Cellobiose hydrolysis using acid-functionalized nanoparticles

Mineral acids have been used effectively for the pretreatment of cellulosic biomass to improve sugar recovery and promote its conversion to ethanol; however, substantial capital investment is required to enable separation of the acid, and corrosion-resistant materials are necessary. Disposal and neutralization costs are also concerns because they can decrease the economic feasibility of the process. In this work, three acid-functionalized nanoparticles were synthesized for pretreatment and hydrolysis of lignocellulosic biomass. Silica-protected cobalt spinel ferrite nanoparticles were functionalized with perfluoroalkylsulfonic acid (PFS), alkylsulfonic acid (AS), and butylcarboxylic acid (BCOOH) groups. These nanoparticles were magnetically separated from the reaction media and reused. TEM images showed that the average diameter was 2 nm for both PFS and BCOOH nanoparticles and 7 nm for AS nanoparticles. FTIR confirmed the presence of sulfonic and carboxylic acid functional groups. Ion exchange titration measurements yielded 0.9, 1.7, and 0.2 mmol H⁺/g of catalyst for PFS, AS, and BCOOH nanoparticles, respectively. Elemental analysis results indicated that PFS and AS nanoparticles had 3.1 and 4.9% sulfur, respectively. Cellobiose hydrolysis was used as a model reaction to evaluate the performance of acid-functionalized magnetic nanoparticles for breaking β-(1→4) glycosidic bonds. Cellobiose conversion of 78% was achieved when using AS nanoparticles as the catalyst at 175°C for 1 h, which was significantly higher than the conversion for the control experiment (52%). AS nanoparticles retained more than 60% of their sulfonic acids groups after the first run, and 65 and 60% conversions were obtained for the second and third runs, respectively.     

Seasonal phenotypic plasticity: wild ladybirds are darker at cold temperatures

Seasons vary in the average environmental conditions a species experiences, meaning that optimum strategies for concealment or feeding may also vary. Populations of the ladybird Harmonia axyridis contain both melanic and non-melanic forms and changes in allele frequency in some populations suggest that melanism may be advantageous in winter, but costly in summer. This could favour the evolution of phenotypic plasticity in colour pattern, as individuals which changed colour throughout the year would be able to maximise their fitness. We have previously shown in the laboratory that melanisation in the “non-melanic” morph of H. axyridis, f. succinea, is predominantly controlled by temperature during development. We now report that wild populations of H. axyridis f. succinea also conform to this principle: lower field temperatures during development produce individuals with more and larger spots. Furthermore, we have found that the critical period of development where temperature affects the level of melanisation covers the pupal and late larval stages, and melanisation increases with the length of time spent at cold temperature. We conclude it is likely that the temperature experienced during this period is used to predict the temperature encountered as an adult. This may allow individuals to produce the level of melanisation necessary to maintain activity levels at the temperatures encountered when they emerge. The long sensitive period seen in H. axyridis may be in order to avoid mismatches between melanisation and seasonal environment.     

Cryptic plasmid pBf1 fromButyrivibrio fibrisolvens AR10: Its use as a replicon for recombinant plasmids

A cryptic 2.85 kb plasmid (pBf1) was isolated from the rumen bacteriumButyrivibrio fibrisolvens strain AR10, ampped with restriction endonucleases, and cleavage sites suitable for attachment toEscherichia coli plasmids were identified. AR10 was not able to be cured of pBf1 by growth at 42°C or in 0.25 g ampicillin/ml, but growth in 50 g acridine orange/ml for three culture passages produced cured colonies at a frequency of <1%. Chimeric plasmids were constructed by combining pBf1 with theE. coli plasmid pUC18, in addition to the clindamycin resistance gene fromBacteroides fragilis plasmid pDP1 (pCW2 and pCW3), or the CAT gene fromE. coli plasmid pKK232-8 (pCK1). For plasmid construction, pBf1 was cleaved at two alternative restriction sites to increase the likelihood that replication control sequences would remain functional in at least one of the plasmids. Electroporation of AR10 yielded transformant populations that clearly maintained the plasmids and that appeared to express the ampicillinase gene of pUC18, although transformants were not readily selectable with any of the three antibiotics. The suitability of pBf1 as a replicon on which to base the construction of shuttle vectors was demonstrated clearly, by persistence of plasmid pCW3 in the absence of selective pressure, and the addition of appropriate selection factors is expected to yield practical transformation vectors.     

