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Estudo da produção de Polihidroxibutirato por Herbaspirillum seropedicae SmR1 e seu mutante ntrC em diferentes fontes de carbono e relações carbono/nitrogênio

  • Sacomboio, Euclides Nenga Manuel
Publication Date
Dec 02, 2014
Repositório Digital Institucional da UFPR
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Abstract: Studies aiming to produce bioplastics such as polyhydroxyalkanoates (PHA) has grown in recent decades to be a sustainable alternative for production of biodegradable plastics is therefore an environmentally feasible alternative to the substitution of petrochemical processes use in massively days today. Herbaspirillum seropedicae has great biotechnological potential for the production of PHA, and this ability has been reported under different culture conditions. The main objective of this study was to evaluate the production of PHB in the parental strain H. seropedicae SmR1 and its ntrC mutant, defective in the expression of NtrC, an important regulator of nitrogen metabolism in various bacteria. The strategy allowed us to evaluate the production in high and low carbon/nitrogen (C/N) using NH4Cl as a nitrogen source and monosaccharides or carboxylic acids as carbon sources compared. Among the tested monosaccharides, D-fructose emerged as the best source of carbon this group, reaching yields of 30.5% and 65.8% PHB for SMR1 and ntrC, respectively. Interestingly, the carbon source that seropedicae H. had the best performance as PHB production was glycerol. The PHB production was achieved of 74.4% and 78% for H. seropedicae SMR1 and mutant ntrC, respectively. In general, it was observed that independent of the carbon source used, the highest production of PHB were obtained when the concentration of ammonia in the medium were lower than 5mM / L, indicating that high C/N ratios favoring the synthesis of PHB H. seropedicae. The ntrC mutant demonstrated in all conditions evaluated to produce between 20 and 100% higher than PHB SMR1 parental strain. The complementation of mutant ntrC integrates with a copy of the ntrC gene of H. seropedicae SmR1 reversed its largest production of PHB, returning to levels of strain SmR1. The complementation of mutant ntrC integrates with the copy of the ntrC gene of H. seropedicae SmR1 reversed its largest production of PHB, returning to levels of strain SmR1. This result indicates that indeed the NtrC protein is regulating the process of synthesis of PHB in H. seropedicae. The main conclusions are: (i) the production of PHB depends on the nature of the carbon source and probably its route of metabolism and the production of metabolites such as acetyl-CoA and reduced equivalnetes (NADPH and NADH); (ii) the ntrC mutant under all conditions tested showed higher production of PHB, indicating that the absence of NtrC can affect the metabolic balance in H. seropedicae favoring the production of PHA. Key words: Herbaspirillum seropedicae, Pohidroxibutirato (PHB), carbon/nitrogen ratio, NTR system, ntrC. XIII

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