Abstract
Production of polyhydroxyalkanoates (PHA) by bacteria isolated from spent engine oil (SEO) contaminated soils was investigated using nitrogen limitation in the production medium. Out of ten isolates, three were selected as the best based on their ability to metabolize SEO effectively and fluoresce orange when stained with Nile Blue A dye. Fourier Transform Infrared spectrophometer was used as a confirmatory test for PHA detection by tracking the carbonyl bands on the spectra. Optimum growth of the isolates occurred at 1% (v/v) SEO, pH 7, 37°C for K1+VE and Kar5+VE1 while for Kar5+VE2 was at 1% (v/v) SEO, PH 7, 40°C and 150 RPM. Sequencing of 16S rDNA partial genes grouped the isolates into 6 different genera: Ochrobactrum, Pseudoxanthomonas, Bodetella, Achromobacter, Alcaligenes and Acinetobacter species. Isolate K1+VE, identified as an Ochrobactrum produced Poly (3-hydroxyheptanoate) 46% (w/w), isolate Kar5+VE1, identified as Achromobacter spp. produced poly (3-hydroxybutyrate) 20% (w/w)) while isolate Kar5+VE2, identified as an Alcaligenes spp. produced a co-polymer poly-3- (3-hydroxybutyrate-Co-3-hydroxyoctanoate) 45% (w/w). Orthoxylene and ethylbenzene were the major hydrocarbons in spent engine oil before degradation while ethylhexanol was the major degradation product as identified by Gas Chromatography-Mass Spectrophotometry. The isolates were able to degrade hydrocarbons as well as produce polyhydroxyalkanoates. Key words: Polyhydroxyalkanoates, spent engine oil, 16S rDNA, co-polymer.
Highlights
Synthetic plastics pose a big challenge as they generate non-degradable waste products
The main objective of this study was to screen for production of polyhydroxyalkanoates by microorganisms isolated from spent engine oil contaminated sites within Nairobi, Kenya
Sixteen soil samples were collected from six spent engine oil (SEO) contaminated sites in Kenya, Nairobi County and the coordinates captured on Global Positioning System (GPS)
Summary
Synthetic plastics pose a big challenge as they generate non-degradable waste products. They remain in water bodies, soil and landfill for many years without decomposing generating a high environmental burden. This has resulted in exploration of eco-friendly polyesters such as polylactic acid and polyhydroxyalkanoic acid (Akaraonye et al, 2010). Microbial fermentation produces polymeric materials like polyhydroxyalkanoates (PHA) that are carbonic and a form of energy storage (Maheshwari et al, 2018). PHAs are natural polyesters of 3-, 4-, 5-, and 6-hydroxyalkanoic acids which are biodegradable, biocompatible and thermoplastic. Accumulation of PHAs can occur either during nutrient limitation such as phosphorous, nitrogen, oxygen or magnesium, and in excess of carbon source (fed batch culture) or in a single batch culture that does not require any nutrient limitation (Nitschke et al., 2011)
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