A tropical marine bacterium isolated from the hard coral, Symphyllia sp. was identified as Serratia marcescens on the basis of morphological, biochemical and 16S rDNA analysis. The bacterium showed antimicrobial activity towards the pathogens Candida albicans and Pseudomonas aeruginosa and the marine biofouling bacterium Bacillus pumilus. S. marcescens displayed biosurfactant activity as evidenced by drop collapse, blood hemolysis and surface tension reduction (52.0-27 mN m(-1)). The active compound was purified by solvent extraction and silicic acid chromatography. Characterization was by thin layer chromatography, gas chromatography mass spectroscopy (GC-MS), Fourier transform infrared (FTIR) spectroscopy and (1)H as well as (13)C nuclear magnetic resonance (NMR) analysis. The surfactant was found to be a glycolipid composed of glucose and palmitic acid. The glycolipid prevented adhesion of C. albicans BH, P. aeruginosa PAO1 and B. pumilus TiO1. The glycolipid also disrupted preformed biofilms of these cultures in microtitre plates. Confocal laser scanning microscopy and electron microscopy confirmed the effective removal of biofilms from glass surfaces. The glycolipid derived from S. marcescens could thus serve as a potential anti-biofilm agent.

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The green mussel Perna viridis has been receiving a lot of attention from workers working in the research areas of intertidal ecology, aquaculture, pollution monitoring, biofouling, zoogeography and invasion biology. P. viridis is a remarkable species in terms of its ability to reach very high biomass levels, to withstand environmental fluctuations, to concentrate a variety of organic and inorganic environmental pollutants, to colonise artificial marine habitats and to invade new geographic territories. This review collates data available on salient aspects of the distribution, biology and ecology of P. viridis. It is argued that the remarkable success of P. viridis as an invasive species basically stems from its long larval duration, fast growth rate, high fecundity, early maturity, high productivity and ability to withstand fluctuating environmental conditions (temperature, salinity, water turbidity and pollutants). Relevant aspects of the data are compared with the data available for a similar species Perna perna, which too is an invasive species, but to a more limited extent.

Quorum sensing (QS) has received significant attention in the past few decades. QS describes population density dependent cell to cell communication in bacteria using diffusible signal molecules. These signal molecules produced by bacterial cells, regulate various physiological processes important for social behavior and pathogenesis. One such process regulated by quorum sensing molecules is the production of a biosurfactant, rhamnolipid. Rhamnolipids are important microbially derived surface active agents produced by Pseudomonas spp. under the control of two interrelated quorum sensing systems; namely las and rhl. Rhamnolipids possess antibacterial, antifungal and antiviral properties. They are important in motility, cell to cell interactions, cellular differentiation and formation of water channels that Biotechnology and Genetic Engineering Reviews -Vol. 27, 159-184 (2010) Quorum sensing (QS) has received significant attention in the past few decades. QS describes population density dependent cell to cell communication in bacteria using diffusible signal molecules. These signal molecules produced by bacterial cells, regulate various physiological processes important for social behavior and pathogenesis. One such process regulated by quorum sensing molecules is the production of a biosurfactant, rhamnolipid Rhamnolipids are important microbially derived surface active agents produced by Pseudomonas spp. under the control of two interrelated quorum sensing systems; namely las and rhl Rhamnolipids possess antibacterial, antifungal and antiviral properties. They are important in motility, cell to cell interactions, cellular differentiation and formation of water channels that *To whom correspondence may be addressed (p.rahman@tees.ac.uk) Abbreviations: QS: quorum sensing; AI: autoinducer; HSL: homoserine lactone; AHL: acyl homoserine lactone; PQS: pseudomonas quinolone signal; sRNA: small ribonucleic acid; RL: rhamnolipid; HAA: 3-(3-hydroxyalkanoyloxy) alkanoic acid; CTAB: cetyl trimethyl ammonium bromide; TLC: thin layer chromatography; GC: gas chromatography; MS: mass spectroscopy; FTIR: fourier transform infrared spectroscopy; ATR: attenuated total reflectance; NMR: nuclear magnetic resonance; SDS: sodium dodecyl sulfate; CMC: critical micelle concentration; LPS: lipopolysaccharide; TMV: tobacco mosaic virus; PAT: pseudomonas autoinducer; FAD: flavin adenine dinucleotide; NAD: nicotinamide adenine dinucleotide; TDP: thiamine di-phosphate; mN/m-milli-Newton per meter 160 D.H. Dusane et al. are characteristics of Pseudomonas biofilms. Rhamnolipids have biotechnological applications in the uptake of hydrophobic substrates, bioremediation of contaminated soils and polluted waters. Rhamnolipid biosurfactants are biodegradable as compared to chemical surfactants and hence are more preferred in environmental applications. In this review, we examine the biochemical and genetic mechanism of rhamnolipid production by P. aeruginosa and propose the application of QS signal molecules in enhancing the rhamnoli...

