Colanic acid

Colanic acid is an exopolysaccharide synthesized by the bacteria Enterobacteriaceae. It is produced as a chemical defense to protect the cell surface, and it assists in the formation of biofilms.

Not to be confused with cholanic acid.
Colanic acid
Identifiers
3D model (JSmol)
  • repeating unit: InChI=1S/C41H64O33/c1-8-25(16(47)19(50)35(62-8)69-26-9(2)63-38(24(55)31(26)64-10(3)44)70-28-14(45)11(5-42)65-34(58)22(28)53)68-39-23(54)29(15(46)12(6-43)66-39)71-37-21(52)18(49)30(32(73-37)33(56)57)72-36-20(51)17(48)27-13(67-36)7-61-41(4,74-27)40(59)60/h8-9,11-32,34-39,42-43,45-55,58H,5-7H2,1-4H3,(H,56,57)(H,59,60)/p-2/t8-,9+,11-,12-,13+,14-,15+,16-,17+,18-,19-,20+,21-,22-,23-,24+,25+,26-,27-,28+,29+,30+,31+,32+,34-,35+,36-,37-,38+,39+,41+/m0/s1
    Key: DUGKXGQZYHUOFV-SOLNNGHASA-L
  • repeating unit: C[C@H]1[C@H]([C@H]([C@@H]([C@H](O1)O[C@H]2[C@H](O[C@@H]([C@@H]([C@H]2OC(=O)C)O)O[C@@H]3[C@H]([C@@H](O[C@@H]([C@H]3O)O)CO)O)C)O)O)O[C@@H]4[C@H]([C@@H]([C@@H]([C@@H](O4)CO)O)O[C@@H]5[C@H]([C@@H]([C@H]([C@@H](O5)C(=O)[O-])O[C@H]6[C@@H]([C@H]([C@@H]7[C@H](O6)CO[C@@](O7)(C)C(=O)[O-])O)O)O)O)O
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Structure

Colanic acid is composed of polyanionic heteropolysaccharides[1] with hexasaccharide repeating units, consisting of glucose, fucose, galactose, and glucuronic acid.[2] It also consists of O-acetyl groups and pyruvate side chains around these sugar molecules.[3] It forms a protective capsule around cells, primarily Enterobacteriaceae.[4] Colanic acid is highly viscous and has strong acidic properties due to its relatively high mobility. It is considered mildly toxic when injected intraperitoneally in mice, and, its effect on mammals can be compared to the effects of small doses of endotoxin,[2] which can cause diarrhea and malaise.

When a strain of E. coli was observed on a neo-peptone agar by Pierre Fredericq, it initially appeared as translucent colonies around 3-4 mm in diameter. Shortly after, single opaque colonies began to form and produced more colicine than that of the parent. Over time, another variant formed where the colonies are now 5-6 mm in diameter and appear to be more glistening, opaque, and mucoid than the previous strain.[2] These strains are said to be colicinogenic. They are also observed as amorphous, white, and fibrous substances that are water-soluble as well as dilute in salt solutions.[2]

Function

The main function of colanic acid is to form a slimy capsule around the cell surface under stressful conditions to increase its chances of survival when stressful environmental stimuli arise.[5] The stressful environment can come in the forms of desiccation, oxidative stress, and a low pH. Expression of colanic acid in E. coli has been shown to be required for the creation of normal E. coli biofilm architecture. E. coli secretes heteropolysaccharide colanic acid which forms a slimy capsule surrounding the cell surface under stressful conditions.[5]

Synthesis of colanic acid is up-regulated in biofilms. Acetylation plays a crucial role in modulating structural conformation Physical and chemical properties. Colanic acid, plays an essential role in biofilm formation, in Escherichia coli. Colanic acid does not enhance bacterial adhesion but it blocks the establishment of binding specificity.[5]

Environmental factors

Temperature and pH

Colanic acid begins to accumulate and synthesize at 19 °C. Nutrients modulate the production of colanic acid with maximal production occurring when glucose and proline are used as carbon and nitrogen sources. E. coli is a type of Enterobacteriaceae that is commonly used to study the conditions and effects of colanic acid production. A study showed that E. coli K92 is able to produce colanic acid at temperatures ranging from 19 °C to 42 °C, but it predominates at around 20 °C.[6]

Colanic acid is typically produced at a low pH. A study was conducted to see just how low of a pH E.coli could withstand. It was concluded that the production of colanic acid can range from a pH of 2 to a pH of 8; with initial acid adaptation at a pH of 5.5.[7]

Colanic acid production in E. coli is dependent on both lipopolysaccharide structure and glucose availability, because important nucleotide-sugar precursors are needed and provided by both.[8]

