Towards a bacterial biofertiliser for the rehabilitation of disturbed and degraded land
- Authors: Masudi, Wiya Leon
- Date: 2024-10-11
- Subjects: Biofertilizers , Land degradation , Ecological disturbances , Plant-growth promoting rhizobacteria , Restoration ecology
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466826 , vital:76790 , DOI https://doi.org/10.21504/10962/466826
- Description: Agriculture, mining, industry, and human activity disturb, degrade, and pollute pristine environments and particularly the soil environment. Excessive land exploitation slows or disrupts the soil potential, rendering it incapable of playing its role leading to land degradation. In the mining sector, specifically coal mining, rehabilitation of disturbed and degraded land involves strategies that include importing topsoil and using fossil fuel-derived fertilisers. Both practices are unsustainable. To address the unsustainability, a myco-phytoremediation technology known as Fungcoal was developed to facilitate successful revegetation of mining-disturbed and degraded land following the bioconversion of waste coal into a soil-like humic-rich substrate. To offset the dependence on chemical-based fertilisers, efforts were/are focussed on finding mutualistic and cost-effective microbial resources with plant growth-promoting (PGP) activity as a bacterial biofertiliser. This study made use of 22 isolated bacteria and the three Fungcoal coal-degrading fungi viz., Aspergillus sp. ECCN 84, Aspergillus sp. ECCN 225 and Penicillium sp. ECCN 243 as the microbial resource. Initially, characterisation of the substrate waste coal and molecular identification of the selected bacterial isolates were carried out. Physicochemical analysis of the low-rank coal (LRC) substrate revealed a pH of 3.60 with background S content equivalent to 7.13 g L-1, N at 20 mg L-1, P at 7.8 mg L-1 and K at 3.3 mg L-1. Energy-dispersive X-ray spectroscopy (EDX) analysis revealed a C and O content of 23.09 and 69.03 wt%, respectively. Metagenomic analysis of the microbial population associated with the LRC substrate showed that among the 96.32% of bacteria, 59.46 to 62.18% belonged to Bacillota (also called Firmicutes), a phylum of largely Gram-positive bacteria, and 33.01 to 35.74% to Pseudomonadota (synonymous with Proteobacteria), a phylum of mostly Gram-negative bacteria. Following purification of the selected bacterial isolates and molecular characterisation by PCR, phylogenetic relatedness to known plant growth-promoting bacteria (PGPB) contained in the GenBank database showed that these bacterial isolates clustered with high bootstrap values to the reference PGPB strains. Only Pseudomonas sp. ECCN 10b (MW672582) was outside of the tree and shared significant similarity (100%) with Pseudomonas fluorescens (CP015638). A biochemical study revealed that the two Proteus sp. strains, Exiguobacterium sp., Enterobacter sp., and Ancylobacter, tolerated high salt and a wide range of temperatures. Bacterial isolates showed a high pH tolerance between 3 and 11, with the best growth at pH around 7. Nine of the identified strains, four Bacillus sp., Exiguobacterium sp., Enterobacter sp., Pseudomonas sp., Arthrobacter sp., and Aeromonas sp., were able to grow and increase in a medium containing either glucose, mannitol, sodium L-glutamate, sucrose, or fructose. Growth was highest in media containing either sodium L-glutamate, sucrose, or fructose. All the coal degrading strains and 83% of those isolated from municipal wastewater used more complex carbon sources such as high and LRC. The potential for PGP activity was quantified spectrophotometrically by measuring the production of auxins, as indole-3-acetic acid (IAA) equivalents; gibberellins, as gibberellic acid (GA3) equivalents, along with 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore activity. Additionally, nutrient mobilisation was evaluated by monitoring an ability to mineralise NH4+, PO43−, and K+. Competent PGP strains for the coal degrading isolates included Proteus strain ECCN 20b, Proteus strain ECCN 23b, and Serratia strain ECCN 24b. In response to L-trp supplementation, the concentration of indolic compounds (measured as indole-3-acetic acid) increased. Production of ammonium and solubilisation of insoluble P by these strains was also apparent. Only Serratia strain ECCN 24b could solubilise insoluble K. Production of indoles increased following exposure to increasing aliquots of LRC, suggesting no negative effect of this material on indole production and that these bacteria may possess PGP potential. Of the twelve bacterial strains isolated from wastewater MaB-flocs, three produced indoles, nine mineralised NH4+, seven solubilised P, and one K. Potential of isolated strains for PGP activity according to a one-way ANOVA on ranks was: ECCN 7b > ECCN 4b > ECCN 6b > ECCN 3b = ECCN 10b > ECCN 1b = ECCN 5b > ECCN 8b > ECCN 2b > ECCN 12b > ECCN 9b = ECCN 11b. Further study revealed that cell-free filtrate from indole-producing cultures of Aeromonas strain ECCN 4b, Enterobacter strain ECCN 7b, and Arthrobacter strain ECCN 6b promoted mung bean adventitious root formation. Based on a biochemical study and the outcome of the ranking of bacterial strains according to PGP-like activities, three bacteria, Enterobacter sp., strain ECCN 7b, Proteus sp., strain ECCN 20b and Serratia sp., strain ECCN 24b that showed great mutualistic relationship with the most effective Fungcoal biocatalyst, A. fischeri ECCN 84, were used to prepare a bacterial bio-fertiliser. This consortium grew well in NB supplemented with L-tryptophan and produced indole compounds that could activate the adventitious rooting of mung bean (Vigna radiata L.) hypocotyls. Finally, the consortium showed no antibiotic resistance activity; however, they produced better biofertiliser with good responses to root/plant biomass production of the same Fabaceae, mung bean (Vigna radiata L.). The further development of this consortium into a cost-effective, environmentally friendly biofertiliser may help reduce dependence on chemical-based fertilisers and improve the sustainability of Fungcoal and other land rehabilitation strategies. Further studies are therefore underway to investigate in greater detail the PGP activity of these isolates individually and in consortium under field conditions to support the Fungcoal myco-phytoremediation strategy. , Thesis (PhD) -- Faculty of Science, Institute for Environmental Biotechnology, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Masudi, Wiya Leon
- Date: 2024-10-11
- Subjects: Biofertilizers , Land degradation , Ecological disturbances , Plant-growth promoting rhizobacteria , Restoration ecology
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466826 , vital:76790 , DOI https://doi.org/10.21504/10962/466826
- Description: Agriculture, mining, industry, and human activity disturb, degrade, and pollute pristine environments and particularly the soil environment. Excessive land exploitation slows or disrupts the soil potential, rendering it incapable of playing its role leading to land degradation. In the mining sector, specifically coal mining, rehabilitation of disturbed and degraded land involves strategies that include importing topsoil and using fossil fuel-derived fertilisers. Both practices are unsustainable. To address the unsustainability, a myco-phytoremediation technology known as Fungcoal was developed to facilitate successful revegetation of mining-disturbed and degraded land following the bioconversion of waste coal into a soil-like humic-rich substrate. To offset the dependence on chemical-based fertilisers, efforts were/are focussed on finding mutualistic and cost-effective microbial resources with plant growth-promoting (PGP) activity as a bacterial biofertiliser. This study made use of 22 isolated bacteria and the three Fungcoal coal-degrading fungi viz., Aspergillus sp. ECCN 84, Aspergillus sp. ECCN 225 and Penicillium sp. ECCN 243 as the microbial resource. Initially, characterisation of the substrate waste coal and molecular identification of the selected bacterial isolates were carried out. Physicochemical analysis of the low-rank coal (LRC) substrate revealed a pH of 3.60 with background S content equivalent to 7.13 g L-1, N at 20 mg L-1, P at 7.8 mg L-1 and K at 3.3 mg L-1. Energy-dispersive X-ray spectroscopy (EDX) analysis revealed a C and O content of 23.09 and 69.03 wt%, respectively. Metagenomic analysis of the microbial population associated with the LRC substrate showed that among the 96.32% of bacteria, 59.46 to 62.18% belonged to Bacillota (also called Firmicutes), a phylum of largely Gram-positive bacteria, and 33.01 to 35.74% to Pseudomonadota (synonymous with Proteobacteria), a phylum of mostly Gram-negative bacteria. Following purification of the selected bacterial isolates and molecular characterisation by PCR, phylogenetic relatedness to known plant growth-promoting bacteria (PGPB) contained in the GenBank database showed that these bacterial isolates clustered with high bootstrap values to the reference PGPB strains. Only Pseudomonas sp. ECCN 10b (MW672582) was outside of the tree and shared significant similarity (100%) with Pseudomonas fluorescens (CP015638). A biochemical study revealed that the two Proteus sp. strains, Exiguobacterium sp., Enterobacter sp., and Ancylobacter, tolerated high salt and a wide range of temperatures. Bacterial isolates showed a high pH tolerance between 3 and 11, with the best growth at pH around 7. Nine of the identified strains, four Bacillus sp., Exiguobacterium sp., Enterobacter sp., Pseudomonas sp., Arthrobacter sp., and Aeromonas sp., were able to grow and increase in a medium containing either glucose, mannitol, sodium