Clumping characteristics and hydrophobic behaviour of an isolated bacterial strain from sewage sludge

Summary A clump-forming bacterial strain was isolated from a sludge community derived from a waste water treatment plant. The Gram-negative bacterium is hydrophobic and forms an extensive capsule while clumping in dilute medium (0.1% bacto peptone). Emulsan, a capsule inhibitor, does not affect the clumping ability of this bacterium. Clumps are not dispersed with high and low pH, detergents or chelators. Bacterial clumping selected by the waste water treatment processes appears to be a complex set of interactions within and between the strains of bacteria. This study reveals some of the complexities.     

Molecular cloning,sequence analysis and homology modeling of galE encoding UDP-galactose 4-epimerase of Aeromonas hydrophila

A. hydrophila, a ubiquitous gram-negative bacterium present in aquatic environments, has been implicated in illness in humans, fish and amphibians. Lipopolysaccharides (LPS), a surface component of the outer membrane, are one of the main virulent factors of gram-negative bacteria. UDP-galactose 4-epimerase (GalE) catalyses the last step in the Leloir pathway of galactose metabolism and provides precursor for the biosynthesis of extracellular LPS and capsule. Due to its key role in LPS biosynthesis, it is a potential drug target. The present study describes cloning, sequence analysis and prediction of three dimensional structure of the deduced amino acid sequence of the galE of A. hydrophila AH17. The cloned galE consists of the putative promoter-operator region, and an open reading frame of 338 amino acid residues. Sequence alignment and predicted 3Dstructure revealed that the GalE of A. hydrophila consists of the signature sequences of the epimerase super family. The present study reports the molecular modeling / 3D-structure prediction of GalE of A. hydrophila. Further, the potential regions of the enzyme that can be targeted for drug design are identified.     

Mitochondria as determinant of nucleotide pools and chromosomal stability

Mitochondrial function plays an important role in multiple human diseases and mutations in the mitochondrial genome have been detected in nearly every type of cancer investigated to date. However, the mechanism underlying the interrelation is unknown. We used human cell lines depleted of mitochondrial DNA as models and analyzed the outcome of mitochondrial dysfunction on major cellular repair activities. We show that the deoxyribonucleoside triphosphate (dNTP) pools are affected, most prominently we detect a 3-fold reduction of the dTTP pool when normalized to the number of cells in S-phase. It is known that imbalanced dNTP pools are mutagenic and in accordance, we show that mitochondrial dysfunction results in chromosomal instability, which can explain its role in tumor development. We did not find any straightforward correlation between ATP levels and dNTP pools in cells with defective mitochondrial activity. Our results suggest that mitochondria are central players in maintaining genomic stability and in controlling essential nuclear processes such as upholding a balanced supply of nucleotides.     

Illness-induced exacerbation of Leigh syndrome in a patient with the MTATP6 mutation,m. 9185 T>C

The most common mitochondrial DNA (mtDNA) mutations giving rise to Leigh syndrome reside in the MTATP6 gene. We report a rare mutation, m. 9185 T>C that gives rise to a progressive, but episodic pattern of neurological impairment with partial recovery. Disease progression corresponded to febrile viral illness and nuclear magnetic resonance imaging (MRI) changes. The patient displayed nearly 100% homoplasmy, while his asymptomatic mother was 30%. Phenotypically, exacerbations of muscle weakness with endurance intolerance, dysarthric speech, ataxia, and eyelid ptosis accompanied febrile viral illness. This case demonstrates an episodic pattern of febrile illness-induced disease exacerbation with corresponding MRI changes.     

Study on quantitative structure-toxicity relationships of benzene derivatives acting by narcosis

Hydrophobicity (logP) as well as quantiative structure-toxicity relationships (QSTRs) of some benzene derivatives acting by narcosis have been established based on narcotic mechanisms of action and toxicity data to the fathead minnow, Daphnia magna and Vibrio fischeri using information-theoretic topological index (Id). Excellent results are obtained in multiparametric regression upon introduction of dummy parameters (indicator variables). Consistent increase in R(2)(A) values indicated that inspite of collinarity between Id and one of the indicator variables (I(3-6)) the proposed models are statistically significant.     

