Samuel Cirés

Natural Photodegradation of the Cyanobacterial Toxins Microcystin and Cylindrospermopsin

Microcystins (MC) and cylindrospermopsin (CYN) are potent toxins produced by diverse cyanobacterial genera found in waterbodies throughout the world. In the present study, and in order to achieve a better understanding of the fate of cyanobacterial toxins in the environment, we assessed the photodegradation of MC and CYN along the water column and by different radiation bands of the natural solar spectrum: photosynthetic active radiation (PAR), UV-A, and UV-B. Photodegradation of CYN seemed to be highly dependent on UV-A and was very low under natural conditions. This fact could be one of the reasons explaining the high extracellular CYN concentration found in diverse waterbodies. Microcystin photodegradation was higher, all three radiation bands (PAR, UV-A, and UV-B) being responsible for its degradation, although PAR and UV-A were more efficient because of their high natural irradiance. Modeling of MC photodegradation along the watercolumn was performed, using specific MC breakdown rates for the different radiation bands and including calculated attenuation coefficients for these bands. As a result, we suggest that rapid and efficient MC photodegradation may be expected in shallow systems or thin mixed layers.

Review of Sustainable Methane Mitigation and Biopolymer Production

Biological methane (CH4) mitigation combined with biopolymer (PHA-polyhydroxyalkaonate/PHB-polyhydroxybutyrate) production is a viable option in this fossil fuel-constrained era. Methantrophs are bacteria that can re-route CH4 into PHA/PHB under nutrient-starved conditions. However, most studies (up to 90%) investigated pure cultures to demonstrate capacity for PHA/PHB accumulation, which on an industrial scale is unlikely to be serviceable. Furthermore, commercialization is handicapped as there are still a number of unresolved issues which affect productivities, such as optimized process variables, characterization of robust consortia, and optimized reactor design. This review will summarize existing knowledge and highlight research needs to fast track methanotrophic PHA/PHB production from CH4.

A review of the phylogeny, ecology and toxin production of bloom-forming Aphanizomenon spp. and related species within the Nostocales (cyanobacteria)

The traditional genus Aphanizomenon comprises a group of filamentous nitrogen-fixing cyanobacteria of which several memebers are able to develop blooms and to produce toxic metabolites (cyanotoxins), including hepatotoxins (microcystins), neurotoxins (anatoxins and saxitoxins) and cytotoxins (cylindrospermopsin). This genus, representing geographically widespread and extensively studied cyanobacteria, is in fact heterogeneous and composed of at least five phylogenetically distant groups (Aphanizomenon, Anabaena/Aphanizomenon like cluster A, Cuspidothrix, Sphaerospermopsis and Chrysosporum) whose taxonomy is still under revision. This review provides a thorough insight into the phylogeny, ecology, biogeography and toxicogenomics (cyr, sxt, and ana genes) of the five best documented Aphanizomenon species with special relevance for water risk assessment: Aphanizomenon flos-aquae, Aphanizomenon gracile, Cuspidothrix issatschenkoi, Sphaerospermopsis aphanizomenoides and Chrysosporum ovalisporum. Aph. flos-aquae, Aph. gracile and C. issatschenkoi have been reported from temperate areas only whereas S. aphanizomenoides shows the widest distribution from the tropics to temperate areas. Ch. ovalisporum is found in tropical, subtropical and Mediterranean areas. While all five species show moderate growth rates (0.1-0.4day-1) within a wide range of temperatures (15-30°C), Aph. gracile and A. flos-aquae can grow from around (or below) 10°C, whereas Ch. ovalisporum and S. aphanizomenoides are much better competitors at high temperatures over 30°C or even close to 35°C. A. gracile has been confirmed as the producer of saxitoxins and cylindrospermopsin, C. issatschenkoi of anatoxins and saxitoxins and Ch. ovalisporum of cylindrospermopsin. The suspected cylindrospermopsin or anatoxin-a production of A. flos-aquae or microcystin production of S. aphanizomenoides is still uncertain. This review includes a critical discussion on the the reliability of toxicity reports and on the invasive potential of Aphanizomenon species in a climate change scenario, together with derived knowledge gaps and research needs. As a whole, this work is intended to represent a key reference for scientists and water managers involved in the major challenges of identifying, preventing and mitigating toxic Aphanizomenon blooms.

Diversity of toxin and non-toxin containing cyanobacterial mats of meltwater ponds on the Antarctic Peninsula: a pyrosequencing approach

Abstract Despite their pivotal role as primary producers, there is little information as to the diversity and physiology of cyanobacteria in the meltwater ecosystems of polar regions. Thirty cyanobacterial mats from Adelaide Island, Antarctica were investigated using 16S rRNA gene pyrosequencing and automated ribosomal intergenic spacer analysis, and screened for cyanobacterial toxins using molecular and chemical approaches. A total of 274 operational taxonomic units (OTUs) were detected. The richness ranged between 8 and 33 cyanobacterial OTUs per sample, reflecting a high mat diversity. Leptolyngbya and Phormidium (c. 55% and 37% of the OTUs per mat) were dominant. Cyanobacterial community composition was similar between mats, particularly those obtained from closely adjacent locations. The cyanotoxin microcystin was detected in 26 of 27 mats (10–300 ng g-1 organic mass), while cylindrospermopsin, detected for the first time in Antarctica, was present in 21 of 30 mats (2–156 ng g-1 organic mass). The latter was confirmed via liquid chromatography-mass spectrometry and by the presence of the cyrAB and cyrJ genes. This study demonstrates the usefulness of pyrosequencing for characterizing diverse cyanobacterial communities, and confirms that cyanobacteria from extreme environments produce a similar range of cyanotoxins as their temperate counterparts.