L-glutamate, sucrose, or fructose. Growth was highest in media containing either sodium L-glutamate, sucrose, or fructose. All the coal degrading strains and 83% of those isolated from municipal wastewater used more complex carbon sources such as high and LRC. The potential for PGP activity was quantified spectrophotometrically by measuring the production of auxins, as indole-3-acetic acid (IAA) equivalents; gibberellins, as gibberellic acid (GA3) equivalents, along with 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore activity. Additionally, nutrient mobilisation was evaluated by monitoring an ability to mineralise NH4+, PO43−, and K+. Competent PGP strains for the coal degrading isolates included Proteus strain ECCN 20b, Proteus strain ECCN 23b, and Serratia strain ECCN 24b. In response to L-trp supplementation, the concentration of indolic compounds (measured as indole-3-acetic acid) increased. Production of ammonium and solubilisation of insoluble P by these strains was also apparent. Only Serratia strain ECCN 24b could solubilise insoluble K. Production of indoles increased following exposure to increasing aliquots of LRC, suggesting no negative effect of this material on indole production and that these bacteria may possess PGP potential. Of the twelve bacterial strains isolated from wastewater MaB-flocs, three produced indoles, nine mineralised NH4+, seven solubilised P, and one K. Potential of isolated strains for PGP activity according to a one-way ANOVA on ranks was: ECCN 7b > ECCN 4b > ECCN 6b > ECCN 3b = ECCN 10b > ECCN 1b = ECCN 5b > ECCN 8b > ECCN 2b > ECCN 12b > ECCN 9b = ECCN 11b. Further study revealed that cell-free filtrate from indole-producing cultures of Aeromonas strain ECCN 4b, Enterobacter strain ECCN 7b, and Arthrobacter strain ECCN 6b promoted mung bean adventitious root formation. Based on a biochemical study and the outcome of the ranking of bacterial strains according to PGP-like activities, three bacteria, Enterobacter sp., strain ECCN 7b, Proteus sp., strain ECCN 20b and Serratia sp., strain ECCN 24b that showed great mutualistic relationship with the most effective Fungcoal biocatalyst, A. fischeri ECCN 84, were used to prepare a bacterial bio-fertiliser. This consortium grew well in NB supplemented with L-tryptophan and produced indole compounds that could activate the adventitious rooting of mung bean (Vigna radiata L.) hypocotyls. Finally, the consortium showed no antibiotic resistance activity; however, they produced better biofertiliser with good responses to root/plant biomass production of the same Fabaceae, mung bean (Vigna radiata L.). The further development of this consortium into a cost-effective, environmentally friendly biofertiliser may help reduce dependence on chemical-based fertilisers and improve the sustainability of Fungcoal and other land rehabilitation strategies. Further studies are therefore underway to investigate in greater detail the PGP activity of these isolates individually and in consortium under field conditions to support the Fungcoal myco-phytoremediation strategy. , Thesis (PhD) -- Faculty of Science, Institute for Environmental Biotechnology, 2024
- Full Text:
- Date Issued: 2024-10-11
Crop fields abandonment: assessing the dynamics of degradation in relation to leverage points for sustainable land management in the Macubeni catchment, South Africa
- Authors: Sibiya, Silindile
- Date: 2023-03-29
- Subjects: Land degradation , Sustainable land management , Multiple criteria decision making , Twelve leverage points , Soil erosion South Africa eMalahleni , ArcGIS
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422470 , vital:71945
- Description: Soil erosion is a major global environmental problem and a pervasive forms of land degradation that threatens land productivity and food and water security. Some of the biggest sources of sediment in catchments are previously cultivated lands. Regardless of this factor, the abandonment of cultivated fields is not well-researched. Sustainable land management (SLM) interventions can play a significant role in mitigating and halting land degradation. This study investigated the dynamics of degradation exhibited by crop fields and the potential impacts of SLM interventions, using a leverage points framework and a case study in the Macubeni catchment of South Africa. The research answers three questions: (1) What is the relationship between the usage status of crop fields and degradation in Macubeni? (2) What are the drivers of crop field abandonment and how do they interact in the system? (3) Can proposed sustainable land management interventions tackle the dynamics of land abandonment, and associated degradation, at the root cause level? An empirical-analytical approach using a four step multi-method process was followed, in which crop fields were mapped using ArcGIS tools, literature was reviewed alongside stakeholder engagements, qualitative systems mapping modelling was undertaken, and a Multi-Criteria Analysis (MCA) with leverage points hierarchy was used to integrate all the steps together. The results revealed that the various drivers of crop field abandonment include natural environmental factors, socio-economic and social factors. 