Characterization of <Emphasis Type="Italic">Bacillus</Emphasis> phage-K2 isolated from chungkookjang,a fermented soybean foodstuff

An investigation of a virulent Bacillus phage-K2 (named Bp-K2) isolated from chungkookjang (a fermented soybean foodstuff) was made. Bp-K2 differed in infectivity against a number of Bacillus subtilis strains including starter strains of chungkookjang and natto, being more infectious to Bacillus strains isolated from the chungkookjang, but much less active against a natto strain. Bp-K2 is a small DNA phage whose genome size is about 21 kb. Bp-K2 is a tailed bacteriophage with an isometric icosahedral head (50 nm long on the lateral side, 80 nm wide), a long contractile sheath (85–90 nm × 28 nm), a thin tail fiber (80–85 nm long, 10 nm wide), and a basal plate (29 nm long, 47 nm wide) with a number of spikes, but no collar. The details of the structures of Bp-K2 differ from natto phage ϕBN100 as well as other known Bacillus phages such as SPO1-like or ϕ 29-like viruses. These data suggest that Bp-K2 would be a new member of the Myoviridae family of Bacillus bacteriophages.     

Reinvasion by ship rats (<Emphasis Type="Italic">Rattus rattus</Emphasis>) of forest fragments after eradication

Reinvasions provide prime examples of source-sink population dynamics, and are a major reason for failure of eradications of invasive rats from protected areas. Yet little is known about the origins and population structure of the replacement population compared with the original one. We eradicated eight populations of ship rats from separate podocarp-broadleaved forest fragments surrounded by open grassland (averaging 5.3 ha, scattered across 20,000 ha) in rural landscapes of Waikato, New Zealand, and monitored the- re-establishment of new populations. Rats were kill-trapped to extinction during January to April 2008, and then again after reinvasion in April–May (total n = 517). Rats carrying Rhodamine B dye (n = 94), available only in baits placed 1–2 months in advance in adjacent source areas located 170–380 m (average 228 m edge to edge) away, appeared in 7 of the 8 fragments from the first day of the first eradication. The distribution of age groups, genders and proportions of reproductively mature adults (more immature juvenile males and fewer fully mature old females) was different among marked rats compared with all other rats (P = 0.001, n = 509); in all rats caught on days 7+ of the first eradication compared with on days 1–6 (P = 0.000); and in the total sample collected in fragments by trapping to and after local extinction compared with in brief, fixed-schedule sampling of populations in continuous forests (P = 0.000). Genotyping of 493 carcases found no significant population-level differentiation among the 8 fragments, confirming that the rats in all fragments belonged to a single dynamic metapopulation. Marked rats of both genders travelled up to 600 m in a few days. Conservation of forest fragments is compromised by the problem that ship rats cannot be prevented from rapidly reinvading any cleared area after eradication.     

Isolation and characterization of a new bacteriophage MMP17 from <Emphasis Type="Italic">Meiothermus</Emphasis>

Thermophiles and their viruses are extraordinarily important because of their roles in processes of evolution, biogeochemistry and ecology. Species of the genus Meiothermus share close relationship with genus Thermus, but no Meiothermus bacteriophage has been reported yet. In this work, a new thermophilic bacteriophage named MMP17 (Meiothermus Myoviridae phage 17) was isolated from a Meiothermus strain and was further characterized. MMP17 was a typical myovirus with an icosahedral head (42 nm in diameter) and a tail (120 nm in length and 17 nm in width). Its DNA was about 33.5–39.5 kb in size. MMP17 was very stable at 55–60°C and pH 6–7. According to the one-step growth curve, the latent period and the burst period were 60 and 30 min, respectively. An average of 15 phage particles was released from each infected cell. Four major bands were detected in purified virion preparation by SDS-PAGE. As MMP17 was a thermophilic bacteriophage with lower production temperature, its characterization and the relationship between MMP17 and Thermus bacteriophages deserved for further study.     

