Selection and cultivation conditions of Bacillus thuringiensis L25.1  for poly (3-hydroxybutyrate-co-3-hydroxyvalerate) production  using native rice bran waste as the main nutrient

Wimol  Chobchuenchom

Authors

Wimol Chobchuenchom Faculty of Medical Technology, Rangsit University, Patumthani, 12000 Thailand

Keywords:

Bacillus thuringiensis L25.1, cultivation condition, native rice bran waste, polyhydroxybutyrate P(3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV))

Abstract

Among the bioplastics produced by microorganisms, polyhydroxyalkanoate (PHA) copolymers are particularly biocompatible. These compounds do not cause inflammation or allergies to human tissue, and they are more elastic than homopolymers; hence, they are suitable for medical applications. However, PHA production costs are still relatively high, and the development of a low-cost PHA is, therefore, necessary. This research aimed to study the cultivation conditions for the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) by Bacillus thuringiensis L25.1 using low-cost native rice bran waste from rice bran oil production via a cold press method as the main carbon source. The cultivation of Bacillus thuringiensis L25.1 on minimal salt agar (MSA) at various medium pHs, cultivation temperatures, percentages of native rice bran waste, incubation times, percentages of levulinic acid (LA), and enrichment of the bacterium in LA were studied. Production of P(3HB) and P(3HB-co-3HV) was determined via gas chromatography (GC). Using the 5^th subculture of Bacillus thuringiensis L25.1 cultured on MSA with additional 24% native rice bran waste with citric acid, a medium pH of 7.0, and incubation at 30 ^oC for 48 hours, the % and weight per plate of poly (3-hydroxybutyrate) P(3HB):P(3HB-co-3HV) was 2.07%, 3.47 mg and 12.90%, 21.59 mg, respectively. This finding suggested that P(3HB-co-3HV) in the presence of low P(3HB) content could be produced by using low-cost waste as a carbon source and LA as a co-substrate in a semi-solid medium.

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