Localization of an accessory helicase at the replisome is critical in sustaining efficient genome duplication

Genome duplication requires accessory helicases to displace proteins ahead of advancing replication forks. Escherichia coli contains three helicases, Rep, UvrD and DinG, that might promote replication of protein-bound DNA. One of these helicases, Rep, also interacts with the replicative helicase DnaB. We demonstrate that Rep is the only putative accessory helicase whose absence results in an increased chromosome duplication time. We show also that the interaction between Rep and DnaB is required for Rep to maintain rapid genome duplication. Furthermore, this Rep-DnaB interaction is critical in minimizing the need for both recombinational processing of blocked replication forks and replisome reassembly, indicating that colocalization of Rep and DnaB minimizes stalling and subsequent inactivation of replication forks. These data indicate that E. coli contains only one helicase that acts as an accessory motor at the fork in wild-type cells, that such an activity is critical for the maintenance of rapid genome duplication and that colocalization with the replisome is crucial for this function. Given that the only other characterized accessory motor, Saccharomyces cerevisiae Rrm3p, associates physically with the replisome, our demonstration of the functional importance of such an association indicates that colocalization may be a conserved feature of accessory replicative motors.     

Matita, a new retroelement from peanut: characterization and evolutionary context in the light of the Arachis A–B genome divergence

Cultivated peanut is an allotetraploid with an AB-genome. In order to learn more of the genomic structure of peanut, we characterized and studied the evolution of a retrotransposon originally isolated from a resistance gene analog (RGA)-containing bacterial artificial chromosome (BAC) clone. It is a moderate copy number Ty1-copia retrotransposon from the Bianca lineage and we named it Matita. Fluorescent in situ hybridization (FISH) experiments showed that Matita is mainly located on the distal regions of chromosome arms and is of approximately equal frequency on both A- and B-chromosomes. Its chromosome-specific hybridization pattern facilitates the identification of individual chromosomes, a useful cytogenetic tool considering that chromosomes in peanut are mostly metacentric and of similar size. Phylogenetic analysis of Matita elements, molecular dating of transposition events, and an estimation of the evolutionary divergence of the most probable A- and B-donor species suggest that Matita underwent its last major burst of transposition activity at around the same time of the A- and B-genome divergence about 3.5 million years ago. By probing BAC libraries with overgos probes for Matita, resistance gene analogues, and single- or low-copy genes, it was demonstrated that Matita is not randomly distributed in the genome but exhibits a significant tendency of being more abundant near resistance gene homologues than near single-copy genes. The described work is a further step towards broadening the knowledge on genomic and chromosomal structure of peanut and on its evolution.     

Presence of two types of flowers with respect to nectar sugar in two gregariously flowering species

Many species of animal-pollinated flowers are known to vary widely in the nectar content of flowers. Some proportion of flowers in many species is apparently nectarless, and such flowers are believed to be ‘cheaters’. Cheating may explain a part of the variability in nectar content. If cheating exists as a qualitatively different strategy then we expect bimodality in the distribution of nectar content of flowers. It has been shown in a multispecies study that gregarious species have a higher proportion of cheater flowers. We studied the frequency distribution of total nectar sugar in two gregariously flowering species Lantana camara and Utricularia purpurascens, which differed in other floral and ecological characters. At the population level, both the species showed significant bimodality in the total sugar content of flowers. The obvious sources of heterogeneity in the data did not explain bimodality. In Lantana camara, bimodality was observed within flowers of some of the individual plants sampled. In Utricularia purpurascens the proportion of nectarless flowers was more in high-density patches, suggesting that the gregariousness hypothesis may work within a species as well. The results support the hypothesis of cheating as a distinct strategy since two distinct types of flowers were observed in both the species. The effect of density in Utricularia purpurascens also supports the gregariousness hypothesis.     

Phage Associated Bacteriocins Reveal a Novel Mechanism for Bacteriocin Diversification in Klebsiella

Ninety-six isolates of Klebsiella pneumoniae and K. oxytoca were recovered from wild mammals in Australia. 14.6% of these bacteria produce killing phenotypes that suggest the production of bacteriocin toxins. Cloning and sequencing of the gene clusters encoding two of these killing phenotypes revealed two instances of a bacteriocin associated with a bacteriophage gene, the first such genetic organization described. The newly identified klebicin C gene cluster was discovered in both K. pneumoniae and K. oxytoca. The newly identified klebicin D gene cluster was detected in K. oxytoca. Protein sequence comparisons and phylogenetic inference suggest that klebicin C is most closely related to the rRNase group of colicins (such as colicin E4), while klebicin D is most closely related to the tRNase group of colicins (such as colicin D). The klebicin C and D gene clusters have similar genetic and regulatory organizations. In both cases, an operon structure is inferred consisting of a phage-associated open reading frame and klebicin activity and associated immunity genes. This novel bacteriophage/bacteriocin organization may provide a novel mechanism for the generation of bacteriocin diversity in Klebsiella.Reviewing Editor: Prof. David Guttman     

