Development of a new Agrobacterium-mediated transformation system based on a dual auxotrophic approach in the filamentous fungus Aspergillus oryzae.

Genetic engineering of the filamentous fungus Aspergillus oryzae still requires more suitable selection markers for fungal transformation. Our previous work has shown that Agrobacterium tumefaciens-mediated transformation (ATMT) based on the uridine/uracil auxotrophic mechanism with pyrG as the selection marker is very efficient for gene transfer in A. oryzae. In the present study, we delete the hisB gene, which is essential for histidine biosynthesis, in A. oryzae via homologous recombination and demonstrate that hisB is a reliable selection marker for genetic transformation of this fungus. Under optimal conditions, the ATMT efficiency of the histidine auxotrophic A. oryzae reached 515 transformants per 106 spores. Especially, we have succeeded in constructing a new ATMT system based on dual auxotrophic A. oryzae mutants with two different selection markers including hisB and pyrG. This dual auxotrophic ATMT system displayed a transformation efficiency of 232 transformants per 106 spores for the hisB marker and 318 transformants per 106 spores for the pyrG marker. By using these selectable markers, the co-expression of the DsRed and GFP fluorescent reporter genes was implemented in a single fungal strain. Furthermore, we could perform both the deletion and complementation of the laeA regulatory gene in the same strain of A. oryzae to examine its function. Conclusively, the ATMT system constructed in our work represents a promising genetic tool for studies on recombinant expression and gene function in the industrially important fungus A. oryzae.

Biochemistry of plants N-heterocyclic non-protein amino acids.

Plants catalyze the biosynthesis of a large number of non-protein amino acids, which are usually toxic for other organisms. In this review, the chemistry and metabolism of N-heterocyclic non-protein amino acids from plants are described. These N-heterocyclic non-protein amino acids are composed of ß-substituted alanines and include mimosine, ß-pyrazol-1-yl-L-alanine, willardiine, isowillardiine, and lathyrine. These ß-substituted alanines consisted of an N-heterocyclic moiety and an alanyl side chain. This review explains how these individual moieties are derived from their precursors and how they are used as the substrate for biosynthesizing the respective N-heterocyclic non-protein amino acids. In addition, known catabolism and possible role of these non-protein amino acids in the actual host is explained.

Genome-wide alterations of uracil distribution patterns in human DNA upon chemotherapeutic treatments.

Numerous anti-cancer drugs perturb thymidylate biosynthesis and lead to genomic uracil incorporation contributing to their antiproliferative effect. Still, it is not yet characterized if uracil incorporations have any positional preference. Here, we aimed to uncover genome-wide alterations in uracil pattern upon drug treatments in human cancer cell line models derived from HCT116. We developed a straightforward U-DNA sequencing method (U-DNA-Seq) that was combined with in situ super-resolution imaging. Using a novel robust analysis pipeline, we found broad regions with elevated probability of uracil occurrence both in treated and non-treated cells. Correlation with chromatin markers and other genomic features shows that non-treated cells possess uracil in the late replicating constitutive heterochromatic regions, while drug treatment induced a shift of incorporated uracil towards segments that are normally more active/functional. Data were corroborated by colocalization studies via dSTORM microscopy. This approach can be applied to study the dynamic spatio-temporal nature of genomic uracil.

Plasmid-based complementation of large deletions in Phaeodactylum tricornutum biosynthetic genes generated by Cas9 editing.

