Molecular genetics of aminoglycoside resistance genes and familial relationships of the aminoglycoside-modifying enzymes.

The three classes of enzymes which inactivate aminoglycosides and lead to bacterial resistance are reviewed. DNA hybridization studies have shown that different genes can encode aminoglycoside-modifying enzymes with identical resistance profiles. Comparisons of the amino acid sequences of 49 aminoglycoside-modifying enzymes have revealed new insights into the evolution and relatedness of these proteins. A preliminary assessment of the amino acids which may be important in binding aminoglycosides was obtained from these data and from the results of mutational analysis of several of the genes encoding aminoglycoside-modifying enzymes. Recent studies have demonstrated that aminoglycoside resistance can emerge as a result of alterations in the regulation of normally quiescent cellular genes or as a result of acquiring genes which may have originated from aminoglycoside-producing organisms or from other resistant organisms. Dissemination of these genes is aided by a variety of genetic elements including integrons, transposons, and broad-host-range plasmids. As knowledge of the molecular structure of these enzymes increases, progress can be made in our understanding of how resistance to new aminoglycosides emerges.     

Glycyrrhizic acid (GA), a triterpenoid saponin glycoside alleviates ultraviolet-B irradiation-induced photoaging in human dermal fibroblasts

Glycyrrhizic acid (GA), a triterpenoid saponin glycoside from the roots and rhizomes of licorice is used in traditional and modern medicine for the treatment of numerous medical conditions including skin diseases and beauty care product. In the present study, we investigated the effect of GA against ultraviolet B (UVB) irradiation-induced photoaging in human dermal fibroblasts (HDFs) and its possible mechanism of action. HDFs were subjected to photoaging by sub-toxic dose of UVB (10 mj/cm(2)) irradiation. Cell viability, matrix metalloproteinase 1 (MMP1), pro-collagen 1, cellular and nuclear morphology, cell cycle, intracellular reactive oxygen species (ROS), caspase 3 and hyaluronidase inhibition assays were performed. Western blotting was used to evaluate the expression of NF-kappa B (NF-κB) and cytochrome-C proteins. GA treatment significantly inhibited photoaging. It achieved this by reducing ROS, NF-κB, cytochrome c, caspase 3 levels and inhibiting hyaluronidase enzyme. The main mechanism seems to be, most likely by blocking MMP1 activation by modulating NF-κB signaling. These findings may be useful for development of natural and safe photoprotective agents against UVB irradiation.     

Indole Can Act as an Extracellular Signal in Escherichia coli

Previous work has shown that lacZ fusions to the cysK, astD, tnaB, and gabT genes in Escherichia coli are activated by self-produced extracellular signals. Using a combination of ethyl acetate extraction, reversed-phase C(18) chromatography, and thin-layer chromatography, we have purified an extracellular activating signal from E. coli supernatants. Mass spectrometry revealed a molecule with an m/z peak of 117, consistent with indole. Nuclear magnetic resonance analysis of the purified E. coli factor and synthetic indole revealed identical profiles. Using synthetic indole, a dose-dependent activation was observed with lacZ fusions to the gabT, astD, and tnaB genes. However, cysK::lacZ and several control fusions were not significantly activated by indole. Conditioned medium prepared from a tnaA (tryptophanase) mutant, deficient in indole production, supported 26 to 41% lower activation of the gabT and astD fusions. The residual level of activation may be due to a second activating signal. Activation of the tnaB::lacZ fusion was reduced by greater than 70% in conditioned medium from a tnaA mutant.     

Role of CysE in production of an extracellular signaling molecule in Providencia stuartii and Escherichia coli: loss of CysE enhances biofilm formation in Escherichia coli

A mini-Tn5Cm insertion has been identified that significantly reduced the amount of an extracellular activating signal for a lacZ fusion (cma37::lacZ) in Providencia stuartii. The transposon insertion was located immediately upstream of an open reading frame encoding a putative CysE ortholog. The CysE enzyme, serine acetyltransferase, catalyzes the conversion of serine to O-acetyl-L-serine (OAS). This activating signal was also produced by Escherichia coli, and production was abolished in a strain containing a null allele of cysE. Products of the CysE enzyme (OAS, N-acetyl-L-serine [NAS], O-acetyl-L-threonine, and N-acetyl-L-threonine) were individually tested for the ability to activate cma37::lacZ. Only OAS was capable of activating the cma37::lacZ fusion. The ability of OAS to activate the cma37::lacZ fusion was abolished by pretreatment at pH 8.5, which converts OAS to NAS. However, the activity of the native signal in conditioned medium was not decreased by treatment at pH 8.5. In contrast, conditioned medium prepared from cells grown at pH 8.5 exhibited a 4- to 10-fold-higher activity, relative to pH 6.0. Additional genes regulated by the CysE-dependent signal and OAS were identified in P. stuartii and E. coli. The response to the extracellular signal in E. coli was dependent on CysB, a positive activator that requires NAS as a coactivator. In E. coli, a cysE mutant formed biofilms at an accelerated rate compared to the wild type, suggesting a physiological role for this extracellular signal.     

Standardization of in vitro micropropagation procedure of Oriental Lilium Hybrid Cv. ‘Ravenna’

Micropropagation protocol of Oriental Hybrid Lilium cv. Ravenna was developed using bulb scale segments (Basal and Tip) as explants. Surface sterilization of healthy bulb scales with carbendazim 200 ppm for 30 min, then 0.1 percent mercuric chloride for 10 min, then 70% ethyl alcohol for 30 s was superior to all other treatments in recording highest culture asepsis (77.08%) and higher explant survival (86.12%). Explant survival was higher in basal segments (88.54%) compared to tip segments (85.52%). Highest culture establishment was recorded in basal scale segments (68.26%) followed by tip scale segments (55.21%). MS medium augmented with 0.50 mgl⁻¹ Naphthalene acetic acid and 2.0 mgl⁻¹. 6-Benzylamino Purine recorded maximum culture establishment (76.17%), highest bulblet number/explant (5.52) with maximum length of shoots (2.20 cm) and number of leaves (3.39). This treatment combination of growth regulators resulted in highest shoot proliferation (83.33%) along with maximum shoot number (2.41explant⁻¹), shoot length (2.35 cm) and leaf number (5.44) of micro shoots during proliferation stage. Rooting of explants was superior with Indole-3-butyric acid compared to Naphthalene acetic acid. Highest rooting of 92.71% along with maximum number of primary roots shoot⁻¹ (12.06), maximum primary root length (3.17 cm) was documented in Murashige and Skoog medium added with Indole-3-butyric acid 1.50 mgl⁻¹ with best ex vitro survival rate (98.96%) of rooted plantlets during primary hardening in perlite + vermiculite (1:1) mixture.     

Ovarian development and histological observations of threatened dwarf snakehead fish,Channa gachua (Hamilton, 1822)

Channa gachua were monthly sampled throughout a year and the histological analysis of their ovaries was done to determine the changes occurring in ovarian development. Based on histological examination of the ovaries, the oogenic process of C. gachua undergoes distinct cyclic and seasonal morphological changes. Five different developmental stages were identified under three major categories: pre-spawning (immature, maturing, mature), spawning (ripe-running) and post-spawning (spent). The peak spawning period of C. gachua was noticed during December - February. The gonadosomatic index (GSI) and ova diameter ranged from 0.79 to 3.61% and 543–1123 μm respectively. The highest mean GSI (3.61 ± 0.16) and oocyte diameter (1123 ± 55 μm) were observed in December indicating that during this month the gonadal development reached maturity.