Polyphosphate storage in the family Beggiatoaceae with a focus on the species Beggiatoa alba Sandra

Abstract

Sulfur bacteria of the family Beggiatoaceae are of special interest with respect to the phosphorus cycle, because they can store large amounts of polyphosphate and are proposed to influence phosphorus sequestration in marine sediments (e.g. Schulz and Schulz, 2005). The aim of this thesis was to study different aspects of polyphosphate storage in members of the family Beggiatoaceae on a physiological and genomic level with a special focus on the heterotrophic freshwater strain Beggiatoa alba B15LD. In addition, polyphosphate- related enzymes, which are encoded in different members of the Beggiatoaceae, were identified and possible pathways of polyphosphate utilization were discussed, including its exploitation as an energy source. In the second part, the structure and elemental composition of polyphosphate inclusions in Beggiatoa alba were analyzed. Studies using various techniques revealed that these inclusions are not acidic and are associated with sodium cations. This is the first time that a co-occurrence of polyphosphate with Na+ was observed in Beggiatoaceae and among bacteria in general. In addition, the factors controlling the storage and degradation of polyphosphate in Beggiatoa alba were studied under laboratory conditions. Comparison of the triggers for polyphosphate synthesis and degradation to those effective in other members of the family Beggiatoaceae, which are lithoautotrophic and originate from freshwater, marine, and hypersaline environments, revealed that only Beggiatoa alba stored polyphosphate at nitrogen limitation. Under these conditions, polyphosphate was possibly stored as an energy reserve, since growth was inhibited and excess energy was available through the oxidation of acetate. In E. coli, it was shown that polyphosphate was stored at nitrogen limitation to induce the degradation of ribosomal proteins to use them as an intracellular amino acid pool. The produced guanosine tetraphosphate (ppGpp) serves as an important signaling molecule during this process. Elevated ppGpp concentrations were also measured in nitrogenlimited cultures of Beggiatoa alba, suggesting that this mechanism is also present in this species. Polyphosphate degradation in Beggiatoa alba was induced by different stress factors, such as high and low pH (Havemeyer, 2010), elevated temperatures, and high ammonium concentrations, which did not affect polyphosphate storage in the marine strain Beggiatoa sp. 35Flor. In contrast, the marine strain degraded polyphosphate in response to high sulfide concentrations and anoxia (Brock and Schulz-Vogt, 2011). While sulfide concentrations in freshwater sediments are much lower than in marine sediments, pH changes are more likely to occur, since freshwater is, in contrast to seawater, not carbonate buffered. Hence, polyphosphate degradation in Beggiatoaceae seems to be related to habitat-specific environmental factors. Finally, polyphosphate storage in environmental samples of filamentous Beggiatoaceae from Lake Grevelingen, The Netherlands, and Aarhus Bay, Denmark, were investigated. Fluctuations in redox conditions together with high sulfide concentrations are a prerequisite for polyphosphate degradation and phosphate release in a marine Beggiatoa strain (Brock and Schulz-Vogt, 2011). Although both sampling sites have fluctuations in redox conditions, no polyphosphate storage was observed and therefore a potential influence on benthic phosphorus cycling cannot be assumed. The facts that sulfide concentrations were not very high and fluctuations of redox conditions occurred seasonally and not more frequently might explain the difference. Hence, sulfur bacteria do not in general influence benthic phosphorus cycling. Instead, it seems that only special conditions, as found at sites of recent phosphorus sequestration, have the potential to induce massive accumulation of polyphosphate and rapid phosphate release by sulfur bacteria