Microbial survival in the stratosphere and implications for global dispersal

Spores of Bacillus subtilis were exposed to a series of stratosphere simulations. In total, five distinct treatments measured the effect of reduced pressure, low temperature, high desiccation, and intense ultraviolet (UV) irradiation on stratosphere-isolated and ground-isolated B. subtilis strains. Environmental conditions were based on springtime data from a mid-latitude region of the lower stratosphere (20 km). Experimentally, each treatment consisted of the following independent or combined conditions: −70°C, 56 mb, 10–12% relative humidity and 0.00421, 5.11, and 54.64 W/m² of UVC (200–280 nm), UVB (280–315 nm), UVA (315–400 nm), respectively. Bacteria were deposited on metal coupon surfaces in monolayers of ~1 × 10⁶ spores and prepared with palagonite (particle size < 20 μm). After 6 h of exposure to the stratosphere environment, 99.9% of B. subtilis spores were killed due to UV irradiation. In contrast, temperature, desiccation, and pressure simulations without UV had no effect on spore viability up through 96 h. There were no differences in survival between the stratosphere-isolated versus ground-isolated B. subtilis strains. Inactivation of most bacteria in our simulation indicates that the stratosphere can be a critical barrier to long-distance microbial dispersal and that survival in the upper atmosphere may be constrained by UV irradiation.     

Strong regeneration ability from rhizome fragments in two invasive clonal plants (Solidagocanadensis and S. gigantea)

The two rhizomatous perennials Solidago canadensis and S. gigantea belong to the most widespread alien plants in Europe. Anecdotal observations suggest that they disperse also by rhizome fragments. For testing their resprouting ability, rhizome fragments of different sizes from both species were buried at four different soil depths (0, 5, 10 and 20 cm, respectively) in a common garden. Rhizome fragments of S. canadensis ranged 3–6 cm in length, those of S. gigantea 5–20 cm in length. Resprouting plants were harvested after 3 months and growth related traits measured to assess their vitality. Resprouting rate in S. gigantea was far higher than in S. canadensis (85 and 19%, respectively). In S. gigantea, fragments of all sizes resprouted from all soil depths whereas none rhizome of S. canadensis emerged from 20 cm burial depth. In S. gigantea, size related traits showed significant interactions between fragment size and burial depth, but not relative shoot growth rate. At all burial depths, vitality of plants emerging from small rhizomes was lower than plants emerging from large rhizomes. Effects of rhizome size became stronger with increasing burial depth. The results show that both species are able to resprout from buried rhizome fragments, and that succesful regeneration is more likely to occur in S. gigantea. Managing these species should avoid any activities promoting rhizome fragmentation and dispersal of fragments.     

Isolation and characterization of the ejectisomes of the prasinophyte Pyramimonas grossii

For the first time, ejectisome-enriched fractions were isolated from the marine prasinophyte Pyramimonas grossii. Transmission electron microscopy revealed that most of the ejectisomes were discharged and formed long, spirally twisted filaments. Some ejectisomes were still fully or partly furled. Discharged ejectisomes measured up to 26 μm in length and 200 nm in width; those still furled measured up to 900 nm in width and 1,000 nm in length. Particle periodicities of approximately 4.2 and 5.8 nm could be measured from freeze-fractured filaments. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed a protein banding pattern, dominated by polypeptides of 16–20 kDa. These polypeptides were not glycosylated and did not cross-react with antisera directed against recombinant R-body polypeptides of Caedibacter taeniospiralis or directed against reconstituted cryptophycean ejectisomes.     

