with compost, and foliar spray with cyanobacteria did not change yield, yield components and most of growth parameters tested in both stations. However, application of 50% CFs along with the treatments that included either the coating of grains with compost amended with cyanobacteria or the foliar spray with cyanobacteria extract resulted in grains yield, yield components, biological yield, harvest index, and test growth parameters similar to those achieved by the recommended dose of CFs. This study suggests that this approach can be applied to reduce the input of chemical fertilizers into the field and thereby reducing the cost and pollution of agroecosystem.

A comparative assessment of growth, pigment and enhanced lipid production by two toxic freshwater cyanobacteria Anabaena circinalis FSS 124 and Cylindrospermopsis raciborskii FSS 127 under various combinations of nitrogen and phosphorous inputs.

Nitrogen and phosphorous are important nutritional regulators for the growth of cyanobacteria, thereby having a significant impact in bloom formation by toxic species. Usage of toxic cyanobacteria for increasing valuable metabolite production by nutrient manipulation is still unexplored. Hence, the current work is aimed to estimate and compare growth, pigment, and increased lipid production coupled with the identification of fatty acids between two toxic strains-Anabaena circinalis FSS 124 and Cylindrospermopsis raciborskii FSS 127 under various combinations of these two nutrients. Low level of nitrogen and phosphorous enhanced lipid content in both strains (˃ 20% and 30% respectively) and C. raciborskii, respectively. Lipid productivity in low phosphorous concentration (P0.5) was achieved significantly high in C. raciborskii. Similarly, a substantial amount of carotenoids was obtained at reduced nitrogen and phosphorous in C. raciborskii accompanied by lessened growth and Chl a concentration. Unlikely, enough biomass (˃ 2 g L-1) was produced at high nutrient levels in both species. Comparative statistical significance (p < 0.05) was found between two species regarding biomass production, chlorophyll concentration, lipid content, and productivity and between these factors in each species under both nutrient variations. FAME of Cylindrospermopsis is composed of saturated fatty acids (˃ 50%) and MUFA (˃ 25%) while Anabaena contains PUFA (˃ 21%) additionally. However, the study highlights C. raciborskii as potential lipid and carotenoid producer at nutrient stress and finds a novel way to utilize these cyanobacterial biomasses, which cause immense environmental hazards and life threats.

Synechococcus and Other Bloom‐Forming Cyanobacteria Exhibit Unique Redox Signatures

AbstractCyanobacteria form dense blooms that impair water quality. Although the impact of blooms on water quality largely differs depending on the species of cyanobacteria, it is challenging to distinguish cyanobacterial species with conventional sensors due to their similar physicochemical properties. Here, we conducted cyclic voltammetry to three major bloom‐forming cyanobacteria, Synechococcus sp., Microcystis aeruginosa, and Anabaena circinalis without addition of redox active compounds nor chemical modifications of the working electrode. These cyanobacteria exhibited redox peaks with distinct potentials from each other, in the range of +0.60 – +0.75 V vs SHE. Because these redox potentials hardly overlap with those of other environmental electroactive bacteria, those redox peaks may be used as indicators of the onset of a cyanobacterial bloom. Given that the photo‐responsive current correlated with the cell density of Synechococcus sp., electrochemical measurement would be a promising technique for a novel cyanobacterial quantification sensor, with in‐built ability to identify cyanobacterial species.

Dynamics of nutrient and phytoplankton in Epe Lagoon, Nigeria: possible causes and consequences of reoccurring cyanobacterial blooms

