Abiotic Substrates Research Articles

Environmental reservoirs of Vibrio cholerae and their role in cholera

In the aquatic environment, Vibrio cholerae has been reported to be associated with a variety of living organisms, including animals with an exoskeleton of chitin, aquatic plants, protozoa, bivalves, waterbirds, as well as abiotic substrates (e.g. sediments). Most of these are well-known or putative environmental reservoirs for the bacterium, defined as places where the pathogen lives over time, with the potential to be released and to cause human infection. Environmental reservoirs also serve as V. cholerae disseminators and vectors. They can be responsible for the start of an epidemic, may be critical to cholera endemicity, and affect the evolution of pathogen virulence. To date, in addition to the generally recognized role of zooplankton as the largest environmental reservoir for V. cholerae, other environmental reservoirs play some role in cholera epidemiology by favouring persistence of the pathogen during inter-epidemic periods. Little is known about the ecological factors affecting V. cholerae survival in association with aquatic substrates. Studies aimed at these aspects, i.e. understanding how environmental reservoirs interact, are affected by climate, and contribute to disease epidemiology, will be useful for understanding global implications of V. cholerae and the disease cholera.

Amyloids — a functional coat for microorganisms

Amyloids are filamentous protein structures approximately 10 nm wide and 0.1-10 mum long that share a structural motif, the cross-beta structure. These fibrils are usually associated with degenerative diseases in mammals. However, recent research has shown that these proteins are also expressed on bacterial and fungal cell surfaces. Microbial amyloids are important in mediating mechanical invasion of abiotic and biotic substrates. In animal hosts, evidence indicates that these protein structures also contribute to colonization by activating host proteases that are involved in haemostasis, inflammation and remodelling of the extracellular matrix. Activation of proteases by amyloids is also implicated in modulating blood coagulation, resulting in potentially life-threatening complications.

Novel, Attached, Sulfur-Oxidizing Bacteria at Shallow Hydrothermal Vents Possess Vacuoles Not Involved in Respiratory Nitrate Accumulation

Novel, vacuolate sulfur bacteria occur at shallow hydrothermal vents near White Point, Calif. There, these filaments are attached densely to diverse biotic and abiotic substrates and extend one to several centimeters into the surrounding environment, where they are alternately exposed to sulfidic and oxygenated seawater. Characterizations of native filaments collected from this location indicate that these filaments possess novel morphological and physiological properties compared to all other vacuolate bacteria characterized to date. Attached filaments, ranging in diameter from 4 to 100 microm or more, were composed of cylindrical cells, each containing a thin annulus of sulfur globule-filled cytoplasm surrounding a large central vacuole. A near-complete 16S rRNA gene sequence was obtained and confirmed by fluorescent in situ hybridization to be associated only with filaments having a diameter of 10 microm or more. Phylogenetic analysis indicates that these wider, attached filaments form within the gamma proteobacteria a monophyletic group that includes all previously described vacuolate sulfur bacteria (the genera Beggiatoa, Thioploca, and Thiomargarita) and no nonvacuolate genera. However, unlike for all previously described vacuolate bacteria, repeated measurements of cell lysates from samples collected over 2 years indicate that the attached White Point filaments do not store internal nitrate. It is possible that these vacuoles are involved in transient storage of oxygen or contribute to the relative buoyancy of these filaments.

Tissue Regeneration in the Shell of the Giant Queen Conch, Strombus gigas

The crossed-lamellar microarchitecture (microstructure) of the shell of Strombus gigas, the giant Queen conch native to Caribbean habitats, is the most common of the several shell microarchitectures known in the mollusk family. We have studied tissue regeneration in juvenile S. gigas conchs and compared the microstructure in this regenerated tissue to the microstructure of wild S. gigas shells. The regenerated hard tissue was of two types: hard tissue grown during wound repair, and so-called “flat pearls” which are hard tissue grown on abiotic substrates inserted between the mantle and the outer covering. In both cases, the crossed-lamellar microstructure is observed after formation of a transition structure consisting of a large quantity of matrix and aggregates of aragonite crystallites.

Hard Tissue Regeneration InStrombus Gigas, the Giant Queen Conch

AbstractHard tissue regeneration (i.e. shell repair) is an important biomineralization process in mollusks. Rapid regeneration is important in avoiding loss of fluids and preventing attacks by predators. We have studied such tissue regeneration in the Queen conch (Strombus Gigas) by inserting an abiotic glass cover slide between the mantle tissue and the shell. The glass cover slides were removed after mineralization periods extending from 6 hours to 4 days, and the deposited materials on the glass substrates (“flat pearls”) analyzed by X-ray diffraction, and scanning and transmission electron microscopy.Although the CaCO3in native Queen conch shell is exclusively aragonite, calcite was detected in the regenerated materials grown on glass substrates. Calcite formation occurred only during the very early stage of mineralization and the initial minerals formed were soon overgrown by aragonite. The initial aragonite overgrowth had a spherulitic morphology, and was thus relatively poorly oriented; after this spherulitic transient, the microstructure was recognizable as the crossed-lamellar structure of the natural shell.Thus, shell regeneration on abiotic substrates differs from shell formation during growth of conchs only in the very early stage. Once the crossed-lamellar microstructure has formed, further hard tissue development is identical to that occurring during natural shell growth.

