Narrow Results

The bioconversion of xenobiotics often involves oxidation-reduction reactions and one representative example is the reductive decolorization of azo dyes. The bioreduction of an azo dye as model xenobiotic by a mixed microbial culture (activated sludge) was thus chosen as a model system in the present study. The aim was to investigate the effect of a respiratory inhibitor, namely sodium azide (a cytochrome oxidase inhibitor) on this bioconversion, when carried out by two different activated sludge mixed culture inocula. Different biomass conditioning pretreatments were also studied, i.e., using a mixed culture freshly harvested from the growth bioreactor or after aerobic incubation in the absence of carbon source (starved). The azide inhibition effect was observed to lessen with the increase in starvation time for both mixed cultures. This result points to the existence of an alternative dye bioconversion mechanism, triggered in the starved biomass, in which the involved pathways are not inhibited by azide. For one of the inocula, this alternative mechanism was found to be dependent on the availability of glucose in the bioconversion medium.

Scots pine (Pinus sylvestris) produces several small, highly homologous, disulfide-rich proteins (Sp-AMPs) in response to fungal pathogenic attacks. We report here the expression, structure and function of these proteins. One of the Sp-AMPs was cloned into and over-expressed in Pichia pastoris. The purified protein shows antifungal activity against Heterobasidion annosum, causing morphological changes in spores and hyphae. Binding studies revealed that it binds to soluble and insoluble β-(1,3)-glucans, major components of the fungal cell wall, with high affinity. Homology modeling studies suggest a Greek-key-β-barrel fold having a conserved patch on the surface that can accommodate at least 4 sugar units. We conclude that these proteins represent a new class of antimicrobial proteins that can be classified as pathogenesis related (PR) protein family 18.

Bioleaching is the dissolution of metal sulfides like pyrite by bacterial oxidation processes. Beside desired heap or tank leaching for winning metals such as copper or gold, unwanted bioleaching causes acid mine drainage (AMD)/acid rock drainage (ARD) e.g. in during coal mining processes. Bioleaching can cause acidification of surface- and groundwater concomitant with pollution by high amounts of heavy metals. The addition of a surfactant to active leaching cultures decreases bacterial cell numbers and leaching. To investigate the inhibition effect of the surfactant in situ, a percolator system was used. Percolators were filled with pyrite containing material from a brown coal area where unwanted bacterial leaching occurs. The surfactant was added after bacterial leaching was established. The addition of the surfactant inhibited leaching within one week till the end of the experiment after 13 weeks. Based on these findings, applications for the inhibition of bacterial leaching in brown coal mining areas can be established.