No abstract

Laboratory growth experiments were conducted to investigate the oxygen isotope effects associated with bacterial metabolism of phosphatic compounds commonly available in nature. The observed oxygen isotope fractionations suggest complex patterns of exchange between dissolved inorganic phosphate (P i) and water, and significant circulation of P i between intracellular and extracellular locations with extensive recycling of the dissolved P i pool, even at high concentrations of dissolved P i. Results of these experiments also support current models for bacterial utilization of phosphate. These results have important implications for the use of ␦ 18 O values of dissolved P i to trace sources of P, and bear on integrity of original oxygen isotope compositions of biogenic and sedimentary apatite minerals that have been subjected to processes of recrystallization and diagenesis. SEM images of laboratory synthesized apatite minerals show that similar textural features may be produced by microbially mediated and abiotic reactions, and that spheroidal structures may be produced by processes of dissolution as well as precipitation. The interpretation of certain mineral structures as microbial in origin solely on the basis of morphological and textural features may be misleading.

The present study investigated the existence of a relationship between Extracellular Enzyme Activity (EEA) of glucosidase and alkaline phosphatase and pollution by carbon and phosphorous at five stations on the Chinchiná River in the water main and the biofilm (epilithon/episammon) during three seasons (rainy, dry and transition). Specific substrates were used as sources: 4-Nitrophenyl-β-D-Glucopyranose as a carbon source and 4-Nitrophenylphosphate as a phosphorus source. The product of catalysis (4-nitrophenol) was detected spectrophotometrically at an emission of 405nm. The ratio of EEA to temperature and pH was also determined. All sampling stations displayed EEA; however, reported results were higher for phosphatase, specifically in the biofilm, in all seasons; this indicates that certain associated microorganisms in this matrix can act as a multi-enzyme system which allows for easy disposal of substrate and the presence of catalysis. A relationship could not be established to describe EEA in dissolved organic carbon (DOC), because EEA was not detected in water samples from all stations during the three sampling seasons (E1, E2 and E4), because the bioavailability of nutrients attributed to the discharge of domestic wastewater from the municipalities of Manizales and Villamaría. Additionally, the complexity of the links between the monosaccharides which comprise polymers affects the degradation rate of the material, since the enzymes produced by microorganisms in the water prefer to hydrolyze specific regions (regiospecific) of the molecule. Enzyme activity can be affected by the structure of the polysaccharide being degraded. Therefore, some trends, such as those which occur at lower DOC concentrations, exhibit greater EEA. During the dry season, a correlation was found between phosphatase and glucosidase EEA in samples of water related to the concentration of orthophosphates and filtered COD, respectively. This indicates that higher concentrations of orthophosphates result in higher EEA of the phosphatase, and that higher concentrations of CODs result in higher EEA of the glucosidase.