Phylogeny and taxonomy of the Prenolepis genus‐group of ants (Hymenoptera: Formicidae)

Abstract. We investigated the phylogeny and taxonomy of the Prenolepis genus‐group, a clade of ants we define within the subfamily Formicinae comprising the genera Euprenolepis, Nylanderia, gen. rev. , Paraparatrechina, gen. rev. & stat. nov. , Paratrechina, Prenolepis and Pseudolasius. We inferred a phylogeny of the Prenolepis genus‐group using DNA sequence data from five genes (CAD, EF1αF1, EF1αF2, wingless and COI) sampled from 50 taxa. Based on the results of this phylogeny the taxonomy of the Prenolepis genus‐group was re‐examined. Paratrechina (broad sense) species segregated into three distinct, robust clades. Paratrechina longicornis represents a distinct lineage, a result consistent with morphological evidence; because this is the type species for the genus, Paratrechina is redefined as a monotypic genus. Two formerly synonymized subgenera, Nylanderia and Paraparatrechina, are raised to generic status in order to provide names for the other two clades. The majority of taxa formerly placed in Paratrechina, 133 species and subspecies, are transferred to Nylanderia, and 28 species and subspecies are transferred to Paraparatrechina. In addition, two species are transferred from Pseudolasius to Paraparatrechina and one species of Pseudolasius is transferred to Nylanderia. A morphological diagnosis for the worker caste of all six genera is provided, with a discussion of the morphological characters used to define each genus. Two genera, Prenolepis and Pseudolasius, were not recovered as monophyletic by the molecular data, and the implications of this result are discussed. A worker‐based key to the genera of the Prenolepis genus‐group is provided.     

Divergence estimates and early evolutionary history of Figitidae (Hymenoptera: Cynipoidea)

We examine the phylogenetic relationships of Figitidae and discuss host use within this group in light of our own and previously published divergence time data. Our results suggest Figitidae, as currently defined, is not monophyletic. Furthermore, Mikeiinae and Pycnostigminae are sister‐groups, nested adjacent to Thrasorinae, Plectocynipinae and Euceroptrinae. The recovery of Pycnostigminae as sister‐group to Mikeiinae suggests two major patterns of evolution: (i) early Figitidae lineages demonstrate a Gondawanan origin (Plectocynipinae: Neotropical; Mikeiinae and Thrasorinae: Australia; Pycnostigminae: Africa); and (ii) based on host records for Mikeiinae, Thrasorinae and Plectocynipinae, Pycnostigminae are predicted to be parasitic on gall‐inducing Hymenoptera. The phylogenetic position of Parnips (Parnipinae) was unstable, and various analyses were conducted to determine the impact of this uncertainty on both the recovery of other clades and inferred divergence times; when Parnips was excluded from the total evidence analysis, Cynipidae was found to be sister‐group to [Euceroptrinae + (Plectocynipinae (Thrasorinae + (Mikeiinae + Pycnostigminae)))], with low support. Divergence dating analyses using BEAST indicate the stem‐group node of Figitidae to be c. 126 Ma; the dipteran parasitoids (Eucoilinae and Figitinae), were estimated to have a median age of 80 and 88 Ma, respectively; the neuropteran parasitoids (Anacharitinae), were estimated to have a median age of 97 Ma; sternorrhynchan hyperparasitoids (Charipinae), were estimated to have a median age of 110 Ma; the Hymenoptera‐parasitic subfamilies (Euceroptinae, Plectocynipinae, Trasorinae, Mikeiinae, Pycnostigminae, and Parnipinae), ranged in median ages from 48 to 108 Ma. Rapid radiation of Eucoilinae subclades appears chronologically synchronized with the origin of their hosts, Schizophora (Diptera). Overall, the exclusion of Parnips from the BEAST analysis did not result in significant changes to divergence estimates. Finally, though sparsely represented in the analysis, our data suggest Cynipidae have a median age of 54 Ma, which is somewhat older than the age of Quercus spp (30–50 Ma), their most common host.     

Characterization of the putative operon containing arylamine N-acetyltransferase (nat) in Mycobacterium bovis BCG

