Critical evaluation of phosphate solubilizing pseudomonads isolated from a partially recultivated potash tailings pile.

Ten phosphate solubilizing pseudomonads isolated from a partially recultivated potash tailings pile in Germany were characterized and tested for their potential to assist in the ongoing recultivation process. Despite fertilization, the plants which are grown for recultivation show phosphate deficiency symptoms, and therefore the isolates are intended to be used as biofertilizer inoculants. On agar plates incubated at five different temperatures, some of the strains showed a temperature-dependent ability to solubilize tricalcium phosphate, while others performed the same at any given temperature. In liquid medium, the isolates solubilized between 271 and 730 µg ml(-1) of phosphate from tricalcium phosphate. Both the weakest (designated S10) and the strongest solubilizing strain (S06) were further tested for their viability during solubilization. In an assay over the course of 1 week, both strains released their maximum amount of phosphate after 2-4 days. At that later point of time, however, viable cells of isolate S06 were no longer detectable, whereas the weaker strain S10 could be cultured after 1 week in broth. Taking all in vitro observations into account, the usability of the isolates as biofertilizers is critically discussed regarding both the in situ conditions on the tailings pile and the lowered viability due to the excess production of organic acids.

The high biofilm-encoding Bee locus: a second pilus gene cluster in Enterococcus faecalis?

An Enterococcus faecalis mutant strain with a reduced ability for biofilm formation and primary attachment when compared to the high biofilm-forming wild-type strain was characterized by molecular biological and proteomic approaches. A point mutation in the srt-1 gene, which encodes a sortase-type enzyme and is part of the recently described bee (biofilm enhancer in Enterococcus) gene cluster, could be identified in the mutant strain. The Srt-1 deficiency resulted in a loss of the Bee-2 protein within a high molecular weight complex in cell surface protein extracts, as determined by mass spectrometry. These findings strongly suggest a specific linkage of Bee-2 to Bee-1 and Bee-3 within a complex by Srt-1. Furthermore, the identification of specific pilin motifs conserved in surface proteins of gram-positive bacteria indicated a possible involvement of the bee genes in the formation of pili structures, and may thus play a role in enhancing biofilm formation in Enterococcus faecalis.