Optimizing the Methanotrophic Production of Polyhydroxyalkanoates Using Mixed Microbial Bacteria Cultures

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Optimizing the Methanotrophic Production of Polyhydroxyalkanoates Using Mixed Microbial Bacteria Cultures, Is A Well-Researched Topic, It Is To Be Used As A Guide Or Framework For Your Research.

Abstract

The use of petroleum-based plastics has caused serious economic and environmental problems. It is imperative to develop sustainable ways to produce valuable and environmentally-friendly materials. Methanotrophic bacteria are known for assimilating methane while generating polyhydroxyalkanoates (PHAs) biopolymers, which are potential substitutes for conventional plastics.

In this study, a feast-famine based cultivation system was developed to produce PHAs using Hyphomicrobium, and Methylocysits dominated mixed culture, which was fed with methane with and without acetic acid as co-substrates. Throughout the 27 cycles of cultivations, the mixed bacterial culture fed with methane alone started to produce the PHB consistently and achieved an average of 26.4 ± 3.5 wt%. By comparison, the PHB production significantly increased up to 34.8 ± 1.8 wt% when acetic acid was added at an optimal concentration of 300 mg/L under controlled pH conditions. Additionally, the characterization of PHB polymers (e.g., chemical composition and molecular weight) illustrated that the presence of acetic acid at optimal pH conditions facilitated the elongation of the polymer chain with higher molecular weight.

TABLE OF CONTENTS

………………………………………………………………………………………………… iii
LIST OF TABLES ………………………………………………………………………………………………………… vii
LIST OF FIGURES ……………………………………………………………………………………………………… viii
ACKNOWLEDGEMENTS ……………………………………………………………………………………………… x
Chapter 1 ……………………………………………………………………………………………………………………….. 1
INTRODUCTION ………………………………………………………………………………………………………….. 1
1.1. Methanotrophs ……………………………………………………………………………………………………… 3
1.2. Structural features of methanotrophic bacteria ………………………………………………………….. 4
1.3. Biochemical and physiological features of methanotrophs …………………………………………. 5
1.4. Production of PHB and its environmental significance ………………………………………………. 7
1.5. Research Objectives ………………………………………………………………………………………………. 9
1.6. Thesis organization ……………………………………………………………………………………………… 10
Chapter 2 ……………………………………………………………………………………………………………………… 11
MATERIALS AND METHODS …………………………………………………………………………………….. 11
2.1. Experiment setup ………………………………………………………………………………………………… 11
2.2. Analytical methods ……………………………………………………………………………………………… 13
2.2.1. Analysis of volatile fatty acids ………………………………………………………………………… 13

2.2.2. Analysis of gases composition ………………………………………………………………………… 13
2.2.3. PHB extraction ……………………………………………………………………………………………… 13
2.2.4. PHB weight percentage and monomer composition …………………………………………… 14
2.3. PHB Characterization ………………………………………………………………………………………….. 15
2.4. The optimization of PHB generation by adding acetate ……………………………………………. 16
2.4.1. Culture conditions …………………………………………………………………………………………. 16
Chapter 3 ……………………………………………………………………………………………………………………… 17
OPTIMIZING THE METHANOTROHIC PRODUCTION OF POLYHYDROXYALKANOATES (PHAs) USING HIGHLY ENRICHED CULTURE IN THE PRESENCE OF ACETIC ACID …………………………………………………………………………………….. 17
Abstract ……………………………………………………………………………………………………………………. 17
3.1. Introduction ………………………………………………………………………………………………………… 18
3.2. Materials and methods …………………………………………………………………………………………. 19
3.3. Results and discussions ………………………………………………………………………………………… 20
3.3.1. Microbial community analysis of mixed enrichment culture ………………………………. 20
3.3.2. PHB generation with acetic acid addition and the impact of pH ………………………….. 23
3.3.3. Metabolic kinetics …………………………………………………………………………………………. 27
3.3.4. The role of acetic acid in the methanotrophic metabolism ………………………………….. 35
3.3.5. The characterization of PHB biopolymer …………………………………………………………. 39
3.4 Conclusions …………………………………………………………………………………………………………. 43

Chapter 4 ……………………………………………………………………………………………………………………… 44
MOLECULAR EVIDENCE FOR ENRICHMENT OF METHANOTROPHIC CULTURE FROM WASTEWATER TREATMENT SYSTEM ………………………………………………………….. 44
Abstract ……………………………………………………………………………………………………………………. 44
4.1. Introduction ………………………………………………………………………………………………………… 45
4.2. Materials and methods …………………………………………………………………………………………. 46
4.2.1. Cultivation of enrichment cultures…………………………………………………………………… 46
4.2.2. DNA extraction …………………………………………………………………………………………….. 49
4.2.3. PCR amplification and gel electrophoresis ……………………………………………………….. 49
4.3. Results and discussions ………………………………………………………………………………………… 51
4.3.1. Bacterial community diversity and abundance ………………………………………………….. 51
4.3.2. 16S rRNA gene sequencing ……………………………………………………………………………. 54
4.3.3. The detection of functional genes ……………………………………………………………………. 59
4.4 Conclusions …………………………………………………………………………………………………………. 62
Chapter 5 ……………………………………………………………………………………………………………………… 64
CONCLUSION AND RECOMMENDATIONS FOR FUTURE WORK …………………………….. 64
5.1. Conclusions ………………………………………………………………………………………………………… 64
5.2. Recommendations for future work ………………………………………………………………………… 65
APPENDIX I ……………………………………………………………………………………………………………….. 66
APPENDIX II ………………………………………………………………………………………………………………. 69

BIBLIOGRAPHY …………………………………………………………………………………………………………. 71

Additional information

Author

Kai Cheng

No of Chapters

5

No of Pages

91

Reference

YES

Format

PDF

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