Induction of anaerobic, photoautotrophic growth in the cyanobacterium Oscillatoria limnetica.

Anaerobic photoautotrophic growth of the cyanobacterium Oscillatoria limnetica was demonstrated under nitrogen in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (5micron), a constant concentration of Na2S (2.5 mM), and constant pH (7.3). The photoanaerobic growth rate (2 days doubling time) was similar to that obtained under oxygenic photoautotrophic growth conditions. The potential of oxygenic photosynthesis is constitutive in the cells; that of anoxygenic photosynthesis is rapidly (2 h) induced in the presence of Na2S in the light in a process requiring protein synthesis. The facultative anaerobic phototrophic growth physiology exhibited by O. limnetica would seem to represent an intermediate physiological pattern between the obligate anaerobic one of photosynthetic bacteria and the oxygenic one of eucaryotic algae.     

Composition changes of phototrophic microbial communities along the salinity gradient in the solar saltern evaporation ponds of Eilat,Israel

There are several conflicting hypothesis that deal with the influence of flooding in the natural river–floodplain systems. According to the Flood Pulse Concept, the flood pulses are not considered to be a disturbance, while some recent studies have proven that floods can be a disturbance factor of phytoplankton development. In order to test whether flooding acts as a disturbance factor in the shallow Danubian floodplain lake (Lake Sakadaš), phytoplankton dynamics was investigated during two different hydrological years—extremely dry (2003) without flooding and usually flooded (2004). A total of 18 phytoplankton functional groups were established. The sequence of phytoplankton seasonality can be summarized P/D → E (W1, W2) → C/P (only in potamophase) → S2/H1/S_N/S1 → W1/W2 → P/D. The canonical correspondence analysis (CCA) demonstrated that the water level was a significant environmental variable in 2004. Due to the higher total biomass of Bacillariophyceae established under potamophase conditions, floodings in the early spring seem to be a stimulating factor for phytoplankton development. On the other hand, the flood pulses in May and June had dilution effects on nutrients, so that a significantly lower phytoplankton biomass was established indicating that flooding pulses can be regarded as a disturbance event. Such conditions supported diatom development (D, P, C species) and prolonged its dominance in the total phytoplankton biomass. A long-lasting Cyanoprokaryota bloom (various filamentous species—S1, S2, S_N and H1 representatives) with very high biomass characterized the limnophase (dry conditions) in summer and autumn of both years. In-lake variables (lake morphology, internal loadings of nutrients from sediments, light conditions) seem to be important for the appearance of Cyanoprokaryota bloom. The equilibrium phase was found during the Cyanoprokaryota bloom only in the extremely dry year. This study showed that depending on the time scale occurrence, flood pulses can be a stimulating or a disturbance factor for phytoplankton development in Lake Sakadaš. Handling editor: J. Padisak     

Haloarcula marismortui (Volcani) sp. nov., nom. rev., an extremely halophilic bacterium from the Dead Sea

An extremely halophilic red archaebacterium isolated from the Dead Sea (Ginzburg et al., J. Gen. Physiol. 55: 187-207, 1970) belongs to the genus Haloarcula and differs sufficiently from the previously described species of the genus to be designated a new species; we propose the name Haloarcula marismortui (Volcani) sp. nov., nom. rev. because of the close resemblance of this organism to "Halobacterium marismortui," which was first described by Volcani in 1940. The type strain is strain ATCC 43049.     

2D-NMR and ATR-FTIR study of the structure of a cell-selective diastereomer of melittin and its orientation in phospholipids

