Water. Desalination + reuse
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May-June 2015 | Desalination & Water Reuse | 27 | RESEARCH Figure 1. Strains of two bacteria species found in a pilot plant at Carlsbad, California show production of an AI-1 messenger molecule, N-butyryl-homoserine lactone Foul language: synthesizing protein (S) in the primary foulant bacteria generates chemical messages (QS). When the messages reach a certain density they link with receptor protein (R) in other foulant bacteria which switches on bioflm formation. Interrupting the passage of chemical messages could silence biofouling. Figure 2. Known QSI vanillin inhibited bioflm formation by seven species of bacterium but flm formation in an eighth (RO32) was increased. Figure 3. Multi-bacteria QSI, cinnamaldehyde, suppressed bioflm formation in three natural marine bacterial groups taken from sites in California. will include investigations into the stability of the QSI-deposited membranes as well as using chemicals to bound QSIs on the membrane surface. We will compare the anti-biofouling ability of the QSI-bound RO membrane with a conventional RO membrane to look for enhanced membrane resistance to bioflm formation. We hope soon to have a new generation of membranes in the fght against biofouling. l Message in a molecule QS messenger molecules fall into two categories – those specifc to individual species of bacteria and others that are active in a range of species – sometimes referred to as universal messengers. Of the single species messengers there are two types of molecule associated with the two categories that most bacteria fall into: Gram- positive and Gram-negative. Autoinducer 1 (AI-1) molecules, commonly produced by Gram- negative bacteria, are typically derivatives of the amino acid, homoserine, known as acyl homoserine lactones. They differ in structure depending on the species they are from. The differences are notably in the number of carbon atoms and other components in a carbon chain bound to the amino acid part – see fgure 1 which identifes a molecule with a four-carbon acid attached to the homoserine core. Gram-positive bacteria's messaging molecules are commonly protein-like fragments called oligopeptides and again differ in structure according to their parent species. The universal messenger molecules are categorized as autoinducer 2 (AI-2). They activate many different types of bacterium and have been identifed in 70 different species. AI-2 molecules typically comprise a base structure that is similar to the common industrial solvent tetrahydrofuran but other, quite different AI-2s are known.