IGEM:IMPERIAL/2009/Encapsulation/Phase2/Alginate Biosynthesis/Bacteria1

Summary of Useful Info:

The genes for alginate biosynthesis are all located on the bacterial chromosome, with no evidence to date of plasmid involvement.
At least 24 genes have been directly implicated in alginate biosynthesis in P. aeruginosa.

The table below shows the genes involves in alginate production for P. aeruginosa.[1]

[2]

Generally, the alginate biosynthesis pathway can be divided into four different stages:

• 1) synthesis of precursor substrate
• 2) polymerization and cytoplasmic membrane transfer
• 3) periplasmic transfer and modification
• 4) export through the outer membrane.

The Common Genes

The pathway forming alginate presented here in P. aeruginosa has some overlap with genes naturally present in E.coli. We will investigate the pathway and identify those also in E.coli. This will enable us to only insert as few genes as possible.

The initial steps in the alginate biosynthesis pathway are essentially those of general carbohydrate metabolism and the intermediates are widely utilized.
In particular, the steps up to and including GDP mannose are common to alginate and LPS biosynthesis.

Studies into the algC gene found in the biosynthesis pathway of alginate in P. aeruginosa, encodes phosphomannomutase which interconverts mannose-6-phosphate and mannose-1-phosphate. This was confirmed by successful complementation of an E.coli pgm mutation with the P. aeruginosa algC gene.

The P. aeruginosa alginate export gene (AlgE) has been functionally expressed in E.coli. [3]

E.coli Gene Homologues

1) Fructose 6 phosphate to mannose 6 phosphate (manA)

2) Mannose 6 phosphate to mannose 1 phosphate (manB)

3) Mannose 1 phosphate to GDP mannose (manC)

Control

The properties of pure alginates are determined by their degree of poly-merization and acetylation, and by their monomer composition and sequence.
It seems probable that it will become largely possible to control all these three parameters in bacterial alginates [4]

Issue of monomer composition

M to G transitions can be done using bacterial epimerases.

Pseudomonas species have only one mannuronan C-5- epimerase, encoded by the algG gene, and this enzyme is only able to introduce single guluronic acid residues in to the mannuronan chain.

In A. vinelandii, there are 5 AlgE genes for epimerisation. In particular, AlgE2 introduces G-blocks (gel-forming alginate). AlgE2 should probably be the gene for epimerisation that we clone

It is well-established that alginates from P. aeruginosa do not contain polyguluronate blocks, whereas those from A. vinelandii may do so

Alginates which contain polyguluronate form rigid gels in the presence of Ca2+ and are therefore important in structural roles, e.g. gel formation.

Conversely, an absence of polyguluronate, as in P. aeruginosa, produces relatively flexible gels in the presence of Ca2+ eg biofilm.

Deacetylated alginates are needed because early studies indicate that acetylation seems to protect them from epimerization of the AlgE type [4] So we probably can knock out the O-acetylation gene

Production

Amount of alginate produced expressed as micrograms of alginate per milligram of cell dry weight [5]

Useful Papers

1. Gacesa P. Bacterial alginate biosynthesis--recent progress and future prospects. Microbiology (Reading). 1998 May;144 ( Pt 5):1133-1143. DOI:10.1099/00221287-144-5-1133 |

2. Remminghorst U and Rehm BH. Bacterial alginates: from biosynthesis to applications. Biotechnol Lett. 2006 Nov;28(21):1701-12. DOI:10.1007/s10529-006-9156-x |

5. Hassett DJ. Anaerobic production of alginate by Pseudomonas aeruginosa: alginate restricts diffusion of oxygen. J Bacteriol. 1996 Dec;178(24):7322-5. DOI:10.1128/jb.178.24.7322-7325.1996 |

4. Rehm BH and Valla S. Bacterial alginates: biosynthesis and applications. Appl Microbiol Biotechnol. 1997 Sep;48(3):281-8. DOI:10.1007/s002530051051 |

3. Sabra W, Zeng AP, and Deckwer WD. Bacterial alginate: physiology, product quality and process aspects. Appl Microbiol Biotechnol. 2001 Aug;56(3-4):315-25. DOI:10.1007/s002530100699 |