A comparison of genes involved in sphingan biosynthesis brought up to date

Abstract

Microbial polysaccharides have a wide range of functional properties and show high relevance in industrial applications. The possibility to create tailor-made polysaccharides by genetic engineering will further enhance the product portfolio and may open new fields of application. Here, we have examined in detail the recently sequenced genome of the welan-producing strain Sphingomonas sp. ATCC 31555 to identify the complete welan cluster and further genes involved in EPS production. The corresponding genes were compared on the nucleotide and amino acid sequence level to the EPS clusters of the described gellan-producing Sphingomonas elodea ATCC 31461, diutan-producing Sphingomonas sp. ATCC 53159, and the S-88-producing Sphingomonas sp. ATCC 31554 strains. We also compared the previously mentioned strains to each other and included the genes upstream of the main cluster in gellan and welan cluster. The cluster organization of Sphingomonas strain S-7 was also compared based on previous hybridization experiments, without nucleotide sequences. We have found that the occurrence of genes in all biosynthesis clusters is connected to the structures of the various produced sphingans. Along these lines, homologous genes responsible for the assembly of the identical repeating unit generally show high sequence identity, whereas genes for putative side chain attachment urf31, urf31.4, and urf34 vary more in distinct areas. Moreover, gene clusters for biosynthesis of diutan, welan, gellan, and S-88 as well as S-7 are similar in general organization but differ in location and arrangement of some genes. Finally, we summarized genetic and mutational engineering approaches toward modified sphingan variants as described in literature.

Production and Rheological Properties of Welan Gum Produced by <b><i>Sphingomonas</i></b> sp. ATCC 31555 with Different Nitrogen Sources

“…Sphingans are a group of exopolysaccharides (EPS) secreted by Sphingomonas , such as gellan, welan, diutan, and rhamsan [Coleman et al, 2008;Hagiwara et al, 2010;Schmid et al, 2014Schmid et al, , 2015Wang et al, 2012]. Sphingans have a common tetrasaccharide backbone structure which contains glucose, glucuronic acid, rhamnose, and mannose [Seo et al, 2004].…”

Enzymatic Transformations Involved in the Biosynthesis of Microbial Exo‐polysaccharides Based on the Assembly of Repeat Units

“…Interestingly,a lthoughb oth primingG Ts having the same functioni nt he biosynthetic pathway of ap olysaccharide, they only have an identity of around6 0% at the nucleotide level and even less (35 %) at the amino-acid level. Replacement of SpnB (general name for enzymes involved in sphingan biosynthesis, such as gellan, welan and diutan [12] )w ith GumD results in unaltered production of sphingan polysaccharides in various sphingomonades, thus indicating that even with less homology at the nucleotide and structural levels, the same functionc an be obtained in different organisms. [23] Ah igherd egree of identity is described for priming GTsi nG ram-positive bacteria, especially lactobacilli.…”

“…[13,14] Most of the genes responsible for production of the polysaccharide precursors have ah igh similarity at the nucleotide and amino acid levels amongst the various EPS producers, and are arranged in the same order within the gene clusters of closely related species. [12,15] Other genes responsible for the formation Figure 1. Graphical demonstration of the recentlysequencedg enomes of A) the welan-producing strain Sphingomonas sp.…”

“…In the case of welan biosynthesis, four different genes (rmlABCD)a re involved in synthesis of dTDP-rhamnose ( Figure 1A), whichi so ne of the sugars included in the backbone as well as the side chain in this sphingan variant (Scheme 1). [12] The enzymes involved in precursor synthesis belong to the families of phosphoglucomutases, thymidilyltransferases, glucosed ehydratases,e pimerases and reductases. Some of them show bifunctional activities, qualifying them to be involved in the production of more than one EPS precursor.…”

“…[9] Next-generation sequencing will be ap owerful tool to enhancet he amount of available genomic information on EPS operons and, as such, could allow comparison of larger numberso fr elated clusters in order to improveo ur understanding of EPS biosynthetic pathways for targeted interventiontowards designated applications. [10][11][12] Microbial exo-polysaccharides can serve as valuable biopolymers in medicine, food and the feed industry as well as in various technical applications as substitutes of petro-based polymers or with unusual performance. Due to their different natural functions, they have vastly diverses tructures, which lead to av ery different properties.…”