The model diatom Phaeodactylum tricornutum is an attractive candidate for synthetic biology applications. Development of auxotrophic strains of P. tricornutum would provide alternative selective markers to commonly used antibiotic resistance genes. Here, using CRISPR/Cas9, we show successful editing of genes in the uracil, histidine, and tryptophan biosynthetic pathways. Nanopore long-read sequencing indicates that editing events are characterized by the occurrence of large deletions of up to ~ 2.7 kb centered on the editing site. The uracil and histidine-requiring phenotypes can be complemented by plasmid-based copies of the intact genes after curing of the Cas9-editing plasmid. Growth of uracil auxotrophs on media supplemented with 5-fluoroorotic acid and uracil results in loss of the complementing plasmid, providing a facile method for plasmid curing with potential applications in strain engineering and CRISPR editing. Metabolomic characterization of uracil auxotrophs revealed changes in cellular orotate concentrations consistent with partial or complete loss of orotate phosphoribosyltransferase activity. Our results expand the range of P. tricornutum auxotrophic strains and demonstrate that auxotrophic complementation markers provide a viable alternative to traditionally used antibiotic selection markers. Plasmid-based auxotrophic markers should expand the range of genome engineering applications and provide a means for biocontainment of engineered P. tricornutum strains.

Genetic and Chemical Screening in Human Blood Serum Reveals Unique Antibacterial Targets and Compounds against Klebsiella pneumoniae.

Antibiotics halt the growth of bacteria by targeting core, essential physiology that is required for life on standard microbiological media. Many more biochemical and virulence processes, however, are required for bacteria to cause infection in a host. Indeed, chemical inhibitors of the latter processes are overlooked using conventional antibiotic drug discovery approaches. Here, we use human blood serum as an alternative growth medium to explore new targets and compounds. High-throughput screening of genetic and chemical libraries identified compounds targeting biological activities required by Klebsiella pneumoniae to grow in serum, such as nucleobase biosynthesis and iron acquisition, and showed that serum can chemically transform compounds to reveal cryptic antibacterial activity. One of these compounds, ruthenium red, was effective in a rat bloodstream infection model. Our data demonstrate that human serum is an effective tool to find new chemical matter to address the current antibiotic resistance crisis.

Microbial production of uracil by an isolated Methylobacterium sp. WJ4 using methanol.

In this study, we report the production of uracil from methanol by an isolated methylotrophic bacterium, Methylobacterium sp. WJ4. The use of methanol as alternative carbon feedstock is attractive option in biotechnology. As a feedstock of biotechnological processes, methanol has distinct advantages over methane. This is not only due to physical and chemical considerations, but also to the properties of the pertinent organisms. Besides, with a wide array of biological activities and synthetic accessibility, uracil is considered as privileged structures in drug discovery. Uracil analogues have been applied to treatments of patients with cancer or viral infections. In this respect, it is meaningful to produce uracil using methanol. The effect of process parameters and methanol concentration for uracil production were investigated and optimized. Uracil production was remarkably increased to 5.76mgg cell dry weight-1 in optimized condition. The results were significant for further understanding of methylotrophic bacteria on uracil production.

Isolation of uracil auxotroph mutants of coral symbiont alga for symbiosis studies.

Coral reef ecosystems rely on stable symbiotic relationship between the dinoflagellate Symbiodinium spp. and host cnidarian animals. The collapse of such symbiosis could cause coral 'bleaching' and subsequent host death. Despite huge interest on Symbiodinium, lack of mutant strains and readily available genetic tools have hampered molecular research. A major issue was the tolerance to marker antibiotics. Here, we isolated Symbiodinium mutants requiring uracil for growth, and hence, useful in transformation screening. We cultured Symbiodinium spp. cells in the presence of 5-fluoroorotic acid (5FOA), which inhibits the growth of cells expressing URA3 encoding orotidine-5'-monophosphate decarboxylase, and isolated cells that require uracil for growth. Sequence analyses and genetic complementation tests using yeast demonstrated that one of the mutant cell lines had a point mutation in URA3, resulting in a splicing error at an unusual exon-intron junction, and consequently, loss of enzyme activity. This mutant could maintain a symbiotic relationship with the model sea anemone Exaiptasia pallida only in sea water containing uracil. Results show that the URA3 mutant will be a useful tool for screening Symbiodinium transformants, both ex and in hospite, as survival in the absence of uracil is possible only upon successful introduction of URA3.

