Clean technology in aquaculture — a production without waste products?

A method has been developed for the determination of H₂S and FeS in sediments. FeS is converted into H₂S which is flushed from the samples directly into an excess of chlorine bleach, NaC1O or KClO with some Zn²⁺ added. Either the excess can be titrated back potentiometrically with As₂O₃, or the sulphate formed can be measured colorimetrically. The precision is primarily controlled by the homogeneity of the sediment suspensions and can be better than 99%.     

The conduction of protons in different stereoisomers of dioxolane-linked gramicidin A channels

Two different stereoisomers of the dioxolane-linked gramicidin A (gA) channels were individually synthesized (the SS and RR dimers;. Science. 244:813-817). The structural differences between these dimers arise from different chiralities within the dioxolane linker. The SS dimer mimics the helicity and the inter- and intramolecular hydrogen bonding of the monomer-monomer association of gA's. In contrast, there is a significant disruption of the helicity and hydrogen bonding pattern of the ion channel in the RR dimer. Single ion channels formed by the SS and RR dimers in planar lipid bilayers have different proton transport properties. The lipid environment in which the different dimers are reconstituted also has significant effects on single-channel proton conductance (g(H)). g(H) in the SS dimer is about 2-4 times as large as in the RR. In phospholipid bilayers with 1 M [H(+)](bulk), the current-voltage (I-V) relationship of the SS dimer is sublinear. Under identical experimental conditions, the I-V plot of the RR dimer is supralinear (S-shaped). In glycerylmonooleate bilayers with 1 M [H(+)](bulk), both the SS and RR dimers have a supralinear I-V plot. Consistent with results previously published (. Biophys. J. 73:2489-2502), the SS dimer is stable in lipid bilayers and has fast closures. In contrast, the open state of the RR channel has closed states that can last a few seconds, and the channel eventually inactivates into a closed state in either phospholipid or glycerylmonooleate bilayers. It is concluded that the water dynamics inside the pore as related to proton wire transfer is significantly different in the RR and SS dimers. Different physical mechanisms that could account for this hypothesis are discussed. The gating of the synthetic gA dimers seems to depend on the conformation of the dioxolane link between gA's. The experimental results provide an important framework for a detailed investigation at the atomic level of proton conduction in different and relatively simple ion channel structures.     

An Acinetobacter baumannii,Zinc-Regulated Peptidase Maintains Cell Wall Integrity during Immune-Mediated Nutrient Sequestration

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Membrane Damage Elicits an Immunomodulatory Program in Staphylococcus aureus

The Staphylococcus aureus HrtAB system is a hemin-regulated ABC transporter composed of an ATPase (HrtA) and a permease (HrtB) that protect S. aureus against hemin toxicity. S. aureus strains lacking hrtA exhibit liver-specific hyper-virulence and upon hemin exposure over-express and secrete immunomodulatory factors that interfere with neutrophil recruitment to the site of infection. It has been proposed that heme accumulation in strains lacking hrtAB is the signal which triggers S. aureus to elaborate this anti-neutrophil response. However, we report here that S. aureus strains expressing catalytically inactive HrtA do not elaborate the same secreted protein profile. This result indicates that the physical absence of HrtA is responsible for the increased expression of immunomodulatory factors, whereas deficiencies in the ATPase activity of HrtA do not contribute to this process. Furthermore, HrtB expression in strains lacking hrtA decreases membrane integrity consistent with dysregulated permease function. Based on these findings, we propose a model whereby hemin-mediated over-expression of HrtB in the absence of HrtA damages the staphylococcal membrane through pore formation. In turn, S. aureus senses this membrane damage, triggering the increased expression of immunomodulatory factors. In support of this model, wildtype S. aureus treated with anti-staphylococcal channel-forming peptides produce a secreted protein profile that mimics the effect of treating ΔhrtA with hemin. These results suggest that S. aureus senses membrane damage and elaborates a gene expression program that protects the organism from the innate immune response of the host.     

Diversity of Aquatic Pseudomonas Species and Their Activity against the Fish Pathogenic Oomycete Saprolegnia

Emerging fungal and oomycete pathogens are increasingly threatening animals and plants globally. Amongst oomycetes, Saprolegnia species adversely affect wild and cultivated populations of amphibians and fish, leading to substantial reductions in biodiversity and food productivity. With the ban of several chemical control measures, new sustainable methods are needed to mitigate Saprolegnia infections in aquaculture. Here, PhyloChip-based community analyses showed that the Pseudomonadales, particularly Pseudomonas species, represent one of the largest bacterial orders associated with salmon eggs from a commercial hatchery. Among the Pseudomonas species isolated from salmon eggs, significantly more biosurfactant producers were retrieved from healthy salmon eggs than from Saprolegnia-infected eggs. Subsequent in vivo activity bioassays showed that Pseudomonas isolate H6 significantly reduced salmon egg mortality caused by Saprolegnia diclina. Live colony mass spectrometry showed that strain H6 produces a viscosin-like lipopeptide surfactant. This biosurfactant inhibited growth of Saprolegnia in vitro, but no significant protection of salmon eggs against Saprolegniosis was observed. These results indicate that live inocula of aquatic Pseudomonas strains, instead of their bioactive compound, can provide new (micro)biological and sustainable means to mitigate oomycete diseases in aquaculture.     

