Alginates are polysaccharides with many industrial and medical uses, from food additives to encapsulation agents in the emerging transplantation technologies. Alginate is composed of variable proportions of beta-D-mannuronic acid and alpha-Lguluronic acid linked by 1-4 glycosidic bonds. Traditionally, commercial alginate has been produced by farmed brown seaweeds, but this alginate suffers from heterogeneity in composition and quality partly due to environmental variation. Two bacterial genera, Pseudomonas and Azotobacter, are also capable of producing alginate as an exopolysaccharide. These bacterial alginate producers can provide the means to produce alginates with defined monomer composition and possibly through genetic and protein engineering may allow for the production of 'tailor made' bacterial alginates. The paper discusses the mechanisms behind alginate production in bacteria and how they may be used in the commercial production of alginates. (C) 2010 Society of Chemical Industry