Isolation of Polyhydroxyalkanoates (PHAs) Accumulating Bacteria from Waste Dumpsites

Abstract

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters (bioplastics) produced by some microorganisms. Their 100% biodegradability means they have nontoxic residual products and low environmental permanence and their biocompatibility means they are not harmful to living tissue and therefore can and have been utilized in a variety of medical and surgical applications. In this study standard procedures were used to isolate bacteria from soils obtained from various waste dump sites. Isolates were screened for PHA production using Sudan Black B dye. Isolates were identified at molecular level using 16SrRNA amplification, sequencing and analysis. A total of twenty-six (26) bacterial isolates were obtained. Of these twenty-six (26) isolates, nine (9) each were isolated from cassava mill waste dump site and palm oil mill waste dump site soils while abattoir waste dump site soil yielded eight (8) isolates. Thirteen (13) isolates were remarkably positive for Sudan Black B stain test for PHA accumulation. The PHA yield from the thirteen (13) selected isolates as determined by spectrophotometric analysis of the crotonic acid that the PHA was converted to, ranged from 1.95mg/l to 10.79mg/l. The isolate with the highest yield was from the abattoir dump waste site. Molecular studies of the best ten (10) PHA yielding isolates showed that their extracted genomic DNA was of high quality and high molecular weight. The 16SrRNA gene was amplified at 1500bp according to the primers used for amplification. The PHA synthase gene amplified from genomic DNA of the bacterial isolates was amplified at 239bp. Sequence analysis of the amplified 16SrRNA genes of the selected isolates revealed their identities as Gayadomonas joobiniege AAU1, Providencia vermicola AAU2, Muricauda pacifica AAU3, Proteus mirabilis AAU4, Hafnia psychrotolerans AAU5, Photorhabdus luminescens AAU6, Xanthovirga aplysinae AAU7, Methylomarinovum caldicuralii AAU8, Photobacterium aquimaris AAU9 and Proteus terrae AAU10 with corresponding GenBank assigned accession numbers of OP776063 - OP776072 respectively. This study has elucidated bacterial speciesthat can produce PHA from waste dumpsites. This is very important for industries producing bioplastics, to greatly reduce cost of production as these new bacterial isolates can be utilized in the production of PHA, thereby reducing the high cost of production.