Anthocyanins with unusual furanose sugar (apiose) from leaves of Synadeniumgrantii (Euphorbiaceae)

Four anthocyanins, cyanidin 3-O-(2″-(5?-(E-p-coumaroyl)-β-apiofuranosyl)-β-xylopyranoside)-5-O-β-glucopyranoside, cyanidin 3-O-(2″-(5?-(E-p-coumaroyl)-β-apiofuranosyl)-β-xylopyranoside), cyanidin 3-O-(2″-(5?-(E-caffeoyl)-β-apiofuranosyl)-β-xylopyranoside) and cyanidin 3-O-(2″-(5?-(E-feroyl)-β-apiofuranosyl)-β-xylopyranoside) were isolated from leaves of African milk bush, (Synadeniumgrantii Hook, Euphorbiaceae) together with the known cyanidin 3-O-β-xylopyranoside-5-O-β-glucopyranoside and cyanidin 3-O-β-xyloside. The four former pigments are the first reported anthocyanins containing the monosaccharide apiose, and the three 5?-cinnamoyl derivative-2″-(β-apiosyl)-β-xyloside subunits have previously not been reported for any compound.     

Submicronic Fungal Bioaerosols: High-Resolution Microscopic Characterization and Quantification

Submicronic particles released from fungal cultures have been suggested to be additional sources of personal exposure in mold-contaminated buildings. In vitro generation of these particles has been studied with particle counters, eventually supplemented by autofluorescence, that recognize fragments by size and discriminate biotic from abiotic particles. However, the fungal origin of submicronic particles remains unclear. In this study, submicronic fungal particles derived from Aspergillus fumigatus, A. versicolor, and Penicillium chrysogenum cultures grown on agar and gypsum board were aerosolized and enumerated using field emission scanning electron microscopy (FESEM). A novel bioaerosol generator and a fungal spores source strength tester were compared at 12 and 20 liters min⁻¹ airflow. The overall median numbers of aerosolized submicronic particles were 2 × 10⁵ cm⁻², 2.6 × 10³ cm⁻², and 0.9 × 10³ cm⁻² for A. fumigatus, A. versicolor, and P. chrysogenum, respectively. A. fumigatus released significantly (P < 0.001) more particles than A. versicolor and P. chrysogenum. The ratios of submicronic fragments to larger particles, regardless of media type, were 1:3, 5:1, and 1:2 for A. fumigatus, A. versicolor, and P. chrysogenum, respectively. Spore fragments identified by the presence of rodlets amounted to 13%, 2%, and 0% of the submicronic particles released from A. fumigatus, A. versicolor, and P. chrysogenum, respectively. Submicronic particles with and without rodlets were also aerosolized from cultures grown on cellophane-covered media, indirectly confirming their fungal origin. Both hyphae and conidia could fragment into submicronic particles and aerosolize in vitro. These findings further highlight the potential contribution of fungal fragments to personal fungal exposure.     

Intracellular metalloporphyrin metabolism in Staphylococcus aureus

The bacterial pathogen Staphylococcus aureus is responsible for a significant amount of human morbidity and mortality, and the ability of S. aureus to cause disease is absolutely dependent on the acquisition of iron from the host. The most abundant iron source to invading staphylococci is in the form of the porphyrin heme. S. aureus is capable of acquiring nutrient iron from heme and hemoproteins via two heme-acquisition systems, the iron-regulated surface determinant system (Isd) and the heme transport system (Hts). Heme acquisition through these systems is involved in staphylococcal pathogenesis suggesting that the intracellular fate of heme plays a significant role in the infectious process. The valuable heme molecule presents a paradox to invading bacteria because although heme is an abundant source of nutrient iron, the extreme reactivity of heme makes it toxic at high concentrations. Therefore, bacteria must regulate the levels of intracellular heme to avoid toxicity. Although the molecular mechanisms responsible for staphylococcal heme acquisition are beginning to emerge, the mechanisms by which S. aureus regulate intracellular heme homeostasis are largely unknown. In this review we describe three potential fates of host-derived heme acquired by S. aureus during infection: (i) degradation for use as a nutrient iron source, (ii) incorporation into bacterial heme-binding proteins for use as an enzyme cofactor, or (iii) efflux through a dedicated ABC-type transport system. We hypothesize that the ultimate fate of exogenously acquired heme in S. aureus is dependent upon the intracellular and extracellular availability of both iron and heme.