Abstract
Exopolysaccharide (EPS) of two benthic diatoms, Amphora sp. and Stauroneis sp., with different biofilm formation abilities were investigated. The ratio of suspension-cells/biofilm-cells was employed to indicate the diatom biofilm formation abilities. The soluble EPS from the supernatant of whole culture, tightly bound EPS from floating cells, loosely and tightly bound EPS from biofilm cells were fractionated as SL-EPS, F-TB-EPS, BF-LB-EPS and BF-TB-EPS, respectively. The analysis for productions and monosaccharide compositions indicated that EPS from two diatoms were different in terms of the productions, distributions, and monomer compositions. Amphora sp. produced more (1.5-fold) total exopolysaccharides, but less (<0.4-fold) BF-TB-EPS than Stauroneis sp. The monosaccharides of the EPS from Amphora sp. were more diverse than those of Stauroneis sp., with 13 and 10 monomers, respectively. Neutral sugars, Glc, Xyl and Man, were abundant in Stauroneis sp., while Gal, Glc and Xyl were rich in Amphora sp. Uronic acid and hexosamine were present in all fractions of two diatoms, especially Glc-A being the most abundant monomer in SL-EPS of Amphora sp. It was proposed that the high content of uronic acid (especially Glc-A) might be crucial for the strong biofilm formation abilities of Amphora sp.
Highlights
The attachment and growth of unwanted living organisms on man-made surfaces are referred to as biofouling (Townsin 2003, Fusetani 2004, Kristensen et al 2008, Jin et al 2014)
Most cells (79.97%) of Amphora sp. were embedded in the biofilm attached to the bottom of a flask, and 20.03% of the cells were distributed in the suspension
In the case of Stauroneis sp., 57.61% of the cells were floating in the culture system and 42.39% of the cells were embedded in the biofilm attached to the bottom of the flask (Table I)
Summary
The attachment and growth of unwanted living organisms on man-made surfaces are referred to as biofouling (Townsin 2003, Fusetani 2004, Kristensen et al 2008, Jin et al 2014). Due to the development of microscopy techniques, there have been many reports on the characteristics of benthic diatom algae, including the cell microstructures, extracellular polymeric substances composition and excretion site, locomotion route, and biofilm formation abilities (Daniel et al 1980, Lind et al 1997, Higgins et al 2002, Arce et al 2004, Villacorte et al 2015). Diatoms produce large quantities of extracellular polymeric substances during all phases of growth in water environments (Vesna et al 2013, Ai et al 2015). EPS produced by diatoms are increasingly being studied because of the multiple functions of these biopolymers in aquatic systems, including: impacting the aggregation rate of particles and, influencing the flux of organic carbon to deep waters; protecting against desiccation in intertidal flats; aiding in colony formation; and favoring loose symbiosis with bacteria (Magaletti et al 2004, Aslam et al 2012). The contents and compositions of EPS are believed to exhibit substantial effects on biofilm formation of diatoms (Yang et al 2008)
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