Evaluation of nootropic potential of Ocimum sanctum Linn. in mice

Dementia is one of the age related mental problems and a characteristic symptom of various neurodegenerative disorders including Alzheimer's disease. Certain drugs like diazepam, barbiturates and alcohol disrupt learning and memory in animals and man. However, a new class of drugs known as nootropic agents is now used in situations where there is organic disorder in learning abilities. The present work was undertaken to assess the potential of O. sanctum extract as a nootropic and anti-amnesic agent in mice. Aqueous extract of dried whole plant of O. sanctum ameliorated the amnesic effect of scopolamine (0.4 mg/kg), diazepam (1 mg/kg) and aging induced memory deficits in mice. Elevated plus maze and passive avoidance paradigm served as the exteroceptive behavioral models. O. sanctum extract decreased transfer latency and increased step down latency, when compared to control (piracetam treated), scopolamine and aged groups of mice significantly. O. sanctum preparations could of beneficial in the treatment of cognitive disorders such as dementia and Alzheimer's disease.     

Biological characterization of lead-enhanced exopolysaccharide produced by a lead resistant Enterobacter cloacae strain P2B

A lead resistant bacterial strain isolated from effluent of lead battery manufacturing company of Goa, India has been identified as Enterobacter cloacae strain P2B based on morphological, biochemical characters, FAME profile and 16S rDNA sequence data. This bacterial strain could resist lead nitrate up to 1.6?mM. Significant increase in exopolysaccharide (EPS) production was observed as the production increased from 28 to 108?mg/L dry weight when exposed to 1.6?mM lead nitrate in Tris buffered minimal medium. Fourier-transformed infrared spectroscopy of this EPS revealed presence of several functional groups involved in metal binding viz. carboxyl, hydroxyl and amide groups along with glucuronic acid. Gas chromatography coupled with mass spectrometry analysis of alditol-acetate derivatives of acid hydrolysed EPS produced in presence of 1.6?mM lead nitrate demonstrated presence of several neutral sugars such as rhamnose, arabinose, xylose, mannose, galactose and glucose, which contribute to lead binding hydroxyl groups. Scanning electron microscope coupled with energy dispersive X-ray spectrometric analysis of this lead resistant strain exposed to 1.6?mM lead nitrate interestingly revealed mucous EPS surrounding bacterial cells which sequestered 17?% lead (as weight %) extracellularly and protected the bacterial cells from toxic effects of lead. This lead resistant strain also showed multidrug resistance. Thus these results significantly contribute to better understanding of structure, function and environmental application of lead-enhanced EPSs produced by bacteria. This lead-enhanced biopolymer can play a very important role in bioremediation of several heavy metals including lead.     

Effects of co-inoculation of two different plant growth-promoting bacteria on duckweed

Aseptic Lemna minor was soaked for 4 h in pond water where wild L. minor was naturally flourishing. Seven of the eight surface-colonizing bacterial strains were found capable of promoting the growth of L. minor. This high appearance of plant growth-promoting bacteria (PGPB) suggests that association of environmental bacteria is generally beneficial rather than harmful for host plants. One of the PGPB, Pseudomonas sp. Ps6, enhanced the growth of L. minor by 2–2.5-fold in 10 days. This activity was higher than that previously reported for Acinetobacter calcoaceticus P23, which enhanced growth of L. minor by 1.5–2-fold. Ps6 mostly adhered to and colonized the root rather than the frond, a leaf-like structure of duckweed where P23 preferentially adheres. It was expected that these two strains can share niches, coexist, and enhance the growth of duckweed additively upon co-inoculation. However, contrary to expectation, the growth of L. minor was enhanced by only 2.3-fold by co-inoculation of these two bacteria. P23 lowered the initial adhesion of Ps6 cells by 98.2% on the fronds and by 79.5% on the roots. However, initial adhesion of P23 cells to the roots increased dramatically, by 47.2-fold, following co-inoculation with Ps6. However, the number of P23 cells decreased dramatically to 0.7% on the root and to 3.6% on the frond after 10 days, whereas Ps6 cells increased by 12.5-fold on the frond and kept 69% on the root, thereby eventually restoring the population on the plant surfaces. Because duckweed is the fastest growing vascular plant and it is easy to grow an aseptic and axenic plant, the duckweed/bacteria co-culture system will be a model platform for studying multiple interactions among host plants and the associated bacteria.     

Inhibitors of Abeta production: solid-phase synthesis and SAR of alpha-hydroxycarbonyl derivatives

Inhibitors of amyloid-beta (Abeta) protein production have been widely pursued as a potential treatment for Alzheimer's disease. Following the identification of a 5 microM screening hit, SAR was initiated using solid-phase synthetic techniques. Two series of alpha-hydroxy esters and ketones which are sub-micromolar inhibitors of Abeta production were identified. The most potent alpha-hydroxyketone identified is approximately 30-fold more potent than the initial lead.