Viral and bacterioplankton dynamics in two lakes with different humic contents.

Viral and bacterioplankton dynamics were investigated, together with the temporal variation of phage-infected bacterioplankton in two oligotrophic lakes, one humic and the other clearwater. Bacterial abundance was significantly higher in the humic lake, while the abundance of virus-like particles (VLP) was significantly higher in the clearwater lake. There were no differences in either the frequency of infected bacterial cells (FIC), or in burst size between the lakes. Because of the higher bacterial abundance in the humic lake, a larger number of bacteria were lyzed in this lake. FIC showed large seasonal changes, varying between 9 and 43%, which covers almost the entire range of previously published data from both lacustrine and marine environments. The temporal changes in VLP abundance and FIC were slow in both the humic and clearwater lakes. The burst size was low in both lakes (average value, nine in each case), probably because of the oligotrophic status of the lakes. The chlorophyll a concentrations were higher and positively correlated with VLP numbers in the clearwater lake, indicating that a significant proportion of the viruses in this lake may be phytoplankton viruses.

Do neighboring lakes share common taxa of bacterioplankton? Comparison of 16S rDNA fingerprints and sequences from three geographic regions.

Bacterioplankton community composition was studied in 12 lakes in three different geographic regions in Scandinavia using denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rDNA. Area-specific abundant taxa were found in the lakes in two of the regions. In the region of Uppland the lakes had an alpha-proteobacterium, belonging to the subgroup Alpha V in common. The Alpha V bacteria appeared to be favored by neutral or higher pH values. The lakes in Lappland were found to harbor Actinobacteria, which appeared to be favored in bog lakes. No abundant taxon was found to be in common for the lakes in Svalbard, the third region studied.

Investigating Influential Factors on Bacterioplankton Community Composition: Results from a Field Study of Five Mesotrophic Lakes.

In order to investigate which biotic and abiotic factors may have an impact on the community composition of bacterioplankton, five mesotrophic lakes were studied. The composition of the bacterioplankton communities was determined by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA. Multivariate statistical analyses of the gel patterns, in relation to each other and to the chemical, biological, and physical parameters of the lakes, were performed. The analyses showed that the import of allochthonous bacteria and the interaction with other plankton organisms (for example, grazing) in the lakes probably had an impact on the composition of the communities.

Isolation and counting of Athiorhodaceae with membrane filters.

The number, type, and distribution of Athiorhodaceae in two Central Pennsylvania artificial lakes were investigated with an anaerobic modification of the membrane filter technique.

Survey of the photosynthetic bacteria for rhodanese (thiosulfate: cyanide sulfur transferase) activity.

Rhodanese activity was demonstrated in extracts from all three taxonomic families of photosynthetic bacteria, and this activity appeared to be uncorrelated with thiosulfate metabolism.

Effect of thiosulfate on the photosynthetic growth of Rhodopseudomonas palustris.

Cell yields of Rhodopseudomonas palustris grown photoheterotrophically in pyruvate-mineral salts medium were increased by the photooxidation of added thiosulfate. However, thiosulfate had no effect on cell yields of cultures grown aerobically in darkness, although thiosulfate was also oxidized. The presence of thiosulfate increased photosynthetic cell yields on a variety of other organic substrates. Growth of cells in thiosulfate-containing medium, or the addition of thiosulfate to cells grown in thiosulfate-free medium, induced the formation of a thiosulfate-oxidizing system which quantitatively photooxidized thiosulfate to sulfate. R. palustris grew photoautotrophically with thiosulfate as an oxidizable substrate. Large amounts of supplemental bicarbonate carbon were incorporated when cells were grown photosynthetically in pyruvate-thiosulfate medium. Cells harvested after photoautotrophic or photoheterotrophic growth in fumarate-thiosulfate medium fixed (14)CO(2) at an 8- to 10-fold greater rate when provided with thiosulfate. The evolution of (14)CO(2) from pyruvate-1-(14)C during photoassimilation by R. palustris was greatly suppressed by the presence of thiosulfate. The increase in photoheterotrophic cell yields of R. palustris caused by the oxidation of thiosulfate may result from assimilation of substrate carbon which is normally evolved as carbon dioxide.