Trace metal concentrations in the abiotic and biotic components of River Rwizi ecosystem in western Uganda, and the risks to human health

Alleviation of H2O2 toxicity by extracellular catalases in the phycosphere of Microcystis aeruginosa

High levels of environmental H2O2 represent a threat to many freshwater bacterial species, including toxic-bloom-forming Microcystis aeruginosa, particularly under high-intensity light conditions. The highest extracellular catalase activity-possessing Pseudoduganella aquatica HC52 was chosen among 36 culturable symbiotic isolates from the phycosphere in freshly collected M. aeruginosa cells. A zymogram for catalase activity revealed the presence of only one extracellular catalase despite the four putative catalase genes (katA1, katA2, katE, and srpA) identified in the newly sequenced genome (∼6.8 Mb) of P. aquatica HC52. Analysis of secreted catalase using liquid chromatography-tandem mass spectrometry was identified as KatA1, which lacks a typical signal peptide, although the underlying mechanism for its secretion is unknown. The expression of secreted KatA1 appeared to be induced in the presence of H2O2. Proteomic analysis also confirmed the presence of KatA1 inside the outer membrane vesicles secreted by P. aquatica HC52 following exposure to H2O2. High light intensities (> 100 µmol m-2 s-1) are known to kill catalase-less axenic M. aeruginosa cells, but the present study found that the presence of P. aquatica cells supported the growth of M. aeruginosa, while the extracellular catalases in supernatant or purified form also sustained the growth of M. aeruginosa under the same conditions. Our results suggest that the extracellular catalase secreted by P. aquatica HC52 enhances the tolerance of M. aeruginosa to H2O2, thus promoting the formation of M. aeruginosa blooms under high light intensities.

Spatial Distribution, Potential Risks and Source Identification of Heavy Metals in the Coastal Sediments of the Northern Beibu Gulf, South China Sea

Thirty samples of surface sediments (0-5 cm) from the northern Beibu Gulf were analyzed to determine the spatial distribution, potential risks and sources of six heavy metals (Cr, Cu, Zn, As, Cd and Pb). The concentrations (mg/kg, dw) of Cr, Cu, Zn, As, Cd and Pb were 15.38 ± 6.06, 6.54 ± 3.23, 41.86 ± 17.03, 6.92 ± 2.75, 0.04 ± 0.02 and 17.13 ± 6.38, respectively. Higher levels of Cr, Cu, Cd and Zn were observed in the western part of the study area. According to the potential ecological risk indexes and sediment quality guidelines, the measured metals were assessed at low contamination levels, with Pb posing the largest ecological risks. The results of positive matrix factorization (PMF) indicated that Cr and Zn mainly originated from natural geological background sources, while Cu, As, Cd and Pb were influenced by anthropogenic sources such as atmospheric deposition and anthropogenic activities. These three sources contributed 60.4%, 28.1% and 11.5% of the heavy metals, respectively. In addition, further research should be conducted focusing on the general relationships between As and various controls in sediments of the northern Beibu Gulf.

Occurrence, contamination level and ecological risk assessment of dissolved and particulate trace elements in rivers entering the southwestern Mediterranean Sea

Metal pollution in rivers should not be overlooked before their entry into the sea. However, there are few studies for estimating such contamination in rivers entering the Algerian coastal waters. Semimonthly quantification of dissolved and particulate metals, near the mouths of two industrial-tainted rivers, El Harrach and Mazafran rivers, was carried out during a period of one year. All the trace metals analyzed are originating from anthropogenic sources (EF > 1.5), with higher contamination of dissolved Pb, Cd, Zn and Ni and a slight degree of contamination of particulate Cu and Zn (0 < I_geo < 1). Particulate metals show a stable complex with the particulate phase (e.g. 2 < LogK_d < 6). The risk assessment results indicate that particulate Pb and Zn have a 33% likelihood of toxicity for adverse biological effects. A significant toxicity effect (ΣTUi >4) of the combined particulate metals (Pb, Cd, Cu, Zn, Cr, Ni and As) was primarily due to the higher particulate Cd, Zn, and Cr availability.