Anaerobic metabolism of Nitrosomonas europaea

Nitrosomonas europaea is capable of maintaining an anaerobic metabolism, using pyruvate as an electron donor and nitrite as an electron acceptor; utilization of nitrite depends upon supply of both pyruvate and ammonia. The role of ammonia in this reaction was not determined. N europaea also assimilates CO₂ anaerobically into cell material in the presence of nitrite (0.5–1.0 mM), pyruvate and ammonia. This reaction was partially inhibited by nitrite which apparently competed with CO₂ for reducing power. Anaerobic nitrite respiration is sensitive to ionophores, FCCP being the most effective.Non-standard-abbreviations TCA trichloroacetic acid - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazon     

Production of Spirulina biomass: Maintenance of monoalgal culture outdoors

The effects of sodium bicarbonate concentration, population density, and temperature on the maintenance of an outdoor monoculture of the cyanobacterium Spirulina platensis were studied. A clear response by Spirulina to the concentration of bicarbonate was evident, with 0.2M bicarbonate representing the lowest concentration in which a monoculture could be maintained. When the temperatures fell during the winter period to some 20-25 degrees C below the optimum for Spirulina, Chlorella sp. gradually increased and became the dominant species in the culture. Raising the temperature by covering the pond with transparent polyethylene resulted in a sharp decline in the population of Chlorella, and a gradual resumption of species dominance by Spirulina. In winter, there was an inverse relationship in the pond between the population density of Spirulina and the extent of contamination by Chlorella sp.; but no such effect was observed under field conditions at temperatures higher than 25 degrees C.     

Parietochloris incisa comb. nov. (Trebouxiophyceae, Chlorophyta)

A coccoid green alga, Myrmecia incisa Reisigl, was isolated from the soil of Mt Tateyama, Japan. Electronmicroscopy revealed that the organism has pyrenoids sparsely covered with starch segments and traversed by many parallel thylakoid membranes, and zoo-spores with counterclockwise basal body orientation. Due to the presence of these features, we have proposed a reclassification of M. incisa into the genus Parietochloris, Trebouxiophyceae.     

Initial stages in the onset of senescence in tobacco leaves

A marked loss of leucine ¹⁴C incorporation occurred in chloroplasts isolated from Nicotiana rustica L. leaves exposed to 24 hours of darkness. This loss is not due to an initial decline in RNA-synthesis potential of the chloroplasts, as was inferred from the extent of UTP incorporation by the isolated chloroplasts. Upon reillumination of the leaves, leucine incorporation by the isolated chloroplasts reverted to its original level within 3 to 4 hours, hence it is doubtful whether the period of 24 hours after detachment should be regarded as the initial phase of leaf senescence.     

Production of eicosapentaenoic acid (EPA) in Monodus subterraneus grown in a helical tubular photobioreactor as affected by cell density and light intensity

The effect of cell density (1–4.5 g L^-1) and light intensity (44 and 82 mol m^-2 s^-1) on fatty acid composition andeicosapentaenoic acid (EPA, 20:5 3) production was studied ina semi-continuous culture of Monodus subterraneus grown in a helicaltubular photobioreactor (`Biocoil') under laboratory conditions. Under lowlight, the highest proportion of EPA (31.5% of total fatty acids) and EPAcontent (3.5% of dry weight), biomass productivity (1.3 g L^-124 h^-1) and EPA productivity (44 mg L^-1 24 h^-1)occurred at optimal cell density of about 1.7 g L^-1. Cell densityhad no effect on the total fatty acid (TFA) content and was maintained atca. 11% of dry weight. Under high light, the highest proportion ofEPA to fatty acids (31.8%), the total fatty acids content (13.4%) andEPA content (4.3% of dry weight) occurred at cell density of about 3.4gL^-1. But the highest biomass productivity (1.7 g L^-124 h^-1) and EPA productivity (56 mg L^-1 24 h^-1) wereobtained at a cell density of 1.6 and 2.6g L^-1, respectively. Ourresults suggest that manipulating the cell density and light intensity canmodify the composition of fatty acid and production of eicosapentaenoicacid (EPA) in M. subterraneus.     

Steps in reductive activation of the disulfide-generating enzyme Ero1p

Ero1p is the primary catalyst of disulfide bond formation in the yeast endoplasmic reticulum (ER). Ero1p contains a pair of essential disulfide bonds that participate directly in the electron transfer pathway from substrate thiol groups to oxygen. Remarkably, elimination of certain other Ero1p disulfides by mutation enhances enzyme activity. In particular, the C150A/C295A Ero1p mutant exhibits increased thiol oxidation in vitro and in vivo and interferes with redox homeostasis in yeast cells by hyperoxidizing the ER. Inhibitory disulfides of Ero1p are thus important for enzyme regulation. To visualize the differences between de-regulated and wild-type Ero1p, we determined the crystal structure of Ero1p C150A/C295A. The structure revealed local changes compared to the wild-type enzyme around the sites of mutation, but no conformational transitions within 25 Å of the active site were observed. To determine how the C150—C295 disulfide nonetheless participates in redox regulation of Ero1p, we analyzed using mass spectrometry the changes in Ero1p disulfide connectivity as a function of time after encounter with reducing substrates. We found that the C150—C295 disulfide sets a physiologically appropriate threshold for enzyme activation by guarding a key neighboring disulfide from reduction. This study illustrates the diverse and interconnected roles that disulfides can play in redox regulation of protein activity.     

