Comparative chlorine and temperature tolerance of the oyster crassostrea madrasensis: Implications for cooling system fouling

Crassostrea madrasensis is an important fouling oyster in tropical industrial cooling water systems. C. madrasensis individuals attach to surfaces by cementing one of their two valves to the substratum. Therefore, oyster fouling creates more problems than mussel fouling in the cooling conduits of power stations, because unlike the latter, the shell of the former remains attached to the substratum even after the death of the animal. However, there are no published reports on the tolerance of this species to chlorination and heat treatment. The mortality pattern and physiological behaviour (oxygen consumption and filtration rate) of three size groups (13 mm, 44 mm and 64 mm mean shell length) of C. madrasensis were studied at different residual chlorine concentrations (0.25, 0.5, 0.75, 1, 2, 3 to 5 mg l^{m 1}) and temperatures (30°C to 45°C). The effect of shell size (=age) on C. madrasensis mortality in the presence of chlorine and taking into account temperature was significant, with the largest size group oysters showing highest resistance. At 1 mg l^{m 1} residual chlorine, the 13 mm and 64 mm size group oysters took 504 h (21 d) and 744 h (31 d), respectively to reach 100% mortality. At 39°C, the 13 mm size group oysters took 218 min to reach 100% mortality, whereas the 64 mm size group oysters took 325 min. The oxygen consumption and filtration rate of C. madrasensis showed progressive reduction with increasing residual chlorine concentrations. However, the filtration rate and oxygen consumption responses of C. madrasensis were not significantly different between 30°C (control) and 37.5°C. There was a sharp decrease in the filtration rate and oxygen consumption at 38.5°C. A comparison of the present mortality data with previous reports on other bivalves suggests that the chlorine tolerance of C. madrasensis lies in between that of Perna viridis and Perna perna, while its temperature tolerance is significantly higher than that of the other two bivalve species. However, in power station heat exchangers, where simultaneous chlorine and thermal stresses are existent, C. madrasensis may have an edge over other common foulants, because of its high temperature tolerance.     

Utilization of cathodic hydrogen by hydrogen-oxidizing bacteria

Summary Hydrogen is consumed by methanogenic, sulphate-reducing, and homoacetogenic bacteria and members of these bacterial groups are able to grow chemolithotrophically with hydrogen as sole energy source. Cathodic hydrogen consumption by sulphate-reducing bacteria has been proposed as one of the factors in the anaerobic corrosion of metals. Desulfovibrio spp. were able to utilize cathodic hydrogen from mild steel as the only source of energy for growth with sulphate or nitrate as terminal electron acceptor. Other hydrogen-oxidizing bacteria such as Methanospirillum hungatei, Acetobacterium woodii and Wolinella succinogenes were also able to utilize cathodic hydrogen from mild steel for energy generation and growth. Weight loss studies of mild steel coupons under different growth conditions of Desulfovibrio spp. indicated that hydrogen removal alone is not the cause of corrosion and the depolarization phenomenon probably plays a role only in the initiation of the anaerobic microbial corrosion process.     

Papain Does Not Cleave Operator-Bound Lambda Repressor: Structural Characterization of the Carboxy Terminal Domain and the Hinge

Abstract

The circular dichroism spectra of three different purified carboxy terminal fragments 93–236, 112–236 and 132–236 of the bacteriophage γ cI repressor have been measured and compared with those of the intact repressor and the amino terminal fragment 1–92. All three carboxy terminal fragments contain mostly β-strands and loops, a minor helix content increasing with the size of the fragment, showing that the 93–131 region previously called a hinge is structured. Fourier transformed infrared spectra also showed that fragment 93–236 contains α-helices, β-sheets and turns but fragment 132–236 contains no detectable α-helix, only β-sheets and turns. Papain is known to cleave the γ repressor, but it is shown here that it cannot cleave the operator-bound repressor dimer. For the 132–236 fragment, both the wt and the SN228 mutant previously shown to be dimerization defective in the intact, gave similar dimerization properties as investigated by HPLC at 2 to 100 µM protein concentration, with a KD of 13.2 µM and 19.1 µM respectively. The papain cleavage for wt and SN228 proceed at equal rates for the first cleavage at 92–93; however, the subsequent cleavages are faster for SN228. The three Cys residues in the 132–236 fragment were found to be unreactive upon incubation with DTNB, indicating the thiol sulfur atoms are buried in the repressor carboxy terminal domain. Denaturation of the 132–236 fragment studied by tryptophan fluorescence shows two transitions centered at 1.5 M and 4.5 M of urea.     

Isolation and Characterization of Arsenic-Resistant Bacteria from Contaminated Water-Bodies in West Bengal,India

Bengal Basin is known for severe arsenic contamination. In the present study, we have isolated six bacteria from the arsenic contaminated surface water of Bengal Basin. 16S rDNA sequence analysis identified them as Microbacterium oleivorans, Acinetobacter soli, Acinetobacter venetianus, Acinetobacter junii, Acinetobacter baumannii, Acinetobacter calcoaceticus. All the isolates possess arsenic accumulation potential and high molecular weight plasmid (>10 kb). PCR amplification indicated the presence of arsenic-resistance genes (arsB and aoxB) either in the genome or plasmid or in both in the isolated bacteria (except in Acinetobacter venetianus). Exposure to arsenic affected bacterial growth and induced alteration in cytoplasmic membrane integrity.     

