Bacterial alginates: biosynthesis and applications

Abstract

Alginate is a copolymer of beta-D-mannuronic acid and alpha-L-guluronic acid (GulA), linked together by 1-4 linkages. The polymer is a well-established industrial product obtained commercially by harvesting brown seaweeds. Some bacteria, mostly derived from the genus Pseudomonas and belonging to the RNA superfamily I, are also capable of producing copious amounts of this polymer as an exopolysaccharide. The molecular genetics, regulation and biochemistry of alginate biosynthesis have been particularly well characterized in the opportunistic human pathogen Pseudomonas aeruginosa, although the biochemistry of the polymerization process is still poorly understood. In the last 3 years major aspects of the molecular genetics of alginate biosynthesis in Azotobacter vinelandii have also been reported. In both organisms the immediate precursor of polymerization is GDP-mannuronic acid, and the sugar residues in this compound are polymerized into mannuronan. This uniform polymer is then further modified by acetylation at positions O-2 and/or O-3 and by epimerization of some of the residues, leading to a variable content of acetyl groups and GulA residues. In contrast, seaweed alginates are not acetylated. The nature of the epimerization steps are more complex in A. vinelandii than in P. aeruginosa, while other aspects of the biochemistry and genetics of alginate biosynthesis appear to be similar. The GulA residue content and distribution strongly affect the physicochemical properties of alginates, and the epimerization process is therefore of great interest from an applied point of view. This article presents a survey of our current knowledge of the molecular genetics and biochemistry of bacterial alginate biosynthesis, as well as of the biotechnological potential of such polymers.

Calcium is required for ixotrophy of Aureispira sp. CCB-QB1

“…aeruginosa has identified alg genes that are involved in synthesis of precursor substrate (algA, algC and algD), polymerization (algK), modification (algF, algG, algI, algJ, algL and algX) and export (algE) (Remminghorst & Rehm, 2006;Riley et al, 2013). A two-component signal-transduction pathway that regulates alg operon transcription was found (Rehm & Valla, 1997).…”

Production of Poly-β-hydroxybutyric acid (PHB) by Bacillus cereus

“…After 48 h incubation at 30 ºC, isolated colonies were screened for PHB production. Screening test for PHB (poly-β-hydroxybutyrate) production by different isolates was carried out using Nile red [9-diethylamino-5H-benzo α-phenoxazine-5-one-(sigma)] staining approach ( Rehm and Valla 1997;Belal 2013a). Nile red stock solution [0.25 g/ml DMSO (dimethylsulfoxied)], 20 μl was spread onto sterilized pre-made (sucrose/yeast extract agar media) plates to reach a final concentrations of 0.5 μg Nile red /ml medium.…”

Produção de alginato por microrganismos

“…Os resíduos manurônicos podem estar ligados com grupos acetil, no carbono 2 e/ou 3, o que os torna parcialmente acetilados (Figura 1) [9] . Uma característica apresentada por alginatos produzidos por Pseudomonas é a ausência de resíduos ou de blocos constituídos de ácidos gulurônicos [7] .…”

“…Sequencialmente o polimanuronato é acetilado e epimerizado. Na etapa de acetilação, grupos acetil são ligados aos carbonos 2 e/ou 3 dos resíduos manurônicos [9,13] . Os fatores que a afetam esta etapa de biossíntese, não estão definidos para ambos os gêneros e a presença de grupos acetil sugere uma proteção da ação de epimerases [5,14] .…”