New insights into Pseudomonas fluorescens alginate biosynthesis relevant for the establishment of an efficient production process for microbial alginates.
Alginate denotes a family of linear polysaccharides with a wide range of industrial and pharmaceutical applications. Presently, all commercially available alginates are manufactured from brown algae. However, bacterial alginates have advantages with regard to compositional homogeneity and reproducibility. In order to be able to design bacterial strains that are better suited for industrial alginate production, defining limiting factors for alginate biosynthesis is of vital importance. Our group has been studying alginate biosynthesis in Pseudomonas fluorescens using several complementary approaches. Alginate is synthesised and transported out of the cell by a multiprotein complex spanning from the inner to the outer membrane. We have developed an immunogold labelling procedure in which the porin AlgE, as a part of this alginate factory, could be detected by transmission electron microscopy. No time-dependent correlation between the number of such factories on the cell surface and alginate production level was found in alginate-producing strains. Alginate biosynthesis competes with the central carbon metabolism for the key metabolite fructose 6-phosphate. In P. fluorescens, glucose, fructose and glycerol, are metabolised via the Entner-Doudoroff and pentose phosphate pathways. Mutational analysis revealed that disruption of the glucose 6-phosphate dehydrogenase gene zwf-1 resulted in increased alginate production when glycerol was used as carbon source. Furthermore, alginate-producing P. fluorescens strains cultivated on glucose experience acid stress due to the simultaneous production of alginate and gluconate. The combined results from our studies strongly indicate that the availability of fructose 6-phosphate and energy requires more attention in further research aimed at the development of an optimised alginate production process.
Department of Biotechnology, NTNU Norwegian University of Science and Technology, N-7491 Trondheim, Norway; Department of Biotechnology and Nanomedicine, Unit of SINTEF Materials and Chemistry, N-7465 Trondheim, Norway.
Susan
S
Maleki
Department of Biotechnology, NTNU Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
Mali
M
Mærk
Department of Biotechnology, NTNU Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
Radka
R
Hrudikova
Department of Biotechnology, NTNU Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
Svein
S
Valla
Department of Biotechnology, NTNU Norwegian University of Science and Technology, N-7491 Trondheim, Norway. Electronic address: helga.ertesvag@ntnu.no.
Helga
H
Ertesvåg
D000464:Alginates; D053898:Biosynthetic Pathways / Q000235:genetics; D001709:Biotechnology; D005798:Genes, Bacterial; D005947:Glucose / Q000378:metabolism; D005954:Glucosephosphate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism; D020723:Glucuronic Acid / Q000096:biosynthesis; D006603:Hexuronic Acids; D007150:Immunohistochemistry; D007218:Industrial Microbiology; D011551:Pseudomonas fluorescens / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D013312:Stress, Physiological
D000464:Alginates; D006603:Hexuronic Acids; D020723:Glucuronic Acid; D005954:Glucosephosphate Dehydrogenase; D005947:Glucose
Alginate; Fructose 6-phosphate; Pseudomonas fluorescens; Transmission electron microscopy; zwf