47.41% of the total crop fields in Macubeni were classified as highly degraded, and abandoned fields covered 37.47%. The statistical Chi-Square Test also confirmed that there is a significant relationship between the usage status and degradation level in crop fields. The SLM interventions assessed in the study have the potential to tackle the dynamics of land abandonment at a root cause level, however, there is a need to first shift the community’s mental models to address the existing sources of change resistance that are hindering successful implementation. Furthermore, the innovative multi-method approach applied in this study can further provide a holistic, dynamic, and integrated decision-support to land conservation and rehabilitation projects in similar settings across South Africa and other developing countries as opposed to the more traditional one-dimensional approaches. , Thesis (MSc) -- Faculty of Science, Environmental Science, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Sibiya, Silindile
- Date: 2023-03-29
- Subjects: Land degradation , Sustainable land management , Multiple criteria decision making , Twelve leverage points , Soil erosion South Africa eMalahleni , ArcGIS
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422470 , vital:71945
- Description: Soil erosion is a major global environmental problem and a pervasive forms of land degradation that threatens land productivity and food and water security. Some of the biggest sources of sediment in catchments are previously cultivated lands. Regardless of this factor, the abandonment of cultivated fields is not well-researched. Sustainable land management (SLM) interventions can play a significant role in mitigating and halting land degradation. This study investigated the dynamics of degradation exhibited by crop fields and the potential impacts of SLM interventions, using a leverage points framework and a case study in the Macubeni catchment of South Africa. The research answers three questions: (1) What is the relationship between the usage status of crop fields and degradation in Macubeni? (2) What are the drivers of crop field abandonment and how do they interact in the system? (3) Can proposed sustainable land management interventions tackle the dynamics of land abandonment, and associated degradation, at the root cause level? An empirical-analytical approach using a four step multi-method process was followed, in which crop fields were mapped using ArcGIS tools, literature was reviewed alongside stakeholder engagements, qualitative systems mapping modelling was undertaken, and a Multi-Criteria Analysis (MCA) with leverage points hierarchy was used to integrate all the steps together. The results revealed that the various drivers of crop field abandonment include natural environmental factors, socio-economic and social factors. 47.41% of the total crop fields in Macubeni were classified as highly degraded, and abandoned fields covered 37.47%. The statistical Chi-Square Test also confirmed that there is a significant relationship between the usage status and degradation level in crop fields. The SLM interventions assessed in the study have the potential to tackle the dynamics of land abandonment at a root cause level, however, there is a need to first shift the community’s mental models to address the existing sources of change resistance that are hindering successful implementation. Furthermore, the innovative multi-method approach applied in this study can further provide a holistic, dynamic, and integrated decision-support to land conservation and rehabilitation projects in similar settings across South Africa and other developing countries as opposed to the more traditional one-dimensional approaches. , Thesis (MSc) -- Faculty of Science, Environmental Science, 2023
- Full Text:
- Date Issued: 2023-03-29
Bacterial colonisation and degradation of geologically weathered and discard coal
- Authors: Olawale, Jacob Taiwo
- Date: 2018
- Subjects: Coal mine waste , Coal -- Biodegradation , Coal mines and mining -- Environmental aspects , Land degradation , Electron microscopy , Extracellular polymeric substances , Flagella (Microbiology) , Fourier transform infrared spectroscopy , Microbiologically influenced corrosion
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61625 , vital:28043