Mechanisms of lymphocyte-mediated cytotoxicity. I. The effects of anti-human lymphotoxin antisera on the cytolysis of allogeneic B cell lines by MLC-sensitized human lymphocytes in vitro

Goat and rabbit anti-human lymphotoxin sera, IgG and F(ab')2 reagents were investigated for their capacity to effect a specific alloimmune lymphocyte-mediated cytotoxic reaction. The cytotoxic reaction employed human peripheral blood or adenoid lymphocytes sensitized in MLC to allogeneic B lymphocyte cell lines and lysis was measured in a short-term 51Cr-release assay. A polyspecific anti-LT sera (anti-WS), made against unfractionated whole supernatants from lectin-activated lymphocytes and its IgG and F(ab')2 fragments, was found to be a potent inhibitor of this reaction when the anti-WS reagent was present throughout the assay period. Absorption studies indicated the anti-WS was inhibiting cytolysis at the level of effector cell or its products. Two broadly defined antibody specificities were involved in the cytolytic-inhibitory activity of the polyspecific anti-LT; i) antigens present on the normal lymphocyte cell surface; and ii) lymphocyte surface antigens associated with activated cells. These results correlate with the previously defined antigenic structure of the LT Cx and alpha H classes. Anti-LT sera reactive with the smaller m.w. alpha and beta classes and subclasses were not inhibitory, although the anti-beta sera showed a moderate enhancing activity. The results indicated that several anti-LT antibody specificities may be required to inhibit alloimmune cytolysis. The results suggest LT molecules may mediate lymphocyte-induced alloimmune cytolysis as a multi-component toxin system, rather than as an individual toxin.     

Detection and characterization of actin monomers, oligomers, and filaments in solution by measurement of fluorescence photobleaching recovery

Fluorescence photobleaching recovery (FPR) was measured to determine the diffusion coefficient of fluorescein-labeled G-actin in low-salt buffer. The result obtained, 7.15 +/- 0.35 X 10(-7) cm2/s, is in good agreement with that computed from the molecular weight, partial specific volume, and sedimentation coefficient, but is higher than previously obtained values. It is demonstrated from theory that at low ionic strength, the electrostatic contribution to the intrinsic viscosity leads to an overestimate of the hydrodynamic eccentricity of G-actin. Data from FPR, sedimentation, and fluorescence polarization experiments all indicate that the true low-salt form of the actin monomer has an axial ratio less than or equal to 3.0. The G-F transformation of actin was also observed by measurement of FPR during the assembly phase, in the steady state, and in the presence of ligands such as cytochalasin and aldolase. Each FPR record in general yields three data: relative proportion of rapidly and slowly diffusing actin, diffusion coefficient for the high-mobility fraction, and a mean diffusion coefficient for the low-mobility fraction. A relation between the mean low-mobility diffusion coefficient and the number-average filament length is derived and applied to the analysis of FPR data. Under typical conditions, the average filament length was much greater than 10 micron in the steady state. Cytochalasin D was found to decrease filament length and total amount of filament proportionally; total filament number was not greatly affected. In all polymerizations of G-actin, the high-mobility material observed in situ was found to be essentially monomeric actin. Relatively stable oligomers of actin were separated by fractionating G-AF-actin by gel filtration in 50 microM MgCl2 at 4 degrees C. On the basis of the diffusion coefficient, we conclude that monomer and dimer constitute the major particle types present under these conditions. Sedimentation of labeled actin polymerized in 1.0 mM MgCl2 yielded a graded supernatant that contained actin oligomers significantly larger than the monomer.     

