The need to develop and improve sustainable energy resources is of eminent importance due to the finite nature of our fossil fuels. This review paper deals with a third generation renewable energy resource which does not compete with our food resources, cyanobacteria. We discuss the current state of the art in developing different types of bioenergy (ethanol, biodiesel, hydrogen, etc.) from cyanobacteria. The major important biochemical pathways in cyanobacteria are highlighted, and the possibility to influence these pathways to improve the production of specific types of energy forms the major part of this review.

Root exudates influence the surrounding soil microbial community, and recent evidence demonstrates the involvement of ATPbinding cassette (ABC) transporters in root secretion of phytochemicals. In this study, we examined effects of seven Arabidopsis (Arabidopsis thaliana) ABC transporter mutants on the microbial community in native soils. After two generations, only the Arabidopsis abcg30 (Atpdr2) mutant had significantly altered both the fungal and bacterial communities compared with the wild type using automated ribosomal intergenic spacer analysis. Similarly, root exudate profiles differed between the mutants; however, the largest variance from the wild type (Columbia-0) was observed in abcg30, which showed increased phenolics and decreased sugars. In support of this biochemical observation, whole-genome expression analyses of abcg30 roots revealed that some genes involved in biosynthesis and transport of secondary metabolites were up-regulated, while some sugar transporters were down-regulated compared with genome expression in wild-type roots. Microbial taxa associated with Columbia-0 and abcg30 cultured soils determined by pyrosequencing revealed that exudates from abcg30 cultivated a microbial community with a relatively greater abundance of potentially beneficial bacteria (i.e. plant-growth-promoting rhizobacteria and nitrogen fixers) and were specifically enriched in bacteria involved in heavy metal remediation. In summary, we report how a single gene mutation from a functional plant mutant influences the surrounding community of soil organisms, showing that genes are not only important for intrinsic plant physiology but also for the interactions with the surrounding community of organisms as well.

Summary 1.One mechanism explaining the success of invasive weeds may be the production and release of allelopathic compounds by the invader that, due to a lack of co-evolutionary history, have harmful effects on plant neighbours in the introduced range. 2. We partially tested this hypothesis by growing seven competing native European plant species either with the introduced Solidago canadensis s.l., one of the most successful invasive plants in Europe or on soil pre-cultivated with S. canadensis . We added activated carbon to the soil to neutralize organic chemical compounds with putative allelopathic effects. Furthermore, we added unsterilized soil inocula from the introduced (Switzerland) or native (USA) range to the soil to test potential confounding effects of soil microbes on invasion success. Untreated sterilized soil served as control. 3. Five out of the seven native species were more competitive against the invasive species in soils with activated carbon than without, supporting the allelopathy hypothesis. However, competitive outcomes were also influenced by the two sources of soil inoculum and by interactive effects of soil inoculum and Solidago origin suggesting that soil microbes alter allelopathic effects. 4. Achillea millefolium , the species least affected by the presence of S. canadensis and with no response to the activated carbon treatment is the only species used in this experiment reported to grow within Solidago stands in Europe, whereas the other European species tested tend to grow at the periphery of invasive Solidago stands. 5. Chemical analysis by LC-MS of Solidago root extracts revealed four main secondary chemical compounds with potential allelopathic effects. Root exudates of Solidago showed a significant inhibitory effect on growth of the model plant species Arabidopsis thaliana . The magnitude of inhibition increased with increasing concentration of the extract. 6. Synthesis . Levels of the four compounds were lower in Solidago populations from the invasive range than in populations of the same ploidy level from the native range. This suggests lower investment of invasive plants into these secondary compounds, possibly because of a higher susceptibility of plant competitors in the invasive range to these substances.

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An extract of roots of Centaurea diffusa (diffuse knapweed) yielded caryophyllene oxide and linoleic acid which were shown to be phytotoxic. Also isolated were germacrene B, a previouslyknown phytotoxin as well as the inactive polyene aplotaxene. A combination of these compounds, if transferred to the soil, could be one factor in the invasive behavior of this weed. Contrary to a literature report, 8-hydroxyquinoline was not detected in root exudates of in vitro grown C. diffusa nor could it be identified in the root extract. However, a recent report from a different group maintains that 8-hydroxyquinoline can be released from roots of C. diffusa following a diurnal rhythm.

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