Production of uracil from methane by a newly isolated Methylomonas sp. SW1.

Methane is an abundant, inexpensive one-carbon feedstock and one of the most powerful greenhouse gases. Because it does not compete with food demand, it is considered a promising carbon feedstock for the production of valuable products using methanotrophic bacteria. Here, we isolated a novel methanotrophic bacterium, Methylomonas sp. SW1, from a sewage sample obtained from Wonju City Water Supply Drainage Center, Republic of Korea. The conditions for uracil production by Methylomonas sp. SW1, such as Cu2+ concentration and temperature were investigated and optimized. As a result, Methylomonas sp. SW1 produced uracil from methane as a sole carbon source with a titer of 2.1mg/L in 84h without genetic engineering under the optimized condition. The results in this study demonstrate the feasibility of using Methylomonas sp. SW1 for the production of uracil from methane. This is the first report of uracil production from gas feedstock by methanotrophic bacteria.

Escherichia coli-Derived Uracil Increases the Antibacterial Activity and Growth Rate of Lactobacillus plantarum.

Lactobacillus plantarum (L. plantarum) is a representative probiotic. In particular, L. plantarum is the first commensal bacterium to colonize the intestine of infants. For this reason, the initial settlement of L. plantarum can play an important role in determining an infant's health as well as their eventual health status as an adult. In addition, L. plantarum combats pathogenic infections (such as Escherichia coli (E. coli), one of the early pathogenic colonizers in an unhealthy infant gut) by secreting antimicrobial substances. The aim of this research was to determine how L. plantarum combats E. coli infection and why it is a representative probiotic in the intestine. Consequently, this research observed that E. coli releases uracil. L. plantarum specifically recognizes E. coli-derived uracil, which increases the growth rate and production of antimicrobial substance of L. plantarum. In addition, through the inhibitory activity test, this study postulates that the antimicrobial substance is a protein and can be considered a bacteriocin-like substance. Therefore, this research assumes that L. plantarum exerts its antibacterial ability by recognizing E. coli and increasing its growth rate as a result, and this phenomenon could be one of the reasons for L. plantarum settling in the intestine of infants as a beneficial bacterium.

Pharmacological studies confirm neurotoxic metabolite(s) produced by the bloom-forming Cylindrospermopsis raciborskii in Hungary.

A rapid cyanobacterial bloom of Cylindrospermopsis raciborskii (3.2 × 10(4) filaments/mL) was detected early November, 2012, in the Fancsika pond (East Hungary). The strong discoloration of water was accompanied by a substantial fish mortality (even dead cats were seen on the site), raising the possibility of some toxic metabolites in the water produced by the bloom-forming cyanobacteria (C. raciborskii). The potential neuronal targets of the toxic substances in the bloom sample were studied on identified neurons (RPas) in the central nervous system of Helix pomatia. The effects of the crude aqueous extracts of the Fancsika bloom sample (FBS) and the laboratory isolate of C. raciborskii from the pond (FLI) were compared with reference samples: C. raciborskii ACT 9505 (isolated in 1995 from Lake Balaton, Hungary), the cylindrospermopsin producer AQS, and the neurotoxin (anatoxin-a, homoanatoxin-a) producer Oscillatoria sp. (PCC 6506) strains. Electrophysiological tests showed that both FBS and FLI samples as well the ACT 9505 extracts modulate the acetylcholine receptors (AChRs) of the neurons, evoking ACh agonist effects, then inhibiting the ACh-evoked neuronal responses. Dose-response data suggested about the same range of toxicity of FBS and FLI samples (EC50 = 0.397 mg/mL and 0.917 mg/mL, respectively) and ACT 9505 extracts (EC50 = 0.734 mg/mL). The extract of the neurotoxin-producing PCC 6506 strain, however, proved to be the strongest inhibitor of the ACh responses on the same neurons (EC50 = 0.073 mg/mL). The presented results demonstrated an anatoxin-a-like cholinergic inhibitory effects of cyanobacterial extracts (both the environmental FBS sample, and the laboratory isolate, FLI) by some (yet unidentified) toxic components in the matrix of secondary metabolites. Previous pharmacological studies of cyanobacterial samples collected in other locations (Balaton, West Hungary) resulted in similar conclusions; therefore, we cannot exclude that this chemotype of C. raciborskii which produce anatoxin-a like neuroactive substances is more widely distributed in this region.

