Characterization of heterotrophic and mixotrophic acidophilic bacteria isolated from black shale and acid mine drainage, Khala Chatta, Haripur, Pakistan

Abstract

Acid mine drainage, Black shale, Mixotrophic, Bacillus. Most of the studies have been carried out in extreme acidic environments focusing on chemolithotrophic action of sulfur and iron oxidizing bacteria such as Acidiphilium and Acidithiobacillus species while little is known about the heterotrophic and mixotrophic acidophilic bacteria in these habitats. The aim of current study was to isolate and characterized glucose oxidizing heterotrophic and mixotrophic bacteria from extreme acidic habitats of black shale and acid mine drainage. The elemental analysis of samples was carried out by using atomic absorption spectrophotometry (AA240FS Fast Sequential Atomic Absorption Spectrophotometer) after acid digestion with aqua regia (3:1 HNO3:HClO4) and heated to 150°C. All the samples were processed on glucose containing bacteriological media and colony-forming unit (CFU) was determined. The isolates were characterized and identified by using standard microbiological techniques. Growth and nutritional conditions of isolated strains have been optimized. A total of ten gram-positive bacteria were isolated, most of them were identified as Bacillus along with Micrococcus and Corynebacterium species. The isolates were acidophilic and acid-tolerant with growth temperature ranges between 25°C to 35°C. Four of the bacteria were mixotrophic in nature because they utilize both organic and inorganic substrates as energy source. Both true heterotrophic and mixotrophic gram positive acidophiles were isolated from low pH environments. The mixotrophs are mostly reported from the environments where the dissolved organic matter is limited such as acid mine drainage.