Sorption of paraquat and 2,4-D by an Oscillatoria sp.-dominated cyanobacterial mat.

The present study characterises sorption of two pesticides, namely, paraquat (PQ) and 2,4-dichlorophenoxyacetic acid (2,4-D) by an Oscillatoria sp.-dominated cyanobacterial mat. Sorption of PQ onto the test mat was not significantly affected by the pH of the solution within the pH range 2-7. However, 2,4-D sorption was strongly influenced by the solution pH and was maximum at pH 2. Whereas PQ sorption increased with increase in temperature, 2,4-D sorption showed an opposite trend. The sorption of PQ and 2,4-D achieved equilibrium within 1 h of incubation, independent of concentration of pesticide and mat biomass in the solution. The pseudo-second-order kinetic model better defined PQ sorption than the pseudo-first-order model, whereas 2,4-D sorption was well defined by both the models. Sorption isotherms of both the pesticides showed L-type curve. Freundlich model more precisely defined PQ sorption than Langmuir model, thereby suggesting heterogeneous distribution of PQ binding sites onto the biomass surface. However, the Langmuir model more correctly defined 2,4-D sorption, thus, indicating homogeneous distribution of 2,4-D binding sites onto the biomass surface. The test biomass is a good sorbent for the removal of PQ because it could, independent of pH of the solution, sorb substantial amount of PQ (q(max) = 0.13 mmol g(-1)).

Phylogenetic classification of heterotrophic bacteria associated with filamentous marine cyanobacteria in culture.

Fifty-one heterotrophic bacterial strains were isolated from the marine cyanobacterial cultures of heterocystous Nodularia harveyana strain Bo53 and non-heterocystous Oscillatoria brevis strain Bo10. Fluorescence in situ hybridisation and fingerprinting methods were used for a preliminary taxonomical classification of 44 of the 51 isolates. The strains obtained from Bo53 were mostly Alphaproteobacteria (10/24), followed by Bacteroidetes (7/24), and Gammaproteobacteria (3/24). The affiliation of the isolates originating from Bo10 was dominated by Alphaproteobacteria (8/20) and Bacteroidetes (7/20), followed by Gammaproteobacteria (3/20). The 16S rRNA genes of four selected isolates were sequenced. A red-coloured bacterium from Bo53 grouped with the alphaproteobacterial genus Porphyrobacter, while the other three strains, obtained from Bo10, belonged to the alphaproteobacterial genera Roseobacter (pink) and Rhodobacter (colourless), and to the genus Muricauda (yellow) of Bacteroidetes. The findings indicated that the aerobic anoxygenic phototroph Porphyrobacter and its relatives only occurred in Bo10 culture, whereas members of the Roseobacter clade and the Bacteroidetes bacterium Muricauda sp. seemed to be more ubiquitous.

[A laboratory model of the cyanobacterial mat from the Kotel'nikovskii hot spring (Baikal Region)].

A laboratory model of the cyanobacterial community of the Kotel'nikovskii hot spring (Baikal Region) was developed. A step-by-step description of the algocenosis formation along both the time and temperature gradient was given. The natural and laboratory mats were compared, and the major differences in the qualitative and quantitative composition of the cyanobacterial community were revealed. The laboratory algocenosis was stratified by species composition and was characterized by rapid replacement of the dominant cyanobacterial species depending on the temperature gradient. The formation of the community structure occurred over the 18 days of the experiment. In space and time, the sequence of species emergence in the cyanobacterial mat was as follows: Mastigocladus laminosus --> Phormidium tenue --> Ph. ambiguum --> Ph. valderiae. The species composition of the laboratory mat was similar to that of the natural mat; however it was found to be less diverse.