Composition and significance of picophytoplankton in Antarctic waters

Filter fractionated picophytoplankton from Antarctic coastal waters (summer 2001) represented only 7–33% of total phytoplankton, even though total stocks were low (average Chl a = 0.32 μg l⁻¹, range = 0.13–1.03 μg l⁻¹). Though all cells passed a 2 μm filter, electron microscopy revealed most cells were over 2 μm, principally Parmales, Phaeocystis sp., and small diatoms. CHEMTAX analysis of HPLC pigment data suggested type 8 haptophytes (e.g. Phaeocystis sp. plus Parmales and pelagophytes) contributed 7–58% of picoplanktonic chlorophyll a, type 6 haptophytes (e.g. coccolithophorids) 18–59%, diatoms 0–18% (mostly type 2 diatoms, e.g. Pseudonitzschia sp., 0–15%), prasinophytes 0–17%, with cell fragments of cryptophytes 0–40%, and dinoflagellates 0–11%. Only stocks of type 8 haptophytes and prasinophytes differed significantly due to successional changes. Zeaxanthin concentrations exceeded estimates from previous cyanobacterial counts and may derive from non-photosynthetic bacteria.     

Optimization of variable fluorescence measurements of phytoplankton communities with cyanobacteria

Excitation–emission fluorescence matrices of phytoplankton communities were simulated from laboratory-grown algae and cyanobacteria cultures, to define the optical configurations of theoretical fluorometers that either minimize or maximize the representation of these phytoplankton groups in community variable fluorescence measurements. Excitation sources that match the photosystem II (PSII) action spectrum of cyanobacteria do not necessarily lead to equal representation of cyanobacteria in community fluorescence. In communities with an equal share of algae and cyanobacteria, inducible PSII fluorescence in algae can be retrieved from community fluorescence under blue excitation (450–470 nm) with high accuracy (R ² = 1.00). The highest correlation between community and cyanobacterial variable fluorescence is obtained under orange-red excitation in the 590–650 nm range (R ² = 0.54). Gaussian band decomposition reveals that in the presence of cyanobacteria, the emission detection slit must be narrow (up to 10 nm) and centred on PSII chlorophyll-a emission (~683 nm) to avoid severe dampening of the signal by weakly variable phycobilisomal fluorescence and non-variable photosystem I fluorescence. When these optimizations of the optical configuration of the fluorometer are followed, both cyanobacterial and algal cultures in nutrient replete exponential growth exhibit values of the maximum quantum yield of charge separation in PSII in the range of 0.65–0.7.     

On visual pigment templates and the spectral shape of invertebrate rhodopsins and metarhodopsins

The absorbance spectra of visual pigments can be approximated with mathematical expressions using as single parameter the absorbance peak wavelength. A comparison of the formulae of Stavenga et al. in Vision Res 33:1011–1017 (1993) and Govardovskii et al. in Vis Neurosci 17:509–528 (2000) applied to a number of invertebrate rhodopsins reveals that both templates well describe the normalized α-band of rhodopsins with peak wavelength > 400 nm; the template spectra are virtually indistinguishable in an absorbance range of about three log units. The template formulae of Govardovskii et al. in Vis Neurosci 17:509–528 (2000) describe the rhodopsin spectra better for absorbances below 10⁻³. The template predicted spectra deviate in the ultraviolet wavelength range from each other as well as from measured spectra, preventing a definite conclusion about the spectral shape in the wavelength range <400 nm. The metarhodopsin spectra of blowfly and fruitfly R1-6 photoreceptors derived from measured data appear to be virtually identical. The established templates describe the spectral shape of fly metarhodopsin reasonably well. However, the best fitting template spectrum slightly deviates from the experimental spectra near the peak and in the long-wavelength tail. Improved formulae for fitting the fly metarhodopsin spectra are proposed.     