First report of cylindrospermopsin production by two cyanobacteria (Dolichospermum mendotae and Chrysosporum ovalisporum) in Lake Iznik, Turkey.

Cylindrospermopsin (CYN) is a cytotoxic alkaloid produced by cyanobacteria. The distribution of this toxin is expanding around the world and the number of cyanobacteria species producing this toxin is also increasing. CYN was detected for the first time in Turkey during the summer months of 2013. The responsible species were identified as Dolichospermum (Anabaena) mendotae and Chrysosporum (Aphanizomenon) ovalisporum. The D. mendotae increased in May, however, C. ovalisporum formed a prolonged bloom in August. CYN concentrations were measured by LC-MS/MS and ranged from 0.12 µg·mg⁻¹ to 4.92 µg·mg⁻¹ as dry weight, respectively. Both species were the only cyanobacteria actively growing and CYN production was attributed solely to these species. Despite CYN production by C. ovalisporum being a well-known phenomenon, to our knowledge, this is the first report of CYN found in D. mendotae bloom.

Nitrogen limitation promotes accumulation and suppresses release of cylindrospermopsins in cells of Aphanizomenon sp.

As the biosynthesis of cylindrospermopsin (CYN) is assumed to depend on nitrogen availability, this study investigated the impact of nitrogen availability on intra- and extracellular CYN and deoxy-CYN (D-CYN) contents in three Aphanizomenon strains from temperate waters. Nitrogen deficient (-N) cultures showed a prolonged growth phase and intracellular toxin accumulation by a factor of 2-6. In contrast, cultures with additional nitrate supply (+N) did not accumulate CYN within the cells. Instead, the maximum conceivable CYN release estimated for dead cells (identified by SYTOX Green staining) was much lower than the concentrations of dissolved CYN actually observed, suggesting these cultures actively release CYN from intact cells. Furthermore, we found remarkably altered proportions of CYN to D-CYN: as batch cultures grew, the proportion of D-CYN increased by up to 40% in +N medium, whereas D-CYN remained constant or decreased slightly in -N medium. Since +N cultures showed similar toxin patterns as -P cultures with increased extracellular CYNs and higher proportion of D-CYN we conclude that nitrogen limitation may affect the way the cells economize resources, especially the yield from phosphorus pools, and that this has an impact on CYN production and release. For water management, these result imply that nutrient availability not only determines the abundance of potentially CYN-producing cyanobacteria, but also the amount of extracellular CYNs (challenging drinking-water treatment) as well as the ratio of D-CYN to CYN (affecting toxicity).

Dynamics of the toxin cylindrospermopsin and the cyanobacterium Chrysosporum (Aphanizomenon) ovalisporum in a Mediterranean eutrophic reservoir.