Mycobacterium bovis BCG and Mycobacterium tuberculosis possess a single arylamine N-acetyltransferase whose gene is predicted to occur within a six-gene operon. Deletion of the nat gene caused an extended lag phase in M. bovis BCG and a cell morphology associated with an altered pattern of cell wall mycolates. Analysis of cDNA from M. bovis BCG shows that during in vitro growth all the genes in the putative nat operon are expressed and the open reading frames are contiguous, supporting the existence of an operon. Two genes in the operon, Mb3599c and Mb3600c, are predicted to encode homologues of enzymes annotated as a 2,3-dihydroxybiphenyl 1,2-dioxygenase (bphC5) and a 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase (bphD2), respectively, in Rhodococcus RHA1. As predicted, M. bovis BCG cell lysates metabolized the BphC substrate 2,3-dihydroxybiphenyl (2,3-DHB) to 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA), a BphD substrate, which was subsequently hydrolysed. Immunoprecipitation of the BphD homologue from these lysates led to an accumulation of HOPDA. M. bovis BCG growth on both solid and liquid media was inhibited with either 2,3-DHB or an inhibitor of BphC, 3-chlorocatechol (3-CC). In addition, incubation with 2,3-DHB affects the lipid composition of the cell wall resulting in a diminished level of mycolates and an altered cell morphology similar to the Deltanat strain. We propose the enzymes encoded by the putative operon have a similar endogenous role to that of the NAT enzyme and are part of a pathway important for cell wall synthesis.     

Arabinan-deficient mutants of Corynebacterium glutamicum and the consequent flux in decaprenylmonophosphoryl-D-arabinose metabolism

The arabinogalactan (AG) of Corynebacterianeae is a critical macromolecule that tethers mycolic acids to peptidoglycan, thus forming a highly impermeable cell wall matrix termed the mycolyl-arabinogalactan peptidoglycan complex (mAGP). The front line anti-tuberculosis drug, ethambutol (Emb), targets the Mycobacterium tuberculosis and Corynebacterium glutamicum arabinofuranosyltransferase Mt-EmbA, Mt-EmbB and Cg-Emb enzymes, respectively, which are responsible for the biosynthesis of the arabinan domain of AG. The substrate utilized by these important glycosyltransferases, decaprenylmonophosphoryl-D-arabinose (DPA), is synthesized via a decaprenylphosphoryl-5-phosphoribose (DPPR) synthase (UbiA), which catalyzes the transfer of 5-phospho-ribofuranose-pyrophosphate (pRpp) to decaprenol phosphate to form DPPR. Glycosyl compositional analysis of cell walls extracted from a C. glutamicum::ubiA mutant revealed a galactan core consisting of alternating beta(1-->5)-Galf and beta(1-->6)-Galf residues, completely devoid of arabinan and a concomitant loss of cell-wall-bound mycolic acids. In addition, in vitro assays demonstrated a complete loss of arabinofuranosyltransferase activity and DPA biosynthesis in the C. glutamicum::ubiA mutant when supplemented with p[14C]Rpp, the precursor of DPA. Interestingly, in vitro arabinofuranosyltransferase activity was restored in the C. glutamicum::ubiA mutant when supplemented with exogenous DP[14C]A substrate, and C. glutamicum strains deficient in ubiA, emb, and aftA all exhibited different levels of DPA biosynthesis.     

Sequence and analysis of a plasmid-encoded mercury resistance operon from Mycobacterium marinum identifies MerH, a new mercuric ion transporter

In this study, we report the DNA sequence and biological analysis of a mycobacterial mercury resistance operon encoding a novel Hg²⁺ transporter. MerH was found to transport mercuric ions in Escherichia coli via a pair of essential cysteine residues but only when coexpressed with the mercuric reductase.     

Characterization of the Corynebacterium glutamicum ΔpimB′ ΔmgtA Double Deletion Mutant and the Role of Mycobacterium tuberculosis Orthologues Rv2188c and Rv0557 in Glycolipid Biosynthesis