UV-susceptibility of zoospores of the brown macroalga Laminaria digitata from Spitsbergen

The UV-susceptibility of zoospores of the lower sublittoral kelp Laminaria digitata was studied in the laboratory under varying fluence of spectral irradiance consisting of photosynthetically active radiation (PAR, 400–700 nm; = P), PAR + UV-A radiation (UV-A, 320–400 nm; = PA), and PAR + UV-A + UV-B radiation (UV-B, 280–320 nm; = PAB). In vivo absorption of phlorotannin, localisation of phlorotannin-containing physodes, structural changes, DNA damage and repair, photosynthesis and germination of zoospores were measured after exposure treatments and after 2–6 days of recovery in dim white light. Photodegradation of phlorotannins was observed after extended exposure to ultraviolet radiation (UVR). The UV-protective function of extra- and intracellular phlorotannins was, therefore, observed only after 8 h, but not after 16-h UVR exposure. The energetic cost of photoprotection may have caused the delay in ontogenic development of zoospores after 8-h exposure to PA and PAB treatment; longer exposure time corresponding to 16-h PA and PAB treatment eventually lead to cell degeneration at 6 days post-cultivation. The formation of cyclobutane–pyrimidine dimers (CPDs), as indicator of DNA damage, was not blocked by the UV-absorbing phlorotannins during the 16-h PAB exposure and the inability for DNA damage repair was likely responsible for low photosynthetic recovery and spore mortality. The higher sensitivity of L. digitata zoospores to UVR compared to other kelps such as Saccorhiza dermatodea and Alaria esculenta confirmed our hypothesis that the depth distribution of adult sporophytes in the field correlates to the sensitivity of their corresponding early life history stages to different stress factors in general and UVR in particular.     

Effect of ultrafine-grained titanium surfaces on adhesion of bacteria

The influence of the ultrafine crystallinity of commercial purity grade 2 (as-received) titanium and titanium modified by equal channel angular pressing (modified titanium) on bacterial attachment was studied. A topographic profile analysis of the surface of the modified titanium revealed a complex morphology of the surface. Its prominent micro- and nano-scale features were 100–200-nm-scale undulations with 10–15 μm spacing. The undulating surfaces were nano-smooth, with height variations not exceeding 5–10 nm. These surface topography characteristics were distinctly different from those of the as-received samples, where broad valleys (up to 40–60 μm) were detected, whose inner surfaces exhibited asperities approximately 100 nm in height spaced at 1–2 μm. It was found that each of the three bacteria strains used in this study as adsorbates, viz. Staphylococcus aureus CIP 68.5, Pseudomonas aeruginosa ATCC 9025 and Escherichia coli K12, responded differently to the two types of titanium surfaces. Extreme grain refinement by ECAP resulted in substantially increased numbers of cells attached to the surface compared to as-received titanium. This enhanced degree of attachment was accompanied with an increased level of extracellular polymeric substances (EPS) production by the bacteria. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The cone photoreceptors and visual pigments of chameleons

Visual pigments, oil droplets and photoreceptor types in the retinas of four species of true chameleons have been examined by microspectrophotometry. The species occupy different photic environments: two species of Chamaeleo are from Madagascar and two species of Furcifer are from Africa and the Arabian Peninsula. In addition to double cones, four spectrally distinct classes of single cone were identified. No rod photoreceptors were observed. The visual pigments appear to be mixtures of rhodopsins and porphyropsins. Double cones contained a pale oil droplet in the principle member and both outer segments contained a long-wave-sensitive visual pigment with a spectral maximum between about 555 nm and 610 nm, depending on the rhodopsin/porphyropsin mixture. Long-wave-sensitive single cones contained a visual pigment spectrally identical to the double cones, but combined with a yellow oil droplet. The other three classes of single cone contained visual pigments with maxima at about 480–505, 440–450 and 375–385 nm, combined with yellow, clear and transparent oil droplets respectively. The latter two classes were sparsely distributed. The transmission of the lens and cornea of C. dilepis was measured and found to be transparent throughout the visible and near ultraviolet, with a cut off at about 350 nm.     

