Correlation of foliar MT2b expression with Cd and Zn concentrations in hybrid aspen (Populus tremulaxtremuloides) grown in contaminated soil.

Metal uptake and its effect on foliar metallothionein 2b (MT2b) mRNA levels were studied in hybrid aspen (Populus tremulaxtremuloides) in field conditions. The trees were planted on a site contaminated with several metals, including cadmium (mean 5.1 mgkg(-1)), chromium (80 mgkg(-1)), copper (180 mgkg(-1)), nickel (81 mgkg(-1)), vanadium (240 mgkg(-1)) and zinc (520 mgkg(-1)). Of the ten trace elements analyzed, only Cd and Zn accumulated in the leaves with maximal foliar concentrations of 35 and 2400 mgkg(-1) (dry weight), respectively. There was a strong correlation between Cd and Zn concentrations and bioaccumulation factors (concentration in plant/soil) in the leaves, branches and roots, suggesting similar transport mechanisms for these two metals. The levels of MT2b correlated with Cd and Zn concentrations in the leaves, demonstrating that increased MT2b expression is one of the responses of hybrid aspen to chronic metal exposure.

Community structure of the bacteria associated with Nodularia sp. (Cyanobacteria) aggregates in the Baltic Sea.

The community structure of the bacteria associated with Nodularia spumigena (Mertens) cyanobacterial aggregates in the Baltic Sea was studied with temperature gradient gel electrophoresis (TGGE), using a 16S rRNA gene fragment as a target. Various developmental stages of the aggregates and free-floating cyanobacterial filaments were sampled to reveal possible changes in associated microbial community structure during development and senescence of the aggregates. The microbial community structures of all samples differed, and the communities of young and decaying aggregates were separated by cluster analysis of the TGGE fingerprint data. Sequencing of the TGGE fragments indicated the presence of bacteria from the alpha-, beta-, and gamma-proteobacterial groups, as well as members of Cytophaga-Flexibacter-Bacteroides lineages and gram-positive Actinobacteria spp. The majority of the Nodularia-associated sequences were not closely related to previously reported 16S rDNA sequences from the Baltic Sea or any other environment. The structure of the bacterial assemblage reflects the environmental changes associated with the succession and decay of the cyanobacterial aggregates. In addition, the sequence data suggest that the N. spumigena (Mertens) blooms in the Baltic Sea may host thus far uncharacterized bacterial species.

Occurrence of nitrifiers and diversity of ammonia-oxidizing bacteria in developing drinking water biofilms.

We studied the population dynamics of nitrifying bacteria during the development of biofilms up to 233 or 280 days on polyvinylchloride pipes connected to two full-scale drinking water distribution networks supplying processed and chloraminated surface water. The numbers of nitrifiers in biofilms were enumerated at intervals of 10-64 days by the most probable number (MPN) method at waterworks and at several study sites in distribution network areas. The numbers of nitrifiers increased towards the distal sites. The highest detected MPN counts of ammonia-oxidizing bacteria (AOB) for study areas 1 and 7 were 500 MPN cm(-2) and 1.0 x 10(6) MPN cm(-2), and those of nitrite-oxidizing bacteria (NOB) 96 MPN cm(-2) and 2.2 x 10(3) MPN cm(-2), respectively. The diversity of AOB was determined by PCR amplifying, cloning and sequencing the partial ammonia monooxygenase (amoA) gene of selected biofilm samples presenting different biofilm ages. The PCR primers used, A189 and A682, also amplified a fragment of particulate methane monooxygenase (pmoA) gene of methane-oxidizing bacteria. The majority of biofilm clones (24 out of 30 studied) contained Nitrosomonas amoA-like sequences. There were only two pmoA-like sequences of Type I methanotrophs, and four sequences positioned in amoA/pmoA sequence groups of uncultured bacteria. From both study area very similar or even completely identical Nitrosomonas amoA-like sequences were obtained despite of high difference in AOB numbers. The results show that the conditions in newly formed biofilms in drinking water distribution systems favor the growth of Nitrosomonas-type AOB.

Hereditary minisatellite mutations among the offspring of Estonian Chernobyl cleanup workers.

A single accidental event such as the fallout released from the Chernobyl reactor in 1986 can expose millions of people to non-natural environmental radiation. Ionizing radiation increases the frequency of germline mutations in experimental studies, but the genetic effects of radiation in humans remain largely undefined. To evaluate the hereditary effects of low radiation doses, we compared the minisatellite mutation rates of 155 children born to Estonian Chernobyl cleanup workers after the accident with those of their siblings born prior to it. All together, 94 de novo paternal minisatellite mutations were found at eight tested loci (52 and 42 mutants among children born after and before the accident, respectively). The minisatellite mutation rate was nonsignificantly increased among children born after the accident (0.042 compared to 0.036, OR 1.33, 95% CI 0.80-2.20). Furthermore, there was some indication of an increased mutation rate among offspring born after the accident to workers who had received doses of 20 cSv or above compared with their siblings born before the accident (OR 3.0, 95% CI 0.97-9.30). The mutation rate was not associated with the father's age (OR 1.04, 95% CI 0.94-1.15) or the sex of the child (OR 0.95, 95% CI 0.50-1.79). Our results are consistent with both no effect of radiation on minisatellite mutations and a slight increase at dose levels exceeding 20 cSv.

Baltic Sea cyanobacterial bloom contains denitrification and nitrification genes, but has negligible denitrification activity.

Abstract A cyanobacterial bloom in the Gulf of Finland, Baltic Sea, was sampled throughout the development and senescence of aggregates in August 1999. While conditions inside the aggregates were favourable for denitrification (rich in nitrogen and carbon, with anoxic microzones), essentially none was detected by a sensitive isotope pairing method. Polymerase chain reaction-based methods, targeting functional genes encoding the key enzymes of denitrification and nitrification processes (nirS, nirK, amoA), revealed that the non-aggregated filaments harboured amoA gene fragments with high similarity to Nitrosospira amoA sequences, as well as both types of nitrite reductase genes, nirS and nirK. Only the nirS-type nitrite reductase gene and no amoA was detected in aggregated filaments. Thus, despite optimal environmental conditions and genetic potential for denitrification, the blooms of filamentous nitrogen-fixing cyanobacteria must be seen solely as a source, and not as a sink of nitrogen in the Baltic Sea.