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Physiology of Achnanthes longipes Ag.: Nutritional requirements for the secretion of extracellular polymeric substances
Abstract
Potential nutrients and physical and chemical factors contributing to extracellular polymeric substance (EPS) secretion were examined in defined media in the marine diatom Achnanthes longipes Ag. This common biofouling diatom readily formed stalks in nutrient-enriched natural seawater, while only pad EPS was secreted in nutrient-enriched synthetic seawater media (f/2 and ESAW). It was hypothesized that some factor stimulating stalk formation was present in seawater and absent in defined medium, and that it resisted autoclaving. Subsequently, it was found that Achnanthes longipes and Achnanthes sp. exhibited an absolute requirement for bromide for stalk production, while elevated iodide concentrations in the growth medium inhibited stalk formation. Varying EPS morphologies, including pads stalk/pads, stalks and no insoluble EPS resulted from altering chloride, bromide and iodide levels. Cultures showed no differences in growth with the addition of bromide or iodide, indicating that they were not physiologically stressed under conditions which impaired EPS secretion. Cells grown in media with elevated iodide levels secreted signficantly 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, cells lost their ability to form stalks even in the presence of bromide. Lotus-FITC a fluorescent-tagged lectin was used to visualize and quantify EPS secretion along a bromide gradient in conjunction with an image analysis system. There was a direct correlation between the amount of bromide present in the medium and the specific EPS morphology formed. Stalk formation was proportional to cell density. This phenomenon suggested that crowding on the substratum led to localized nutrient depletion, stimulating cells to secrete stalks to elevate themselves into an upper zone of increased nutrients. X-ray microanalysis (EDS) with the SEM and TEM failed to locate the presence of bromine in either the cell or stalk of A. longipes. Several possibilities explaining the absence of bromine in the X-ray spectra were proposed.
Subject Area
Anatomy & physiology|Animals|Cellular biology|Botany
Recommended Citation
Johnson, Lisa Mary, "Physiology of Achnanthes longipes Ag.: Nutritional requirements for the secretion of extracellular polymeric substances" (1995). ETD collection for University of Nebraska-Lincoln. AAI9538635.
https://digitalcommons.unl.edu/dissertations/AAI9538635