- Description: Bacterial beneficiation of low-grade coal, coal discard, and waste has the potential to mitigate land degradation, water and soil pollution and, be a strategy for mining companies to responsibly extract and process coal with environmental sustainability. This study investigated the colonisation and biodegradation or depolymerisation of coal discard and geologically weathered coal by selected strains of bacteria, and an attempt has been made to describe the mechanisms associated with colonisation and biodegradation of this carbonaceous material. Ten bacterial strains, Bacillus strain ECCN 18b, Citrobacter strain ECCN 19b, Proteus strain ECCN 20b, Exiguobacterium strain ECCN 21b, Microbacterium strain ECCN 22b, Proteus strain ECCN 23b, Serratia strain ECCN 24b, Escherichia strain ECCN 25b, Bacillus strain ECCN 26b and Bacillus strain ECCN 41b, isolated from diesel-contaminated soil and coal slurry and identified using DNA sequencing, were rescreened and their coal biodegradation potential ranked. The ranking of the bacterial strains was undertaken using several indicators including; formation of brown halos on the plate culture (solid), change in colour intensity of the medium in liquid culture, change in culture media pH, and an increase in absorbance at 280nm and 450nm. Although, all the ten strains showed evidence of biodegradation of coal discard and geologically weathered coal based on the ranking employed, and the three strains considered the best candidates were Citrobacter strain ECCN 19b, Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b. The actions of the three bacterial strains were further studied and characterised in relation to coal degradation. Electron microscopy revealed that Citrobacter strain ECCN 19b, Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b attached to the surface of coal discard and geologically weathered coal by a process that appeared to involve extracellular polymeric substances (EPS), and flagella. The presence of flagella for Citrobacter strain ECCN 19b and Serratia strain ECCN 24b was confirmed by transmission electron microscopy. Bacterial degradation of coal discard and geologically weathered coal by these selected strains resulted in the release of soluble and insoluble products. Ultraviolet/ visible spectrophotometric (UV/VIS) analysis revealed that the soluble products resembled humic acid-like substances, which was confirmed following Fourier Transform Infrared (FTIR) spectroscopy. Analysis revealed that the coal-derived humic acid-like substances were similar to commercial humic acid extracted from bituminous coal. Elemental analysis of the insoluble product residue after bacterial biodegradation revealed the modification of the chemical compositions of the coal discard and geologically weathered coal substrates. Characterisation of the functional groups of the insoluble product using FTIR spectroscopy indicated changes, with the appearance of new peaks at 1737cm-1, 1366cm-1, 1228cm-1, and 1216cm-1 characteristic of aldehyde, ketones, carboxylic acids, esters, amines, and alkanes. Broad spectra regions of 3500 -3200cm-1, characteristic of alcohol and phenol, were also observed. Together, these results were taken as evidence for increased oxidation of the coal substrates, presumably as a consequence of bacterial catalysed biodegradation of coal discard and geologically weathered coal. During bacterial degradation of coal discard and geologically weathered coal, strains produced extracellular protein, which was detected and further investigated using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS- PAGE). At least three protein bands with molecular mass 53 kDa, 72 kDa, and 82 kDa were common to the three bacterial strains. Following ammonium sulphate precipitation and gel filtration chromatography, additional bands with molecular mass 16 kDa, 33 kDa, 37 kDa, and 43 kDa were detected. An extracellular laccase activity was detected in cultures of Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b. Cytochrome P450 activity was detected in all the bacterial strains in the presence of both coal discard and geologically weathered coal. This is the first time that cytochrome P450 activity has been reported following exposure of these three bacterial strains to a coal substrate. Overall, this research has successfully demonstrated the partial degradation of coal discard and geologically weathered coal by Citrobacter strain ECCN 19b, Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b and the release of humic acid-like substances. Thus, the biodegradation process involved adherence to and growth of the bacteria on the surface of coal substrate and appeared to require the formation of alkaline substances and the combined activities of extracellular LAC and cytochrome P450. Since bacterial degradation of low-grade coal and discard appears to be viable, the bacteria isolated in this study can potentially be used either for conversion of discard into valuable chemicals or to mitigate the deleterious effects of stockpiled coal discard on the environment.
