title: Chlorophyll f distribution and dynamics in cyanobacterial beachrock biofilms.
abstract: Chlorophyll (Chl) f, the most far-red (720-740 nm) absorbing Chl species, was discovered in cyanobacterial isolates from stromatolites and subsequently in other habitats as well. However, the spatial distribution and temporal dynamics of Chl f in a natural habitat have so far not been documented. Here, we report the presence of Chl f in cyanobacterial beachrock biofilms. Hyperspectral imaging on cross-sections of beachrock from Heron Island (Great Barrier Reef, Australia), showed a strong and widely distributed signature of Chl f absorption in an endolithic layer below the dense cyanobacterial surface biofilm that could be localized to aggregates of Chroococcidiopsis-like unicellular cyanobacteria packed within a thick common sheath. High-pressure liquid chromatography-based pigment analyses showed in situ ratios of Chl f to Chl a of 5% in brown-pigmented zones of the beachrock, with lower ratios of ~0.5% in the black- and pink-pigmented biofilm zones. Enrichment experiments with black beachrock biofilm showed stimulated synthesis of Chl f and Chl d when grown under near-infrared radiation (NIR; 740 nm), with a Chl f to Chl a ratio increasing 4-fold to 2%, whereas the Chl d to Chl a ratio went from 0% to 0.8%. Enrichments grown under white light (400-700 nm) produced no detectable amounts of either Chl d or Chl f. Beachrock cyanobacteria thus exhibited characteristics of far-red light photoacclimation, enabling Chl f -containing cyanobacteria to thrive in optical niches deprived of visible light when sufficient NIR is prevalent.
authors.affiliation: Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, DK-3000, Helsingør, Denmark.
authors.forename: Erik
authors.initials: E
authors.lastname: Trampe
authors.affiliation: Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, DK-3000, Helsingør, Denmark.|Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, New South Wales, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Kühl
mesh_terms: D018441:Biofilms; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000032:analysis; D057894:Coral Reefs; D000458:Cyanobacteria / Q000737:chemistry* / Q000502:physiology*; D011793:Queensland
chemical_list: C583352:chlorophyll f; D002734:Chlorophyll
keywords: Chl f; beachrock; biofilm; cyanobacteria; endolithic; photosynthesis