No abstract

Using chemical, isotopic and microbiologic techniques we tested in laboratory experiments the extent to which the addition of pyrite to groundwater and sediments from a nitrate-contaminated aquifer could stimulate denitrification by indigenous bacteria. In addition to this biostimulated approach, a combined biostimulated and bioaugmented treatment was also evaluated by inoculating the well-known autotrophic denitrifying bacterium Thiobacillus denitrificans. Results showed that the addition of pyrite enhanced nitrate removal and that denitrifying bacteria existing in the aquifer material were able to reduce nitrate using pyrite as the electron donor, obviating the need for the inoculation of T. denitrificans. The results of the 16S rRNA and nosZ gene-based DGGE and the quantitative PCR (qPCR) showed that the addition of pyrite led to an increase in the proportion of denitrifying bacteria and that bacterial populations closely related to the Xanthomonadaceae might probably be the autotrophic denitrifiers that used pyrite as the electron donor. Not only autotrophic but also heterotrophic denitrifying bacteria were stimulated through pyrite addition and both populations probably contributed to nitrate removal. Isotopic analyses (δ 15 N and δ 18 ONO3) were used to monitor enhanced denitrification and the N and O isotopic enrichment factors (-26.3±1.8‰ and-20.4±1.3‰, respectively) allowed to calculate the degree of natural nitrate attenuation in the aquifer. Furthermore, flow-through experiments amended with pyrite confirmed the long-term efficiency of the process under the study conditions. Further research under field conditions is needed to determine whether stimulation of denitrification by pyrite addition constitutes a feasible bioremediation strategy for nitratecontaminated aquifers.

The effect of exposure of bacterial suspensions to UV radiation by means of the dose-response curves was assessed. The D37 and D10 values were used for subsequent statistical analysis of the results. The aim of this article is to evaluate the sensitivity to UV radiation of several microorganisms of different habitats (Rhizobium meliloti, Rhodobacter sphaeroides, Escherichia coli, and Deinococcus radiodurans), two mutants with nonfunctional SOS DNA repair system (R. meliloti recA- and E. coli recA-), and a mutant in the synthesis of carotenoids (R. sphaeroides crtD). The results reveal that D. radiodurans was an extremely resistant bacterium, R. meliloti was more resistant than R. sphaeroides, and E. coli was the most sensitive bacterium tested. The high sensitivity of recA- mutants was also verify. Moreover, it seems that the possession of pigments had no important effect in the sensitivity of R. sphaeroides to UV radiation.

No abstract

Microbial mats are highly productive microbial systems and a source of not-yet characterized microorganisms and metabolic strategies. In this article, we introduced a lipid biomarker/microbial isolation approach to detect short-term variations of microbial diversity, physiological and redox status, and also characterize lipid biomarkers from specific microbial groups that can be further monitored. Phospholipid fractions (PLFA) were examined for plasmalogens, indicative of certain anaerobes. The glycolipid fraction was processed for polyhydroxyalkanoates (PHA) and the neutral lipid fraction was used to evaluate respiratory quinone content. Data demonstrate an increase in the metabolic stress, unbalanced growth, proportion of anaerobic bacteria and respiratory rate after the maximal photosynthetic activity. Higher accumulation of polyhydroxyalkanoates at the same sampling point also suggested a situation of carbon storage by heterotrophs closely related to photosynthetic microorganisms. Besides, the characterization of lipid biomarkers (plasmalogens, sphingolipids) from specific microbial groups provided clues about the dynamics and diversity of less-characterized mat members. In this case, lipid analyses were complemented by the isolation and characterization of anaerobic spore formers and sulfate reducers to obtain insight into their affiliation and lipid composition. The results revealed that temporal shifts in lipid biomarkers are indicative of an intense change in the physiology, redox condition, and community composition along the diel cycle, and support the hypothesis that interactions between heterotrophs and primary producers play an important role in the carbon flow in microbial mats.