EFFECTS OF BROMIDE AND IODIDE ON STALK SECRETION IN THE BIOFOULING DIATOM ACHNANTHES LONGIPES (BACILLARIOPHYCEAE)¹

Abstract

Extracellular polymeric substance (EPS) secretion was examined in the stalked marine diatom Achnanthes longipes Ag. in defined medium. This common biofouling diatom exhibited an absolute requirement for bromide for stalk production and substratum attachment, whereas elevated iodide concentrations in the growth medium inhibited stalk formation and adhesion. Varying EPS morphologtes resulted from altering bromide and iodide levels: pads, stalk‐pads, stalks, and no EPS. Cells showed no differences in growth with bromide or iodide concentrations, indicating that they were not physiologically stressed under conditions that impaired EPS secretion. Cells grown in elevated iodide secreted significantly more soluble extracellular carbohydrate into the medium, suggesting that the EPS was soluble and unable to be polymerized into a morphologically distinct gel. By replacing sulfate with methionine, the diatom lost its ability to form stalks even in the presence of bromide, indicating that free sulphate may be required for proper cross‐linking of stalk polymers. Lotus‐FITC, a fluorescent‐tagged lectin, preferentially labeled the EPS and, thus, was used to visualize and quantify EPS secretion along a bromide gradient in conjunction with an image analysis system. This technique demonstrated a direct correlation between the amount of bromide present in the medium and the specific EPS morphology formed.

Influence of benthic and pelagic environmental factors on the distribution of dinoflagellate cysts in surface sediments along the Swedish west coast

“…In marine macroalgae, the enzyme vanadiumbromoperoxidase is essential for production of bromoform that plays an important role in eliminating epiphytic microalgae (Ohsawa et al 2001). In species of biofouling diatoms, an absolute requirement of the same enzyme for substratum attachment has been reported (Johnson et al 1995). An elevated concentration of vanadium has also been demonstrated to have an inhibitory effect on the photosynthesis of phytoplankton (Nalewajko et al 1995).…”

A new approach to historical reconstruction: Combining descriptive and experimental paleolimnology

“…The physiological requirement for bromine is poorly documented in diatoms, with most reports confined to the red and brown algae (Fries 1966;McLachlan and Craigie 1967;Wolk 1968). However, Johnson et al (1995) recently demonstrated a nutritional requirement of bromine in the stalked marine diatom Achnanthes. Extracellular polymeric substance (EPS) secretion in this species apparently exhibits an absolute requirement for bromide as both stalk formation and adhesion require this compound.…”

Extracellular Matrix Assembly in Diatoms (Bacillariophyceae) (I. A Model of Adhesives Based on Chemical Characterization and Localization of Polysaccharides from the Marine Diatom Achnanthes longipes and Other Diatoms)

“…That A. Zongipes polymers are organized and assembled into networks by phenolic cross-linking components is suggested by several results: (a) the blue autofluorescence of the stalks when excited by UV light >360 nm; (b) Johnson et al (1995) have characterized a bromide dependence for stalk synthesis in A. longipes and also found that iodide inhibits stalk production; and (c) V. Vreeland (personal communication) found preliminary cytochemical evidence for peroxidase activity within intracellular vesicles in A. longipes cells. Phenolic compounds such as dityrosine, ferulic acid, feruloyl esters, caffeic acid, and sinapic acid are known to fluoresce blue when exposed to 366-nm UV light (Fry, 1995).…”