A Cyanobacteria Enriched Layer of Shark Bay Stromatolites Reveals a New Strain Living in Near Infrared Light.

The genus is unique among phototrophic organisms due to the dominance of chlorophyll in its photosynthetic reaction centres and light-harvesting proteins. This allows to capture light energy for photosynthesis over an extended spectrum of up to ~760 nm in the near infra-red (NIR) spectrum. sp. has been reported in a variety of ecological niches, ranging from polar to tropical shallow aquatic sites. Here, we report a new strain isolated from an NIR-enriched stratified microbial layer 4-6 mm under the surface of stromatolite mats located in the Hamelin Pool of Shark Bay, Western Australia. Pigment analysis by spectrometry/fluorometry, flow cytometry and spectral confocal microscopy identifies unique patterns in pigment content that likely reflect niche adaption. For example, unlike the original species (type strain MBIC11017), this new strain, , shows little change in the chlorophyll in response to changes in light wavelength, displays a different Fv/Fm response and lacks detectable levels of phycocyanin. Indeed, 16S rRNA analysis supports the identity of the LARK001 strain as close to but distinct from from the HICR111A strain first isolated from Heron Island and previously found on the Great Barrier Reef under coral rubble on the reef flat. Taken together, LARK001 is a new cyanobacterial strain adapted to the stromatolite mats in Shark Bay.