Activation and regulation

Activation

2 positive protein regulators are regulated by the RcsA and RcsB genes. These two genes go hand-in-hand as RcsA cannot be activated without RcsB. The activation of colanic acid is due to an initial response to an environmental stimulus such as osmotic shock. This stimulus is relayed to MdoH[9] which is tied to the biosynthesis of MDOs. Unstable MDO levels due to changes within the environment, triggers the RcsC sensor to directly or indirectly relay the signal to the RcsB gene, which is a main activator of cps expression.[10] The RcsA gene activates its own expression.[10]

Regulation

The cps colanic acid operon can control the biosynthesis of colanic acid. It is composed of one large transcriptional unit that contains a ugd gene right outside the cps operon. It has been shown that the transcriptional antiterminator rfaH promotes said cps transcription synthesis. It does by mediating the cps operon and promoting ugd expression.[11]

A study was conducted to test whether RfaH was able to enhance cps colanic acid transcription for colanic acid production, E. coli K92 wild-type and rfaH mutant strains were grown in Asn and glucose media at 37 °C and analyzed after 120 h of growth. At this temperature, it was observed that the deletion of rfaH had dramatically decreased colanic acid production in both media.[11]

References
  1. Zhang X, Xu P, Yu B (October 2022). "Chemical Synthesis of a Colanic Acid Hexasaccharide". Organic Letters. 24 (42): 7779–7783. doi:10.1021/acs.orglett.2c03116. PMID 36240128. S2CID 252897096.
  2. Goebel WF (April 1963). "Colanic acid". Proceedings of the National Academy of Sciences of the United States of America. 49 (4): 464–471. Bibcode:1963PNAS...49..464G. doi:10.1073/pnas.49.4.464. PMC 299878. PMID 13963285.
  3. "Pathway: colanic acid building blocks biosynthesis". biocyc.org. Retrieved 2022-12-15. Escherichia coli K-12 substr. MG1655
  4. Sutherland IW (1990-10-18). Biotechnology of Microbial Exopolysaccharides. Cambridge University Press. ISBN 978-0-521-36350-1.
  5. Hanna A, Berg M, Stout V, Razatos A (August 2003). "Role of capsular colanic acid in adhesion of uropathogenic Escherichia coli". Applied and Environmental Microbiology. 69 (8): 4474–4481. Bibcode:2003ApEnM..69.4474H. doi:10.1128/AEM.69.8.4474-4481.2003. PMC 169069. PMID 12902231.
  6. Navasa N, Rodríguez-Aparicio L, Martínez-Blanco H, Arcos M, Ferrero MA (March 2009). "Temperature has reciprocal effects on colanic acid and polysialic acid biosynthesis in E. coli K92". Applied Microbiology and Biotechnology. 82 (4): 721–729. doi:10.1007/s00253-008-1840-4. PMID 19139876. S2CID 23947959.
  7. Mao Y, Doyle MP, Chen J (June 2006). "Role of colanic acid exopolysaccharide in the survival of enterohaemorrhagic Escherichia coli O157:H7 in simulated gastrointestinal fluids". Letters in Applied Microbiology. 42 (6): 642–647. doi:10.1111/j.1472-765X.2006.01875.x. PMID 16706906. S2CID 9954844.
  8. Wang C, Zhang H, Wang J, Chen S, Wang Z, Zhao L, Wang X (October 2020). "Colanic acid biosynthesis in Escherichia coli is dependent on lipopolysaccharide structure and glucose availability". Microbiological Research. 239: 126527. doi:10.1016/j.micres.2020.126527. PMID 32590169. S2CID 220122048.
  9. Ebel, W.; Vaughn, G. J.; Peters, H. K.; Trempy, J. E. (November 1997). "Inactivation of mdoH leads to increased expression of colanic acid capsular polysaccharide in Escherichia coli". Journal of Bacteriology. 179 (21): 6858–6861. doi:10.1128/jb.179.21.6858-6861.1997. ISSN 0021-9193. PMC 179620. PMID 9352941.
  10. Ebel W, Trempy JE (January 1999). "Escherichia coli RcsA, a positive activator of colanic acid capsular polysaccharide synthesis, functions To activate its own expression". Journal of Bacteriology. 181 (2): 577–584. doi:10.1128/JB.181.2.577-584.1999. PMC 93413. PMID 9882673.
  11. Navasa N, Rodríguez-Aparicio LB, Ferrero MÁ, Monteagudo-Mera A, Martínez-Blanco H (March 2014). "Transcriptional control of RfaH on polysialic and colanic acid synthesis by Escherichia coli K92". FEBS Letters. 588 (6): 922–928. doi:10.1016/j.febslet.2014.01.047. PMID 24491998. S2CID 27471371.
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