Molecular Detection and Identification of Polyhydroxyyalkanoate Synthesizing-Bacteria Isolated from Waste Dump Site Soil

Polyhydroxyalkanoates (PHAs) are macromolecular storage polyesters produced by metabolic trans-formation of carbon sources by microorganisms under nutrient limiting conditions. PHA synthesizing-bacteria were isolated from waste dump site soil samples, characterized molecularly and identified using standard microbiological, molecular and biochemical methods. Corn steep liquor (COSL) and minimal salt medium supplemented with glucose, glycerol, maltose and sucrose were used as growth media and the PHAS accumulated by the bacteria were quantified spectrophotometrically. Of the 40 bacteria isolated, 37 were positive for PHA accumulation when subjected to visual screening using Sudan Black B. Nevertheless, 22 bacterial isolates were selected based on their level of sudanophilic positivity for PHA synthase gene analysis. PHA synthase gene (phbC) of the expected base pair size (239 bp) was amplified from the DNA of all the 22 bacterial isolates selected. Quantification of PHA synthesized by the 22 bacterial isolates revealed that the best five PHA synthesizing-bacterial isolates were SB9, SC7, SB1, SD7 and SA4 with PHA yields of 8.26, 7.69, 7.48, 7.43 and 7.41 mg/ml respectively, while the least five PHA accumulating bacterial isolates were SC8, SC4, SD2, SC2 and SB7 which recorded PHA yields of 6.46, 6.35, 6.34, 6.33 and 6.22 mg/ml respectively. Sequence analysis of the amplified 16S RNA genes of the best five PHA synthesizing-bacterial isolates (SB9, SC7, SB1, SD7 and SA4) divulged their identities as Bacillus acidiceler FOGU02, Bacillus megaterium FOGU01, Lysinibacillus macroides FOGU04, Bacillus wiedmannii FOGUOS and Bacillus marisflavi FOGU03 respectively. The yields of PHA by the bacteria tested were generally higher in COSL supplemented with the various carbon sources compared to the PHA yields recorded in minimal salt medium supplemented with the same carbon sources. The molecular methods enhanced the specificity of the results obtained. The COSL used as growth medium for PHA synthesizing-bacteria is expected to reduce the cost of PHA production as the waste is locally available at no extra cost. PHA yield depends to a large extent on the microorganism involved as well as the carbon source used. However, Bacillus acidiceler FOGU02 was the best PHA producer among the bacteria tested, while maltose was the best carbon source examined.