Isolation and optimization of extracellular PHB depolymerase producer Aeromonas caviae Kuk1-(34) for sustainable solid waste management of biodegradable polymers

PLoS One. 2022 Apr 14;17(4):e0264207. doi: 10.1371/journal.pone.0264207. eCollection 2022.

Abstract

Bioplastics, synthesized by several microbes, accumulates inside cells under stress conditions as a storage material. Several microbial enzymes play a crucial role in their degradation. This research was carried to test the biodegradability of poly-β-hydroxybutyrate (PHB) utilizing PHB depolymerase, produced by bacteria isolated from sewage waste soil samples. Potent PHB degrader was screened based on the highest zone of hydrolysis followed by PHB depolymerase activity. Soil burial method was employed to check their degradation ability at different incubation periods of 15, 30, and 45 days at 37±2°C, pH 7.0 at 60% moisture with 1% microbial inoculum of Aeromonas caviae Kuk1-(34) (MN414252). Without optimized conditions, 85.76% of the total weight of the PHB film was degraded after 45 days. This degradation was confirmed with Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscope (SEM) analysis. The presence of bacterial colonies on the surface of the degraded film, along with crest, holes, surface erosion, and roughness, were visible. Media optimization was carried out in statistical mode using Plackett Burman (PB) and Central Composite Design (CCD) of Response Surface Methodology (RSM) by considering ten different factors. Analysis of Variance (ANOVA), Pareto chart, response surface plots, and F-value of 3.82 implies that the above statistical model was significant. The best production of PHB depolymerase enzyme (14.98 U/mL) was observed when strain Kuk1-(34) was grown in a media containing 0.1% PHB, K2HPO4 (1.6 gm/L) at 27 ℃ for seven days. Exploiting these statistically optimized conditions, the culture was found to be a suitable candidate for the management of solid waste, where 94.4% of the total weight of the PHB film was degraded after 45 days of incubation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aeromonas caviae* / metabolism
  • Bacteria / metabolism
  • Carboxylic Ester Hydrolases / metabolism
  • Culture Media
  • Hydroxybutyrates / metabolism
  • Polyesters / chemistry
  • Polymers
  • Soil
  • Solid Waste
  • Waste Management*

Substances

  • Culture Media
  • Hydroxybutyrates
  • Polyesters
  • Polymers
  • Soil
  • Solid Waste
  • Carboxylic Ester Hydrolases

Grants and funding

RR is grateful to the Department of Science and Technology, India (DST-SERB) for providing financial support under the scheme of Early Career Research Award (Project No. ECR/2017/001001). SB would like to thank Deanship of Scientific Research at Majmaah University for supporting this work under Project Number No. R-2022-58. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.