## 4 Discussion  
Fluorescent pseudomonads are known to produce more than 100 phenazine-like compounds, which have been classified as antibiotics. Phenazines have a role in the survival of bacteria under low oxygen tension, iron acquisition, redox homeostasis, and transition to biofilm growth, which give producers an ecological advantage in the environment [6]. _P. chlororapahs_ PA23 was identified as a biocontrol bacterium due to the production of PHZ and PRN antibiotics [4]. This bacterium was also able to use vegetable oils as a sole carbon source to produce mcl-PHAs [23]. PHA is an energy and carbon storage polymer, which acts as food reserve for bacteria. The polymer is degraded under starving condition when nitrogen is present in the environment. Presence of PHAs in rhizosphere bacteria enhances their colonization and promotes plant growth. PHA producing bacteria can survive under starving conditions and under hostile environments. Therefore, both PHZ/PRN and PHA provide ecological benefits to the producing bacteria. A number of mutants defective in the production of PHZ and PRN antibiotics are available [12; 13; 14; 25]. Our preliminary studies indicated that mutants of _P. chlororapahs_ PA23 defective in PHZ production accumulated more PHA than the PA23 parent strain. Both PHZ/PRN and PHA are accumulated in the stationary phase of _P. chlororapahs_ growth and have common global regulators like  
Figure 7: Pathway of PHZ/ PRN and PHA production. Blocking PHZ and PRN production provides more precursors for PHA production. X indicates the gene mutated or deleted in _plz_ and _prn_ gene clusters. Thick arrows indicate higher carbon and reducing power flow for PHA production. GaCA/GaCS, RpoS, and the stringent response (SR). The precursors for PHZ and PRN production are acetyl-CoA and erythrose-4-phosphate, which are provided by \(\beta\)-oxidation and by the ED pathway, respectively [41] (Figure 7). Glucose is a preferred carbon source for cell growth and PHZ synthesis, but not for PHA production. _P. chloroformis_ PA23 produced a deep orange color and 38.5% more cell dry mass in glucose medium with 34% PHAs. In octanoic medium, it produced pale yellow color with low cell dry mass but with higher PHAs (46.25%). Moreover, PHA accumulation was higher in _P. chloroformis plz', prn'_, and _plz' prn'_ mutants cultured on RMM octanoate medium than RMM glucose medium. Higher PHA production in cultures containing fatty acids as the carbon source is correlated with higher gene expression levels of _phaC1_, _phaC2_, and _phaZ_, which was at least 15-fold greater in cells grown on fatty acid than those in cells grown on glucose in _P. putida_ KT2440 [42]. Whether the enhanced PHA production was due to a higher expression of _pha_ genes in PHZ/PRN null mutants or change in metabolic flux for PHA production by supplying more carbon expression of pha genes was studied. To explore the first possibility, we studied the expression of _pha_ genes in _P. chloroformis plz', prn'_, and _plz' prn'_ mutants (PHZ/PRN null mutants). No significant changes in the levels of _phaC1_ and _phaC2_ gene transcription were observed in _P. chloroformis pltz', prn'_, and _plz' prn'_ mutants, compared with the expression levels of these genes in _P. chloroformis_ PA23 cultured in RMM glucose medium. However, when the _P. chloroformis pltz', prn'_, and _pltz' prn'_ mutants were cultured in RMM octanoic acid medium, expression levels of the _phaC2_ gene increased significantly [4; 5; 6; 7; 8 times] compared to _P. chloroformis_ PA23 cultured in the same medium. The greater level of PHA production and accumulation in the _P. chloroformis pltz', prn'_ and _pltz' prn'_ mutants cultured in RMM octanoic acid could be due to higher _phaC2_ expression levels. Earlier, the expression of _phaC2_ along with _phaC1_ was associated with greater PHA production and accumulation than the _phaC1_ gene alone in _Pseudomonas corrugata_[43]. Moreover, PhaC1 and PhaC2 have different substrate specificity to use different carbon sources efficiently [40].