title: Manila clams from Hg polluted sediments of Marano and Grado lagoons (Italy) harbor detoxifying Hg resistant bacteria in soft tissues.
abstract: A mechanism of mercury detoxification has been suggested by a previous study on Hg bioaccumulation in Manila clams (Ruditapes philippinarum) in the polluted Marano and Grado lagoons and in this study we demonstrate that this event could be partly related to the detoxifying activities of Hg-resistant bacteria (MRB) harbored in clam soft tissues. Therefore, natural clams were collected in six stations during two different periods (winter and spring) from Marano and Grado Lagoons. Siphons, gills and hepatopancreas from acclimatized clams were sterile dissected to isolate MRB. These anatomical parts were glass homogenized or used for whole, and they were lying on a solid medium containing 5mgl(-1) HgCl2 and incubated at 30°C. A total of fourteen bacterial strains were isolated and were identified by 16S rDNA sequencing and analysis, revealing that strains were representative of eight bacterial genera, four of which were Gram-positive (Enterococcus, Bacillus, Jeotgalicoccus and Staphylococcus) and other four were Gram-negative (Stenotrophomonas, Vibrio, Raoultella and Enterobacter). Plasmids and merA genes were found and their sequences determined. Fluorescence in situ hybridization (FISH) technique shows the presence of Firmicutes, Actinobacteria and Gammaproteobacteria by using different molecular probes in siphon and gills. Bacterial clumps inside clam flesh were observed and even a Gram-negative endosymbiont was disclosed by transmission electronic microscope inside clam cells. Bacteria harbored in cavities of soft tissue have mercury detoxifying activity. This feature was confirmed by the determination of mercuric reductase in glass-homogenized siphons and gills.
authors: Dipartimento di Scienze Molecolari e Nanosistemi, Cà Foscari University of Venice, Dorsoduro 2137, 30123 Venice, Italy. baldi@unive.it
authors: Franco
authors: F
authors: Baldi
authors: Michele
authors: M
authors: Gallo
authors: Davide
authors: D
authors: Marchetto
authors: Claudia
authors: C
authors: Faleri
authors: Isabel
authors: I
authors: Maida
authors: Renato
authors: R
authors: Fani
mesh_terms: D000818:Animals; D001419:Bacteria / Q000235:genetics*; D001483:Base Sequence; D049872:Bivalvia / Q000378:metabolism* / Q000382:microbiology*; D016000:Cluster Analysis; D019295:Computational Biology; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics*; D004784:Environmental Monitoring / Q000379:methods / Q000706:statistics & numerical data*; D019015:Geologic Sediments / Q000032:analysis; D005880:Gills / Q000378:metabolism / Q000382:microbiology / Q000648:ultrastructure; D043143:Hepatopancreas / Q000378:metabolism / Q000382:microbiology; D017404:In Situ Hybridization, Fluorescence; D007558:Italy; D008522:Mediterranean Sea; D008628:Mercury / Q000032:analysis / Q000493:pharmacokinetics*; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D017931:DNA Primers; D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D010088:Oxidoreductases; C021551:mercuric reductase; D008628:Mercury
keywords: Clams; Hg detoxification; Hg-resistant bacteria; Lagoon