Bioprospecting of Indigenous Microbial Species for Bioethanol Production from the Fruits of Some Selected Exotic Ornamental Plants

Abstract

The study determined the ability of some selected indigenous microbial isolates, namely Bacillus subtilis, Zymomonas mobilis and Saccharomyces cerevisiae, in the production of bioethanol from the fruits of some exotic plants (i.e. Ixora coccinea, Duranta repens and Syzygium guineense). B. subtilis was isolated from soil, while Z. mobilis and S. cerevisiae were isolated from palm wine using cultural methods. The organisms were identified based on their colony characteristics and morphological features, which were observed by microscopic examination of the stained smears of the isolates. The identity of the organisms was confirmed through the molecular study of the 16S rRNA and 18S rRNA regions of the microbial genomes using Polymerase Chain Reaction – Denaturing Gradient Gel Electrophoresis (PCR - DGGE). The fruit samples were collected, washed, blended, filtered using a clean piece of cloth and pretreated using ultrasonication and autoclave. Concentrations of reducing sugars in the fruit filtrates were determined using DNSA-UV-visible spectrophotometry. Seven (7) conical flasks (500ml capacity) were arranged for each fruit sample in duplicate, and 250ml of the fruit filtrates were dispensed in the flasks accordingly. The fermenting organisms were inoculated in the flasks containing the fruit filtrates singly and in combination. Flasks were incubated in shaking incubator for seven days at 35oC. After incubation, the concentrations of bioethanol produced were determined using the UV-visible spectrophotometry. Highest reducing sugars concentrations of 43.7% and 43.6% were found in I. coccinea and S. guineense, respectively, while 36.4% was recorded for D. repens. Highest bioethanol yield of 27.5m/L was found in I. coccinea fermented by S. cerevisiae and Z. mobilis, while the lowest yield of 17.25m/L was found D. repens. The yield in bioethanol production was higher in samples containing a combination of fermenting organisms compared to ones with individual cells. It was recommended that the fruits of these exotic plants should be considered for commercial production of bioethanol.