Harmful Bloom-forming Cyanobacteria Research Articles

Purification and Activity of the Second Recombinant Enzyme for Biodegrading Linearized Microcystins by Sphingopyxis sp. USTB-05.

Hepatotoxic microcystins (MCs) are produced and released by the harmful bloom-forming cyanobacteria, which severely threaten drinking water safety and human health due to their high toxicity, widespread distribution, and structural stability. The linearized microcystinase (MlrB) further hydrolyses the poisonous linearized MCs produced by the microcystinase-catalysed MCs to form tetrapeptides. Here, the purification and activity of MlrB were investigated. The results showed that the linearized products generated by 12.5 mg/L MC-LR and MC-RR were removed by purified recombinant MlrB at a protein concentration of 1 mg/L within 30 min. The high catalytic activity of MlrB can be obtained via heterologous expression and affinity purification, which lays the foundation for further studies on the properties and mechanism of MCs biodegradation enzymes.

Coagulation/flocculation-flotation harvest of Microcystis aeruginosa by cationic hydroxyethyl cellulose and Agrobacterium mucopolysaccharides

Efficient biocoagulants/bioflocculants are desired for removal of Microcystis aeruginosa, the dominant harmful bloom-forming cyanobacterium. Herein, we reported cationic hydroxyethyl cellulose (CHEC) inactivated M. aeruginosa cells after forming coagulates and floating-flocculated them with aid of Agrobacterium mucopolysaccharides (AMP) and surfactant. CHEC exhibited cyanocidal activity at 20mg/L, coagulating 85% of M. aeruginosa biomass within 9h and decreasing 41% of chlorophyll a after 72h. AMP acted as an adhesive flocculation aid that accelerated and strengthened the formation of flocs, approaching a maximum in 10min. Flocs of M. aeruginosa were floated after foaming with cocoamidopropyl betaine (CAB), which facilitated the subsequent filter harvest. 82% of M. aeruginosa biomass was suspended on water surface after treated with the coagulation/flocculation-flotation (CFF) agents containing CHEC (25mg/L), AMP (177mg/L) and CAB (0.1mg/L). All components in CFF agents at the applied concentrations did not inhibit acetylcholinesterase or Vibrio fischeri. Our findings provide new insights in developing bio-based materials for sustainable control of cyanobacterial blooms.

Toward Disentangling the Multiple Nutritional Constraints Imposed by Planktothrix: The Significance of Harmful Secondary Metabolites and Sterol Limitation.

The harmful bloom-forming cyanobacterium Planktothrix is commonly considered to be nutritionally inadequate for zooplankton grazers, resulting in limited top-down control. However, interactions between Planktothrix and zooplankton grazers are poorly understood. The food quality of Planktothrix is potentially constrained by morphological properties (i.e., filament formation), the production of harmful secondary metabolites, and a deficiency in essential lipids (i.e., primarily sterols). Here, we investigated the relative significance of toxin production (microcystins, carboxypeptidase A inhibitors, protease inhibitors) and sterol limitation for the performance of Daphnia feeding on one Planktothrix rubescens and one P. agardhii wild-type/microcystin knock-out mutant pair. Our data suggest that the poor food quality of both Planktothrix spp. is due to deleterious effects mediated by various harmful secondary metabolites and that the impact of sterol limitation is partially or completely superimposed by toxicity. The significance of the different factors seems to depend on the metabolite profile of the considered Planktothrix strain and the Daphnia clone that is used for the experiments. The toxin-responsive gene expression (transporter genes, gpx, and trypsin) and enzyme activity patterns revealed strain-specific food quality constraints and that Daphnia is capable of modulating its physiological responses according to the ingested Planktothrix strain. Future studies need to consider that Planktothrix–grazer interactions are simultaneously modulated by multiple factors to improve our understanding of top-down influences on Planktothrix bloom formation.

Towards defining global ecotypes of the toxic cyanobacterium Raphidiopsis raciborskii

ABSTRACT Raphidiopsis raciborskii is a harmful bloom-forming cyanobacterium with strains that vary in ecophysiology within and between populations around the world. Understanding the extent of intraspecific diversity of strains is needed to design laboratory experiments that capture the breadth of responses the species has to abiotic and biotic interactions; therefore, choice of strains is a critical consideration for experimental design. In this paper, we identified major ecotypes of 12 R. raciborskii strains from three continents, characterizing their morphology via microscopic cell measurements; physiology via growth rates under nitrogen-replete and -free conditions; and genetic variation, via multiplex randomly amplified polymorphic DNA PCR (i.e., DNA fingerprinting). Euclidean distance plots based on morphological and physiological measurements showed three groupings of strains defined as the major ecotypes. Best groupings were obtained using a selection of both morphological and physiological traits. Ecotype groupings did not correlate with geographic location, implying that understanding the ecology of the species does not require in-depth local knowledge of the strains. This study indicates that general average physiology of the global species could be characterized, indicating the existence of major ecotypes across populations.

Are Oligotypes Meaningful Ecological and Phylogenetic Units? A Case Study of Microcystis in Freshwater Lakes.