- Full Text:
- Date Issued: 2018
- Authors: Olawale, Jacob Taiwo
- Date: 2018
- Subjects: Coal mine waste , Coal -- Biodegradation , Coal mines and mining -- Environmental aspects , Land degradation , Electron microscopy , Extracellular polymeric substances , Flagella (Microbiology) , Fourier transform infrared spectroscopy , Microbiologically influenced corrosion
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61625 , vital:28043
- Description: Bacterial beneficiation of low-grade coal, coal discard, and waste has the potential to mitigate land degradation, water and soil pollution and, be a strategy for mining companies to responsibly extract and process coal with environmental sustainability. This study investigated the colonisation and biodegradation or depolymerisation of coal discard and geologically weathered coal by selected strains of bacteria, and an attempt has been made to describe the mechanisms associated with colonisation and biodegradation of this carbonaceous material. Ten bacterial strains, Bacillus strain ECCN 18b, Citrobacter strain ECCN 19b, Proteus strain ECCN 20b, Exiguobacterium strain ECCN 21b, Microbacterium strain ECCN 22b, Proteus strain ECCN 23b, Serratia strain ECCN 24b, Escherichia strain ECCN 25b, Bacillus strain ECCN 26b and Bacillus strain ECCN 41b, isolated from diesel-contaminated soil and coal slurry and identified using DNA sequencing, were rescreened and their coal biodegradation potential ranked. The ranking of the bacterial strains was undertaken using several indicators including; formation of brown halos on the plate culture (solid), change in colour intensity of the medium in liquid culture, change in culture media pH, and an increase in absorbance at 280nm and 450nm. Although, all the ten strains showed evidence of biodegradation of coal discard and geologically weathered coal based on the ranking employed, and the three strains considered the best candidates were Citrobacter strain ECCN 19b, Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b. The actions of the three bacterial strains were further studied and characterised in relation to coal degradation. Electron microscopy revealed that Citrobacter strain ECCN 19b, Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b attached to the surface of coal discard and geologically weathered coal by a process that appeared to involve extracellular polymeric substances (EPS), and flagella. The presence of flagella for Citrobacter strain ECCN 19b and Serratia strain ECCN 24b was confirmed by transmission electron microscopy. Bacterial degradation of coal discard and geologically weathered coal by these selected strains resulted in the release of soluble and insoluble products. Ultraviolet/ visible spectrophotometric (UV/VIS) analysis revealed that the soluble products resembled humic acid-like substances, which was confirmed following Fourier Transform Infrared (FTIR) spectroscopy. Analysis revealed that the coal-derived humic acid-like substances were similar to commercial humic acid extracted from bituminous coal. Elemental analysis of the insoluble product residue after bacterial biodegradation revealed the modification of the chemical compositions of the coal discard and geologically weathered coal substrates. Characterisation of the functional groups of the insoluble product using FTIR spectroscopy indicated changes, with the appearance of new peaks at 1737cm-1, 1366cm-1, 1228cm-1, and 1216cm-1 characteristic of aldehyde, ketones, carboxylic acids, esters, amines, and alkanes. Broad spectra regions of 3500 -3200cm-1, characteristic of alcohol and phenol, were also observed. Together, these results were taken as evidence for increased oxidation of the coal substrates, presumably as a consequence of bacterial catalysed biodegradation of coal discard and geologically weathered coal. During bacterial degradation of coal discard and geologically weathered coal, strains produced extracellular protein, which was detected and further investigated using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS- PAGE). At least three protein bands with molecular mass 53 kDa, 72 kDa, and 82 kDa were common to the three bacterial strains. Following ammonium sulphate precipitation and gel filtration chromatography, additional bands with molecular mass 16 kDa, 33 kDa, 37 kDa, and 43 kDa were detected. An extracellular laccase activity was detected in cultures of Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b. Cytochrome P450 activity was detected in all the bacterial strains in the presence of both coal discard and geologically weathered coal. This is the first time that cytochrome P450 activity has been reported following exposure of these three bacterial strains to a coal substrate. Overall, this research has successfully demonstrated the partial degradation of coal discard and geologically weathered coal by Citrobacter strain ECCN 19b, Exiguobacterium strain ECCN 21b and Serratia strain ECCN 24b and the release of humic acid-like substances. Thus, the biodegradation process involved adherence to and growth of the bacteria on the surface of coal substrate and appeared to require the formation of alkaline substances and the combined activities of extracellular LAC and cytochrome P450. Since bacterial degradation of low-grade coal and discard appears to be viable, the bacteria isolated in this study can potentially be used either for conversion of discard into valuable chemicals or to mitigate the deleterious effects of stockpiled coal discard on the environment.
- Full Text:
- Date Issued: 2018
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