Critical Transitions in the Biofabrication of Abalone Shells and Flat Pearls

Analyses of biopolymer/calcium carbonate composites grown on inorganic abiotic substrates implanted between the shell and the shell-secreting epithelium of live red abalones (Haliotis rufescens) provide detailed spatial and temporal data on the in vivo assembly process that generates the shell. X-ray diffraction and scanning electron microscopy analyses of the growth of these flat pearl composites reveal that biomineralization is initiated by the deposition of an organic sheet on the implanted substrate, followed by the growth of a calcite layer with preferred {10.4} orientation and, finally, by the growth of nacreous aragonite. The calcite layer is structurally similar to the green organic/calcite heterolayer of native shell nacre. It comprises 0.2−2.0-μm-diameter elongated crystallites of typical geological habits in various aggregate arrangements. The shell also contains an external layer of (00.1)-oriented prismatic calcite, which is deposited on one edge of a flat pearl and has a morphology similar to that of the {10.4}-oriented calcite layer. The transition from {10.4}-oriented calcite to aragonite in both the shell and the flat pearl is abrupt. In vitro calcium carbonate growth experiments reveal that a similar calcite-to-aragonite transition is induced by the addition of soluble proteins isolated from the aragonitic nacre. The growth of flat pearls is highly sensitive to physical and chemical properties of the abiotic substrate. Either roughened or hydrophobic substrates result in abnormal arrangements of the basal calcite layer, which are corrected for by a reinitiation of the biomineralization process, beginning with the deposition of an organic sheet. Insertion of flat pearls as substrates, however, results in continued nacre growth without the deposition of an organic sheet and a calcite layer.

Saprotrophic ability of Diaporthe phaseolorum var. caulivora on host and non-host plants, and on abiotic substrates

Four single-spore isolates of Diaporthe phaseolorum var. caulivora originating from diverse, soybean-growing locations in the United States were investigated for their saprotrophic ability and production of perithecia on host, non- host and abiotic substrates. Stem pieces of the host, Glycine max; non-hosts Triticum aestivum, Euphorbia heierophylla, Aeschynomene americana, Xanthium strumarium and Sesbania macrocarpa; toothpicks; and capillary glass tube were used as substrates. Autoclaved substrates were placed on acidified potato-dextrose agar and the medium was seeded with the four isolates of D. phaseolorum var. caulivora and incubated at 24 ± 1 °C. All isolates formed perithecia on substrates of plant origin. The pattern of perithecial arrangement was either clustered, solitary or both. Optimum carbon : nitrogen ratios for the production of perithecia were between 1:1 and 10:1. Ratios of 50:1, 100:1 and 500:1 supported either abundant, poor or no mycelial growth, respectively. Some isolates produced perithecia on acidified potato-dextrose agar without any plant substrates, suggesting that fertile isolates exist in the homothallic Diaporthe phaseolorum var. caulivora.

Effect of pH on Speciation and Toxicity of Aluminum to Rainbow Trout (Salmo gairdneri)

Alum (aluminum sulphate) is used in many water treatment plants as a flocculant. The resultant settled floe (called alum sludge) may be discharged into receiving waters. This study reports the effect of pH on the speciation of released aluminum (Al) from fresh sludge and Al uptake and toxicity to fish in river water in the presence of abiotic substrates enclosed in dialysis sacs. This study shows that freshly precipitated alum sludge holds Al effectively within a wide range of pH (4.50–10.0) and that abiotic substrates compete with the biota as represented by fish for Al. Fish mortalities observed could be due to colloidal particles and acid- and Al-induced stress at pH 4.50, to colloidal particles at pH 6.00, and to high alkalinity at pH 10.0. At pH 7–9, Al in water, present essentially as filterable nonexchangeable Al (FNEX-Al), was not lethal to fish.

Bacterially induced stolon settlement in the scyphopolyp ofAurelia aurita (Cnidaria, Scyphozoa)

Unsettled stoloniferous scyphopolyps ofAurelia aurita Lamarck were offered different substrates for settlement under defined conditions. On addition of different biogenic and abiotic substrates, a pure strain of bacteria, a species of Micrococcaceae, was observed to trigger the settlement of the stolon. The settlement reaction only takes place following direct contact with the bacteria; sterile filtrated culture medium of the same bacterial strain was not able to induce settlement. The bacteria were found to be effective on stolon settlement during the logarithmic growth phase, but not during the stationary phase.