Divergent composition of algal-bacterial biofilms developing under various external factors

Abstract

The influence of external factors other than nutrients on biofilm development and composition was studied with a combination of optical (Confocal Laser Scanning Microscopy, PAM fluorometry) and chemical methods (EPS extraction, HPLC, TOC determination). The development of algal-bacterial biofilms was followed from bare surfaces to mature biofilms in two water reservoirs on Dutch filtration dunes. Biofilms developed under the influence of grazing, light limitation or undisturbed by either of these two factors. Biofilms appeared similar at the beginning of the colonization period at the three sites and laser microscopy observations revealed the predominance of bacteria and capsular EPS (extracellular polymeric substances) in young biofilms. After 3 weeks development, the biofilms had a higher number of taxa; undisturbed biofilms presented the highest biomass, the longest developmental period and showed a significant correlation between organic carbon, chlorophyll and EPS production, indicating a close coupling between autotrophic carbon production and EPS. In light-limited biofilms, this coupling was weaker (although the organic carbon content was similar to that of the undisturbed biofilms) and a lower algal biomass was reached. Light-limited biofilms were mostly composed of diatoms, which are more efficient in low irradiances than green microalgae. Biofilms grazed by the snail Potamopyrgus antipodarum presented the lowest biomass level, but the highest proportion of EPS. Grazing seemed to favour the predominance of EPSrich algae, as well as firmly attached diatoms. Although filamentous cyanobacteria were found in mature biofilms at the three locations, they were more abundant in the grazed biofilms. The differences in carbon uptake with respect to its allocation indicated that external factors influencing biofilm development affect the cycling and transport of carbon in biofilms and hence influence the effect of biofilm metabolism on the overlying water quality.

Rapid determination of the dry weight of single, living cyanobacterial cells using the Mach-Zehnder double-beam interference microscope

“…EPS:chlorophyll a ratios of Microcoleus (Mazor et al, 1996) and of algal biofilms (Barranguet et al, 2005) can be converted to EPS:algal dry weight ratios (C/Chl a ¼ 40 and C ¼ 50% of dry weight, Jo¨rgensen, 1979) resulting in EPS:algal dw ratios of 50.2 (biofilms), to a maximum of 1.0 (Microcoleus). In the case of old cultures of Phormidium uncinatum, Hoiczyk (1998) measured sheath material as 21% of the total culture dry weight.…”

Seasonal succession of phototrophic biofilms in an Italian wastewater treatment plant: biovolume, spatial structure and exopolysaccharides

“…The situation is further complicated in that the EPS matrix originates from different organisms, producing more than one type of polymer that differ in saccharide unit composition and sequence (Neu 1994). The synthesis of these polymers may also significantly vary in response to environmental factors and cell status (De Philippis & Vincenzini 1998, Smith & Underwood 2000, Otero & Vincenzini 2004, Underwood et al 2004, Barranguet et al 2005, Stal & Défarge 2005.…”

“…The situation is further complicated in that the EPS matrix originates from different organisms, producing more than one type of polymer that differ in saccharide unit composition and sequence (Neu 1994). The synthesis of these polymers may also significantly vary in response to environmental factors and cell status (De Philippis & Vincenzini 1998, Smith & Underwood 2000, Otero & Vincenzini 2004, Underwood et al 2004, Barranguet et al 2005, Stal & Défarge 2005.The aim of this study was to investigate the structural integrity, potential productivity and matrix polysaccharide characteristics of phototrophic biofilms colonizing a southern temperate WWTP (Fiumicino Airport WWTP, Rome, Italy). A variety of microscopic and chemico-physical techniques were used to determine seasonal changes in samples taken directly from the WWTP tank walls (providing high biomass for exopolysaccharide studies) or from immersed polypropylene slides (for biovolume estimates).…”

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

“…The biomass obtained from strains grown in batch culture was used to extract two fractions of exopolysaccharides: CPS and RPS following the procedure described in Barranguet et al (2004Barranguet et al ( , 2005. Biomass harvested from **BG11 modified using only nitrates as nitrogen source and increasing the concentration of PO 4 3− in order to obtain a final N:P ratio of 15 in the medium (K 2 HPO 4 16 mg L −1 ) (Guzzon et al 2005) Fig.…”