The invasion and spread of non-native species of many different kinds of organisms is of increasing interest to researchers. Invasions by microscopic organisms, however, are poorly understood, and their impact on the environment is probably underestimated. We collected available data on nonnative and invasive/expansive algae and cyanobacteria in the Czech Republic; we mapped their distribution and assessed their impact on local species and other real or potential risks resulting from their spread. The list of alien species in the Czech Republic contains 10 species of cyanobacteria, 9 species of Bacillariophyceae, 1 species of Dinophyta, 1 species of Ulvophyceae, 2 species of Chlorophyceae, and 1 species complex of Zygnematopyceae. The literature on the worldwide occurrence of these taxa is also reviewed.

We examined the proportions of major Betaproteobacteria subgroups within bacterial communities in diverse nonaxenic, monospecific cultures of algae or cyanobacteria: four species of cryptophyta (genera Cryptomonas and Rhodomonas), four species of chlorophyta (genera Pediastrum, Staurastrum, and Chlamydomonas), and two species of cyanobacteria (genera Dolichospermum and Aphanizomenon). In the cryptophyta cultures, Betaproteobacteria represented 48 to 71% of total bacteria, the genus Limnohabitans represented 18 to 26%, and the Polynucleobacter B subcluster represented 5 to 16%. In the taxonomically diverse chlorophyta group, the genus Limnohabitans accounted for 7 to 45% of total bacteria. In contrast, cyanobacterial cultures contained significantly lower proportions of the Limnohabitans bacteria (1 to 3% of the total) than the cryptophyta and chlorophyta cultures. Notably, largely absent in all of the cultures was Polynucleobacter necessarius (Polynucleobacter C subcluster). Subsequently, we examined the growth of Limnohabitans strains in the presence of different algae or their extracellular products (EPP). Two strains, affiliated with Limnohabitans planktonicus and Limnohabitans parvus, were separately inoculated into axenic cultures of three algal species growing in an inorganic medium: Cryptomonas sp., Chlamydomonas noctigama, and Pediastrum boryanum. The Limnohabitans strains cocultured with these algae or inoculated into their EPP consistently showed (i) pronounced population growth compared to the control without the algae or EPP and (ii) stronger growth stimulation of L. planktonicus than of L. parvus. Overall, growth responses of the Limnohabitans strains cultured with algae were highly species specific, which suggests a pronounced niche separation between two closely related Limnohabitans species likely mediated by different abilities to utilize the substrates produced by different algal species.There is compelling evidence that phytoplankton community dynamics have a significant impact on the composition of bacterioplankton communities (for example, see references 6, 19, and 21). The apparent driving force of such alga-bacterium interactions is likely the nature and quantity of alga-derived substrates available in the form of extracellular phytoplankton products (EPP) or decaying algal biomass. Although it is usually not known which algal species are the major EPP producers in situ, tight species-specific alga-bacterium relationships have been suggested as characterizing bacterium-alga consortia (e.g., 6, 21, 33). Interactions of phytoplankton and bacteria range from symbiotic to parasitic relationships (3). It is not surprising, then, that specific bacterial assemblages associated with different algae can also stimulate or even inhibit algal growth, as documented for cultures of marine diatoms (6). The latter study also demonstrated that free-living and phytoplankton-associated (i.e., attached to algal surfaces) bacteria are significantly different from each other and are dominated by distinct phylog...

A tropical planktic filamentous cyanobacterium, tentatively identified as Lyngbya robusta, recently increased in abundance in Lake Atitlán, Guatemala, and since 2008 annual water-blooms occurred. This was one from the first known cases of L. robusta water-blooms worldwide. A polyphasic evaluation of L. robusta using 16S rRNA gene sequencing, cytomorphological markers, and ecological characteristics was made. This species had several unique features. It produced aerotopes that were irregularly spaced in cells; cyanotoxins were not found, and it fixed nitrogen in spite of the lack of heterocytes. It contained a high amount of carotenoids, which caused an unusual brown color of the macroscopic scum on the water level. Molecular phylogenetic analyses using the 16S rRNA gene showed that L. robusta, together with few other planktic species, formed a clade, separated from typical Lyngbya species. The main diacritical markers of this clade were the planktic type of life and formation of gas vesicles in cells. Based upon molecular, morphological and ecological data, a new genus Limnoraphis was proposed with four species.

Abstract:The traditional cyanobacterial genus Anabaena contains several groups of morphospecies, which should be classified in different genera according to modern phenotypic and molecular criteria. The separation into several clusters was confirmed by 16S rRNA sequencing. The generic name Anabaena must be maintained for the benthic species without gas vesicles, the type species of which is Anabaena oscillarioides. The planktic types are divided also in several subclusters; one of them can be provisionally designated as subg. Dolichospermum THW. ex WITTR. et NORDST. 1889 with the type species Anabaena flos-aquae [LYNGB.] BRÉB. ex BORN. et FLAH. 1888. The taxonomy of this cluster, which contains types with coiled as well as straight filaments, is not yet satisfactory solved. The interspecific features are particularly problematic. However, the review of stable coiled morphotypes from the subg. Dolichospermum which are known and repeatedly occur in natural populations, is presented in this article. This review should help to the orientation of phenotype diversity of coiled Dolichospermum-types, especially in populations occurring in natural habitats.