Oligotyping is a computational method used to increase the resolution of marker gene microbiome studies. Although oligotyping can distinguish highly similar sequence variants, the resulting units are not necessarily phylogenetically and ecologically informative due to limitations of the selected marker gene. In this perspective, we examine how oligotyping data is interpreted in recent literature, and we illustrate some of the method’s constraints with a case study of the harmful bloom-forming cyanobacterium Microcystis. We identified three Microcystis oligotypes from a western Lake Erie bacterial community 16S rRNA gene (V4 region) survey that had previously clustered into one OTU. We found the same three oligotypes and two additional sequence variants in 46 Microcystis cultures isolated from Michigan inland lakes spanning a trophic gradient. In Lake Erie, shifts in Microcystis oligotypes corresponded to spatial nutrient gradients and temporal transitions in bloom toxicity. In the cultures, Microcystis oligotypes showed preferential distributions for different trophic states, but genomic data revealed that the oligotypes identified in Lake Erie did not correspond to toxin gene presence. Thus, oligotypes could not be used for inferring toxic ecotypes. Most strikingly, Microcystis oligotypes were not monophyletic. Our study supports the utility of oligotyping for distinguishing sequence types along certain ecological features, while it stresses that 16S rRNA gene sequence types may not reflect ecologically or phylogenetically cohesive populations. Therefore, we recommend that studies employing oligotyping or related tools consider these caveats during data interpretation.

Screening Assessment of Cyanobacteria and Cyanotoxins in Southern California Lentic Habitats

<p class="emsd"><span lang="EN-GB">Harmful bloom-forming cyanobacteria (CyanoHABs) and associated toxins are increasingly prevalent world-wide. We</span><span lang="EN-GB"> conducted a screening-level study to determine if cyanobacteria and associated cyanotoxins were present in Southern California coastal lakes, ponds, and seasonally tidal lagoons. We evaluated waterbody nutrient status and physiochemical parameters, land use, waterbody type, and habitat type, to determine their utility as screening factors for risk of CyanoHAB blooms. </span><span lang="EN-GB">One-time grab samples were collected from 30 sites during July</span><span lang="EN-GB">–</span><span lang="EN-GB">September 2009. Samples were analyzed for phytoplankton taxonomic composition, nutrients, other physiochemical parameters, and three cyanotoxins: m</span><span lang="EN-GB">icrocystins (MCY), anatoxin-a, and cylindrospermopsin</span><span lang="EN-GB">. </span><span lang="EN-GB">Cyanobacteria was the predominant taxonomic group in most water bodies in this study, and <em>Microcystis</em> spp. was the predominant genus in 96% of the study sites. Cyanobacteria were equally prevalent among coastal lagoons, depressional wetlands, and lakes in this study. We detected MCY in high concentrations in 10% of our sites</span><span lang="EN-GB">, but neither anatoxin-a nor cylindrospermopsin were detected. All of the MCY-positive sites exceeded California action levels for recreational use and World Health Organization (WHO) guidance for human health effects. The prevalence of <em>Microcystis </em>spp. from all study sites indicates a high potential for MCY in these water bodies, although the one-time toxin grab samples likely underestimated the overall toxicity of these sites. Landscape variables, such as developed land use and dominant habitat type, were not found to be predictive indicators of cyanobacterial dominance. However, because cyanobacteria become consistently dominant when chlorophyll-a levels exceed 15 µg L<sup>-1</sup>, chlorophyll-a can serve as a significant predictor of MCY. </span></p>

Influence of UV-B radiation on the fitness and toxin expression of the cyanobacterium Cylindrospermopsis raciborskii

The harmful bloom-forming cyanobacterium Cylindrospermopsis raciborskii grows in freshwaters over a wide range of light conditions. This species has increased its global distribution recently. The influence of ultraviolet radiation (UVR) on the fitness and toxin production of C. raciborskii has not previously been explored. We performed short-term experiments with three C. raciborskii strains (MVCC19, LB2897, and CYP011 K), and we compared their responses with other bloom-forming species (Microcystis sp.1 and Plankthotrix agardhii) to determine the impact of UV-B radiation on pigments, biomass, and morphological traits. In addition, we analyzed the effect of UV-B on the saxitoxin content and sxtU gene expression in the strain MVCC19. C. raciborskii strains were stressed differentially by UV-B exposure as evidenced by changes in growth, morphology, and heterocytes number. A significant increase in saxitoxin concentration and sxtU gene expression under UV-B suggests that toxin production in C. raciborskii can be a response to UV-B stress. In comparison, Microcystis sp.1 was more tolerant, while P. agardhii was severely impacted by UV-B, indicating also different sensitivities among cyanobacteria to UVR. Our results underscore the influence of UVR on C. raciborskii and the differences between strains which showed phenotypic plasticity, which potentially could affect its distribution in freshwaters.

Isolation and Characterization of Bacterial Isolates Algicidal against a Harmful Bloom-forming Cyanobacterium Microcystis aeruginosa

Algicidal bacteria MaI11-2, MaI11-5 and MaI11-10, which inhibited the growth of a harmful bloom-forming cyanobacterium Microcystis aeruginosa, were isolated from a sewage treatment plant. The isolate MaI11-5 was phylogenetically affiliated into the genus Pedobacter, while MaI11-2 and MaI11-10 were closely related to Bacillus aerophilus, Bacillus altitudinis and Bacillus stratosphericus with 100% identity based on 16S ribosomal RNA sequences. Co-cultivation of M. aeruginosa with the algicidal isolates showed their high algicidal activity. MaI11-5 showed the highest inhibitory effect on the cyanobacterial growth: the inhibitory effect exceeded 50% after 2 days, and reached to 75-85% after 10 days, regardless of the bacterial cell density. The cyanobacterial cells aggregated and produced mucilaginous, glycocalyx-like compounds when attacked by the algicidal bacteria. These results suggest that the algicidal bacteria isolated in the present study are potentially useful as biocontrol agents against M. aeruginosa bloom.