English: Biomass distribution in a bacteria mat under different light conditions

Conceptual drawing of the biomass distribution during different light acclimation scenarios and the corresponding radiative energy budgets of the entire photic zone measured under an incident photon irradiance of 1000 μmol photons m^–2 s^–1. The surface layers of the microbial mat were dominated by dense populations of motile cyanobacteria (Microcoleus sp. and other filamentous species) and filamentous sulfide oxidizing bacteria (Beggiatoa spp.). Beneath the narrow photic zone, a dark FeS-containing sediment layer was present. In low light, the upper layers became oxidized driving the O₂-HS interface and thus Beggiatoa deeper into the mat, while the motile cyanobacteria moved toward the mat surface under non-inhibitory light levels. In high light, a larger part of the biofilm is oxidized, Beggiatoa moved further down, while motile cyanobacteria in the top layers started to move downwards to avoid high photoinhibitory light levels at the microbial mat surface. In darkness, the entire mat became anoxic and the Beggiatoa moved to the mat surface forming a white layer on top of the cyanobacteria, to avoid the high levels of H₂S and remain at the O₂-H₂S interface (Preisler et al., 2007), whereas the cyanobacteria remained in a dense layer underneath.

• Reference: Preisler, A., de Beer, D., Lichtschlag, A., Lavik, G., Boetius, A., and Jorgensen, B. B. (2007). "Biological and chemical sulfide oxidation in a Beggiatoa inhabited marine sediment". ISME J., 1: 341–353.