Browsing by Subject "Biotechnology"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Restricted
    The effect of temperature and culture history on the attachment of Metallosphaera hakonensis to mineral sulphides with application to heap bioleaching
    (Elsevier, 2011) Bromfield, L; Africa, C-J; Harrison, S T L; van Hille, R P
    Temperatures in excess of 60 °C are required for efficient bioleaching of chalcopyrite. Within heaps, colonisation of the mineral with thermophilic archaea is important in reaching and maintaining these high temperatures. The effect of temperature and culture history on the attachment of Metallosphaera hakonensis, an extreme thermophilic acidophile identified as a key player in heap bioleaching, to sulfide concentrates and low-grade ore was investigated in shake flasks and packed beds. Attachment studies were conducted at 25 °C, 45 °C and 65 °C. The results show a clear relationship between increasing temperature and attachment efficiency for both suspended and packed bed systems. Attachment at 25 °C was low. Increasing the temperature to 45 °C improved attachment efficiency by between 50% and 100% while a further increase to 65 °C improved attachment by an additional 20–50%. Cells cultured on elemental sulfur as energy source prior to contacting showed 1.3 times greater affinity for the mineral concentrate than those cultured on sulphide mineral concentrates or ferrous sulphate. In contrast to previous studies using mesophilic organisms the selective attachment ofMetallosphaera to sulfide minerals, relative to gangue, was less pronounced. Attachment efficiency was lower in the packed bed system which more closely mimicked flow through a heap. The cell surface properties surface charge and hydrophobicity as well as metabolic activity were investigated to provide insight into the observed phenomena. The data suggest that retention of thermophiles within the heap could be enhanced by a secondary inoculation following elevation of the temperature above 40 °C by the mesophilic pioneer species.
  • Thumbnail Image
    Item
    Open Access
    Microbial solvent formation revisited by comparative genome analysis
    (2017) DYrre, Peter
    Abstract Background Microbial formation of acetone, isopropanol, and butanol is largely restricted to bacteria belonging to the genus Clostridium. This ability has been industrially exploited over the last 100 years. The solvents are important feedstocks for the chemical and biofuel industry. However, biological synthesis suffers from high substrate costs and competition from chemical synthesis supported by the low price of crude oil. To render the biotechnological production economically viable again, improvements in microbial and fermentation performance are necessary. However, no comprehensive comparisons of respective species and strains used and their specific abilities exist today. Results The genomes of a total 30 saccharolytic Clostridium strains, representative of the species Clostridium acetobutylicum, C. aurantibutyricum, C. beijerinckii, C. diolis, C. felsineum, C. pasteurianum, C. puniceum, C. roseum, C. saccharobutylicum, and C. saccharoperbutylacetonicum, have been determined; 10 of them completely, and compared to 14 published genomes of other solvent-forming clostridia. Two major groups could be differentiated and several misclassified species were detected. Conclusions Our findings represent a comprehensive study of phylogeny and taxonomy of clostridial solvent producers that highlights differences in energy conservation mechanisms and substrate utilization between strains, and allow for the first time a direct comparison of sequentially selected industrial strains at the genetic level. Detailed data mining is now possible, supporting the identification of new engineering targets for improved solvent production.