Melittin, a 26 residue, non-cell-selective cytolytic peptide, is the major component of the venom of the honey bee Apis mellifera. In a previous study, a diastereomer ([D]-V(5,8),I(17),K(21)-melittin, D-amino acids at positions V(5,8),I(17),K(21)) of melittin was synthesized and its function was investigated [Oren, Z., and Shai, Y. (1997) Biochemistry 36, 1826-1835]. [D]-V(5,8),I(17),K(21)-melittin lost its cytotoxic effects on mammalian cells; however, it retained antibacterial activity. Furthermore, [D]-V(5,8),I(17),K(21)-melittin binds strongly and destabilizes only negatively charged phospholipid vesicles, in contrast to native melittin, which binds strongly also zwitterionic phospholipids. To understand the differences in the properties of melittin and its diastereomer, 2D-NMR experiments were carried out with [D]-V(5,8),I(17),K(21)-melittin, and polarized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy experiments were done with both melittin and [D]-V(5,8), I(17),K(21)-melittin. The structure of the diastereomer was characterized by NMR in water, as well as in three different membrane-mimicking environment, 40% 2,2,2-trifluoroethanol (TFE)/water, methanol, and dodecylphosphocholine/phosphatidylglycerol (DPC/DMPG) micelles. The NMR data revealed an amphipathic alpha-helix only in the C-terminal region of the diastereomer in TFE/water and methanol solutions and in DPC/DMPG micelles. ATR-FTIR experiments revealed that melittin and [D]-V(5,8),I(17),K(21)-melittin are oriented parallel to the membrane surface. This study indicates the role of secondary structure formation in selective cytolytic activity of [D]-V(5,8), I(17),K(21)-melittin. While the N-terminal helical structure is not required for the cytolytic activity toward negatively charged membranes and bacterial cells, it appears to be a crucial structural element for binding and insertion into zwitterionic membranes and for hemolytic activity.     

Oligonucleotides in human urine do not contain 8-oxo-7,8-dihydrodeoxyguanosine

The promutagenic DNA modification 8-oxo-7,8-dihydrodeoxyguanosine is the most frequently used marker for oxidative stress to DNA. The unmodified base and nucleoside and the 8-hydroxylated guanine base and nucleoside are found in urine, the latter used as a global measure of oxidative stress to DNA. Nucleotide excision repair (NER) excises a 27- to 29-mer oligonucleotide with oxidative lesions, and if found in urine, it could be used as a measure of DNA repair in vivo. Enzymatic hydrolysis of human urines followed by HPLC-tandem mass spectrometry was not able to reveal oligonucleotides and/or mononucleotides with the 8-oxo-7,8-dihydrodeoxyguanosine modification. The recovery of a synthetic oligonucleotide with the modification was complete (95% confidence limits: 98-124%). These experiments show that oligonucleotides are excreted into urine, but that 8-oxo-7,8-dihydrodeoxyguanosine is found only as the mononucleoside and is not present in any significant amounts in oligonucleotides. We conclude that oligonucleotides are excreted into urine, and they do not contain oxidized lesions. Either NER products are degraded after excision or NER functions differently in vivo in humans compared with cellular systems.     

Inhibition of yeast growth by molybdenum-hydroxylamido complexes correlates with their presence in media at differing pH values

The effects of Mo-hydroxylamido complexes on cell growth were determined in Saccharomyces cerevisiae to investigate the biological effects of four different Mo complexes as a function of pH. Studies with yeast, an eukaryotic cell, are particularly suited to examine growth at different pH values because this organism grows well from pH 3 to 6.5. Studies can therefore be performed both in the presence of intact complexes and when the complexes have hydrolyzed to ligand and free metal ion. One of the complexes we examined was structurally characterized by X-ray crystallography. Yeast growth was inhibited in media solutions containing added Mo-dialkylhydroxylamido complexes at pH 3-7. When combining the yeast growth studies with a systematic study of the Mo-hydroxylamido complexes' stability as a function of pH and an examination of their speciation in yeast media, the effects of intact complexes can be distinguished from that of ligand and metal. This is possible because different effects are observed with complex present than when ligand or metal alone is present. At pH 3, the growth inhibition is attributed to the forms of molybdate ion that exist in solution because most of the complexes have hydrolyzed to oxomolybdate and ligand. The monoalkylhydroxylamine ligand inhibited yeast growth at pH 5, 6 and 7, while the dialkylhydroxylamine ligands had little effect on yeast growth. Growth inhibition of the Mo-dialkylhydroxylamido complexes is observed when a complex exists in the media. A complex that is inert to ligand exchange is not effective even at pH 3 where other Mo-hydroxylamido complexes show growth inhibition as molybdate. These results show that the formation of some Mo complexes can protect yeast from the growth inhibition observed when either the ligand or Mo salt alone are present.