The impact of environmental variables and processes of nutrient enrichment on phytoplankton community at Epe lagoon was studied for 18 months (November 2012–April 2014). Two cyanobacterial bloom incidences were observed in the two dry seasons during this period. Rainfall pattern regulated nitrogen limitation which triggered cyanobacterial bloom development and influenced the bloom duration. Nutrient-laden influx from agricultural practices accounted for the increase in nitrate, phosphate and the relatively low silicate. Hypoxic conditions during the two bloom episodes reflected the vulnerability of this lagoon ecosystem. The cyanobacterial blooms were dominated by potentially toxic species; Anabaena circinalis, A. flos-aquae, A. limnetica and A. spiroides. A comparison of ambient nutrient ratios with the Redfield ratio (N/P/Si = 16:1:16) showed clear temporal variations that coincided with phytoplankton dynamics and the bloom regime. Low N/P ratios were recorded during the first 8 months, and there was a shift to higher ratios during the subsequent 8 months, followed by low N/P ratios in the last 2 months. Higher silicate values coincided with decreased cyanobacterial biomass, cyanobacteria bloom collapse and proliferation of diatoms during the first annual cycle. Cyanobacterial abundance exceeded the alert level 1 and almost reached alert level 2 which call for continuous environmental monitoring and management of coastal waters.

Identification of a Novel Saxitoxin Analogue, 12β-Deoxygonyautoxin 3, in the Cyanobacterium, Anabaena circinalis (TA04).

Saxitoxin (STX) and its analogues, the potent voltage-gated sodium channel blockers, are biosynthesized by freshwater cyanobacteria and marine dinoflagellates. We previously identified several biosynthetic intermediates in the extract of the cyanobacterium, Anabaena circinalis (TA04), that are primarily produced during the early and middle stages in the biosynthetic pathway to produce STX. These findings allowed us to propose a putative biosynthetic pathway responsible for STX production based on the structures of these intermediates. In the present study, we identified 12β-deoxygonyautoxin 3 (12β-deoxyGTX3), a novel STX analogue produced by A. circinalis (TA04), by comparing the retention time and MS/MS fragmentation pattern with those of synthetic standards using LC–MS. The presence of this compound in A. circinalis (TA04) is consistent with stereoselective enzymatic oxidations at C11 and C12, and 11-O-sulfation, during the late stage of STX biosynthesis, as proposed in previous studies.

Antibacterial Activity of Anabaena circinalis Isolated from Fresh Water

Cultures of the blue green algae (cyanobacteria) Anabaena circinalis were identified and isolated from freshwater and their antimicrobial effect was studied. The extract of A. circinalis was tested to investigate its efficiency against four bacterial strains (Achromobacter xylosoxidans, Staphylococcus aureus, Escherichia coli, Shigella dysenteriae. Antimicrobial test was determined by disk diffusion method. Different concentrations of algal extracts (25, 50, 75 and 100%) were tested. Results showed that the highest level of antimicrobial activity was recorded against S. dysenteriae at 100% concentration followed by 25% extract concentration against the same bacteria. In comparison with two antibiotics Ampicillin (AMP), oxacilina (OXA), AMP was the most effective on S. dysenteriae followed by OXA. S. aureus and E. coli were resistant to both antibiotics while they were sensitive to A. circinalis extracts at even at low concentrations (25% and 50%). Thus the present study revealed that extracts of A. circinalis extract is would be a promising natural source, for novel antibiotics, hence worthy for more investigations.

The antiproliferative and antimicrobial effects of cultivated &lt;i&gt;Anabaena circinalis&lt;/i&gt; Rabenhorts ex Bornet and Flahault and &lt;i&gt;Nostoc entophytum&lt;/i&gt; Bornet and Flahault

