RECOGNITION OF A BIOFILM AT THE SEDIMENT–WATER INTERFACE OF AN ACID MINE DRAINAGE-CONTAMINATED STREAM, AND ITS ROLE IN CONTROLLING IRON FLUX
✍ Scribed by STEPHEN BOULT; NICHOLAS JOHNSON; CHARLES CURTIS
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 271 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0885-6087
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✦ Synopsis
Material collected over a month on plates attached to the bed of the Afon Goch, Anglesey, a stream highly contaminated by acid mine drainage (AMD), was either examined intact by electron microscopy or suspended and cultured to reveal the presence of microbiota. Certain of the aerobic microbiota were identi®ed, the genus Pseudomonas formed the commonest isolate and cultures of Serratia plymuthica were grown in order to compare the bio®lms formed with the material collected in the Afon Goch. The material at the sediment±water interface of the Afon Goch was of similar underlying morphology to that of the cultured bio®lms. However, the former had a super®cial granular coating of equidimensional (60±100 nm) and evenly spaced iron rich particles (determined by X-ray microanalysis). The sediment± water interface of this AMD-contaminated stream is therefore best described as a highly contaminated bio®lm. Evidence from previous work suggests that the streambed is active in iron removal from the water column. The intimate association of iron with microbiota at the streambed, therefore, implies that iron ¯ux prediction may not be possible from physical and chemical data alone but requires knowledge of bio®lm physiology and ecology.
Microbially mediated metal precipitation, both by single bacteria and by bio®lms, has been reported elsewhere but mass balance considerations suggest that this explanation cannot hold good for the large amounts of iron hydroxide depositing from waters of the prevalent pH and redox status. Filtered stream water analyses indicate the presence of colloidal iron hydroxide and also its removal downstream where ochreous (iron hydroxide rich) material accumulates. The process of iron immobilization is likely to be the attraction and physical trapping of colloidal iron hydroxide by extracellular polymeric substances (EPS) which constitute the matrix of bio®lms. # 1997 by