In this study, utilizing a Corynebacterium glutamicum ΔpimB′ ΔmgtA double deletion mutant, we unequivocally assign the in vivo functions of Rv2188c as an Ac₁PIM₁:mannosyltransferase (originally termed PimB′_Mt [Mycobacterium tuberculosis PimB′]) and Rv0557 as a GlcAGroAc₂:mannosyltransferase (originally termed PimB_Mt), which we have reassigned as PimB_Mt and MgtA_Mt, respectively, in Mycobacterium tuberculosis.The current model of mycobacterial phosphatidyl-myo-inositol mannoside (PIM) biosynthesis, supported by biochemical and genetic studies, follows a linear pathway from phosphatidylinositol (PI) → Ac₁PIM₂ → Ac₁PIM₄ → Ac₁PIM₆ (4, 17, 19) as shown in Fig. ​Fig.1.1. In this pathway, mycobacterial PI is glycosylated by an α-mannopyranosyl residue at the 2-OH position of inositol, followed by the acylation and mannosylation at the 6-OH position of PI to form Ac₁PIM₂ (3), which is further mannosylated to form Ac₁PIM₄ and Ac₁PIM₆, extending the 6-OH position of Ac₁PIM₂ (19).Open in a separate windowFIG. 1.Glycolipid biosynthetic pathways in Corynebacterineae. (A) PIM synthesis in M. tuberculosis; (B) PIMs; (C) ManGlcAGroAc₂ synthesis in C. glutamicum.In view of the identification of genes involved in PIM, lipomannan (LM), and lipoarabinomannan (LAM) biosynthesis, Schaeffer et al. (22) proposed Rv0557 as an α-d-mannose-α-(1→6)-phosphatidyl-myo-inositol-mannosyltransferase that transfers mannose from GDP-Man to Ac₁PIM₁ to form Ac₁PIM₂, a precursor of the immunomodulatory lipoglycans LM and LAM (4, 17). The study was based on a cell-free assay using GDP[¹⁴C]Man, Ac₁PIM_1, Mycobacterium smegmatis membranes, and/or partially purified recombinant Rv0557. On the basis of these in vitro studies, Rv0557 was assigned as PimB_Mt (Mycobacterium tuberculosis PimB) in the synthesis of Ac₁PIM₂. However, on the disruption of Rv0557 in Mycobacterium tuberculosis, PIM biosynthesis remains unaffected (G. S. Besra and L. S. Schlesinger, unpublished data), suggesting that either gene duplication or Rv0557 performed another function in M. tuberculosis. Interestingly, in a recent study, Rv0557 was also shown to be involved in the biosynthesis of 1,2-di-O-C₁₆/C_18:1-(α-d-mannopyranosyl)-(1→4)-(α-d-glucopyranosylu- ronic acid)-(1→3)-glycerol (ManGlcAGroAc₂) and an LM-like molecule in Corynebacterium glutamicum and was termed MgtA_Mt (M. tuberculosis MgtA) (25). More recently, Rv2188c was also proposed to be involved in the synthesis of Ac₁PIM₂ as the second α-d-mannose-α-(1→6)-phosphatidyl-myo-inositol-mannosyl transferase (termed PimB′_Mt) (13, 16), which has augmented ongoing confusion in the field. Due to the essentiality of M. tuberculosis PIM biosynthesis (3) in this study, we have generated C. glutamicum ΔpimB′ ΔmgtA, deficient in pimB′_Cg and mgtA_Cg (C. glutamicum pimB′ and mgtA) and subsequently overexpressed Rv2188c and Rv0557 individually to identify their true in vivo and in vitro biochemical activities.     

Identification of 2-Aminothiazole-4-Carboxylate Derivatives Active against Mycobacterium tuberculosis H37Rv and the β-Ketoacyl-ACP Synthase mtFabH

Background

Tuberculosis (TB) is a disease which kills two million people every year and infects approximately over one-third of the world''s population. The difficulty in managing tuberculosis is the prolonged treatment duration, the emergence of drug resistance and co-infection with HIV/AIDS. Tuberculosis control requires new drugs that act at novel drug targets to help combat resistant forms of Mycobacterium tuberculosis and reduce treatment duration.

Methodology/Principal Findings

Our approach was to modify the naturally occurring and synthetically challenging antibiotic thiolactomycin (TLM) to the more tractable 2-aminothiazole-4-carboxylate scaffold to generate compounds that mimic TLM''s novel mode of action. We report here the identification of a series of compounds possessing excellent activity against M. tuberculosis H₃₇R_v and, dissociatively, against the β-ketoacyl synthase enzyme mtFabH which is targeted by TLM. Specifically, methyl 2-amino-5-benzylthiazole-4-carboxylate was found to inhibit M. tuberculosis H₃₇R_v with an MIC of 0.06 µg/ml (240 nM), but showed no activity against mtFabH, whereas methyl 2-(2-bromoacetamido)-5-(3-chlorophenyl)thiazole-4-carboxylate inhibited mtFabH with an IC₅₀ of 0.95±0.05 µg/ml (2.43±0.13 µM) but was not active against the whole cell organism.

Conclusions/Significance

These findings clearly identify the 2-aminothiazole-4-carboxylate scaffold as a promising new template towards the discovery of a new class of anti-tubercular agents.     

Inhibition of Escherichia coli glycosyltransferase MurG and Mycobacterium tuberculosis Gal transferase by uridine-linked transition state mimics

Glycosyltransferase MurG catalyses the transfer of N-acetyl-d-glucosamine to lipid intermediate I on the bacterial peptidoglycan biosynthesis pathway, and is a target for development of new antibacterial agents. A transition state mimic was designed for MurG, containing a functionalised proline, linked through the α-carboxylic acid, via a spacer, to a uridine nucleoside. A set of 15 functionalised prolines were synthesised, using a convergent dipolar cycloaddition reaction, which were coupled via either a glycine, proline, sarcosine, or diester linkage to the 5′-position of uridine. The library of 18 final compounds were tested as inhibitors of Escherichia coli glycosyltransferase MurG. Ten compounds showed inhibition of MurG at 1 mM concentration, the most active with IC₅₀ 400 μM. The library was also tested against Mycobacterium tuberculosis galactosyltransferase GlfT2, and one compound showed effective inhibition at 1 mM concentration.