Discovery of parallel pathways of kanamycin biosynthesis allows antibiotic manipulation

Kanamycin is one of the most widely used antibiotics, yet its biosynthetic pathway remains unclear. Current proposals suggest that the kanamycin biosynthetic products are linearly related via single enzymatic transformations. To explore this system, we have reconstructed the entire biosynthetic pathway through the heterologous expression of combinations of putative biosynthetic genes from Streptomyces kanamyceticus in the non-aminoglycoside-producing Streptomyces venezuelae. Unexpectedly, we discovered that the biosynthetic pathway contains an early branch point, governed by the substrate promiscuity of a glycosyltransferase, that leads to the formation of two parallel pathways in which early intermediates are further modified. Glycosyltransferase exchange can alter flux through these two parallel pathways, and the addition of other biosynthetic enzymes can be used to synthesize known and new highly active antibiotics. These results complete our understanding of kanamycin biosynthesis and demonstrate the potential of pathway engineering for direct in vivo production of clinically useful antibiotics and more robust aminoglycosides.     

Stabilizing Multi-Electron NASICON-Na1.5V0.5Nb1.5(PO4)3 Anode via Structural Modulation for Long-Life Sodium-Ion Batteries

Multi-electron NAtrium SuperIonic CONductor (NASICON)-Nb₂(PO₄)₃ (N₀NbP) is an attractive Na-ion battery anode, owing to its low intercalation voltage (1.4 V vs Na⁺/Na⁰) and high capacity (≈150 mAh g⁻¹). However, it suffers from poor capacity retention due to structural degradation. To overcome this issue, extra Na⁺ ions are introduced at the Na(1) sites, via V³⁺ substitution, which can act as stabilizing agents to hold lantern units together during cycling, producing NASICON-Na_1.5V_0.5Nb_1.5(PO₄)₃ (N_1.5VNbP). The N_1.5VNbP anode exhibits reversible capacities of ≈140 mAh g⁻¹ at 1.4 V versus Na⁺/Na⁰ through Nb⁵⁺/Nb⁴⁺/Nb³⁺ and V³⁺/V²⁺ redox activities. The extra Na⁺ ions in the framework forms a complete solid-solution during Na (de)intercalation and enhances sodium diffusivity, in agreement with first-principles calculations. Further, N_1.5VNbP demonstrates extraordinary cycling (89% capacity retention at 5C after 500 cycles) and rate performances (105 mAh g⁻¹ at 5C). Upon pairing the N_1.5VNbP anode with the NASICON-Na₃V₂(PO₄)₃ cathode, the full Na-ion cell delivers a remarkable energy density of 98 Wh kg⁻¹ (based on the mass of anode and cathode) and retains 80% of its capacity at 5C rate over 1000 cycles. The study opens new possibilities for enhancing the electrochemical performance of NASICON anodes via chemical and structural modulations.     

Interrogating accessibility of telomeric sequences with FRET-PAINT: evidence for length-dependent telomere compaction

Single-stranded telomeric overhangs are ∼200 nucleotides long and can form tandem G-quadruplex (GQ) structures, which reduce their accessibility to nucleases and proteins that activate DNA damage response. Whether these tandem GQs further stack to form compact superstructures, which may provide better protection for longer telomeres, is not known. We report single-molecule measurements where the accessibility of 24–144 nucleotide long human telomeric DNA molecules is interrogated by a short PNA molecule that is complementary to a single GGGTTA repeat, as implemented in the FRET-PAINT method. Binding of the PNA strand to available GGGTTA sequences results in discrete FRET bursts which were analyzed in terms of their dwell times, binding frequencies, and topographic distributions. The binding frequencies were greater for binding to intermediate regions of telomeric DNA compared to 3′- or 5′-ends, suggesting these regions are more accessible. Significantly, the binding frequency per telomeric repeat monotonically decreased with increasing telomere length. These results are consistent with telomeres forming more compact structures at longer lengths, reducing accessibility of these critical genomic sites.