Chrysosporum ovalisporum is a cylindrospermopsin toxin producing cyanobacterium that was reported in several lakes and reservoirs. Its growth dynamics and toxin distribution in field remain largely undocumented. Chrysosporum ovalisporum was reported in 2009 in Karaoun Reservoir, Lebanon. We investigated the factors controlling the occurrence of this cyanobacterium and vertical distribution of cylindrospermopsin in Karaoun Reservoir. We conducted bi-weekly sampling campaigns between May 2012 and August 2013. Results showed that Chrysosporum ovalisporum is an ecologically plastic species that was observed in all seasons. Unlike the high temperatures, above 26 °C, which is associated with blooms of Chrysosporum ovalisporum in Lakes Kinneret (Israel), Lisimachia and Trichonis (Greece) and Arcos Reservoir (Spain), Chrysosporum ovalisporum in Karaoun Reservoir bloomed in October 2012 at a water temperature of 22 °C during weak stratification. Cylindrospermopsin was detected in almost all water samples even when Chrysosporum ovalisporum was not detected. Chrysosporum ovalisporum biovolumes and cylindrospermopsin concentrations were not correlated (n = 31, r² = -0.05). Cylindrospermopsin reached a maximum concentration of 1.7 µg L⁻¹. The vertical profiles of toxin concentrations suggested its possible degradation or sedimentation resulting in its disappearance from the water column. The field growth conditions of Chrysosporum ovalisporum in this study revealed that it can bloom at the subsurface water temperature of 22 °C increasing the risk of its development and expansion in lakes located in temperate climate regions.

Impact of nitrogen sources on gene expression and toxin production in the diazotroph Cylindrospermopsis raciborskii CS-505 and non-diazotroph Raphidiopsis brookii D9.

Different environmental nitrogen sources play selective roles in the development of cyanobacterial blooms and noxious effects are often exacerbated when toxic cyanobacteria are dominant. Cylindrospermopsis raciborskii CS-505 (heterocystous, nitrogen fixing) and Raphidiopsis brookii D9 (non-N2 fixing) produce the nitrogenous toxins cylindrospermopsin (CYN) and paralytic shellfish toxins (PSTs), respectively. These toxin groups are biosynthesized constitutively by two independent putative gene clusters, whose flanking genes are target for nitrogen (N) regulation. It is not yet known how or if toxin biosynthetic genes are regulated, particularly by N-source dependency. Here we show that binding boxes for NtcA, the master regulator of N metabolism, are located within both gene clusters as potential regulators of toxin biosynthesis. Quantification of intra- and extracellular toxin content in cultures at early stages of growth under nitrate, ammonium, urea and N-free media showed that N-sources influence neither CYN nor PST production. However, CYN and PST profiles were altered under N-free medium resulting in a decrease in the predicted precursor toxins (doCYN and STX, respectively). Reduced STX amounts were also observed under growth in ammonium. Quantification of toxin biosynthesis and transport gene transcripts revealed a constitutive transcription under all tested N-sources. Our data support the hypothesis that PSTs and CYN are constitutive metabolites whose biosynthesis is correlated to cyanobacterial growth rather than directly to specific environmental conditions. Overall, the constant biosynthesis of toxins and expression of the putative toxin-biosynthesis genes supports the usage of qPCR probes in water quality monitoring of toxic cyanobacteria.

Nutrient-related changes in the toxicity of field blooms of the cyanobacterium, Cylindrospermopsis raciborskii.

Nutrients have the capacity to change cyanobacterial toxin loads via growth-related toxin production, or shifts in the dominance of toxic and nontoxic strains. This study examined the effect of nitrogen (N) and phosphorus on cell division and strain-related changes in production of the toxins, cylindrospermopsins (CYNs) by the cyanobacterium, Cylindrospermopsis raciborskii. Two short-term experiments were conducted with mixed phytoplankton populations dominated by C. raciborskii in a subtropical reservoir where treatments had nitrate (NO3 ), urea (U) and inorganic phosphorus (P) added alone or in combination. Cell division rates of C. raciborskii were only statistically higher than the control on day 5 when U and P were co-supplied. In contrast, cell quotas of CYNs (QCYNS ) increased significantly in treatments where P was supplied, irrespective of whether N was supplied, and this increase was not necessarily related to cell division rates. Increased QCYNS did correlate with an increase in the proportion of the cyrA toxin gene to 16S genes in the C. raciborskii-dominated cyanobacterial population. Therefore, changes in strain dominance are the most likely factor driving differences in toxin production between treatments. Our study has demonstrated differential effects of nutrients on cell division and strain dominance reflecting a C. raciborskii population with a range of strategies in response to environmental conditions.