Intracellular mediators of transforming growth factor β superfamily signaling localize to endosomes in chicken embryo and mouse lenses in vivo

Background  

Endocytosis is a key regulator of growth factor signaling pathways. Recent studies showed that the localization to endosomes of intracellular mediators of growth factor signaling may be required for their function. Although there is substantial evidence linking endocytosis and growth factor signaling in cultured cells, there has been little study of the endosomal localization of signaling components in intact tissues or organs.     

Q-FADD: A Mechanistic Approach for Modeling the Accumulation of Proteins at Sites of DNA Damage

The repair of DNA damage requires the ordered recruitment of many different proteins that are responsible for signaling and subsequent repair. A powerful and widely used tool for studying the orchestrated accumulation of these proteins at damage sites is laser microirradiation in live cells, followed by monitoring the accumulation of the fluorescently labeled protein in question. Despite the widespread use of this approach, there exists no rigorous method for characterizing the recruitment process quantitatively. Here, we introduce a diffusion model that explicitly accounts for the unique sizes and shapes of individual nuclei and uses two variables: D_eff, the effective coefficient of diffusion, and F, the fraction of mobile protein that accumulates at sites of DNA damage. Our model quantitatively describes the accumulation of three test proteins, poly-ADP-ribose polymerases 1 and 2 (PARP1/2) and histone PARylation factor 1. D_eff for PARP1, as derived by our approach, is 6× greater than for PARP2 and in agreement with previous literature reports using fluorescence correlation spectroscopy and fluorescence recovery after photobleaching. Our data indicate that histone PARylation factor 1 arrives at sites of DNA damage independently of either PARP. Importantly, our model, which can be applied to existing data, allows for the direct comparison of the coefficient of diffusion for any DNA repair protein between different cell types, obtained in different laboratories and by different methods, and also allows for the interrogation of cell-to-cell variability.     

Comparative Pharmacokinetic Study of Mangiferin After Oral Administration of Pure Mangiferin and US Patented Polyherbal Formulation to Rats

The US patented polyherbal formulation for the prevention and management of type II diabetes and its vascular complications was used for the present study. The xanthone glycoside mangiferin is one of the major effector constituents in the Salacia species with potential anti-diabetic activity. The pharmacokinetic differences of mangiferin following oral administration of pure mangiferin and polyherbal formulation containing Salacia species were studied with approximately the same dose 30 mg/kg mangiferin and its distribution among the major tissue in Wistar rats. Plasma samples were collected at different time points (15, 30, 60, 120, 180, 240, 360, 480, 600, 1,440, 2,160, and 2880 min) and subsequently analyzed using a validated simple and rapid LC-MS method. Plasma concentration versus time profiles were explored by non-compartmental analysis. Mangiferin plasma exposure was significantly increased when administered from formulation compared to the standard mangiferin. Mangiferin resided significantly longer in the body (last mean residence time (MRT_last)) when given in the form of the formulation (3.65 h). C_max values of formulation (44.16 μg/mL) administration were elevated when compared to equivalent dose of the pure mangiferin (15.23 μg/mL). Tissue distribution study of mangiferin from polyherbal formulation was also studied. In conclusion, the exposure of mangiferin is enhanced after formulation and administration and could result in superior efficacy of polyherbal formulation when compared to an equivalent dose of mangiferin. The results indicate that the reason which delays the elimination of mangiferin and enhances its bioavailability might the interactions of the some other constituents present in the polyherbal formulation. Distribution study results indicate that mangiferin was extensively bound to the various tissues like the small intestine, heart, kidney, spleen, and liver except brain tissue.

Electronic supplementary material

The online version of this article (doi:10.1208/s12249-014-0206-8) contains supplementary material, which is available to authorized users.KEY WORDS: bioavailability, mangiferin, pharmacokinetics, polyherbal formulation, tissue distribution     

Membrane-Active Macromolecules Resensitize NDM-1 Gram-Negative Clinical Isolates to Tetracycline Antibiotics

Gram-negative ‘superbugs’ such as New Delhi metallo-beta-lactamase-1 (bla _NDM-1) producing pathogens have become world’s major public health threats. Development of molecular strategies that can rehabilitate the ‘old antibiotics’ and halt the antibiotic resistance is a promising approach to target them. We report membrane-active macromolecules (MAMs) that restore the antibacterial efficacy (enhancement by >80-1250 fold) of tetracycline antibiotics towards bla _NDM-1 Klebsiella pneumonia and bla _NDM-1 Escherichia coli clinical isolates. Organismic studies showed that bacteria had an increased and faster uptake of tetracycline in the presence of MAMs which is attributed to the mechanism of re-sensitization. Moreover, bacteria did not develop resistance to MAMs and MAMs stalled the development of bacterial resistance to tetracycline. MAMs displayed membrane-active properties such as dissipation of membrane potential and membrane-permeabilization that enabled higher uptake of tetracycline in bacteria. In-vivo toxicity studies displayed good safety profiles and preliminary in-vivo antibacterial efficacy studies showed that mice treated with MAMs in combination with antibiotics had significantly decreased bacterial burden compared to the untreated mice. This report of re-instating the efficacy of the antibiotics towards bla _NDM-1 pathogens using membrane-active molecules advocates their potential for synergistic co-delivery of antibiotics to combat Gram-negative superbugs.