Evolution of Aromatic β-Glucoside Utilization by Successive Mutational Steps in Escherichia coli

Abstract

The bglA gene of Escherichia coli encodes phospho-␤-glucosidase A capable of hydrolyzing the plant-derived aromatic ␤-glucoside arbutin. We report that the sequential accumulation of mutations in bglA can confer the ability to hydrolyze the related aromatic ␤-glucosides esculin and salicin in two steps. In the first step, esculin hydrolysis is achieved through the acquisition of a four-nucleotide insertion within the promoter of the bglA gene, resulting in enhanced steady-state levels of the bglA transcript. In the second step, hydrolysis of salicin is achieved through the acquisition of a point mutation within the bglA structural gene close to the active site without the loss of the original catabolic activity against arbutin. These studies underscore the ability of microorganisms to evolve additional metabolic capabilities by mutational modification of preexisting genetic systems under selection pressure, thereby expanding their repertoire of utilizable substrates. The extraordinary versatility and adaptability exhibited by microorganisms are primarily responsible for their success in occupying a broad spectrum of niches. Bacteria have evolved different strategies to cope with a variety of stresses encountered in their natural habitats. When forced to grow in the presence of a novel substrate as the sole carbon source, bacteria are able to evolve the capability to utilize the novel substrate by modifying preexisting genetic systems having related functions (1, 2).Escherichia coli has several catabolic systems for the utilization of plant-derived aromatic ␤-glucosides such as arbutin (Arb), salicin (Sal), and esculin (Esc) (Fig. 1) that encode a sugar-specific permease that is a part of the phosphotransferase system (PTS) and a phospho-␤-glucosidase necessary for the hydrolysis of the sugar. Interestingly, many of these genetic systems are silent and need a step of mutational activation to be functional. The silent bgl operon of E. coli enables the utilization of arbutin and salicin upon mutational activation (3). A homologue of the bgl operon in Erwinia has been shown to confer the ability to utilize esculin in addition to arbutin and salicin (4). Prompted by this observation, el Hassouni et al. have examined the role of the bgl operon of E. coli in esculin utilization. They have reported that Bgl ϩ strains of E. coli can hydrolyze esculin and that this ability is lost in mutants in which the transport and hydrolysis functions have been abrogated (4).The bgl operon consists primarily of three genes, bglG, bglF, and bglB, encoding a positive regulator that acts as an antiterminator of transcription, the permease that transports and concomitantly phosphorylates arbutin and salicin, and the phospho-␤-glucosidase B that hydrolyzes phospho-arbutin and phospho-salicin, respectively. The bgl operon is silent in most wild-type (WT) strains due to the presence of negative elements upstream of the promoter; mutations such as the transposition of insertion elements that abrogate the negative elements result in the activa...

Genome-Based Characterization of Biological Processes That Differentiate Closely Related Bacteria

“…The absence of this ABC transporter in Tatumella and the concomitant antibiotic resistance may increase ecological competitiveness of species exposed to these compounds (Hacker and Carniel, 2001 ). Ecological advantages are likely also obtained from some of the predicted PTSs, which have previously been linked to enhanced recycling of cell wall components under nutrient-poor conditions (e.g., PTSs involving N-acetylmuramic acid and N-acetylglucosamine; Jaeger and Mayer, 2008 ), and the uptake of plant-derived carbon compounds (e.g., PTS involving arbutin and salicin; Zangoui et al, 2015 ).…”

An efficient preparation and biocatalytic synthesis of novel C-glycosylflavonols kaempferol 8-C-glucoside and quercetin 8-C-glucoside by metabolic engineering of Escherichia coli

“…4c). It has been reported that E. coli used the aromatic beta-glucosidases (arbutin, salicin, and esculin) as the carbon source [43]. These results suggested that adding glycerol could avoid the degradation of C-glycosyl avonols by probably suppressing catabolic systems for utilization of the aromatic beta-glucosidases.…”

Genome Insights of the Plant-Growth Promoting Bacterium Cronobacter muytjensii JZ38 With Volatile-Mediated Antagonistic Activity Against Phytophthora infestans

“…These sugars included monosaccharides (L-enantiomers of arabinose and rhamnose and D-enantiomers of ribose, xylose, galactose, glucose, fructose and mannose), disaccharides (D-enantiomers of cellobiose, maltose, lactose, melibiose, saccharose/sucrose and trehalose and gentiobiose), glycosides (amygdalin, arbutin, esculin and salicin), polysaccharides (D-raffinose), polyols (glycerol, galacticol, inositol, and D-mannitol), and salts (potassium gluconate). Isolate JZ38 has the genomic potential for the metabolism of arabinose (araBAD) (Fritz et al, 2014), arabinogalactan (bgaB/ganA, ganB) (Watzlawick et al, 2016), cellulose and cellobiose (bcsZ, two copies of bglX, bglB, yliI) (Xie et al, 2007), citric acid (citABCDEFXG, citA in plasmid p2) (Martín et al, 2004), galactose (lacA, galK, galT) (Chai et al, 2012), galacticol (gatD, gatYZ, gatR) (Nolle et al, 2017), glucose (pgm, yihX, glk, pgi), glycerol (glpK, glpD) (Holmberg et al, 1990;Yang et al, 2014), glycosides (bglB, bglA/ascB, ascG) (Desai et al, 2010;Zangoui et al, 2015), inositol (iolBCDEGHI) (Morinaga et al, 2010), lactose (lacA, lacZ) (Zeng et al, 2010), maltose/matlodextrin (malP, malQ, malS, malZ, glvA) (Boos and Shuman, 1998), mannitol (mtlD) (Wisselink et al, 2004), melibiose and raffinose (rafA, rafR, scrB) (Russell et al, 1992; Hugouvieux-Cotte-Pattat and Charaoui-Boukerzaza, 2009), rhamnose (rhaBAD) (Schwartz et al, 1974;Rodionova et al, 2013), ribose (rbsK, rbsD, rbsR) (Mauzy and Hermodson, 1992;Sigrell et al, 1998), sucrose (scrB, two copies of scrK, scrR) (Hugouvieux-Cotte-Pattat and Charaoui-Boukerzaza, 2009), trehalose (two copies of treA, treC, treR) (Baker et al, 2018), and xylose (xylAB) (Shamanna and Sanderson, 1979).…”