Biology subjects

Pacheco, A. B. F.

Publications and source records attributed to Pacheco, A. B. F..

3 recordsLinked to original sources

bioRxiv2025

Extracellular vesicles from saxitoxin-producing strains of the cyanobacterium Raphidiopsis raciborskii and investigation of their potential allelopathic effect

Raphidiopsis raciborskii is a filamentous cyanobacterium with global distribution in tropical and temperate climates. Toxic strains isolated in Latin America produce saxitoxins (STXs), which are neurotoxins that block voltage-gated ion channels in cells. This cyanobacterium can exert allelopathic effects on other phytoplankton species in response to resource competition through the secretion of substances that impair the target-cell physiology. Extracellular vesicles (EVs) constitute a secretion system that can transport biologically active molecules to distant targets in a protected, concentrated and targeted way. However, the role of EVs in cyanobacterial biology is poorly understood. We aimed to characterize R. raciborskii EVs and test whether this extracellular fraction or other exudate fractions contribute to its allelopathic effect. Exudates from two STX-producing R. raciborskii strains (T3 and CY-10) were subjected to filtration and divided into vesicular fractions (VF, >100 kDa, with EVs), which were concentrated by ultracentrifugation, and dissolved fractions (DF, <100 kDa, no EVs). Characterization of the VF through nanoparticle tracking analysis and transmission electron microscopy revealed spheric structures with diameters of 100-200 nm. Ratios of the number of EVs/cell were estimated as 21.54 {+/-} 1.33 for T3 and 8.79 {+/-} 0.38 for CY-10. The STX content of exudate fractions was determined by ELISA. Total extracellular STX concentrations (STX + neosaxitoxin (neoSTX)) were 170.64 ({+/-}15.43) pg.mL-1 for T3 and 913.84 ({+/-}226.87) pg.mL-1 for CY-10 and these values were similar to those of the DF (<100 kDa fraction). In the VF, STX concentrations were approximately 103-10 times lower. The estimation of toxin quotas (per biovolume) resulted in values 20-40 times lower in EVs (0.27{+/-}0,09 ng.mm-3 for T3 and 1.81{+/-}0.49 ng.mm-3 for CY-10) than in cells (13.05 {+/-}2.16 ng.mm-3 for T3 and 33.65 {+/-}7.31 ng.mm-3 for CY-10). A shift in the predominant analog between compartments was observed, with neoSTX prevailing in cells and STX in EVs. The CY-10 strain exhibited higher toxin concentrations than T3 in the VF, DF, total extracellular fraction and cellular fraction. The allelopathic effect of R. raciborskii exudate fractions was tested on the green algae Monoraphidium capricornutum. The total extracellular fraction and the DF equally inhibited M. capricornutum growth and photosynthesis, but the VF had no effect. Thus, the effect can be attributed to dissolved allelopathic compounds <100 kDa. These results open new opportunities to further investigate the role of EVs in the ecophysiology of R. raciborskii. HighlightsO_LIExtracellular vesicles (EVs) from two toxic strains of R. raciborskii were characterized; C_LIO_LISaxitoxins can be released within EVs; C_LIO_LIExtracellular saxitoxins content includes dissolved and vesicular fractions; C_LIO_LIWhile cyanobacterial EVs had no allelopathic effect the dissolved extracellular fraction (<100 kDa) of R. raciborskii did. C_LI

microbiology↗

bioRxiv2024

Physiological response of Microcystis aeruginosa exposed to aqueous extracts of Pistia stratiotes and Pontederia crassipes

Macrophyte extracts inhibit cyanobacteria growth, offering a sustainable solution for bloom control. The present study aimed to evaluate Microcystis aeruginosas response to aqueous extracts obtained from the dried biomass of Pistia stratiotes L. and Pontederia crassipes Mart. Solms. Physiological parameters analyzed included growth, photosynthesis, and antioxidative response. Reactive oxygen species generation and the chemical profile of the aqueous extracts were analyzed. At 4.0 g L-1, both extracts inhibited cyanobacterial growth in 6 days. P. stratiotes extract achieved 100% inhibition, while P. crassipes extract reached 60%. P. stratiotes extract showed higher photosynthetic inhibition (99% vs. 12% for P. crassipes). This was related to the downregulation of the psbA gene (coding for the photosystem II protein D1). Exposure to both extracts increased intracellular reactive oxygen species content in cyanobacterial cells and increased peroxiredoxin gene (prxA) transcripts. This response was not noted for sod (superoxide dismutase) transcripts, although SOD enzymatic activity increased in cultures exposed to P. stratiotes extracts. Upon incubation of the macrophyte extracts with M. aeruginosa cultures, phenol concentrations decreased, and their general metabolic profile changed. Thus, P. stratiotes extract outperformed P. crassipes, inhibiting M. aeruginosa growth, affecting photosystem II, and inducing oxidative stress. HighlightsO_LIAqueous extracts from dried biomass of P. stratiotes and P. crassipes inhibited M. aeruginosa growth. C_LIO_LIP. stratiotes extract suppressed photosystem II activity, while P. crassipes did not C_LIO_LIBoth extracts elicited ROS production in cells. C_LIO_LIPeroxiredoxin gene expression upregulated by extract exposure. C_LIO_LIP. stratiotes extract increased SOD activity in cells. C_LI

