Abstract
This study aimed at molecular and biochemical characterization of low-density polyethene (LDPE) degrading fungi and bacteria from Dandora dumpsite, Nairobi. Twenty bacterial and 10 fungal isolates were identified using 16S rDNA and 18S rDNA sequences for bacteria and fungi, respectively. The highest fungal degradation was attributed to Aspergillus oryzae strain A5,1 while the highest bacterial degradation was attributed to Bacillus cereus strain A5,a and Brevibacillus borstelensis strain B2,2, respectively. Isolates were screened for their ability to produce extracellular laccase and esterase; Aspergillus fumigatus strain B2,2 exhibited the highest presence of laccase (15.67 mm) while Aspergillus oryzae strain A5,1 exhibited the highest presence of esterase (14.33 mm). Alkane hydroxylase-encoding genes were screened for using primer AlkB 1 which amplified the fragment of size 870 bp. Four bacterial samples were positive for the gene. Optimum growth temperature of the fungal isolates was 30°C. The possession of laccase, esterase, and alkane hydroxylase activities is suggested as key molecular basis for LDPE degrading capacity. Knowledge of optimum growth conditions will serve to better utilize microbes in the bioremediation of LDPE. The application of Aspergillus oryzae strain A5,1 and Bacillus cereus strain A5,a in polyethene degradation is a promising option in this kind of bioremediation as they exhibited significantly high levels of biodegradation. Further investigation of more alkane degrading genes in biodegrading microbes will inform the choice of the right microbial consortia for bioaugmentation strategies.
Highlights
Low-density polyethene is a major cause of environmental pollution due to its high tensile strength, lightness, resistance to water, and microbial attack. e consumption of plastics in the country has increased to 4,000 tons per annum of polyethene bags which together with hard plastics end up scattered in the environment creating “the plastics menace” [1]. rough the National Environmental Management Authority (NEMA), Kenya has embraced the 3Rs, reduce, reuse, and recycle, concept of solid waste management [2] and most recently the ban on the use of polyethene carrier bags but this has not addressed the problem of polyethene which remains scattered in the environment [3]
Phylogenetic relationships were inferred from phylogenetic comparison of the 18S rDNA sequences using Mega 7 and maximumlikelihood algorithms to generate the phylogenetic tree (Figure 2) which shows the phylogenetic relationships among the various Aspergillus species. e tree displays four clades in which the isolates have been clustered
In a study done using untreated low-density polyethene (LDPE) incubated with A. oryzae, 5% weight loss was recorded compared with control
Summary
Low-density polyethene is a major cause of environmental pollution due to its high tensile strength, lightness, resistance to water, and microbial attack. e consumption of plastics in the country has increased to 4,000 tons per annum of polyethene bags which together with hard plastics end up scattered in the environment creating “the plastics menace” [1]. rough the National Environmental Management Authority (NEMA), Kenya has embraced the 3Rs, reduce, reuse, and recycle, concept of solid waste management [2] and most recently the ban on the use of polyethene carrier bags but this has not addressed the problem of polyethene which remains scattered in the environment [3]. Bacteria and fungi of various genera have been implicated previously in the biodegradation of polyethene albeit the low rates. Pseudomonas, Acinetobacter, Brevibacillus, Rhodococcus, and Micrococcus [6, 7, 1], respectively, isolated from different sources proved to be the International Journal of Microbiology potential organisms for polyethene degradation. E involvement of enzymes in microbial biodegradation of polyethene has been investigated, and enzymes such as laccases and esterases have been confirmed to play a role in this process either directly or indirectly [8]. E production of enzyme laccase in the presence of polyethene as the sole carbon source is a clear indication that laccase has a role in breaking down some of the intermediary products produced during this process. Presence of AlkB genes that encode alkane hydroxylases known to hydrolyze alkanes was investigated
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