Search results for "actin"
showing 10 items of 1375 documents
Tryptophan promotes morphological and physiological differentiation in Streptomyces coelicolor.
2015
The molecular mechanisms regulating tryptophan biosynthesis in actinomycetes are poorly understood; similarly, the possible roles of tryptophan in the differentiation program of microorganism life-cycle are still underexplored. To unveil the possible regulatory effect of this amino acid on gene expression, an integrated study based on quantitative teverse transcription-PCR (qRT-PCR) and proteomic approaches was performed on the actinomycete model Streptomyces coelicolor. Comparative analyses on the microorganism growth in a minimal medium with or without tryptophan supplementation showed that biosynthetic trp gene expression in S. coelicolor is not subjected to a negative regulation by the …
Pyrocoll, an Antibiotic, Antiparasitic and Antitumor Compound Produced by a Novel Alkaliphilic Streptomyces Strain
2003
A new secondary metabolite was detected in the culture extract of Streptomyces sp. AK 409 by HPLC-diode-array screening. The metabolite was identified as pyrocoll, which is known to be a constituent of cigarette smoke. Pyrocoll is known as a synthetic compound, but until now had not been isolated as a natural product from a microorganism. The compound showed biological activity against various Arthrobacter strains, filamentous fungi, several pathogenic protozoa, and some human tumor cell lines.
Novel photoreception system in sponges?
2006
Abstract Sponges (phylum Porifera) of the classes Hexactinellida and Demospongiae possess a skeleton composed of siliceous spicules, which are synthesized enzymatically. The longest spicules are found among the Hexactinellida, with the stalk spicules (length: 30 cm; diameter: 300 μm) of Hyalonema sieboldi as prominent examples. These spicules are constructed around a central axial filament, which is formed by approximately 40 siliceous layers. The stratified spicules function as optical glass fibers with unique properties. If free-spaced coupled with a white light source (WLS), the entire fiber is illuminated. Special features of the light transmission: (i) only wavelengths between 615 and …
Bioorganic/inorganic hybrid composition of sponge spicules: matrix of the giant spicules and of the comitalia of the deep sea hexactinellid Monorhaph…
2007
The giant basal spicules of the siliceous sponges Monorhaphis chuni and Monorhaphis intermedia (Hexactinellida) represent the largest biosilica structures on earth (up to 3 m long). Here we describe the construction (lamellar organization) of these spicules and of the comitalia and highlight their organic matrix in order to understand their mechanical properties. The spicules display three distinct regions built of biosilica: (i) the outer lamellar zone (radius: >300 mu m), (ii) the bulky axial cylinder (radius: <75 mu m), and (iii) the central axial canal (diameter: <2 mu m) with its organic axial filament. The spicules are loosely covered with a collagen net which is regularly perforated …
Circumferential spicule growth by pericellular silica deposition in the hexactinellid sponge Monorhaphis chuni.
2011
SUMMARY The giant basal spicule of the hexactinellid sponge Monorhaphis chuni represents the longest natural siliceous structure on Earth. This spicule is composed of concentrically arranged lamellae that are approximately 10 μm thick. In the present study, we investigated the formation of outer lamellae on a cellular level using microscopic and spectroscopic techniques. It is shown that the formation of an outermost lamella begins with the association of cell clusters with the surface of the thickening and/or growing spicule. The cells release silica for controlled formation of a lamella. The pericellular (silica) material fuses to a delimited and textured layer of silica with depressions …
Identification of a silicatein(-related) protease in the giant spicules of the deep-sea hexactinellid Monorhaphis chuni.
2008
SUMMARYSilicateins, members of the cathepsin L family, are enzymes that have been shown to be involved in the biosynthesis/condensation of biosilica in spicules from Demospongiae (phylum Porifera), e.g. Tethya aurantium and Suberites domuncula. The class Hexactinellida also forms spicules from this inorganic material. This class of sponges includes species that form the largest biogenic silica structures on earth. The giant basal spicules from the hexactinellids Monorhaphis chuni and Monorhaphis intermedia can reach lengths of up to 3 m and diameters of 10 mm. The giant spicules as well as the tauactines consist of a biosilica shell that surrounds the axial canal, which harbours the axial f…
Silica-protein composite layers of the giant basal spicules from Monorhaphis: Basis for their mechanical stability
2010
The hexactinellid sponge Monorhaphis chuni possesses with its giant basal spicules the largest biosilica structure on Earth. The approximately 8.5-mm-thick spicules are composed of up to 800 lamellae. By application of high-resolution electron microscopy (HR-SEM), it is shown that within the siliceous lamellae a proteinaceous scaffold exists which is composed of one protein of a size of 27 kDa. Analyses with Fourier transform infrared (FT-IR) emission and energy-dispersive X-ray (EDX) spectroscopy support this localization of the protein. No evidence for the presence of protein on the surfaces of the lamellae could be obtained. Heating the giant basal spicule to 600 °C destroys and eliminat…
Axial growth of hexactinellid spicules: Formation of cone-like structural units in the giant basal spicules of the hexactinellid Monorhaphis
2008
The glass sponge Monorhaphis chuni (Porifera: Hexactinellida) forms the largest bio-silica structures on Earth; their giant basal spicules reach sizes of up to 3 m and diameters of 8.5 mm. Previously, it had been shown that the thickness growth proceeds by appositional layering of individual lamellae; however, the mechanism for the longitudinal growth remained unstudied. Now we show, that the surface of the spicules have towards the tip serrated relief structures that are consistent in size and form with the protrusions on the surface of the spicules. These protrusions fit into the collagen net that surrounds the spicules. The widths of the individual lamellae do not show a pronounced size …
Chapter 3 Giant Siliceous Spicules From the Deep‐sea Glass Sponge Monorhaphis chuni
2009
Only 13 years after realizing, during a repair of a telegraph cable pulled out from the deep sea, that the depth of the ocean is plentifully populated with a highly diverse fauna and flora, the Challenger expedition (1873-1876) treasured up a rich collection of vitreous sponges (Hexactinellida). They had been described by Schulze and represent the phylogenetically oldest class of siliceous sponges (phylum Porifera); they are eye-catching because of their distinct body plan, which relies on a filigree skeleton. It is constructed by an array of morphologically determined elements, the spicules. Soon after, during the German Deep Sea Expedition "Valdivia" (1898-1899), Schulze could describe th…
3D Morphology, ultrastructure and development of Ceratomyxa puntazzi stages: first insights into the mechanisms of motility and budding in the Myxozo…
2012
Free, amoeboid movement of organisms within media as well as substrate-dependent cellular crawling processes of cells and organisms require an actin cytoskeleton. This system is also involved in the cytokinetic processes of all eukaryotic cells. Myxozoan parasites are known for the disease they cause in economical important fishes. Usually, their pathology is related to rapid proliferation in the host. However, the sequences of their development are still poorly understood, especially with regard to pre-sporogonic proliferation mechanisms. The present work employs light microscopy (LM), electron microscopy (SEM, TEM) and confocal laser scanning microscopy (CLSM) in combination with specific…