Comparative genomics of Cylindrospermopsis raciborskii strains with differential toxicities.

BACKGROUND: Cylindrospermopsis raciborskii is an invasive filamentous freshwater cyanobacterium, some strains of which produce toxins. Sporadic toxicity may be the result of gene deletion events, the horizontal transfer of toxin biosynthesis gene clusters, or other genomic variables, yet the evolutionary drivers for cyanotoxin production remain a mystery. Through examining the genomes of toxic and non-toxic strains of C. raciborskii, we hoped to gain a better understanding of the degree of similarity between these strains of common geographical origin, and what the primary differences between these strains might be. Additionally, we hoped to ascertain why some cyanobacteria possess the cylindrospermopsin biosynthesis (cyr) gene cluster and produce toxin, while others do not. It has been hypothesised that toxicity or lack thereof might confer a selective advantage to cyanobacteria under certain environmental conditions. RESULTS: In order to examine the fundamental differences between toxic and non-toxic C. raciborskii strains, we sequenced the genomes of two closely related isolates, CS-506 (CYN+) and CS-509 (CYN-) sourced from different lakes in tropical Queensland, Australia. These genomes were then compared to a third (reference) genome from C. raciborskii CS-505 (CYN+). Genome sizes were similar across all three strains and their G + C contents were almost identical. At least 2,767 genes were shared among all three strains, including the taxonomically important rpoc1, ssuRNA, lsuRNA, cpcA, cpcB, nifB and nifH, which exhibited 99.8-100% nucleotide identity. Strains CS-506 and CS-509 contained at least 176 and 101 strain-specific (or non-homologous) genes, respectively, most of which were associated with DNA repair and modification, nutrient uptake and transport, or adaptive measures such as osmoregulation. However, the only significant genetic difference observed between the two strains was the presence or absence of the cylindrospermopsin biosynthesis gene cluster. Interestingly, we also identified a cryptic secondary metabolite gene cluster in strain CS-509 (CYN-) and a second cryptic cluster common to CS-509 and the reference strain, CS-505 (CYN+). CONCLUSIONS: Our results confirm that the most important factor contributing to toxicity in C. raciborskii is the presence or absence of the cyr gene cluster. We did not identify any other distally encoded genes or gene clusters that correlate with CYN production. The fact that the additional genomic differences between toxic and non-toxic strains were primarily associated with stress and adaptation genes suggests that CYN production may be linked to these physiological processes.

Evidence for endogenous formation of the hepatocarcinogen N-nitrosodihydrouracil in rats treated with dihydrouracil and sodium nitrite: a potential source of human hepatic DNA carboxyethylation.

An earlier study demonstrated that hydrolysates of all human liver DNA samples analyzed contain the DNA adduct 7-(2'-carboxyethyl)guanine (7-CEGua) with an average level of 74.6 adducts per 10(9) nucleotides. One possible source of this DNA adduct would be endogenous nitrosation of the normal pyrimidine metabolites dihydrouracil (DHU) and ß-ureidopropionic acid (ß-UPA), yielding the corresponding nitroso compounds N-nitrosodihydrouracil, a potent hepatocarcinogen, and N-nitroso-ß-ureidopropionic acid. Another potential source would be reaction of endogenously formed acrylic acid with DNA. We tested these hypotheses in a study in which rats were treated with NaNO2 in the drinking water, alone, or in combination with dietary DHU or ß-UPA, or with acrylic acid in the drinking water, for either 2 or 4 weeks. Hepatic DNA from these rats was analyzed for 7-CEGua, using liquid chromatography-tandem mass spectrometry-selected reaction monitoring with confirmation by high resolution mass spectrometry. The results demonstrated consistent statistically significant increases of 7-CEGua in hepatic DNA of the rats treated with the combination of NaNO2 and DHU compared to the corresponding controls, while the other treatments gave variable results. These results support the hypothesis that endogenous nitrosation of DHU could be a major source of 7-CEGua in human hepatic DNA. Development of methodology for analysis of 7-CEGua in human leukocyte DNA is also reported, which will allow testing of this hypothesis in epidemiologic and clinical studies.