Where do adaptive shifts occur during invasion? A multidisciplinary approach to unravelling cold adaptation in a tropical ant species invading the Mediterranean area

Evolution may improve the invasiveness of populations, but it often remains unclear whether key adaptation events occur after introduction into the recipient habitat (i.e. post‐introduction adaptation scenario), or before introduction within the native range (i.e. prior‐adaptation scenario) or at a primary site of invasion (i.e. bridgehead scenario). We used a multidisciplinary approach to determine which of these three scenarios underlies the invasion of the tropical ant Wasmannia auropunctata in a Mediterranean region (i.e. Israel). Species distribution models (SDM), phylogeographical analyses at a broad geographical scale and laboratory experiments on appropriate native and invasive populations indicated that Israeli populations followed an invasion scenario in which adaptation to cold occurred at the southern limit of the native range before dispersal to Israel. We discuss the usefulness of combining SDM, genetic and experimental approaches for unambiguous determination of eco‐evolutionary invasion scenarios.     

ACCLIMATION TO LOW TEMPERATURE OF TWO ARTHROSPIRA PLATENSIS (CYANOBACTERIA) STRAINS INVOLVES DOWN‐REGULATION OF PSII AND IMPROVED RESISTANCE TO PHOTOINHIBITION1

This study aimed to compare the ability of two Arthrospira platensis (Nordst.) Gomont strains, M2 and Kenya, isolated from two different habitats, to acclimate to low temperature (15°C). Both strains had similar growth rates at 30°C, but once acclimated to low temperature, M2 showed a greater decline in growth (59% vs. 41% in the Kenya strain). We suggest that the Kenya strain acclimated better to low temperature by down‐regulating its photosynthetic activity through (i) decreasing antenna size and thus reducing energy flux into the photosystems; (ii) decreasing reaction center density (RC/CS_X) and the performance index, thus decreasing the trapping probability and electron transport rate while maintaining electron transport probability for electron transport beyond Q_A^? unchanged; (iii) increasing the energy dissipation flux. In contrast, the M2 strain showed no difference in antenna size and exhibited a much lower decrease in RC/CS_X and a lower dissipation rate. Hence, the Kenya strain minimized potential damage on the acceptor side of PSII compared to the M2 cells. Furthermore, acclimation to low temperature was accompanied by an improved mechanism for handling excess energy resulting in an enhanced ability of the Kenya strain to rapidly repair damaged PSII RCs and withstand a high photon flux density (HPFD) stress; this finding might be defined as a cross‐adaptation phenomenon. This study may provide a tool to identify strains suitable for outdoor mass‐production in different regions characterized by different climate conditions.     

Sub-optimal morning temperature induces photoinhibition in dense outdoor cultures of the alga Monodus subterraneus (Eustigmatophyta)

Diel changes in photosynthetic oxygen evolution and several photochemical parameters measured by chlorophyll fluorescence quenching and induction were measured in outdoor dense cultures of the alga Monodus subterraneus (Eustigmatophyta). Cultures were maintained under two temperature regimes. In one, a rise in temperature was initiated in the morning by the increase in solar radiation up to the optimal temperature of 28 °C; in the other, a heating device was used to increase the rate of warming up in early morning. Although the two cultures were maintained at the same temperature and light intensity for most of the day, cultures exposed for only a short time to suboptimal morning temperature showed a larger decrease in almost all the photosynthetic parameters. By comparing the diel changes in maximal photochemistry efficiency of photosystem II, the electron transport rate and the photochemical and non‐photochemical chlorophyll fluorescence quenching of the cultures, we concluded that even a relatively short exposure to suboptimal morning temperatures induced photoinhibitory damage. The higher photochemical activity of the heated culture was also reflected in a significant increase in productivity, which was 60% higher in the morning heated cultures than in the non‐heated cultures.     

Photoinhibition and Its Recovery in Two Strains of the Cyanobacterium Spirulina platensis

Two strains of Spirulina platensis, marked Sp-G and Sp-RB, werestudied for their response to high photon flux densities (PFD).Sp-RB, a gas vacuolated strain, appeared more sensitive to thehigh PFD treatment as compared with Sp-G, a non-vacuolated strain.The loss of the photosynthetic activity due to the photoinhibitorytreatment was obtained at the level of whole cells as well asthe membrane level. Sp-RB was more sensitive than Sp-G at bothlevels. Experiments using chloramphenicol during the photoinhibitionprocess, and others in which the fate of radio-active labeledthylakoid proteins was followed, indicated that the differencebetween the strains lies in the rate of loss of the Dl polypeptidewith an electrophoretic mobility of 32–34 kDa. Both strainsrecovered from the photoinhibition when placed under low PFD.The recovery process started immediately after PFD was reduced,without any observed lag period, and was sensitive to chloramphenicol.Light was required for full recovery of activity. The rate ofrecovery of the two strains studied was very similar. ¹Contribution no. 29 of the Micro-Algal Biotechnology Lab. (Received January 11, 1988; Accepted March 31, 1988)