A Composite Polyelectrolytic Matrix for Controlled Oral Drug Delivery

The purpose of this study was to formulate drug-loaded polyelectrolyte matrices constituting blends of pectin, chitosan (CHT) and hydrolyzed polyacrylamide (HPAAm) for controlling the premature solvation of the polymers and modulating drug release. The model drug employed was the highly water-soluble antihistamine, diphenhydramine HCl (DPH). Polyelectrolyte complex formation was validated by infrared spectroscopy. Matrices were characterized by textural profiling, porositometry and SEM. Drug release studies were performed under simulated gastrointestinal conditions using USP apparatus 3. FTIR spectra revealed distinctive peaks indicating the presence of –COO⁻ symmetrical stretching (1,425–1,390 cm⁻¹) and -NH₃⁺ deformation (1,535 cm⁻¹) with evidence of electrostatic interaction between the cationic CHT and anionic HPAAm corroborated by molecular mechanics simulations of the complexes. Pectin–HPAAm matrices showed electrostatic attraction due to residual –NH₂ and –COO⁻ groups of HPAAm and pectin, respectively. Textural profiling demonstrated that CHT-HPAAm matrices were most resilient at 6.1% and pectin–CHT–HPAAm matrices were the least (3.9%). Matrix hardness and deformation energy followed similar behavior. Pectin–CHT–HPAAm and CHT–HPAAm matrices produced type IV isotherms with H3 hysteresis and mesopores (22.46 nm) while pectin–HPAAm matrices were atypical with hysteresis at a low P/P₀ and pore sizes of 5.15 nm and a large surface area. At t _2 h, no DPH was released from CHT–HPAAm matrices, whereas 28.2% and 82.2% was released from pectin–HPAAm and pectin–CHT–HPAAm matrices, respectively. At t _4 h, complete DPH release was achieved from pectin–CHT–HPAAm matrices in contrast to only 35% from CHT–HPAAm matrices. This revealed the release-modulating capability of each matrix signifying their applicability in controlled oral drug delivery applications.     

Genetic Relationship of <Emphasis Type="Italic">Curcuma</Emphasis> Species from Northeast India Using PCR-Based Markers

Molecular genetic fingerprints of nine Curcuma species from Northeast India were developed using PCR-based markers. The aim involves elucidating there intra- and inter-specific genetic diversity important for utilization, management, and conservation. Twelve random amplified polymorphic DNA (RAPD), 19 Inter simple sequence repeats (ISSRs), and four amplified fragment length polymorphism (AFLP) primers produced 266 polymorphic fragments. ISSR confirmed maximum polymorphism of 98.55% whereas RAPD and AFLP showed 93.22 and 97.27%, respectively. Marker index and polymorphic information content varied in the range of 8.64–48.1, 19.75–48.14, and 25–28 and 0.17–0.48, 0.19–0.48, and 0.25–0.29 for RAPD, ISSR, and AFLP markers, respectively. The average value of number of observed alleles, number of effective alleles, mean Nei’s gene diversity, and Shannon’s information index were 1.93–1.98, 1.37–1.62, 0.23–0.36, and 0.38–0.50, respectively, for three DNA markers used. Dendrograms based on three molecular data using unweighted pair group method with arithmetic mean (UPGMA) was congruent and classified the Curcuma species into two major clusters. Cophenetic correlation coefficient between dendrogram and original similarity matrix were significant for RAPD (r = 0.96), ISSR (r = 0.94), and AFLP (r = 0.97). Clustering was further supported by principle coordinate analysis. High genetic polymorphism documented is significant for conservation and further improvement of Curcuma species.     

Investigating Fluorescence Quenching of ZnS Quantum Dots by Silver Nanoparticles

Water dispersible zinc sulfide quantum dots (ZnS QDs) with an average diameter of 2.9 nm were synthesized in an environment friendly method using chitosan as stabilizing agent. These nanocrystals displayed characteristic absorption and emission spectra having an absorbance edge at 300 nm and emission maxima (λ _emission) at 427 nm. Citrate-capped silver nanoparticles (Ag NPs) of ca. 37-nm diameter were prepared by modified Turkevich process. The fluorescence of ZnS QDs was significantly quenched in presence of Ag NPs in a concentration-dependent manner with K _sv value of 9 × 10⁹ M⁻¹. The quenching mechanism was analyzed using Stern–Volmer plot which indicated mixed nature of quenching. Static mechanism was evident from the formation of electrostatic complex between positively charged ZnS QDs and negatively charged Ag NPs as confirmed by absorbance study. Due to excellent overlap between ZnS QDs emission and surface plasmon resonance band of Ag NPs, the role of energy transfer process as an additional quenching mechanism was investigated by time-resolved fluorescence measurements. Time-correlated single-photon counting study demonstrated decrease in average lifetime of ZnS QDs fluorescence in presence of Ag NPs. The corresponding F?rster distance for the present QD–NP pair was calculated to be 18.4 nm.     