Purpose: To investigate the antiproliferative and antimicrobial effects of cultivated Anabaena circinalis Rabenhorst Ex Bornet and Flahault [Synonym: Dolichospermum sigmoideum (Nygaard) Wacklin, L. Hoffmann and Komarek) and Nostoc entophytum Bornet and Flahault (Synonym: Nostoc paludosum Kutzing ex Bornet and Flahault). Methods: The algae extracts were prepared using 0.5 M Tris-HCL pH: 8.00, N-butanol, Ethanol and Dimethyl sulfoxide, and then tested on Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633, Listeria monocytogenes ATCC 7644, Escherichia coli O 157:H7, Pseudomonas aeruginosa ATCC 27853, Salmonella typhimurium CCM 5445, Candida albicans ATCC 10239 using the disc diffusion method in order to determine their antimicrobial effects. The anti-cancer activities of these two algae were tested against cancerous cell lines using BrdU cell proliferation ELISA method. The inhibition of these algae ethanol and butanol extracts were tested against Vero and HeLa carcinoma cells in concentrations of 100, 250 and 500 μg/mL. Results: Anabaena circinalis (AC) and Nostoc entophytum (NE) antimicrobial properties against the tes organisms. The buffer extract obtained from AC showed the highest level of antimicrobial activity against L. monocytogenes ATCC 7644 while the buffer extract from NE displayed the highest antimicrobial activity against E. coli O 157:H7. The anti-proliferative data indicate that NE has effective anti-cancer properties. Furthermore, the results showed that cyanobacteria species were superior to DMSO and control groups in terms of anti-cancer activity in tumor cells. NE exhibited significant (p < 0.05) anti-proliferative effects at all three concentrations (100, 250, 500 μg/mL), compared to DMSO while AC exhibited significant anti-proliferative activity only at 500 μg/mL concentration (p < 0.01). Conclusion: The results indicate that extracts possess antimicrobial and antiproliferative antivities. However, further studies are required to ascertain their clinical efficacy. Keywords: Anabaena circinalis , Nostoc entophytum, Cyanobacteria, Antiproliferative, Antimicrobial

Akinete germination chamber: An experimental device for cyanobacterial akinete germination and plankton emergence

Understanding how algal resting cells (e.g. akinetes) germinate and what factors influence their germination rate is crucial for elucidating the development of algal blooms and their succession. While laboratory studies have demonstrated algal germination rate and some key factors affecting the germination, the use of artificially induced akinetes and/or removal of the sediments are obviously limiting in simulating the natural environment when designing such controlled experiments. This study introduce a laboratory Akinete Germination Chamber (AGC) that facilitates research for cyanobacterial akinete germination and emergence in an environment similar to natural conditions while minimizing sediment disturbance. The fundamental difference between AGC method and the conventional microplate method is that AGC incorporates the substrate from the natural environment whereas the microplate method does not employ sediment. Therefore, authors of this study assume that the characteristics of akinete germination between the two methods differ because the sediment influences the germination environment. The present study developed the AGC method as an efficient tool to understand harmful cyanobacterial bloom formation. For validation of the AGC method, this study evaluated akinete germination of Dolichospermum circinale (Anabaena circinalis) with different temperature and nutrient condition and then compared the results with those generated by conventional methods The results showed a marked difference in the maximal germination rate between two methods (78% and 35% in the AGC and the microplate, respectively; p < 0.05) at optimum germination temperature (25 °C for both the AGC and the microplate). The nutrient effect also demonstrated clear difference (p < 0.01) in the germination rate between two methods; 88%, 68% and 78% in the AGC and 15%, 20% and 15% in the microplate with −N+P, +N−P, and +N+P condition of CB medium, respectively. Importantly, both DW and −N−P treatments in the AGC induced a little germination of akinete (4.2 ± 1.4% and 5.0 ± 7.1%, respectively), whereas no germination was occurred in the DW treatment in the microplate, suggesting a possible positive effect of sediment on akinete germination. With these results, this study suspects that these differences were largely attributable to natural sediment. Also sediment-accompanied properties, possibly such as nutrient availability, heat budget, micronutrients, and bacteria might have some potential effects on akinete germination. The AGC method can overcome the limitations of the conventional microplate method, and that it is applicable in studies on pelagic-benthic coupling.

