organisms both oxygenic and non oxygenic phototrophs as well as non photosynthetic organisms crup was only found in oxygenic phototrophs and only in conjunction with another lycopene u03b2 cyclase crup was never found as the sole cyclase of any organism whereas non oxygenic phototrophs and non phototrophs as well as a few cyanobacteria have only one lycopene cyclase fig1 this phylogenetic distribution of crup in comparison to other lycopene cyclases suggests that either oxygenic photosynthesis has a requirement for more than one lycopene u03b2 cyclase or that crup has a function other than that of lycopene cyclization the former hypothesis that oxygenic photosynthetic organisms require more than one lycopene u03b2 cyclase seems unlikely since many cyanobacterial species have only one lycopene u03b2 cyclase either crtl or crua furthermore this hypothesis does not explain the exclusion of crup from all carotenoid producing non oxygenic organisms a phylogenetic tree was constructed based on 16s rrna from fully sequenced cyanobacteria fig1 this tree identified evolutionarily distinct clades of cyanobacteria one clade contained cyanobacteria with crup while another distinctly separate clade contained cyanobacteria that lacked crup the top clade fig1 was populated by open ocean cyanobacteria encompassing all but two of the non crup containing cyanobacteria these open ocean cyanobacteria are also known as u03b1 cyanobacteria which are characterized by having a co 2 concentrating mechanism involving a csos2 protein that is not found in u03b2 cyanobacteria those cyanobacteria that contain crup bottom clade in fig1 are from diverse ecological habitats including fresh water salt lakes intertidal zones hot springs dry rocks symbiotic relationships etc these crup containing cyanobacteria are known as u03b2 cyanobacteria contain co2 concentrating mechanisms that utilize.