Planck-Benzinger Thermal Work Function: Thermodynamic Characterization of the Carboxy-Terminus of p53 Peptide Fragments

The thermodynamic parameters for six p53 carboxy-terminus peptide fragments as determined by analytical ultracentrifugal analysis were compared over the experimental temperature range of 275–310 K to evaluate the Gibbs free energy change as a function of temperature, ΔG ^o (T), from 0 to 400 K using our general linear third-order fitting function, ΔG ^o (T) = α + βT ² + γT ³. Data obtained at the typical experimental temperature range are not sufficient to accurately describe the variations observed in the oligomerization of these p53 fragments. It is necessary to determine a number of thermodynamic parameters, all of which can be precisely assessed using this general third-order linear fitting function. These are the heat of reaction, innate temperature-invariant enthalpy, compensatory temperatures and the thermodynamic molecular switch occurring at the thermal set point. This methodology can be used to distinguish the characteristic structure and stability of p53 carboxy-terminal fragments or other p53 mutants. It should be used for the thermodynamic characterization of any interacting biological system.     

Photochemical degradation of chromophoric-dissolved organic matter exposed to simulated UV-B and natural solar radiation

Photochemical degradation of chromophoric-dissolved organic matter (CDOM) by UV-B radiation decreases CDOM absorption in the UV region and fluorescence intensity, and alters CDOM composition. CDOM absorption, fluorescence, and the spectral slope indicating the CDOM composition were studied using 0.22-μm-filtered samples of Meiliang Bay water from Lake Taihu that were exposed to short-term (0–12 h) simulated UV-B radiation and long-term (0–12 days) natural solar radiation in summer. CDOM absorption coefficient and fluorescence decreased with increasing exposure time, which relates to the amounts of absorbed light energy. The decreases of CDOM absorption and normalized fluorescence corresponded to first order kinetics reactions. Different decreases of CDOM absorption and fluorescence at different wavelengths suggested that the composition of CDOM changed when it absorbed ultraviolet radiation. Photochemical degradation increased the spectral slope during 275–295 nm region (S _275–295) but decreased the spectral slope during 275–295 nm region (S _350–400). The slope ratio S _R (S _275–295:S _350–400) increased in the photochemical process, which could be used as an indicator of photobleaching and composition change of CDOM. Our results show that photochemical degradation is important in the cycling of CDOM, which indicated change in the composition of CDOM. Handling editor: Luigi Naselli-Flores     

Effects of solar ultraviolet radiation on photochemical efficiency of <Emphasis Type="Italic">Chaetoceros curvisetus</Emphasis> (Bacillariophyceae)

