Ocean Microbe Reveals Its Unique Photosynthesis Survival Kit

Aerobic anoxygenic phototrophic (AAP) bacteria are vital players in the ocean's carbon cycle, yet how they perform photosynthesis in oxygen-rich waters has been a puzzle. Now, researchers have used cryo-electron microscopy to reveal the atomic-level structure of the photosynthetic machinery in a marine bacterium, Dinoroseobacter shibae.

The study details a 'supercomplex' with several surprising features. Its main light-harvesting ring is a closed loop of 17 subunits, each holding a pair of spheroidenone molecules – a configuration never reported before in phototrophic bacteria. Compared to its anaerobic relatives, a key cytochrome component is truncated to three hemes instead of four.

Furthermore, the spacing of its bacteriochlorophyll molecules is elongated, a trait that likely optimises the absorption of blue-shifted light found in its low-light seafloor habitat. Scientists also identified a completely new subunit, hypothesised to link the bacterium's photosynthesis and respiration pathways. Together, these features provide a blueprint for how these microbes balance energy generation with protection against oxidative damage, allowing them to thrive in their unique marine environment.