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

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

Sometimes Sperm Whales (Physeter macrocephalus) Cannot Find Their Way Back to the High Seas: A Multidisciplinary Study on a Mass Stranding

BACKGROUND: Mass strandings of sperm whales (Physeter macrocephalus) remain peculiar and rather unexplained events, which rarely occur in the Mediterranean Sea. Solar cycles and related changes in the geomagnetic field, variations in water temperature and weather conditions, coast geographical features and human activities have been proposed as possible causes. In December 2009, a pod of seven male sperm whales stranded along the Adriatic coast of Southern Italy. This is the sixth instance from 1555 in this basin. METHODOLOGY/PRINCIPAL FINDINGS: Complete necropsies were performed on three whales whose bodies were in good condition, carrying out on sampled tissues histopathology, virology, bacteriology, parasitology, and screening of veins looking for gas emboli. Furthermore, samples for age determination, genetic studies, gastric content evaluation, stable isotopes and toxicology were taken from all the seven specimens. The animals were part of the same group and determined by genetic and photo-identification to be part of the Mediterranean population. Causes of death did not include biological agents, or the "gas and fat embolic syndrome", associated with direct sonar exposure. Environmental pollutant tissue concentrations were relatively high, in particular organochlorinated xenobiotics. Gastric content and morphologic tissue examinations showed a prolonged starvation, which likely caused, at its turn, the mobilization of lipophilic contaminants from the adipose tissue. Chemical compounds subsequently entered the blood circulation and may have impaired immune and nervous functions. CONCLUSIONS/SIGNIFICANCE: A multi-factorial cause underlying this sperm whales' mass stranding is proposed herein based upon the results of postmortem investigations as well as of the detailed analyses of the geographical and historical background. The seven sperm whales took the same "wrong way" into the Adriatic Sea, a potentially dangerous trap for Mediterranean sperm whales. Seismic surveys should be also regarded as potential co-factors, even if no evidence of direct impact has been detected

Production of methyl mercury by sulphate-reducing bacteria in sediments from the Orbetello lagoon in presence of high macroalgal loads

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 stud