To assess the short- and long-term impacts of Ultraviolet radiation (UVR, 280–400 nm) on the red tide alga Chaetoceros curvisetus, we exposed cells to three different solar radiation treatments–PAB:280–700 nm, PA:320–700 nm, and P:400–700 nm under 20°C incubated temperature. Short-term exposures were investigated: the photochemical efficiency (Φ_PSII) versus irradiance curves under six levels of solar radiation by covering the incubators with a variable number of neutral density screens (the irradiance thus varied from 100 to 3%) lasting 1 h, and long-term exposures were designed to assess how the cells acclimate to solar radiation (the growth, UV_abc and ratio of repair to damage rates of D1 protein were detected). A significant decrease in the photochemical efficiency (Φ_PSII) at high irradiance (100% of incident solar radiation, 261.6 Wm⁻²) was observed in short-term exposure (1 h). UVR-induced photoinhibition was reduced to 7% in 3% solar radiation (4.08 Wm⁻²), compared with 66% in 100% solar radiation (261.6 Wm⁻²). In long-term experiments (11 days) using batch cultures, cell densities during the first 6 days were relatively constant for treatment P, and decreased slightly under PA and PAB treaments, reflecting a change in the irradiance experienced in the laboratory to that of incident solar irradiance. Thereafter, cell density increased and UV-induced photoinhibition decreased with the following days, indicating acclimation to solar UV. At the end of experiment, cells were found to exhibit both higher ratios of repair to UV-related damage and increased concentrations of UV-absorbing compounds, whose maximum absorption was found to be at 329 nm. Our data indicate that C. curvisetus is sensitive to ultraviolet radiation, but was able to acclimate relatively rapidly (ca. 6 days) by synthesizing UV-absorbing compounds and by increasing the rates of repair processes of D1 protein in PSII.     

In Vitro Characterization and Mosquito (Aedes aegypti) Repellent Activity of Essential-Oils-Loaded Nanoemulsions

The nanoemulsions composed of citronella oil, hairy basil oil, and vetiver oil with mean droplet sizes ranging from 150 to 220 nm were prepared and investigated both in vitro and in vivo. Larger emulsion droplets (195–220 nm) shifted toward a smaller size (150–160 nm) after high-pressure homogenization and resulted in higher release rate. We proposed that thin films obtained from the nanoemulsions with smaller droplet size would have higher integrity, thus increasing the vaporization of essential oils and subsequently prolonging the mosquito repellant activity. The release rates were fitted with Avrami’s equations and n values were in the same range of 0.6 to 1.0, implying that the release of encapsulated limonene was controlled by the diffusion mechanism from the emulsion droplet. By using high-pressure homogenization together with optimum concentrations of 5% (w/w) hairy basil oil, 5% (w/w) vetiver oil (5%), and 10% (w/w) citronella oil could improve physical stability and prolong mosquito protection time to 4.7 h due to the combination of these three essential oils as well as small droplet size of nanoemulsion.     

Behavior of Freezable Bound Water in the Bacterial Cellulose Produced by Acetobacter xylinum: An Approach Using Thermoporosimetry

The aim of the study is to examine thermal behavior of water within reticulated structure of bacterial cellulose (BC) films by sub-ambient differential scanning calorimetry (DSC). BC films with different carbon source, either manitol (BC (a)) or glycerol (BC (b)), were produced by Acetobacter xylinum using Hestrin and Shramm culture medium under static condition at 30 ± 0.2°C for 3 days. BC samples were characterized by electron scanning microscopy and X-ray diffraction spectroscopy. The pore analysis was done by B.H.J. nitrogen adsorption. The pre-treated with 100% relative humidity, at 30.0 ± 0.2°C for 7 days samples were subjected to a between 25 and −150°C-cooling–heating cycle of DSC at 5.00°C/min rate. The pre-treated samples were also hydrated by adding 1 μl of water and thermally run with identical conditions. It is observed that cellulose fibrils of BC (a) were thinner and reticulated to form slightly smaller porosity than those of BC (b). They exhibited slightly but non-significantly different crystalline features. The freezable bound water behaved as a water confinement within pores rather than a solvent of polymer which is possible to use thermoporosimetry based on Gibb–Thomson equation to approach pore structure of BC. In comparison with nitrogen adsorption, it was found that thermoporosimetry underestimated the BC porosity, i.e., the mean diameters of 23.0 nm vs. 27.8 nm and 27.9 nm vs. 33.9 nm for BC (a) and BC (b), respectively, by thermoporosimetry vs. B.H.J. nitrogen adsorption. It may be due to large non-freezable water fraction interacting with cellulose, and the validity of pore range based on thermodynamic assumptions of Gibb–Thomson theory.