Production of methylmercury by sulphate-reducing bacteria in sediments from the orbetello lagoon in presence of high macroalgal loads

Abstract

Methylmercury is a potent neurotoxin affecting shallow-water ecosystems. Mercury polluted sediment samples were collected at six different sites in the Orbetello Lagoon (central Italy) characterized by high levels of silt, iron, manganese hydroxides, and organic matter originated the latter originated from the decomposition of macroalgae. Porous water pointed out the presence of sulphates, methylmercury, and sulphides. Slurries arranged in anaerobic conditions from sediment aliquots from the six sites, with the addition of ionic mercury, highlighted the production of methylmercury. Sulphate reducing bacteria (SRB) were quantified in lagoon sediments; furthermore, sediments cultured under anaerobic conditions showed SRBs active in mercury methylation. Anaerobic cultures of SRB, amended with ionic mercury, produced methylmercury during the growth of bacterial cells. The percentage of aerobic mercury resistant bacteria was pointed out at each sampling site, evidencing the presence of bioavailable mercury. Several aerobic mercury resistant bacteria were isolated and their level of resistance to inorganic and organic forms of mercury was evaluated. These isolates may be potentially used for eventual bioremediation processes. Mercury methylation by SRB in the Orbetello Lagoon sediments was described for the first time, focusing the attention on the need for possible bioremediation processes by using autochthonous mercury resistant bacteria. Moreover, the influence of algal biomass on mercury methylation was highlighted for the first time in this lagoon ecosystem. The importance of removing algal biomass, as it represents a source of organic matter favouring the process of mercury methylation, was strongly pointed out in this study.

Navigating a Microplastic Sea: How the Pacific Cupped Oyster (Magallana gigas) Respond to Microplastic Pollution in Lagoons

“…The lagoon’s shallow brackish waters, limited circulation, low volume, and partial isolation from the sea hinder its ability to dilute nutrients and contaminants from urban, aquacultural, and agricultural sources. Sediment analysis has revealed elevated levels of trace elements like arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc [ 30 ]. In contrast, the Varano Lagoon, situated on the northern coast of the Gargano Promontory in the Southern Adriatic Sea, covers 6500 ha with an average depth of 4 m. It is partially isolated by coastal barriers, with communication to the sea facilitated by channels influenced by tidal and wind dynamics.…”

“…Following this, the length of each specimen was measured using calipers (precision ± 0.1 mm). The Orbetello Lagoon, located on the west coast of Tuscany, spans approximately 2300 ha with an average depth of 1 m. It has been extensively studied due to its exposure to both natural and human-induced pressures [30]. Eutrophication is a significant issue in this coastal lagoon, exacerbated by the coexistence of various submerged vegetation types, resulting in uneven biomass decomposition and phanerogam seed dispersal.…”

“…After acclimation, oysters from Orbetello and Varano were assigned to specific treatment groups, following a 2 (location) × 3 (color) × 3 (replicates) design, resulting in 18 treatment groups and one set of negative control triplicates. Each oyster was exposed to its allocated treatment in an individual glass jar The Orbetello Lagoon, located on the west coast of Tuscany, spans approximately 2300 ha with an average depth of 1 m. It has been extensively studied due to its exposure to both natural and human-induced pressures [30]. Eutrophication is a significant issue in this coastal lagoon, exacerbated by the coexistence of various submerged vegetation types, resulting in uneven biomass decomposition and phanerogam seed dispersal.…”

Electronic Nose (E-Nose) for Quality Detection of Tuna (Thunnus thynnus) Contaminated Bacteria

“…Each gas sensor will respond to aroma or odor by changing its resistance. 19 Each gas sensor's resistance will fluctuate, changing the voltage as a result. This voltage changes yielded data in the form of digital computer data.…”