Characterization of Aphanizomenon ovalisporum amidinotransferase involved in cylindrospermopsin synthesis.

An increasing abundance of Aphanizomenon ovalisporum in water bodies from diverse world regions has been reported in the last few years, with the majority of the isolated strains producing the toxin cylindrospermopsin (CYN), leading to a rise in ecological and health risks. The understanding of CYN synthesis is crucial in the control of CYN production. An amidinotransferase (AMDT) seems to be the first enzyme involved in the synthesis of CYN. In this study, we have cloned and overexpressed the aoaA gene from the constitutive CYN producer A. ovalisporum UAM-MAO. The recombinant purified AoaA was characterized, confirming that it is an l-arginine:glycine AMDT. It shows an optimal activity between 32 and 37°C, at pH from 8 to 9. The activity exhibits a mixed (ping-pong/sequential) kinetic mechanism, and is inhibited by the reaction product guanidine acetate (GAA) in a noncompetitive manner. Mg(2+) stimulates AoaA activity while Co(2+) and Mn(2+) inhibit it. AoaA conserves the critical residues of the catalytic site and substrate specificity of AMDTs, as the previously reported AMDT from Cylindrospermopsis raciborskii Cyr. Both proteins can be included in a new group of prokaryotic AMDTs involved in CYN production.

Aphanizomenon gracile (Nostocales), a cylindrospermopsin-producing cyanobacterium in Polish lakes.

The cyanobacterial cytotoxin cylindrospermopsin (CYN) has become increasingly common in fresh waters worldwide. It was originally isolated from Cylindrospermopsis raciborskii in Australia; however, in European waters, its occurrence is associated with other cyanobacterial species belonging to the genera Aphanizomenon and Anabaena. Moreover, cylindrospermopsin-producing strains of widely distributed C. raciborskii have not yet been observed in European waters. The aims of this work were to assess the occurrence of CYN in lakes of western Poland and to identify the CYN producers. The ELISA tests, high-performance liquid chromatography (HPLC)-DAD, and HPLC-mass spectrometry (MS)/MS were conducted to assess the occurrence of CYN in 36 lakes. The cyrJ, cyrA, and pks genes were amplified to identify toxigenic genotypes of cyanobacteria that are capable of producing CYN. The toxicity and toxigenicity of the C. raciborskii and Aphanizomenon gracile strains isolated from the studied lakes were examined. Overall, CYN was detected in 13 lakes using HPLC-MS/MS, and its concentrations varied from trace levels to 3.0 µg L(-1). CYN was widely observed in lakes of western Poland during the whole summer under different environmental conditions. Mineral forms of nutrients and temperature were related to CYN production. The molecular studies confirmed the presence of toxigenic cyanobacterial populations in all of the samples where CYN was detected. The toxicity and toxigenicity analyses of isolated cyanobacteria strains revealed that A. gracile was the major producer of CYN.

Cylindrospermopsin: occurrence, methods of detection and toxicology.

Cyanobacteria are aquatic micro-organisms that pose a great threat to aquatic ecosystems by the production of dense blooms, but most importantly by the production of secondary metabolites, namely the cyanotoxins. One of these is cylindrospermopsin (CYN), a hepatotoxic polyketide-derived alkaloid with well-known associated cases of animal mortalities and human morbidity. First described as being associated with liver damage, this toxin is now considered a cytotoxic and a genotoxic toxin, due to its effects in other organs and in DNA. Its occurrence has been reported so far in eight different cyanobacteria species and in several water samples from four of the five continents. With a guideline value of 1 µg l(-1), CYN is now considered the second most studied cyanotoxin worldwide. It is important to review the information regarding the findings made until now about this cyanotoxin 30 years since its first report.