Sulfated glycosaminoglycan-like polymers are present in an acidophilic biofilm from a sulfidic cave.

Sulfated glycosaminoglycans (sGAG) are negatively charged extracellular polymeric substances that occur in biofilms from various environments. Yet, it remains unclear whether these polymers are acquired from the external environment or produced by microbes in the biofilm. To resolve this, we analyzed the presence of sGAGs in samples of an acidophilic biofilm collected from Sulfur Cave in Puturosu Mountain (Romania), an environment that is largely inaccessible to contamination. A maximum of 55.16 ± 2.06 µg sGAG-like polymers were recovered per mg of EPS. Enzymatic treatment with chondroitinase ABC resulted in a decrease of the mass of these polymers, suggesting the structure of the recovered sGAG is similar to chondroitin. Subsequent FT-IR analysis of these polymers revealed absorbance bands at 1230 cm-1, 1167 cm-1 and 900 cm-1, indicating a possible presence of polysaccharides and sulfate. Analysis of genomic sequences closely related to those predominant in the acidophilic biofilm, contained genes coding for sulfotransferase (an enzyme needed for the production of sGAG), which supports the hypothesis of microbial synthesis of sGAGs within the biofilm.

Rapid redox signal transmission by "Cable Bacteria" beneath a photosynthetic biofilm.

Recently, long filamentous bacteria, belonging to the family Desulfobulbaceae, were shown to induce electrical currents over long distances in the surface layer of marine sediments. These "cable bacteria" are capable of harvesting electrons from free sulfide in deeper sediment horizons and transferring these electrons along their longitudinal axes to oxygen present near the sediment-water interface. In the present work, we investigated the relationship between cable bacteria and a photosynthetic algal biofilm. In a first experiment, we investigated sediment that hosted both cable bacteria and a photosynthetic biofilm and tested the effect of an imposed diel light-dark cycle by continuously monitoring sulfide at depth. Changes in photosynthesis at the sediment surface had an immediate and repeatable effect on sulfide concentrations at depth, indicating that cable bacteria can rapidly transmit a geochemical effect to centimeters of depth in response to changing conditions at the sediment surface. We also observed a secondary response of the free sulfide at depth manifest on the time scale of hours, suggesting that cable bacteria adjust to a moving oxygen front with a regulatory or a behavioral response, such as motility. Finally, we show that on the time scale of days, the presence of an oxygenic biofilm results in a deeper and more acidic suboxic zone, indicating that a greater oxygen supply can enable cable bacteria to harvest a greater quantity of electrons from marine sediments. Rapid acclimation strategies and highly efficient electron harvesting are likely key advantages of cable bacteria, enabling their success in high sulfide generating coastal sediments.