Diversity of far-red light photoacclimation responses in cyanobacteria

The discovery of cyanobacteria capable of harvesting far-red light has changed the paradigm that oxygenic photosynthesis is only driven by visible light and exclusively by chlorophyll a. There are two known types of far-red photosynthesis. Firstly, a constitutive adaptation that uses a majority of chlorophyll d, which is restricted to a single genus (Acaryochloris). Moreover, an acclimation response, known as Far-Red Light Photoacclimation (FaRLiP), which uses chlorophyll f and is present in phylogenetically diverse cyanobacteria (1). FaRLiP involves the extensive remodelling of the photosynthetic machinery, via a cluster of approximately 19 genes coding for paralogous subunits of Photosystem I, Photosystem II, phycobilisomes and master control elements. Here, I will highlight the similarities and differences of FaRLiP among cyanobacteria on a cell, membrane, protein and DNA level by using bioinformatics, biochemical and biophysical methods. Our study focuses on cyanobacteria of the genus "Chroococcidiopsis" (2), as well as the phylogenetically early-branching group of "Halomicronema/Nodosilineales". The latter group are especially underrepresented. We could increase the number of FaRLiP cyanobacteria among them by using stringent far-red cultivation methods on samples from the hypersaline environment of the Sebkha Ooum Dba (Morocco). Furthermore, a strain was discovered that only contains a partial FaRLiP cluster, without genes for a far-red PSI variant, but with a normal growth behaviour under far-red light (3). This raises the question of the minimal requirements for FaRLiP.

(1) Antonaru LA, Cardona T, Larkum AWD and Nürnberg DJ (2020). ISME J 14, 2275–2287.

(2) Antonaru LA, Selinger VM,... and Nürnberg DJ (2023). ISME Commun 3, 113.

(3) Billi D, Napoli A,… and Nürnberg DJ (2022). Front Microbiol 13:933404.