Sergey Dobretsov

The current study investigated the microbial community composition of the biofilms that developed on 11 commercial biocidal coatings, including examples of the three main historic types, namely self-polishing copolymer (SPC), self-polishing hybrid (SPH) and controlled depletion polymer (CDP), after immersion in the sea for one year. The total wet weight of the biofilm and the total bacterial density were significantly influenced by all coatings. Pyrosequencing of 16S rRNA genes revealed distinct bacterial community structures on the different types of coatings. Flavobacteria accounted for the dissimilarity between communities developed on the control and SPC (16%) and the control and SPH coatings (17%), while Alphaproteobacteria contributed to 14% of the dissimilarity between the control and CDP coatings. The lowest number of operational taxonomic units was found on Intersmooth 100, while the lowest biomass and density of bacteria was detected on other SPC coatings. The experiments ...

ABSTRACT Like multicellular organisms, bacteria can regulate gene expression at the multicellular level. The coordination of multicellular bacterial behavior occurs via a chemically mediated process known as quorum sensing (QS). Currently, there are five well-defined classes of chemical signals in bacteria that support the concept of QS. By coupling an extracellular bacterial signal with gene expression, bacteria can control gene expression in such a way that the majority of the population expresses the same phenotype simultaneously. In this chapter, the molecular mechanisms of QS, the effective range of QS-regulated processes, and the ecological role of quorum quenching, namely the inhibition of QS, are discussed. QS occurs most frequently in bacterial species that associate with surfaces or higher organisms, either as a pathogen or as a beneficial associate. Three seminal examples of QS-mediated cross-kingdom signaling in the marine environment are reviewed: (i) the chemical defense of the red seaweed Delisea pulchra; (ii) the mutualistic association of Vibrio fischeri with the Hawaiian bobtail squid; and (iii) the exploitation of bacterial QS during settlement of marine spores and invertebrate larvae.

In laboratory experiments, the antifouling (AF) properties of zinc oxide (ZnO) nanorod coatings were investigated using the marine bacterium Acinetobacter sp. AZ4C, larvae of the bryozoan Bugula neritina and the microalga Tetraselmis sp. ZnO nanorod coatings were fabricated on microscope glass substrata by a simple hydrothermal technique using two different molar concentrations (5 and 10 mM) of zinc precursors. These coatings were tested for 5 h under artificial sunlight (1060 W m(-2) or 530 W m(-2)) and in the dark (no irradiation). In the presence of light, both the ZnO nanorod coatings significantly reduced the density of Acinetobacter sp. AZ4C and Tetraselmis sp. in comparison to the control (microscope glass substratum without a ZnO coating). High mortality and low settlement of B. neritina larvae was observed on ZnO nanorod coatings subjected to light irradiation. In darkness, neither mortality nor enhanced settlement of larvae was observed. Larvae of B. neritina were not affected by Zn(2+) ions. The AF effect of the ZnO nanorod coatings was thus attributed to the reactive oxygen species (ROS) produced by photocatalysis. It was concluded that ZnO nanorod coatings effectively prevented marine micro and macrofouling in static conditions.

Extracts of several cyanobacterial species collected from different marine and estuarine locations predominately in Florida (USA), with one sample each from Belize and Oman, were screened for their ability to disrupt quorum sensing (QS) in the reporter strain Chromobacterium violaceum CV017. Inhibitory activities were detected in the ethyl acetate : methanol (1:1) extracts of several Lyngbya spp., and extracts of Lyngbya majuscula contained the strongest QS inhibitory activities. Extracts of L. majuscula from the Indian River Lagoon, FL, USA, were further purified by bioassay-guided fractionation. The antibiotic malyngolide (MAL) was identified as a QS inhibitor. Activity of MAL was investigated using N-acyl homoserine lactone (AHL) reporters based on the LasR receptor of Pseudomonas aeruginosa. MAL at concentrations ranging from 3.57 µM to 57 µM (EC50  = 12.2 ± 1.6 µM) inhibited responses of the LasR reporters without affecting bacterial growth. MAL inhibited (EC50  =  10.6 ± 1.8 µM) Las QS-dependent production of elastase by P. aeruginosa PAO1. We propose that this QS inhibitor plays a role in controlling interactions of heterotrophic bacteria associated with the cyanobacterium L. majuscula.

The effect of substratum colour on the formation of micro- and macro fouling communities was investigated. Acrylic tiles, painted either black or white were covered with transparent sheets in order to ensure similar surface properties. All substrata were exposed to biofouling at 1 m depth for 40 d in the Marina Bandar al Rowdha (Muscat, Sea of Oman). Studies were conducted in 2010 over a time course of 5, 10 and 20 d, and in 2012 samples were collected at 7, 14 and 21 d. The densities of bacteria on the black and white substrata were similar with the exception of day 10, when the black substrata had a higher abundance than white ones. Pyrosequencing via 454 of 16S rRNA genes of bacteria from white and black substrata revealed that Alphaproteobacteria and Firmicutes were the dominant groups. SIMPER analysis demonstrated that bacterial phylotypes (uncultured Gammaproteobacteria, Actibacter, Gaetbulicola, Thalassobius and Silicibacter) and the diatoms (Navicula directa, Navicula sp. and Nitzschia sp.) contributed to the dissimilarities between communities developed on white and black substrata. At day 20, the highest amount of chlorophyll a was recorded in biofilms developed on black substrata. SIMPER analysis showed that Folliculina sp., Ulva sp. and Balanus amphitrite were the major macro fouling species that contributed to the dissimilarities between the communities formed on white and black substrata. Higher densities of these species were observed on black tiles. The results emphasise the effect of substratum colour on the formation of micro and macro fouling communities; substratum colour should to be taken into account in future studies.