Bdellovibrio and like organisms (BALO) are obligate predators of Gram-negative bacteria, belonging to the a-and d-proteobacteria. BALO prey using either a periplasmic or an epibiotic predatory strategy, but the genetic background underlying these phenotypes is not known. Here we compare the epibiotic Bdellovibrio exovorus and Micavibrio aeruginosavorus to the periplasmic B. bacteriovorus and Bacteriovorax marinus. Electron microscopy showed that M. aeruginosavorus, but not B. exovorus, can attach to prey cells in a non-polar manner through its longitudinal side. Both these predators were resistant to a surprisingly high number of antibiotic compounds, possibly via 26 and 19 antibiotic-resistance genes, respectively, most of them encoding efflux pumps. Comparative genomic analysis of all the BALOs revealed that epibiotic predators have a much smaller genome (ca. 2.5 Mbp) than the periplasmic predators (ca. 3.5 Mbp). Additionally, periplasmic predators have, on average, 888 more proteins, at least 60% more peptidases, and one more rRNA operon. Fifteen and 219 protein families were specific to the epibiotic and the periplasmic predators, respectively, the latter clearly forming the core of the periplasmic 'predatome', which is upregulated during the growth phase. Metabolic deficiencies of epibiotic genomes include the synthesis of inosine, riboflavin, vitamin B6 and the siderophore aerobactin. The phylogeny of the epibiotic predators suggests that they evolved by convergent evolution, with M. aeruginosavorus originating from a non-predatory ancestor while B. exovorus evolved from periplasmic predators by gene loss.

The sNdy is focused on the development and the application of a stochastic economic optimisation model by which optimal levels of applied water and sprinkler spacing are determined. Data on cropwater production function and uniformity of water application are taken from a sprinkler irrigation plot of sweet corn. It was found that a saving of irrigation water can be achieved not only by raising water prices but also by increasing application uniformity. The spatial variability of applied irrigation water has been well recognised by both agricultural researchers and growers for many years. The level of appiication uniformity is highly dependent on the type and performance of the irrigation method. The yield of a given crop, grown during a specific season in a certain field and under certain management and cultivation conditions. is also spatially variable and is assumed to be dependent directly on the spatially variable water application. It was generally noticed that the variation of the applied water as well as of the yield is not completely disordered in space but can be analysed within the frame of stochastic modelling, that is, regarding the applied water and the resulting yield of a given field as random functions of space coordinates characterised by their probability density function (pdf) and correlation structure, rather than by their deterministic values. Most economic studies of efficient water use under non-uniform irrigation focus on optimisation with respect to the quantity of irrigation water and tend to ignore the optimisation with respect to the uniformity level (for example, Seginer 1978; Feinerman, Letey and Vaux 1983: Feinerman. Bresler and Dagan 1985). in a few previous economic studies (for example, