Effect of growth media on heavy metal tolerant bacteria isolated from Owode-Onirin iron scrap market in Nigeria

Abstract

Heavy metals often form complexes with the organic components of most growth media resulting in decrease metal availability to  bacteria cells. Hence, this study assessed different growth media used in studying heavy metal tolerance in bacteria vis elucidating the  impact of heavy metals on the biochemical traits of heavy-metal tolerant bacteria. Standard cultural techniques were used to recover  heavy metals (cadmium, lead and nickel) tolerant bacteria from Owode-Onirin metal-laden soil. The isolates were presumptively  identified using their biochemical characteristics and further authenticated using 16S rRNA gene sequence analysis. Three different heavy  metals supplemented media (nutrient broth, low-phosphate broth and Luria-Bertani broth) were used to determine the growth  and physiological effect of the metals on the selected isolates. The nine isolates obtained from the soil samples tolerated 3 mM of  cadmium, lead and nickel. The isolates recorded least growth in the low phosphate broth compared to the other two media because it  prevented complexation of the metals in the medium. The order of bacterial growth in the media is low phosphate broth < nutrient broth  < Luria-Bertani broth. Also, an increase in metal concentration resulted in loss of oxidase, catalase and pigmentation ability in some of the  isolates. This study therefore recommends the use of a minimal nutrient medium such as low phosphate broth in evaluating heavy  metal tolerance in bacteria