Extracellular Matrix Assembly in Diatoms (Bacillariophyceae)1

Abstract

Achnanthes longipes is a marine, biofouling diatom that adheres to surfaces via adhesive polymers extruded during motility or organized into structures called stalks that contain three distinct regions: the pad, shaft, and collar. Four monoclonal antibodies (AL.C1-AL.C4) and antibodies from two uncloned hybridomas (AL.E1 and AL.E2) were raised against the extracellular adhesives of A. longipes. Antibodies were screened against a hot-water-insoluble/ hot-bicarbonate-soluble-fraction.The hot-water-insoluble/hotbicarbonate-soluble fraction was fractionated to yield polymers in three size ranges: F 1 , > 20,000,000 M r ; F 2 , Х100,000 M r ; and F 3 , <10,000 M r relative to dextran standards. The Х100,000-M r fraction consisted of highly sulfated (approximately 11%) fucoglucuronogalactans (FGGs) and low-sulfate (approximately 2%) FGGs, whereas F 1 was composed of O-linked FGG (F 2 )-polypeptide (F 3 ) complexes. AL.C1, AL.C2, AL.C4, AL.E1, and AL.E2 recognized carbohydrate complementary regions on FGGs, with antigenicity dependent on fucosyl-containing side chains. AL.C3 was unique in that it had a lower affinity for FGGs and did not label any portion of the shaft. Enzyme-linked immunosorbent assay and immunocytochemistry indicated that low-sulfate FGGs are expelled from pores surrounding the raphe terminus, creating the cylindrical outer layers of the shaft, and that highly sulfated FGGs are extruded from the raphe, forming the central core. Antibody-labeling patterns and other evidence indicated that the shaft central-core region is related to material exuded from the raphe during cell motility.Because of the complexity of the higher-plant ECM, we have only recently begun to understand the spatial relationships between ECM components, and know little about the intra-and intermolecular interactions responsible for cell wall organization and assembly (Levy and Staehelin, 1992). McCann et al. (1990) succeeded in visualizing the intermolecular organization of the onion primary cell wall, demonstrating cross-links between cellulose and hemicellulose and a separate surrounding network made up pectic polymers. Taylor and Haigler (1993) found that cellulose serves as a template mediating the self-organization of other molecules such as xylan and Gly-rich proteins in the secondary cell walls of tracheary elements. ECM polymers appear to interact initially through short-range forces, most notably hydrogen binding. Hydrogen binding, hydrophobic interactions, and ionic cross-bridging are noncovalent associations essential to maintenance of cell wall integrity. Recently, Ca 2ϩ -dependent pectin-binding proteins were isolated (Penel and Greppin, 1996), including several vitronectin-like proteins and isoperoxidases. These results indicate that an ion-binding mechanism may be responsible for the organization of some proteins in the plant cell wall. Covalent binding may be a final step in the selfassembly process, cementing together all of the individual components of the matrix. The most common covalent linkages are: (a) sugar-s...

Characterization of the extracellular matrix of Phaeodactylum tricornutum (Bacillariophyceae): structure, composition, and adhesive characteristics

“…The major aim of this study was to compare the ovoid and fusiform EPS to ascertain whether a difference in polysaccharide or protein composition could be identified in relation to cell adhesion. Wustman et al (1998) suggested increased Rha and Fuc content could be related to adhesion, as these hydrophobic polymers could increase surface interactions. In this study the constituent monosaccharide profiles and linkages of the fractions that correspond to extracellular mucilage (OM, OB, OF, FF) for the ovoid and fusiform cultures are broadly similar (Table 2).…”

Bacteria–algae association in batch cultures of phytoplankton from a tropical reservoir: the significance of algal carbohydrates

“…However, independent of the deoxysugar origin, these sugars have been reported to have hydrophobic properties. As these properties became more pronounced throughout the incubation period, the carbohydrate pool also became more hydrophobic (Giroldo et al, 2003) and, therefore, more susceptible to aggregation, as the enhancement of the hydrophobic properties of TDCHO increases the tendency for aggregation in the medium (Wustman, Gretz & Hoagland, 1997).…”

RELATIVE INCREASE OF DEOXY SUGARS DURING MICROBIAL DEGRADATION OF AN EXTRACELLULAR POLYSACCHARIDE RELEASED BY A TROPICAL FRESHWATER THALASSIOSIRA SP. (BACILLARIOPHYCEAE)1

“…The data available on the composition of phytoplanktonic EPS as well as EPS utilization by bacteria are quite rare, considering the number of taxa, and are especially sparse for planktonic freshwater diatoms. Most results concern biofouling organisms (Cooksey and Cooksey 1985, Wustman et al 1997) or epipelic diatoms (Smith and Underwood 1998, Underwood and Smith 1998, Staats et al 1999). The structure and composition of the EPS have remarkable influence on their physical and chemical properties, defining many of the features of such EPS.…”