Cyanobacteria occur worldwide but play an important role in the formation and primary activity of biological soil crusts (BSCs) in arid and semi-arid ecosystems. The cyanobacterial diversity in BSCs of the northwest Negev desert of Israel was surveyed at three fixed sampling stations situated along a precipitation gradient in the years 2010 to 2012. The three stations also are characterized by marked differences in soil features such as soil carbon, nitrogen, or electrical conductivity. The cyanobacterial biodiversity was analyzed by sequencing inserts of clone libraries harboring partial 16S rRNA gene sequences obtained with cyanobacteria-specific primers. Filamentous, non-diazotrophic strains (subsection III), particularly Microcoleus-like, dominated the cyanobacterial community (30% proportion) in all years. Specific cyanobacterial groups showed increased (e.g., Chroococcidiopsis, Leptolyngbya, and Nostoc strains) or decreased (e.g., unicellular strains belonging to the subsection I and Scytonema strains) abundances with declining water availability at the most arid, southern station, whereas many cyanobacterial strains were frequently found in the soils of all three stations. The cyanobacterial diversity at the three sampling stations appears dependent on the available precipitation, whereas the differences in soil chemistry were of lower importance.

Biological soil crusts (BSCs) fulfil numerous ecological functions in arid and semiarid areas. Cyanobacteria are important BSC organisms, which are responsible for carbon fixation, N2 fixation and binding of soil via extracellular polysaccharides. The cyanobacterial populations were characterised in different sampling plots established in three experimental stations along a rainfall gradient within NW Negev Desert, Israel. Cyanobacterial crust thickness and osmolyte accumulation therein decreased in plots with lower moisture. The cyanobacterial population structure also changed in different plots. We observed an increase of subsection III cyanobacteria such as Microcoleus spp. and Leptolyngbya spp. and a decreasing proportion of strains belonging to subsections I and IV in drier areas on the rainfall gradient. This population shift was also observed in the sampling plots, which were situated at various relief positions within the sand dune experimental sites. We also characterised the cyanobacterial populations within mechanically disturbed plots. After 4 years, they reached between 80% and 50% of the control populations in the northernmost and southern stations, respectively. Our results suggest that the cyanobacterial population is sensitive not only to macroscale factors but may also be subject to local climate variations and that 4 years was insufficient for complete recovery of the cyanobacterial population.

Summary The frequent production of the hepatotoxin microcystin (MC) and its impact on the lifestyle of bloom‐forming cyanobacteria are poorly understood. Here, we report that MC interferes with the assembly and the subcellular localization of RubisCO, in Microcystis aeruginosa PCC7806. Immunofluorescence, electron microscopic and cellular fractionation studies revealed a pronounced heterogeneity in the subcellular localization of RubisCO. At high cell density, RubisCO particles are largely separate from carboxysomes in M. aeruginosa and relocate to the cytoplasmic membrane under high‐light conditions. We hypothesize that the binding of MC to RubisCO promotes its membrane association and enables an extreme versatility of the enzyme. Steady‐state levels of the RubisCO CO2 fixation product 3‐phosphoglycerate are significantly higher in the MC‐producing wild type. We also detected noticeable amounts of the RubisCO oxygenase reaction product secreted into the medium that may support the mutual interaction of M. aeruginosa with its heterotrophic microbial community.

Plants and bacteria synthesize compatible solutes to adapt towards various environmental stress conditions. Moderate halotolerant cyanobacteria and some heterotrophic bacteria accumulate the compatible solute glucosylglycerol (GG), a compound not commonly found in higher plants. We aimed to investigate whether GG can be produced in potato and if it has an improving effect regarding stress tolerance. Potato plants were transformed with the ggpPS gene of Azotobacter vinelandii, which codes the bifunctional enzyme GG-phosphate phosphate/synthase (GgpPS) catalyzing the two-step synthesis of GG. Potato plants were generated expressing ggpPS under control of the constitutive CaMV-35S promoter or the stress-inducible rd29A promoter. The integration of T-DNA in transgenic clones was verified by PCR and transgene expression was detected on mRNA level. Transgenic potatoes with constitutive ggpPS expression accumulated GG up to 19 µmol/g fresh mass (FM) in leaves but no GG in tubers, while plants with rd29A-controlled ggpPS expression contained 10 µmol GG/g FM in leaves and up to 2.6 µmol GG/g FM in tubers. In greenhouse experiments, an increased shoot growth of the GG-accumulating potato plants was observed under salt and drought stress conditions. These results demonstrate that GG synthesis can be achieved in potato plants and might have a protective role on plant metabolism.

14The frequent production of the hepatotoxin microcystin and its impact on the life-style of 15 bloom-forming cyanobacteria are poorly understood. Here we report that microcystin 16 interferes with the assembly and the subcellular localization of RubisCO, in Microcystis 17 aeruginosa PCC7806. Immunofluorescence, electron microscopic and cellular fractionation 18 studies revealed a pronounced heterogeneity in the subcellular localization of RubisCO. At 19 high cell density, RubisCO particles are largely separate from carboxysomes in M. 20aeruginosa and relocate to the cytoplasmic membrane under high-light conditions. We 21 hypothesize that the binding of microcystin to RubisCO promotes its membrane association 22 and enables an extreme versatility of the enzyme. Steady-state levels of the RubisCO CO2 23 fixation product 3-phosphoglycerate are significantly higher in the microcystin-producing 24 wild type. We also detected noticeable amounts of the RubisCO oxygenase reaction product 25 secreted into the medium that may support the mutual interaction of M. aeruginosa with its 26