First report of microcystin-producing Fischerella sp. (Stigonematales, Cyanobacteria) in tropical Australia

A polyphasic study of four Stigonematales cyanobacteria from tropical Australia (Queensland) revealed production of the hepatotoxins microcystins (MC-LR, MC-LA, MC-LF, MC-FR and demethyl-MC-LR) by Fischerella sp. NQAIF311 isolated from a seasonal creek. Total microcystin content reached 43xa0μgxa0g(-1) dry weight. Phylogeny demonstrated high sequence similarities for 16S rRNA (99%), mcyE (97%) and mcyD (95%) genes with microcystin-producing Fischerella sp. CENA161 from Brazil. This is the first report of a cyanotoxin-producing Stigonematal in Australia.

Limited Stability of Microcystins in Oligopeptide Compositions of Microcystis aeruginosa (Cyanobacteria): Implications in the Definition of Chemotypes

The occurrence of diverse oligopeptides in cyanobacteria, including the cyanotoxins microcystins, has been recently used to classify individual clones into sub-specific oligopeptide chemotypes, whose composition and dynamics modulate microcystin concentrations in cyanobacterial blooms. Cyanobacterial chemotyping allows the study of the ecology of chemotypical subpopulations, which have been shown to possess dissimilar ecological traits. However, the stability of chemotypes under changing abiotic conditions is usually assumed and has not been assessed in detail. We monitored oligopeptide patterns of three strains of Microcystis aeruginosa under different nutrient and light conditions. MALDI-TOF MS revealed alterations in the microcystins signatures under N and P poor conditions and high light intensities (150 and 400 μmol photons m−2s−1). Variations in the general oligopeptide composition were caused by a gradual disappearance of microcystins with low relative intensity signals from the fingerprint. The extent of such variations seems to be closely related to physiological stress caused by treatments. Under identical clonal compositions, alterations in the oligopeptide fingerprint may be misinterpreted as apparent shifts in chemotype succession. We discuss the nature of such variations, as well as the consequent implications in the use of cyanobacterial chemotyping in studies at the subpopulation level and propose new guidance for the definition of chemotypes as a consistent subpopulation marker.

Culture scale-up and immobilisation of a mixed methanotrophic consortium for methane remediation in pilot-scale bio-filters

ABSTRACT Robust methanotrophic consortia for methane (CH4) remediation and by-product development are presently not readily available for industrial use. In this study, a mixed methanotrophic consortium (MMC), sequentially enriched from a marine sediment, was assessed for CH4 removal efficiency and potential biomass-generated by-product development. Suitable packing material for bio-filters to support MMC biofilm establishment and growth was also evaluated. The enriched MMC removed ∼7–13% CH4 under a very high gas flow rate (2.5u2005Lu2005min−1; 20–25% CH4) in continuous-stirred tank reactors (∼10u2005L working volume) and the biomass contained long-chain fatty acids (i.e. C16 and C18). Cultivation of the MMC on plastic bio-balls abated ∼95–97% CH4 in pilot-scale non-sterile outdoor-operated bio-filters (0.1u2005Lu2005min−1; 1% CH4). Contamination by cyanobacteria had beneficial effects on treating low-level CH4, by providing additional oxygen for methane oxidation by MMC, suggesting that the co-cultivation of MMC with cyanobacterial mats does not interfere with and may actually be beneficial for remediation of CH4 and CO2 at industrial scale.

Variability in the sxt gene clusters of PSP toxin producing Aphanizomenon gracile strains from Norway, Spain, Germany and North America

