IMPLICATION OF HEAVY METAL TOLERANCE ON MICROBIAL COLONY SIZE

Abstract

In this study, we evaluated the effect of heavy metals on colony size of microbes isolated from mechanic workshop soils in Iganmu and Bariga areas of Lagos state, Nigeria. Heterotrophic microbial counts in Bariga samples ranged from 3.74 × 105 to 2.98 ×106 and 9.5 × 104 to 5.4 × 105cfu/ml for bacterial and fungal isolates respectively. While for Iganmu, heterotrophic counts ranged from 2.73 × 105 to 1.46 × 106 and 5.1 × 104 to 3.8 × 105cfu/ml for bacteria and fungi respectively. To evaluate heavy metal tolerance and establish its relationship with colony morphology especially colony size, the isolated strains were subjected to PbCl2, NiSO4 and CdCl2 and a combination of the three heavy metal salts in the same ratio. After 96 hours, larger bacterial and fungal colonies (>100?m) were observed from 100-400mg/L and moderate (>50?m) to small (<25?m) colonies from 800-3200mg/L of individual heavy metals. The combination of heavy metals produced greater reduction in colony size at concentrations ranging from 300-1500mg/L. The various heavy metal tolerant bacteria (Bacillus subtilis, B.megaterium, Pseudomonas aeruginosa, P.fluorescens, Acinetobacter baumanniiand Staphylococcus aureus) were identified using analytical profile index (API) kits while fungi (Aspergillus niger, A. tamari, A.flavus, Rhizopusstolonifer, R.arrhizusand Fusarium oxysporium) were identified by standard microbiological methods. The study established a positive correlation between microbial colony size and heavy metal concentration