Three-factor combination was achieved in Aulosira fertilissima which 7.92 folds increased in PHB content was acquired under citrate supplemented combined with phosphorus deficiency in the dark (Samantaray and Mallick 2012). In agreement with these results from other cyanobacteria, this study found that the three-factor combination of 0.4% (w/v) acetate, nitrogen limitation and the darkness (C8) enhanced PHB content in O. okeni to 50.38 folds compare with standard condition (C1) (table 4-2). Mixed carbon sources were also investigated in Nostoc muscorum as PHB was enhanced by 4.84 folds under acetate and glucose supplemented together with the dark (Sharma et al. 2007).