Bacterial community structure and activity in fish farm sediments of the Ligurian sea (Western Mediterranean)

The environmental impact of a well-established fish farm has beeninvestigated in surface sediments of the Ligurian Sea in order to assess thebiodeposition, bacterial community structure and dynamics at a mature stage oforganic enrichment.The Biopolymeric carbon (BPC) fraction of organic matter and phytopigmentconcentrations displayed very high values beneath the fish cages. In particularlipid, carbohydrate and chlorophyll-a concentrations werehigher in farm sediment while protein concentrations did not show significantchange between farm sediment and control.Benthic bacteria were closely related to organic enrichment and their densitywas three times higher (up to 3 × 1010 cellsg–1) in stations beneath the cages being positivelycorrelated with BPC (n = 10, p < 0.05) and lipid (n = 10, p < 0.05)concentrations. Colony forming units (CFU) counts of heterotrophic bacteriaindicate a shift in the relative importance of the gram negative bacterialfraction, displaying the predominance of theCytophaga/Flexibacter-like bacteria (CBF), as well as theoccurrence of pathogenic bacteria (such as Vibrio) insediments beneath the farm. In contrast, Gram positive bacteria were moreprevalent in control site where they represented up to 90% of total isolates.Aminopeptidase activity displayed higher values in sediment beneath the cages,whereas the enzymatic activity per bacterial cell was lower. These data suggesta functional stress of bacterial degradation rates and represent a potentialvaluable environmental index of imbalance between supply and removal of organicmatter in eutrophicated environments.Data presented in this study also suggest that either the biochemicalcomposition of sedimentary organic matter as well as the selected microbialvariables may represent useful tools for evaluating the effects of organicenrichment due to fish farming and could be proposed as new environmentalindices of aquaculture impact on marine sediment

Bacterial community structure and activity in fish farm sediments of the Ligurian Sea (Western Mediterranean)

The environmental impact of a well-established fish farm has been investigated in surface sediments of the Ligurian Sea in order to assess the biodeposition, bacterial community structure and dynamics at a mature stage of organic enrichment. The Biopolymeric carbon (BPC) fraction of organic matter and phytopigment concentrations displayed very high values beneath the fish cages. In particular lipid, carbohydrate and chlorophyll-a concentrations were higher in farm sediment while protein concentrations did not show significant change between farm sediment and control. Benthic bacteria were closely related to organic enrichment and their density was three times higher (up to 3 7 1010 cells g 121) in stations beneath the cages being positively correlated with BPC (n = 10, p < 0.05) and lipid (n = 10, p < 0.05) concentrations. Colony forming units (CFU) counts of heterotrophic bacteria indicate a shift in the relative importance of the gram negative bacterial fraction, displaying the predominance of the Cytophaga/Flexibacter-like bacteria (CBF), as well as the occurrence of pathogenic bacteria (such as Vibrio) in sediments beneath the farm. In contrast, Gram positive bacteria were more prevalent in control site where they represented up to 90% of total isolates. Aminopeptidase activity displayed higher values in sediment beneath the cages, whereas the enzymatic activity per bacterial cell was lower. These data suggest a functional stress of bacterial degradation rates and represent a potential valuable environmental index of imbalance between supply and removal of organic matter in eutrophicated environments. Data presented in this study also suggest that either the biochemical composition of sedimentary organic matter as well as the selected microbial variables may represent useful tools for evaluating the effects of organic enrichment due to fish farming and could be proposed as new environmental indices of aquaculture impact on marine sediment

Characterisation and antimicrobial activity of epibiotic bacteria from Petrosia ficiformis (Porifera, Demospongiae)

Numerous natural products from marine invertebrates show striking structural similarities to known metabolites of microbial origin, suggesting that microorganisms (bacteria, microalgae) are at least involved in their biosynthesis or are in fact the true sources of these respective metabolites. The viable epibiotic microbial community of the marine sponge Petrosia ficiformis was screened and characterised using classical and molecular techniques. Fifty-seven aerobic heterotrophic bacterial strains were isolated and presumptively identified by their phenotypic characters. Random Amplified Polymorphic DNA (RAPD) analysis of the non-fermentative Gram-negative strains and Corynebacteria was performed. Cluster analysis of RAPD data showed genetic relatedness among sponge isolates. Antimicrobial activity was found in several isolates, two of which were identified as Rhodococcus sp. and Pseudomonas sp. by partial 16S rRNA gene sequencing. The recovery of strains with antimicrobial activity suggests that marine sponges represent an ecological niche which harbours a largely uncharacterised microbial diversity and a yet unexploited potential in the search for new secondary metabolites

Bacteria with antimicrobial properties isolated from the Mediterranean sponges Chondrilla nucula and Petrosia ficiformis

Bacteria were isolated seasonally from the Mediterranean sponges Chondrilla nucula and Petrosia ficiformis and screened for antibacterial activities. Selected isolates were taxonomically identified by 16S rRNA gene sequencing. A total of 416 different bacterial strains were isolated, 60 (14.4%) of which displayed variable degrees of antimicrobial activity. Of the bioactive strains, 58.3% were able to inhibit Staphylococcus aureus, 6.7% were active against Bacillus subtilis, 11.7% against both Enterococcus faecalis and Escherichia coli, 38.3% against Pseudoalteromonas atlantica and 33.3% against Pseudomonas elongata. 16S rRNA gene sequence analysis showed that 2 isolates, 1 from seawater samples and 1 from P. ficiformis, were most closely related to Bacillus subtilis (99% similarity) and that another isolate from P. ficiformis was most closely related to a previously described sponge-associated Alphaproteobacterium NW001 (98% similarity). Two isolates from C. nucula were most closely related to Brachybacterium paraconglomeratum (99% similarity) and Shewanella algae (89% similarity). The high percentage of bioactive isolates derived from the 2 sponges suggests that marine microorganisms, whether animal-associated or planktonic, are promising sources for drug discovery

Cathodic protection of carbon steel in natural seawater: Effect of sunlight radiation

Cathodic protection of metals in seawater is known to be influenced by chemical-physical parameters affecting cathodic processes (oxygen discharge, hydrogen evolution and calcareous deposit precipitation). In shallow seawater, these parameters are influenced by sunlight photoperiod and photosynthetic activity. The results presented here represent the first step in studies dedicated to cathodic protection in shallow photic seawater. This paper reports on carbon steel protected at -850 mV vs. Ag/AgCl (oxygen limiting current regime) in the presence of sunlight radiation but in the absence of biological and photosynthetic activity, the role of which deserves future research. Comparison of results obtained by exposing electrochemical cells to daylight cycles in both biologically inactivated natural seawater and in NaCl 3.5 wt.% solutions showed that sunlight affects current densities and that calcareous deposit interfere with light-currents effects. Sunlight radiation and induced heating of the solution have been separated, highlighting results not otherwise obvious: (1) observed current waves concomitant with sunlight radiation depend fundamentally on solar radiation, (2) solar radiation can determine current enhancements from early to late phases of aragonite crystal growth, (3) a three-day-old CaCO3 layer reduces but does not eliminate the amplitude of the current waves. Theoretical calculations for oxygen limiting currents and additional field tests showed that sunlight, rather than bulk solution heating, is the main cause of daily current enhancements. This was confirmed by polarizations performed at -850 and -1000 mV vs. Ag/AgCl (constant bulk temperature), during which the electrode was irradiated with artificial lighting. This test also confirmed O-2 discharge to be the cathodic process involved. A mechanism of radiation conversion to heat in the oxygen diffusion layer region is proposed. (c) 2009 Elsevier Ltd. All rights reserved