Occurrences of rare cyanobacteria Anabaena reniformis Lemmerm. and Aphanizomenon aphanizomenoides (Forti) Horecká et Komárek were recently detected at several localities in the Czech Republic. Two monoclonal strains of An. reniformis and one strain of Aph. aphanizomenoides were isolated from distant localities and different sampling years. They were characterized by a combination of morphological, genetic, and biochemical approaches. For the first time, partial 16S rRNA gene sequences were obtained for these morphospecies. Based on this gene, all of these strains clustered separately from other planktonic Anabaena and Aphanizomenon strains. They appeared in a cluster with Cylindrospermopsis Seenaya et Subba Raju and Raphidiopsis F. E. Fritsch et M. F. Rich, clustered closely together with two An. kisseleviana Elenkin strains available from GenBank. A new generic entity was defined (Sphaerospermum gen. nov., with the type species S. reniforme, based on the traditional species An. reniformis). These results contribute significantly to the knowledge base about genetic heterogeneity among planktonic Anabaena-like and Aphanizomenon-like morphospecies. Accordingly, the subgenus Dolichospermum, previously proposed for the group of planktonic Anabaena, should be revaluated. Secondary metabolite profiles of the An. reniformis and Aph. aphanizomenoides strains differed considerably from 17 other planktonic Anabaena strains of eight morphospecies isolated from Czech water bodies. Production of puwainaphycin A was found in both of the An. reniformis strains. Despite the relatively short phylogenetic distance from Cylidrospermopsis, the production of cylindrospermopsin was not detected in any of our strains.

During the summer of 2006, phytoplankton succession and vertical distribution were studied in the eutrophic Ř ímov Reservoir (Czech Republic). Disturbances in the form of dramatic summer storms had a crucial effect on phytoplankton succession and its vertical distribution. Two extreme rainfalls substantially increased flushing rate, yielding a fairly short retention time within the reservoir that disrupted established thermal stratification. The first storm initiated the development of summer phytoplankton, while the second storm reversed the phytoplankton succession to an earlier stage. The measurement of vertical profiles of chlorophyll a showed that the phytoplankton were heterogeneously distributed in the water column and formed subsurface diatom maxima (SDM) over most of the summer. Biogenic silica deposition studied by PDMPO (2-(4-pyridyl)-5{[4-dimethylaminoethyl-aminocarbamyl)-methoxy] phenyl}oxazole) was measured to compare diatom growth rates over the season and between surface and depth of SDM. Diatoms deposited 20 times more silica at the surface than at the SDM depth, although only a half of diatom population was involved in the silica deposition. Maximum rates of silica deposition were measured in samples just after both summer storms events. When diatoms dominated the phytoplankton, the amounts of available Si and P in water were significantly correlated (r 2 = 0.81, p < 0.001, df = 42). Outliers from the linear relationship were found only during a period when substantial picocyanobacterial population developed in the reservoir. Due to their lack of Si requirements, ambient Si concentration markedly increased while P was depleted to growth limiting levels. Temporal variations in Si:P ratio therefore illustrate the importance of resource competition in phytoplankton seasonal succession.

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In mid-July and August 2003 and 2004, 18 reservoirs in the Czech Republic were sampled for phytoplankton species composition and concentration of intracellular microcystins (MCs). As a consequence of high nutrient loading, most of the reservoirs experienced cyanobacterial blooms of various intensities, with the prevalence of cyanobacteria increasing markedly in August, along with a conspicuous shift in species composition toward dominance of Microcystis spp. Microcystins were detected in 90% of the samples, and their amount also increased considerably in August, reflecting the cyanobacterial biomass. In Microcystis-dominated samples, a significantly higher amount of MCs (p < 0.001) occurred than in samples in which other taxa prevailed. Microcystins were positively correlated with chlorophyll a and cyanobacterial biovolume (p < 0.05, R2 = 0.61 and 0.66, respectively), with the strongest correlation found for Microcystis spp. biovolume (p < 0.001, R2 = 0.87). This taxon was the most important producer of MCs in Czech reservoirs. The main structural variants of MCs were MC-LR, MC-RR, and MC-YR. This study's data also indicate that the relative share of MC variants (MC-LR and MC-RR) varies considerably with time, most likely as a consequence of different species and strain compositions during the summer. This study clearly demonstrates a high prevalence of MC-producing cyanobacteria in Czech reservoirs. Therefore, regular monitoring of these reservoirs is highly desirable in an effort to minimize potential health risks to the human population.