The mechanism that cells can enhance PHB accumulation under nitrogen limitation was speculated previously Nitrogen limitation is predicted to block amino acid synthesis in tricarboxylic acid cycle (TCA cycle), resulting in the increase of the substrate of PHB synthesis such as the nicotinamide adenine dinucleotide phosphate (NADPH). As a result, the PHB synthesis increases (Balaji et al, 2012). Thus, NADPH is likely to be response in enhanced PHB accumulation in nitrogen-limiting cells. For an effect of phosphorus limitation on PHB synthesis, it might involve in the increase allocation of carbon-type substrates to the PHB synthetic pathway but does not relate to the enzyme activities in PHB synthesis (Gonzalez-Fernandez and Ballesteros, 2012).