Biogenic Stabilization of Intertidal Sediments: The Importance of Extracellular Polymeric Substances Produced by Benthic Diatoms

Abstract

The sediment-stabilizing effect of benthic diatoms was investigated in a laboratory setting. Axenic cultures of the benthic diatoms Nitzschia cf. brevissima and Cylindrotheca closterium were inoculated in Petri dishes containing sand and incubated under axenic conditions. By ensuring aseptic routines throughout the experiments, interference from other organisms occurring with diatoms in natural photothrophic biofilms was avoided. This allowed the examination of the role of benthic diatoms in sediment stabilization. Increases in the critical erosion shear stress of the sediment were observed in the presence of both diatom taxa relative to sterile sediment. However, N. cf. brevissima was more effective than C. closterium. Values of critical shear stress in the experimental system were in the same range as those observed in natural biofilms, which indicates that diatoms are important agents for biogenic stabilization. Extracellular carbohydrate contents in the microcosms were similar for both diatom species. However, in the presence of N cf. brevissima, extracellular carbohydrate correlated significantly to critical shear stress, explaining up to 80% of the variation, whereas this was not the case for C. closterium. Therefore, it was concluded that the quantity of extracellular polymeric substances (EPS) alone did not explain the biogenic stabilization. Observed adsorption of EPS to sediment particles depended on the relative amount of uronic acids in the exopolymers. Using fluorescently labeled lectins, confocal laser scanning microscopy showed that EPS secretion by N. cf. brevissima resulted in ordered three-dimensional matrix structures. It is suggested that the structuring of EPS plays an prominent role in the process of biostabilization, and that diatoms such as N. cf. brevissima are actively involved in producing the structure of EPS, whereas others such as C. closterium do not do so to the same extent.

Toward a Regional Classification to Provide a More Inclusive Examination of the Ocean Biogeochemistry of Iron-Binding Ligands

“…It is to be noted that Alteromonas sp., which synthesize strong iron binding ligands (L 1 typically assigned to siderophores, Hogle et al, 2016) also produce EPS able to strongly bind iron (Hassler et al, 2011a). Since EPS are produced for many functions (Decho, 1990;Hoagland et al, 1993;de Brouwer et al, 2005), they are likely to be present in relatively high concentrations (Hassler et al, 2011a;Norman et al, 2015). EPS are expected to be particularly abundant in waters characterized by high chlorophyll concentrations or on the base of sea-ice (Table 1).…”

Kinneyia: A Flow-Induced Anisotropic Fossil Pattern from Ancient Microbial Mats

“…Their thickness ranges from a few millimeters to about a centimeter, depending on habitat, growth conditions, and on the microbial species they consist of (Neu and Lawrence, 1997;Gerdes et al, 2000). These may include bacteria, archaea (Zolghadr et al, 2010), protozoans, algae (de Brouwer et al, 2005), and fungi (Verstrepen and Klis, 2006). Due to the lack of large-scale internal organization, the material MM consist of appears rather homogeneous.…”

Heterotrophic Pioneers Facilitate Phototrophic Biofilm Development

“…The photosynthetic activity fuels processes in the total biofilm community, including the heterotrophic fraction [6,21]. The microorganisms produce extracellular polymeric substances (EPS) that hold the biofilm together [8,23].…”