Comparative Study of Different Methods for Analyzing Denitrifying Bacteria in Fresh Water Ecosystems

Bacteria capable of denitrification play a significant role in the nitrogen cycle of freshwater ecosystems. By metabolizing nitrogen compounds they e.g. counteract the eutrophication of natural waters. To get detailed insights into the in situ turnover rates of nitrogen a reliable tool of quantification for active microorganisms is essential. In the present investigation, quantification capabilities of a molecular tool (Polymerase Chain Reaction—PCR) and a cultivation based tool (Most probable number—MPN) were investigated and compared. The total bacterial concentration yielded by the molecular PCR approach was up to 6-fold higher compared to the results of the MPN approach. However, the portion of culturable denitrifying bacteria compared to the number of specific gene copies (nirS) was much lower. Depending on the environmental conditions, the difference between the PCR and the MPN approach was up to three orders of magnitude. From lab scale experiments with a pure P. aeroginosa strain it can be concludes, that these differences are not the result of inappropriate culture conditions but rather reflect the portion of so called viable but not culturable bacteria (VBNC). Low nitrate concentrations as found in many fresh water ecosystems induced a significant increase in the portion of non culturable denitrifying bacteria. Referred to the investigation of dynamic populations, the number of metabolic active bacteria is represented by the MPN rather than by the PCR approach.

Photolysis of hexamethylenediaminetetra(methylenephosphonic acid)(HDTMP)using manganese and hydrogen peroxide

Aminophosphonates such as hexamethylenediaminetreta(methylene phosphonic acid)(HDTMP)are categorised as persistent substances.They are commonly used as scale inhibitors in cooling water systems and desalination processes.After utilisation,they are often discharged into aquatic environment without pre-treatment.Advanced oxidation processes(AOP)are promising pre-treatments for industrial wastewater treatments.We investigated the photodegradation of HDTMP with or without addition of manganese(Mn2t)and/or H2O2.Similar to results of our former photodegradation studies,we found that HDTMP also undergoes conversion with or without additives during the ultra violet(UV)irradiation.The reaction rate was most affected by the addition of H2O2,i.e.the HDTMP degradation was accelerated by a factor 3.85 compared with UV treatment without additives.The addition of Mn2t accelerated the degradation of HDTMP only by a factor 1.53 compared with the UV treatment without additives.The combined addition of Mn2t and H2O2 accelerated the HDTMP degradation by a factor 2.81.Interestingly,the initial cleavage is not initiated as expected at the CeN bond but at the CeP bond of the methyl carbon and the phosphorus of the methylenephosphonic acid group of HDTMP.This initial cleavage was independent whether the UV treatment was performed with or without additives.Therefore,we conclude that the degradation mechanism is similar independent of the four tested treatment conditions.We identified amino(methylenephosphonic acid)AMPA,dimethylamino(methylenephosphonic acid)DAMP and iminodi(methylenephosphonic acid)IDMP as the major breakdown products by performing LC/MS analyses.The major mineralisation products were ortho-phosphate,ammonium and carbon dioxide.The mass balances of unknown breakdown products allowed us to speculate about the molecular size of the unknown organic breakdown products.