Molecular and morphological survey of saxitoxin-producing cyanobacterium Dolichospermum circinale (Anabaena circinalis) isolated from geographically distinct regions of Australia

The cyanobacterium Dolichospermum circinale (formerly Anabaena circinalis) is responsible for neurotoxic saxitoxin-producing blooms in Australia. Previous studies have reported distinct isolates of toxic D. circinale producing different saxitoxin analogues at varying amounts, but the mechanisms responsible remain poorly understood. To assess the characteristics that may be responsible for this variance, a morphological, molecular and chemical survey of 28 Anabaena isolates was conducted. Morphological characteristics, presence or absence of saxitoxin biosynthetic genes and toxin amount and profile were assessed.The 28 isolates were collected from 16 locations. A correlation between the size of the isolates and its reported toxicity or geographical location could not be found. Molecular screening for the presence of several sxt genes revealed eight out of the 28 strains harboured the sxt gene cluster and all tailoring genes except sxtX. Furthermore, the presence of PSTs was correlated with the presence of the sxt cluster using quantitative pre-column oxidation high performance liquid chromatography with fluorescence detection (HPLC-FLD) and LC-MS/MS. Interestingly, isolates differed in the amount and type of toxins produced, with the eight toxic strains containing the core and tailoring biosynthetic genes while non-toxic strains were devoid of these genes. Moreover, the presence of sxt tailoring genes in toxic strains correlated with the biosynthesis of analogues.A greater understanding of toxin profile/quantity from distinct sites around Australia will aid the management of these at-risk areas and provide information on the molecular control or physiological characteristics responsible for toxin production.

Detection of potential harmful algal bloom-causing microalgae from freshwater prawn farms in Central Luzon, Philippines, for bloom monitoring and prediction

Prawn aquaculture industry is one of the developing economic activities in the Philippines. Generally, a wide range of microalgae typically grow and proliferate in many aquaculture ponds. However, certain species of microalgae have the ability to form harmful algal blooms (HABs) which often bring damaging consequences to the aquaculture industry, food safety, and the environment. The study aims to identify and characterize the composition of microalgae (particularly Cyanophyta) that are capable of forming HABs in selected freshwater prawn culture ponds in Central Luzon, Philippines, using morphological, ultrastructural, and molecular characterizations. From water samples collected in ten selected ponds across Central Luzon (Bulacan, Nueva Ecija, Pampanga, Tarlac, and Zambales), potential HAB formers such as Oscillatoria agardhii, O. princeps, Microcystis aeruginosa, and M. wesenbergii were observed to have occurred mostly, while Anabaena circinalis was only observed in one site. Both morphological and ultrastructural methods brought upon some challenges and limitations while molecular methods using 16S rRNA gene and phylogenetic analysis which were optimized in this study offered better and more efficient ways of identification and were helpful in resolving genus-level and species-level relationships. The influence of physicochemical properties of pond water, especially nutrient levels (nitrate, nitrite, and orthophosphate) on the occurrence of these cyanobacteria was also analyzed. As a pioneering study on freshwater HABs in aquaculture ponds in the country, results of the study can provide information to improve the knowledge in bloom occurrence and prediction, and to develop freshwater HAB prevention and control methods.

Biosynthetic route towards saxitoxin and shunt pathway.

Saxitoxin, the most potent voltage-gated sodium channel blocker, is one of the paralytic shellfish toxins (PSTs) produced by cyanobacteria and dinoflagellates. Recently, putative biosynthetic genes of PSTs were reported in these microorganisms. We previously synthesized genetically predicted biosynthetic intermediates, Int-A’ and Int-C’2, and also Cyclic-C’ which was not predicted based on gene, and identified them all in the toxin-producing cyanobacterium Anabaena circinalis (TA04) and the dinoflagellate Alexandrium tamarense (Axat-2). This study examined the incorporation of 15N-labeled intermediates into PSTs (C1 and C2) in A. circinalis (TA04). Conversions from Int-A’ to Int-C’2, from Int-C’2 to Cyclic-C’, and from Int-A’ and Int-C’2 to C1 and C2 were indicated using high resolution-LC/MS. However, Cyclic-C’ was not converted to C1 and C2 and was detected primarily in the extracellular medium. These results suggest that Int-A’ and Int-C’2 are genuine precursors of PSTs, but Int-C’2 converts partially to Cyclic-C’ which is a shunt product excreted to outside the cells. This paper provides the first direct demonstration of the biosynthetic route towards saxitoxin and a shunt pathway.