microbiology↗

bioRxiv2024

WHO WINS? COMPARISON BETWEEN EMERGENT MACROPHYTES AND PONTEDERIA CRASSIPES (WATER HYACINTH) AS NATURE-BASED SOLUTIONS FOR NUTRIENT PHYTOREMEDIATION AND CYANOBACTERIA MITIGATION

AO_SCPLOWBSTRACTC_SCPLOWEmergent macrophytes are commonly used to control eutrophication in Constructed Floating Wetlands (CFW) systems. However, tropical emergent macrophyte species, particularly from South America, are underrepresented in these applications. This study aims to investigate the potential of five emergent macrophytes, Alternanthera philoxeroides, Ludwigia leptocarpa, Polygonum ferrugineum, Typha domingensis, and Urochloa mutica in controlling eutrophication and inhibiting cyanobacterial growth, compared to the floating macrophyte Pontederia crassipes, the most studied macrophyte for this purpose. Phytoremediation experiments were performed ex-situ in mesocosms (50 L) with high soluble reactive phosphorus (SRP) concentration (400 {micro}g L-1). Allelopathic effects of the macrophytes root exudates on cyanobacteria were tested in vitro using a strain of Microcystis aeruginosa. While P. crassipes reduced SRP concentration by 86% in 14 days, the tested macrophytes reduced SRP concentration by > 94%, except for T. domingensis, which showed a reduction of 64%. NH4+ and NO3- removal in 14 days were 96% and 62%, respectively, for P. crassipes. These values corresponded to 96% and 63% for the five tested macrophytes. Root exudates of A. philoxeroides, L. leptocarpa, and P. ferrugineum caused inhibition of M. aeruginosa growth with no detection of Chl-a after 7 days. Thus, three emergent macrophytes were more efficient in removing nutrients than P. crassipes. and showed allelopathic potential against cyanobacteria, indicating that using local emergent macrophytes in CFW systems can be a valuable and sustainable tool to mitigate eutrophication and its consequences in aquatic environments. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/603719v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@e09e31org.highwire.dtl.DTLVardef@b1d4a7org.highwire.dtl.DTLVardef@1003e0borg.highwire.dtl.DTLVardef@e97e22_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIEmergent macrophytes were similarly efficient to P. crassipes in nutrient removal C_LIO_LILudwigia leptocarpa was the most efficient in SRP removal in 7 days C_LIO_LIAllelopathy on cyanobacterium M. aeruginosa by A. philoxeroides, L. leptocarpa, and P. ferrugineum root exudates C_LIO_LIAdapting emergent macrophytes in CFW structures can be helpful in in situ phytoremediation. C_LI SO_SCPLOWTATEMENTC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWOFC_SCPLOW NO_SCPLOWOVELTYC_SCPLOWThis study lies in its comparative analysis of underrepresented tropical emergent macrophytes from South America against the widely studied floating macrophyte, Pontederia crassipes (water hyacinth). By focusing on these local emergent macrophytes, the research addresses a significant knowledge gap. It provides insights into their potential application in Constructed Floating Wetlands (CFWs) for nutrient removal and cyanobacteria control. Key findings demonstrate that the selected emergent macrophytes outperform P. crassipes in reducing soluble reactive phosphorus (SRP) concentrations and exhibit substantial nitrogen removal efficiencies. Furthermore, the allelopathic potential of A. philoxeroides, L. leptocarpa, and P. ferrugineum against the harmful cyanobacterium Microcystis aeruginosa showcases their dual functionality in mitigating eutrophication and inhibiting harmful algal blooms.

ecology↗