Title: Phosphate, Phosphonate and Polyphosphate Metabolismin Acidithiobacillus ferrooxidans

Presenter: Dr. Mario Vera

University: Biofilm Center, Willkommen an der Universität Duisburg-Essen

Time: 13:00-14:00, Sept. 15, 2011

Venue: A102

Abstract:

During bioleaching of ores, microorganisms are subjected to several environmental stresses such as pH and temperature changes besides the lack of some nutrients. Phosphate is an essential nutrient for all living cells; therefore, the lack of this compound may affect the bioleaching of ores.

The primary phosphate source for the microorganisms is Pi, although many bacteria are also able to metabolize phosphate esters (C-O-P bond) and phosphonates (C-P bond). A. ferrooxidans Pi starved cells show lower cellular densities, cell filamentation and less ability to oxidize ferrous iron. As part of this response, several characteristic proteins of this state are synthesized. One of these proteins was homologous to the E. coli PstS protein, which in this microorganism and many other bacteria is the periplasmic phosphate binding protein, expressed as part of the genetic system known as Pho regulon, which is used by microorganisms as a response to the lack of Pi for scavening traces of this nutrient.. At. ferrooxidans ATCC 23270 genome sequence possess 23 genes homologous to Pho regulon components of E. coli. Within these genes we found the two component system phoB/phoR, the Pst transport system encoded by genes pstSCAB-phoU, a duplication of part of this system formed by the genes pstS2C2A2, and the phn operon, in which the gene cluster phnGHIJKLM, that codifies for the C-P lyase enzyme complex is complete. This is the main enzyme involved in bacterial phosphonate degradation, suggesting that A. ferrooxidans could use these compounds as alternative Pi sources.

We have shown that A. ferrooxidans is able to grow in the presence of Methyl-Phosphonate or Ethyl-Phosphonates as the unique Pi sources. By means of RT-PCR, DNA macroarrays and real time PCR experiments we showed that phn genes are co transcribed, and their expression is increased when A. ferrooxidans is grown in phosphonates.

A. ferrooxidans, also accumulate polyphosphates (polyP). These are linear polymers of several tens or hundreds of orthophosphate residues linked by phosphoanhydride bonds, which are frequently observed as electrondense granules. The main enzyme involved in polyP biosynthesis is the polyphosphate kinase (PPK), which catalizes the transfer of the terminal phosphoryl group of ATP to polyP, while the exopolyphosphatase (PPX) is responsible for polyP hydrolysis, rendering Pi. In E. coli ppk and ppx genes are linked together and form an operon, whereas in A. ferrooxidans the ppx gene is located downstream of the pstSCAB-phoU genes and we found that in this microorganism is co-transcribed with this genes, suggesting that poliP metabolism in this microorganism could be connected with Pho regulon expression. In this seminar, bioinformatic, transcriptomic and microscopical data involving these systems and their importance for biofilm formation will be discussed.