A national survey integrating clinical,laboratory, and WASH data to determine the typology of trachoma in Nauru

BackgroundThe epidemiology of trachoma in several Pacific Islands differs from other endemic settings, in that there is a high prevalence of clinical signs of trachoma, particularly trachomatous inflammation—follicular (TF), but few cases of trichiasis and limited evidence of ocular chlamydial infection. This so-called “Pacific enigma” has led to uncertainty regarding the appropriate public health response. In 2019 alongside Nauru’s national trachoma population survey, we performed bacteriological and serological assessments of children to better understand the typology of trachoma and to determine whether there is a need for trachoma interventions.MethodsWe used two-stage cluster sampling, examining residents aged ≥1 year and collecting household-level water, sanitation, and hygiene (WASH) variables. Children aged 1–9 years provided conjunctival swabs and finger-prick dried blood spots to investigate the presence of Chlamydia trachomatis nucleic acid and anti-Pgp3 antibodies, respectively.Principal FindingsIn 818 participants aged 1–9 years, the age-adjusted TF prevalence was 21.8% (95% CI 15.2–26.2%); ocular C. trachomatis prevalence was 34.5% (95% CI 30.6–38.9), and anti-Pgp3 antibody prevalence was 32.1% (95% CI 28.4%–36.3%). The age- and gender-adjusted prevalence of trichiasis in ≥15-year-olds was 0.3% (95% CI 0.00–0.85), but no individual with trichiasis had trachomatous scarring (TS). Multivariable analysis showed an association between age and both TF (OR per year of age 1.3 [95% CI 1.2–1.4]) and anti-Pgp3 positivity (OR 1.2 [95% CI 1.2–1.3]). There were high rates of access to water and sanitation and no WASH variable was associated with the presence of TF.ConclusionsTF, nucleic acid, and age-specific antibody prevalence collectively indicate that high levels of C. trachomatis transmission among children present a high risk of ocular damage due to trachoma. The absence of trichiasis with trachomatous scarring suggest a relatively recent increase in transmission intensity.     

Synthetic routes to mixed-ligand cobalt(III) dithiocarbamato complexes containing imidazole, amine and pyridine donors and the X-ray crystal structure of a cobalt(III) bis(dithiocarbamato) histamine complex

The binuclear cobalt complex [Co(2)(Me(2)dtc)(5)](+) reacts with a range of nitrogen donor ligands L' or L' to form an equimolar mixture of Co(Me(2)dtc)(3) and the mixed-ligand complexes [Co(Me(2)dtc)(2)(L')(2)](+) or [Co(Me(2)dtc)(2)(L')](+), where (L')(2) is two monodentate ligands and (L') is one bidentate ligand. The complexes prepared by this route contain the monodentate ligands L'=1-methyl-imidazole, 1-methyl-5-nitro-imidazole and benzimidazole, all of which coordinate to cobalt through an imidazole nitrogen atom. Symmetrical bidentate ligand complexes contain the bisimidazole L'=2,2'-bis(4,5-dimethylimidazole), the diamine L'=1,2-diaminobenzene and the pyridine donors L'=2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine and 1,10-phenanthroline. Two examples of complexes with unsymmetrical bidentate imidazole-amine donors were prepared in which L'=4-(2-aminoethyl)imidazole (histamine) and 2-aminomethylbenzimidazole. All new complexes were fully characterised, and the X-ray crystal structure of the histamine complex [Co(Me(2)dtc)(2)(hist)]ClO(4) is also reported.     

A complementation analysis of mobilization deficient mutants of the plasmid colE1

Summary Hydroxylamine was used to induce mutants of the ColE1 derived plamid pML2 that are inefficiently mobilized (Mob^-) during conjugation by an Hfr donor. The ability of those mutants to be complemented by deletion mutants and Tn3 insertion mutants of ColE1 was examined. Three complementation groups were identified and localized on the ColE1 genetic map (Mob1, Mob2, and Mob3). One hydroxylamine mutant was not complemented by any mobilization deficient mutant but was complemented by mobilizable ColE1 mutants. Two hydroxylamine mutants were not complemented by any ColE1 derivatives. A mutant that had its relaxation nick site deleted had a markedly reduced mobilizability. The relationship between DNA relaxation, replication and mobilization is considered.