## 1 Introduction  
RNA molecules consist of four basic nucleosides, adenosine (A), uridine (U), cytidine (C), and guanosine (G). Post-transcriptional RNA modifications are present in many types of RNAs including transfer RNA (tRNA), messenger RNA (mRNA), ribosomal RNA (rRNA), and others. Modifications consist of methylation of a ribose or base, thiolation, deamination, base isomerization, or complex hypermodifications [1]. These modifications are important for altering the chemical and physical properties of nucleotides resulting in increased efficiency of RNA functions. Of all the RNAs, tRNAs display the greatest number and variety of modifications, with organisms from all domains of life allocating a large portion of their genome to encoding enzymes involved in the post-transcriptional modification of nucleosides in tRNA [2]. Post-transcriptional modification of the anticodon domain in tRNA is a major factor in controlling gene expression which allows bacteria to adapt and survive in many different types of environments [3]. Modifications of uridine at the wobble position of the anticodon (U34) are required for the recognition of rare codons. In the absence of modifications, a shift in the translational reading frame occurs resulting in the expression of alternate protein sequences [3]. Numerous enzymes have been identified in the modification pathways of bacterial tRNAs. For example, the IscS-MnmA pathway is responsible for thiolation at position 2 of U34 [4, 5, 6]. MnmA is a member of the ATP-pyrophosphate family which recognizes nucleotides U34 and U35 of the anticodon region of bacterial tRNAs [6]. IscS is a highly conserved master enzyme that catalyzes the formation of alanine and sulfane sulfur from cysteine to provide sulfur for the IscS-MnmA pathway as well as three other modification pathways [7, 8, 9]. Other pathways include known tRNA modification enzymes like glucose-inhibited division (GidA) protein, MnmE. GidA has been classified into two groups based on the size of the protein with the larger protein, GidA (also known as MnmG), consisting of 611-679 amino acid residues, while the smaller protein, Gid (also known as TrmFO), contains 435-482 amino acid residues [10, 11]. GidA was first described in _Escherichia coli_ as a cell division protein because deletion of _gidA_ resulted in a filamentous morphology when grown in a rich medium supplemented with glucose [12]. Further studies have suggested a role for GidA in the cell division and morphology of _Salmonella enterica_ serovar Typhimurium (STM) and _Aeromonas hydrophila_[13, 14]. Most importantly, studies in _E. coli_ suggest GidA is a tRNA modification enzyme responsible for the proper biosynthesis of 5-methylaminomethyl-2-thiouridine (mnm\({}^{5}\)s\({}^{2}\)U) at the 5 position of the wobble uridine (U34) of tRNAs [15, 16]. MnmE, also known as TrmE, is a multi-domain GTPase that is highly conserved amongst bacteria and eukarya [15]. GTPases are well known for regulating a number of cellular processes such as ribosome assembly, membrane trafficking, signal transduction, and protein biosynthesis [17]. The GTPase properties of MnmE, however, are very unique in that MnmE displays a hydrolysis rate at a low affinity for GTP and GDP in the presence of potassium ions suggesting that the MnmE GTPase cycle proceeds in an efficient manner without GTPase activating proteins and guanine nucleotide exchange factors [18, 19, 20]. Furthermore, similar to GidA, MnmE appears to be responsible for the proper biosynthesis of mmm\({}^{5}\)s\({}^{2}\)U at the 5 position of U34 of tRNAs [21, 22]. In _E. coli_, the general hypothesis is that GidA and MnmE are part of the same tRNA modification pathway [21, 22]. The study by [PERSON] _et al._ reported that mutations in _E.