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SUMMARY 1. Colonisation, species composition, succession of microalgae and nutrient dynamics in biofilms grown under light and dark conditions were examined during the initial phases of biofilm development in a lentic freshwater environment. 2. Biofilms were developed on inert (perspex) panels under natural illuminated and experimental dark conditions and the panels were retrieved for analysis after different incubation periods. Analysed parameters included biofilm thickness, algal density, biomass, chlorophyll a, species composition, total bacterial density and nutrients such as nitrite, nitrate, phosphate and silicate. 3. Biofilm thickness, algal density, biomass, chlorophyll a and species richness were significantly higher in light‐grown biofilms, compared with dark‐grown biofilms. The light‐grown biofilms showed a three‐phased succession pattern, with an initial domination of Chlorophyceae followed by diatoms (Bacillariophyceae) and finally by cyanobacteria. Dark‐grown biofilms were mostly dominated by diatoms. 4. Nutrients were invariably more concentrated in biofilms than in ambient water. Nutrient concentrations were generally higher in dark‐grown biofilms except in the case of phosphate, which was more concentrated in light‐grown biofilms. Significant correlations between nutrients and biofilm parameters were observed only in light‐grown biofilms. 5. The N : P ratio in the biofilm matrix decreased sharply in the initial 4 days of biofilm growth; ensuing N‐limitation status seemed to influence biofilm community structure. The N : P ratios showed significant positive correlations with the chlorophycean fraction in both light and dark‐grown biofilms, and low N : P ratio in the older biofilms favoured cyanobacteria. Our data indicate that nutrient chemistry of biofilm matrix shapes community structure in microalgal biofilms.

Biofilms are problematic in health and industry because they are resistant to various antimicrobial treatments. Ionic liquids are a novel class of low temperature liquid salts consisting of discrete anions and cations, and have attracted considerable interest as safer alternatives to organic solvents. Ionic liquids have interesting antimicrobial properties and some could find use in the development of novel antiseptics, biocides and antifouling agents. The antimicrobial and antibiofilm activity of 1-dodecyl-3-methylimiazolium iodide ([C(12)MIM]I) was studied using the clinically important bacterial pathogens, Staphylococcus aureus SAV329 and Pseudomonas aeruginosa PAO1. The ionic liquid increased cell membrane permeability in both S. aureus and P. aeruginosa cells and impaired their growth, attachment and biofilm development. The ionic liquid exhibited superior antimicrobial and antibiofilm activity against the Gram-positive S. aureus compared to the Gram-negative P. aeruginosa cells. BacLight™ staining and confocal microscope imaging confirmed that the ionic liquid treatment increased the cell membrane permeability of both the Gram-positive and Gram-negative bacteria. In addition, the antimicrobial and antibiofilm properties of [C(12)MIM]I were similar or superior to those of cetyltrimethylammonium bromide (CTAB), a well-known cationic surfactant. It is concluded that the ionic liquid induced damage to bacterial cells by disrupting cell membrane, leading to inhibition of growth and biofilm formation. Overall, the results indicate that the ionic liquid 1-dodecyl-3-methylimiazolium iodide was effective in preventing S. aureus and P. aeruginosa biofilms and could have applications in the control of bacterial biofilms.

Enhancement or induction of antimicrobial, biosurfactant, and quorum-sensing inhibition property in marine bacteria due to cross-species and cross-genera interactions was investigated. Four marine epibiotic bacteria (Bacillus sp. S3, B. pumilus S8, B. licheniformis D1, and Serratia marcescens V1) displaying antimicrobial activity against pathogenic or biofouling fungi (Candida albicans CA and Yarrowia lipolytica YL), and bacteria (Pseudomonas aeruginosa PA and Bacillus pumilus BP) were chosen for this study. The marine epibiotic bacteria when co-cultivated with the aforementioned fungi or bacteria showed induction or enhancement in antimicrobial activity, biosurfactant production, and quorum-sensing inhibition. Antifungal activity against Y. lipolytica YL was induced by co-cultivation of the pathogens or biofouling strains with the marine Bacillus sp. S3, B. pumilus S8, or B. licheniformis D1. Antibacterial activity against Ps. aeruginosa PA or B. pumilus BP was enhanced in most of the marine isolates after co-cultivation. Biosurfactant activity was significantly increased when cells of B. pumilus BP were co-cultivated with S. marcescens V1, B. pumilus S8, or B. licheniformis D1. Pigment reduction in the quorum-sensing inhibition indicator strain Chromobacterium violaceum 12472 was evident when the marine strain of Bacillus sp. S3 was grown in the presence of the inducer strain Ps. aeruginosa PA, suggesting quorum-sensing inhibition. The study has important ecological and biotechnological implications in terms of microbial competition in natural environments and enhancement of secondary metabolite production.