Viridis Cells Research Articles

Degradation of the toxic cyanobacterium Microcystis viridis using predaceous micro‐animals combined with bacteria

SUMMARYToxic microcystins from cyanobacteria belonging to the genus Microcystis have been responsible for the death of various animals. In batch culture experiments, pre‐dation and degradation characteristics of Microcystis viridis and its toxic metabolite, microcystin‐RR, were examined using the micro‐animals, Aeolosoma hempri‐chi and Philodina erythrophthalma combined with endemic aggregated bacteria isolated from a biofilm. Although M. viridis was favorably predated and decomposed by the two micro‐animals, the reduction of microcystin‐RR was relatively low compared to the culture with the animals in the presence of the mixed bacteria, where degradation of the toxin was enhanced under aerated conditions. The aerated bacteria could degrade the eluted toxin faster than in any other condition and an initial toxin concentration of above 40 μg L‐1 was completely degraded in 10 days. Furthermore, in a continuous bioreactor packed with biofilm carrier, a toxin level of 9.74 μg g‐1 in the inflow water was reduced by 94.0% at a hydraulic retention time of less than 12 h. Moreover, in a practical biofilm plant, a toxin concentration of 34.9 μg g‐1 was degraded at a short hydraulic retention time (HRT) of 2 h. The efficiency of toxin removal in the plant at the short HRT coincided with that of laboratory studies. It was considered that A. hemprichi and P. erythrophthalma contributed to the predation and decomposition of viable M. viridis cells, subsequently these released toxin which could be efficiently degraded by the aerated bacteria.

Sequence analysis and transcriptional organization of the Rhodopseudomonas viridis cytochrome c2 gene

The cytochrome c2 gene (cycA) of the purple nonsulfur bacterium Rhodopseudomonas viridis was isolated from a genomic library by using two degenerate oligonucleotides containing all possible DNA sequences predicted from the published amino acid sequence of this protein (Ambler et al., Proc. Natl. Acad. Sci. USA 73:472-475, 1976). Cloning and sequence analysis of the cytochrome c2 gene indicated the presence of a typical procaryotic 20-residue signal peptide, suggesting that this periplasmic protein in synthesized in vivo as a precursor. In addition, four amino acids were found to be different by comparing the published sequence of the mature protein with that deduced from the isolated cycA gene (Lys-14----Leu, Ser-46----Ala, Ile-84----Val, Leu-97----Ile). Northern (RNA) blot analysis and fine mapping of the 5' and 3' ends of the cycA gene transcript from photoheterotrophically grown R. viridis cells revealed one abundant transcript of 523 to 530 nucleotides in length, with the transcription start site at position -39 relative to the coding region of cytochrome c2. A low-abundance transcript with an extended 3' end (about 600 bases in length) is thought to be processed by exonucleases, resulting in the slightly shorter main transcript.

Exometabolites of Lipid Nature from Two Species of Marine Microalgae

The lipid composition of cellular and extracellular products of actively growing marine algae Platymonas viridis Rouch and Nephrochlo- ris salina Rouch cultures has been studied. High content of the triacylglycerols was shown to be characteristic of the N. salina cells. Polar lipids and sterols were found in P. viridis cells in great amounts. The lipid compounds have been found at all stages of the culture development. Polar lipids, sterols, free fatty acids, triacylglycerols, esters of sterols and hydrocarbons were observed in the extracellular lipids. The compositional differ- ences between lipids from two cultures of marine algae as well as between the cell and the medium are reported.

Photoinhibition by flash and continuous light of oxygen uptake by intact photosynthetic bacteria

The inhibition of respiration by continuous or flashing light has been studied in intact cells of different species of photosynthetic bacteria. For Rhodopseudomonas palustris, Rhodopseudomonas sphaeroides and Rhodopseudomonas capsulata, the inhibition by short actinic flashes shows a remarkable periodicity of two: each flash induces an inhibition of respiration, but a stimulation is observed after an even number of flashes. On the other hand, no oscillation is observed for Rhodospirillum rubrum and Rhodopseudomonas viridis cells. These different behaviours are explained by a difference in the redox state of the secondary electron acceptor as shown by the effect of ortho-phenanthroline on the amperometric signal. Addition of uncouplers (carbonyl cyanide m-chlorophenylhydrazone) or of an ATPase inhibitor (tri- N-butyl tin), has little effect on the oscillatory pattern induced by flash excitation. However, inhibition of respiration by continuous light is suppressed in the presence of carbonyl cyanide m-chlorophenylhydrazone. In the presence of tri- N-butyl tin the steady-state level is reached more rapidly than in the control experiment for a given light intensity. These results are interpreted as evidence of two modes of light inhibition of respiration in photosynthetic bacteria. A first type of inhibition, clearly shown under flash excitation, is due to interaction between respiratory and photosynthetic chains at the level of electron carriers. After each flash, an electron is diverted from the respiratory chain to the photooxidized reaction center. Because of the gating mechanism at the level of the secondary acceptor, the respiration is stimulated after an even number of flashes. The second mode of inhibition prevails under continuous illumination. Under these conditions, the rate of respiration is controlled essentially by the photoinduced proton electrochemical gradient.

Nitrogen fixation and ammonia switch-off in the photosynthetic bacterium Rhodopseudomonas viridis.

Rhodopseudomonas viridis ATCC 19567 grows by means of nitrogen fixation in yeast extract-N2 or nitrogen-free medium when sparged with 5% CO2 and 95% N2 in the light at 30 degrees C. Acetylene reduction assays for nitrogenase activity revealed an initially high level of activity during early-logarithmic growth phase, a lower plateau during mid- to late-logarithmic phase, and a dramatic reduction of activity at the beginning of the stationary phase. When viewed by electron microscopy, nitrogen-fixing R. viridis cells appeared to be morphologically and ultrastructurally similar to cells grown on nitrogen-rich media. Whole cells prepared under reducing conditions in the dark for electron spin resonance spectroscopy yielded g4.26 and g3.66 signals characteristic of the molybdenum-iron protein of nitrogenase. During growth on N2 in the absence of fixed-nitrogen sources, the nitrogenase activity of R. viridis measured by acetylene reduction stopped rapidly in response to the addition of NH4Cl as has been observed in other Rhodospirillaceae. However, unlike the nitrogenase of Rhodopseudomonas palustris or Rhodospirillum rubrum, which recover from this treatment within 40 min, the nitrogenase activity of R. viridis was not detectable for nearly 4 h.