Ole in withstanding stress from external and internal forces in addition to maintaining the shape of bacteria. As such, the cell wall is essential for cell viability due to its overarching function in providing physical support for the cytoplasmic membrane. The cell wall of bacteria is mainly composed of a cross-linked polymer known as peptidoglycan (PG). PG Epigenetic Reader Domain contains glycan chains and peptide stems, and its monomer unit Epigenetic Reader Domain consists of a disaccharide tetrapeptide (Fig. 1) [1]. Its synthesis is divided into three main steps. In the first step, the nucleotide sugar-linked precursors UDP-N-acetylmuramyl-pentapeptide (UDP-MurNAc-pentapeptide) and UDP-N-acetylglucosa-mine (UDP-GlcNAc) are synthesized in the cytoplasm. In the second step, precursor lipid intermediates (lipids I and II) are synthesized at the cytoplasmic membrane. The polymerization of newly synthesized disaccharide-peptide units and incorporation into the growing PG by penicillin-binding proteins (PBPs) is the third and final step of the pathway [2]. Verrucomicrobium spinosum is a Gram-negative heterotrophic bacterium that is generally found in fresh water and soil. The morphology of V. spinosum is very interesting in that it possesses protruding wart-like and tube-like appendages known as prosthecae that are an extension of the cell membrane (Fig. 2). The bacterium has garnered a lot of interest from the scientific community due to its close evolutionarily relationship withMurE from Verrucomicrobium spinosum DSM 4136TFigure 2. Scanning electron microscopy of V. spinosum DSM 4136T. The white arrows show the wart-like prosthecae (WLP) and the white bar depicts a tube-like prosthecae (TLP). The picture was taken at 25 K magnification. The scale bar is 1 mm. doi:10.1371/journal.pone.0066458.gFigure 1. The monomer unit of the peptidoglycan structure. The disaccharide moiety is composed of the amino sugars Nacetylglucosamine (GlcNAc) and N-acetylmuramic (MurNAc) linked via a b-1,4 glycosidic bond. The amino acid at position 3 of the stem peptide is meso-diaminopimelic acid (R = COOH) in most Gramnegative bacteria and L-lysine (R = H) in most Gram-positive bacteria. doi:10.1371/journal.pone.0066458.gbacteria from the genus Chlamydia [3]. Annotation of the genome suggests that the bacterium employs a protein secretion system known as Type III that is involved in pathogenicity [4]. A recent study shows that V. spinosum is pathogenic to Drosophila melanogaster and Caenorhabditis elegans [5]. V. spinosum was found to employ the recently discovered L,Ldiaminopimelate aminotransferase (DapL) pathway [6,7,8,9] as the sole route for the synthesis of diaminopimelate (A2pm) and Llysine (L-Lys), based on biochemical and bioinformatical evidence [10]. In the anabolism of PG, the penultimate intermediate in the L-lysine biosynthesis pathway, meso-diaminopimelate (meso-A2pm), serves as one of the cross-linking amino acids in Gram-negative bacteria, and L-Lys serves the same purpose in many Grampositive bacteria [11]. The enzyme UDP-N-acetylmuramoyl-L-alanyl-D-glutamate:meso-2,6-diaminopimelate ligase (MurE) (E.C. 6.3.2.15) catalyzes the addition of the third amino acid residue 23977191 to the peptide stem of PG in the cytoplasmic step of PG synthesis. In most bacteria, this third residue is either meso-A2pm or L-Lys (Fig. 1). In particular species, other amino acids can be found, such as L-ornithine, mesolanthionine, L,L-A2pm, L-diaminobutyric acid or L-homoserine [1,12,13]. Since the third residue in the ba.Ole in withstanding stress from external and internal forces in addition to maintaining the shape of bacteria. As such, the cell wall is essential for cell viability due to its overarching function in providing physical support for the cytoplasmic membrane. The cell wall of bacteria is mainly composed of a cross-linked polymer known as peptidoglycan (PG). PG contains glycan chains and peptide stems, and its monomer unit consists of a disaccharide tetrapeptide (Fig. 1) [1]. Its synthesis is divided into three main steps. In the first step, the nucleotide sugar-linked precursors UDP-N-acetylmuramyl-pentapeptide (UDP-MurNAc-pentapeptide) and UDP-N-acetylglucosa-mine (UDP-GlcNAc) are synthesized in the cytoplasm. In the second step, precursor lipid intermediates (lipids I and II) are synthesized at the cytoplasmic membrane. The polymerization of newly synthesized disaccharide-peptide units and incorporation into the growing PG by penicillin-binding proteins (PBPs) is the third and final step of the pathway [2]. Verrucomicrobium spinosum is a Gram-negative heterotrophic bacterium that is generally found in fresh water and soil. The morphology of V. spinosum is very interesting in that it possesses protruding wart-like and tube-like appendages known as prosthecae that are an extension of the cell membrane (Fig. 2). The bacterium has garnered a lot of interest from the scientific community due to its close evolutionarily relationship withMurE from Verrucomicrobium spinosum DSM 4136TFigure 2. Scanning electron microscopy of V. spinosum DSM 4136T. The white arrows show the wart-like prosthecae (WLP) and the white bar depicts a tube-like prosthecae (TLP). The picture was taken at 25 K magnification. The scale bar is 1 mm. doi:10.1371/journal.pone.0066458.gFigure 1. The monomer unit of the peptidoglycan structure. The disaccharide moiety is composed of the amino sugars Nacetylglucosamine (GlcNAc) and N-acetylmuramic (MurNAc) linked via a b-1,4 glycosidic bond. The amino acid at position 3 of the stem peptide is meso-diaminopimelic acid (R = COOH) in most Gramnegative bacteria and L-lysine (R = H) in most Gram-positive bacteria. doi:10.1371/journal.pone.0066458.gbacteria from the genus Chlamydia [3]. Annotation of the genome suggests that the bacterium employs a protein secretion system known as Type III that is involved in pathogenicity [4]. A recent study shows that V. spinosum is pathogenic to Drosophila melanogaster and Caenorhabditis elegans [5]. V. spinosum was found to employ the recently discovered L,Ldiaminopimelate aminotransferase (DapL) pathway [6,7,8,9] as the sole route for the synthesis of diaminopimelate (A2pm) and Llysine (L-Lys), based on biochemical and bioinformatical evidence [10]. In the anabolism of PG, the penultimate intermediate in the L-lysine biosynthesis pathway, meso-diaminopimelate (meso-A2pm), serves as one of the cross-linking amino acids in Gram-negative bacteria, and L-Lys serves the same purpose in many Grampositive bacteria [11]. The enzyme UDP-N-acetylmuramoyl-L-alanyl-D-glutamate:meso-2,6-diaminopimelate ligase (MurE) (E.C. 6.3.2.15) catalyzes the addition of the third amino acid residue 23977191 to the peptide stem of PG in the cytoplasmic step of PG synthesis. In most bacteria, this third residue is either meso-A2pm or L-Lys (Fig. 1). In particular species, other amino acids can be found, such as L-ornithine, mesolanthionine, L,L-A2pm, L-diaminobutyric acid or L-homoserine [1,12,13]. Since the third residue in the ba.