Applying cathodically polarised substrata to the restoration of a high value coral.

Larval settlement of the high value red coral, Corallium rubrum, was studied on three different CaCO(3) substrata, viz. lithogenic (marble), electro-accreted calcium carbonate in the presence and in the absence of cathodic polarisation. The last two substrata consisted of stainless steel plates galvanically coupled with Zn anodes. The electrochemical characterization of the settlement device was studied in order to investigate correlations between cathodic parameters (polarisation potential, current density, calcareous deposit composition) and larval settlement. The results obtained in the natural habitat (at 35 m depth) showed that settlement was five times lower on the electro-accreted aragonite in the presence of low cathodic current densities (i≤1 µA cm(-2)) compared to both marble tiles and electro-accreted aragonite in the absence of polarisation. These last two substrata showed similar settlement values. The implications of these findings on restoration strategies for C. rubrum are discussed.

Evidence of enzymatic catalysis of oxygen reduction on stainless steels under marine biofilm.

Cathodic current trends on stainless steel samples with different surface percentages covered by biofilm and potentiostatically polarized in natural seawater were studied under oxygen concentration changes, temperature increases, and additions of enzymic inhibitors to the solution. The results showed that on each surface fraction covered by biofilm the oxygen reduction kinetics resembled a reaction catalyzed by an immobilised enzyme with high oxygen affinity (apparent Michaelis-Menten dissociation constant close to K(O(2))(M)  ≈ 10 µM) and low activation energy (W ≈ 20 KJ mole(-1)). The proposed enzyme rapidly degraded when the temperature was increased above the ambient (half-life time of ∼1 day at 25°C, and of a few minutes at 50°C). Furthermore, when reversible enzymic inhibitors (eg sodium azide and cyanide) were added, the cathodic current induced by biofilm growth was inhibited.

Exploiting a new electrochemical sensor for biofilm monitoring and water treatment optimization.

Bacterial biofilm development is a serious problem in many fields, and the existing biofilm monitoring sensors often turn out to be inadequate. In this perspective, a new sensor (ALVIM) has been developed, exploiting the natural marine and freshwater biofilms electrochemical activity, proportional to surface covering. The results presented in this work, obtained testing the ALVIM system both in laboratory and in an industrial environment, show that the sensor gives a fast and accurate response to biofilm growth, and that this response can be used to optimize cleaning treatments inside pipelines. Compared to the existing biofilm sensors, the proposed system show significant technological innovations, higher sensitivity and precision.

Electrochemical activity and bacterial diversity of natural marine biofilm in laboratory closed-systems.

Even if a widely shared mechanism actually does not exist, it is now generally accepted that, in aerobic conditions, marine electrochemically active biofilms (MEABs) induce faster oxygen reduction on stainless steel immersed in seawater. This phenomenon has been widely studied, but nearly all the experiments found in literature have been conducted in open-systems (i.e. experimental environments where seawater is constantly renewed). In this work we tried to obtain, in open circuit and potentiostatic conditions, MEABs in different laboratory closed-systems without water renewal (mesocosms), in order to verify the relationship between electrochemical activity and biofilm composition. The diversity of the microbial populations of biofilms obtained by our new kind of approach was examined by the DGGE technique (denaturing gradient gel electrophoresis). MEABs were obtained in all the mesocosms from 2000 to 2 L, showing in some cases electrochemical performances comparable to those of open-systems, and a very high genetic variability. Our DGGE results underline the difficulty in finding a correlation between electrochemical activity and composition of microbial populations.