Paralytic shellfish poisoning (PSP) toxin production has been detected worldwide in the cyanobacterial genera Anabaena, Lyngbya, Scytonema, Cuspidothrix and Aphanizomenon. In Europe Aphanizomenon gracile and Cuspidothrix issatschenkoi are the only known producers of PSP toxins and are found in Southwest and Central European freshwater bodies. In this study the PSP toxin producing Aphanizomenon sp. strain NIVA-CYA 851 was isolated from the Norwegian Lake Hillestadvannet. In a polyphasic approach NIVA-CYA 851 was morphologically and phylogenetically classified, and investigated for toxin production. The strain NIVA-CYA 851 was identified as A. gracile using 16S rRNA gene phylogeny and was confirmed to produce neosaxitoxin, saxitoxin and gonyautoxin 5 by LC-MS. The whole sxt gene clusters (circa 27.3 kb) of four A. gracile strains: NIVA-CYA 851 (Norway); NIVA-CYA 655 & NIVA-CYA 676 (Germany); and UAM 529 (Spain), all from latitudes between 40° and 59° North were sequenced and compared with the sxt gene cluster of reference strain A. gracile NH-5 from the USA. All five sxt gene clusters are highly conserved with similarities exceeding 99.4%, but they differ slightly in the number and presence of single nucleotide polymorphisms (SNPs) and insertions/deletions (In/Dels). Altogether 178 variable sites (44 SNPs and 4 In/Dels, comprising 134 nucleotides) were found in the sxt gene clusters of the Norwegian, German and Spanish strains compared to the reference strain. Thirty-nine SNPs were located in 16 of the 27 coding regions. The sxt gene clusters of NIVA-CYA 851, NIVA-CYA 655, NIVA-CYA 676 and UAM 529, were characterized by 15, 16, 19 and 23 SNPs respectively. Only the Norwegian strain NIVA-CYA 851 possessed an insertion of 126 base pairs (bp) in the noncoding area between the sxtA and sxtE genes and a deletion of 6 nucleotides in the sxtN gene. The sxtI gene showed the highest variability and is recommended as the best genetic marker for further phylogenetic studies of the sxt gene cluster of A. gracile. This study confirms for the first time the role of A. gracile as a PSP toxin producer in Norwegian waters, representing the northernmost occurrence of PSP toxin producing A. gracile in Europe known so far.

Toxicity at the Edge of Life: A Review on Cyanobacterial Toxins from Extreme Environments

Cyanotoxins are secondary metabolites produced by cyanobacteria, of varied chemical nature and toxic effects. Although cyanobacteria thrive in all kinds of ecosystems on Earth even under very harsh conditions, current knowledge on cyanotoxin distribution is almost restricted to freshwaters from temperate latitudes. In this review, we bring to the forefront the presence of cyanotoxins in extreme environments. Cyanotoxins have been reported especially in polar deserts (both from the Arctic and Antarctica) and alkaline lakes, but also in hot deserts, hypersaline environments, and hot springs. Cyanotoxins detected in these ecosystems include neurotoxins—anatoxin-a, anatoxin-a (S), paralytic shellfish toxins, β-methylaminopropionic acid, N-(2-aminoethyl) glycine and 2,4-diaminobutyric acid- and hepatotoxins –cylindrospermopsins, microcystins and nodularins—with microcystins being the most frequently reported. Toxin production there has been linked to at least eleven cyanobacterial genera yet only three of these (Arthrospira, Synechococcus and Oscillatoria) have been confirmed as producers in culture. Beyond a comprehensive analysis of cyanotoxin presence in each of the extreme environments, this review also identifies the main knowledge gaps to overcome (e.g., scarcity of isolates and –omics data, among others) toward an initial assessment of ecological and human health risks in these amazing ecosystems developing at the very edge of life.

First outdoor cultivation of the N2-fixing cyanobacterium Tolypothrix sp. in low-cost suspension and biofilm systems in tropical Australia

Tropical N2-fixing cyanobacteria offer an attractive alternative for production of biomass and bioproducts with potentially low cultivation and harvesting costs. The present study evaluated the biomass productivity of the N2-fixing cyanobacterium Tolypothrix sp. NQAIF319 grown in nitrogen-free medium in outdoor suspension and biofilm prototype cultivation systems in tropical Australia (Queensland). One-weekxa0cycles yielded maximum biomass productivities—estimated based on ground area occupied by single systems—of 45–49xa0gxa0dry weightxa0m−2xa0day−1 (suspension) and 1.0–1.2xa0gxa0dryxa0weightxa0m−2xa0day−1 (biofilm) with minimal biological contamination (Tolypothrix sp. biomass representing 94–98xa0% of the photosynthetic community). Moderate productivities of the pigments phycocyanin/phycoerythrin (0.1–2.8xa0gxa0m−2xa0day−1), fatty acids (0.1–2.0xa0gxa0m−2xa0day−1), and nitrogen stored in the biomass (0.1–5.9xa0gxa0m−2xa0day−1) were reached in biofilm and suspension systems, respectively, opening avenues for production of low-value commodities with potentially big markets (nitrogen-rich biofertilizers and aquaculture feed) and higher-value chemicals (phycobiliproteins and fatty acids). Simulated multi-system arrangements yielded theoretical overall areal productivities four to six times lower than those in single systems thus highlighting the need for future tests fine-tuning inter-system separation to minimize shadowing while maximizing the efficiency in land use in larger-scale production plants. Biofilm and self-flocculated biomass showed 80-fold and 53-fold reduced extracellular-water contents compared to suspension cultures, respectively, which will need to be considered for techno-economic and water/carbon footprint evaluation of each of the possible bioproduct synthesis pathways. In conclusion, the flexible and simple prototypes developed together with the good properties of Tolypothrix sp. represent a promising platform for low-cost production of cyanobacterial bioproducts in tropical regions using low nitrogen-containing water sources.