Oxygenic photosynthesis as driving process in exopolysaccharide production of benthic diatoms

Abstract

The secretion of exopolysaccharide in an axenic culture of the marine benthic diatom Cylindrotheca clostenum was investigated. The central question of the experiments was if polysaccharide secretion was dependent on light and photosynthesis. Cells were incubated in the light, in the dark, or in the light with addition of the inhibitor of Photosystem II,3-(3,4-dichloropheny1)-l, l-dimethyl urea (DCMU). These treatments were also applied to a population of benthic diatoms on an intertidal mudflat in the Westerschelde (Scheldt estuary, The Netherlands). In the light (60 p 0 1 photons m-' S-') C. clostenum showed high rates of polysaccharide secretion, while no secretion was observed in the dark or in the presence of DCMU. No intracellular carbohydrate was converted to exopolysaccharide in the dark or in the light with DCMU added. This indicated that secretion of exopolysaccharide was dependent on oxygenic photosynthesis. Similarly, high rates of exopolysaccharide accumulation were observed during daytime emersion on the mudflat, but not in darkened or DCMU-treated sediment. This demonstrated that the pattern observed in cultures of C. closterium was reproducible in situ. It was observed that dunng daytime emersion patterns of vertical migration in the dark and DCMU-treated plots did not differ from those in the light. This implies that motility was not the steering factor for the observed accumulation of exopolysaccharide in the light. When an axenic culture of C. closterium was incubated under an alternating 12 h light:12 h dark cycle, exopolysaccharide concentrations decreased in the dark. Degradation of exopolysaccharide was also observed in the natural population on the mudflat during emersion at night. Because no bacteria were present in the C. clostenum cultures, it was conceived that the degradation of exopolysaccharide observed in cultures was due to secretion of hydrolytic enzymes by C. clostenum.

Characterization of exopolysaccharides produced by seven biofilm-forming cyanobacterial strains for biotechnological applications

“…It is known that higher temperature and light intensities favor the increase of EPS production (Di ). This has been previously reported on EPS production by diatoms (Staats et al 2000;Wolfstein and Stal 2002) and cyanobacteria (Vincenzini et al 1990;Moreno et al 1998;Otero and Vincenzini 2003) demonstrating a clear and direct relationship between the production of EPS and oxygenic photosynthesis; it would therefore be quite reasonable to expect increasing EPS production with an increase in temperature and light. It is possible that the biofilm thickness and its multi-stratified structure caused strong attenuation of light in the upper biofilm layers.…”

Diversity and biomass accumulation in cultured phototrophic biofilms

“…Thus, an interaction between irradiance and temperature appeared to affect initial biofilm stages. High irradiance promotes the synthesis of EPS and a positive effect of high temperature on EPS production by benthic diatoms and cultured phototrophic biofilms has been documented (Staats et al, 2000;Di Pippo et al, 2009. It seems that increased EPS synthesis could have aided cell adhesion to the bare substrata in our system.…”

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

“…Such effects have largely been overlooked, though it is well established that EPS production by benthic diatoms is affected by light-dark cycles (Staats et al, 2000;Smith & Underwood, 2000). Crocosphaera watsonii, an ecologically significant N-fixing cyanobacterium, has diel cycles of carbohydrate accumulation and release, with the internal carbohydrate pool decreasing as the cells release EPS and TEP into the surrounding water (Dron et al, 2012).…”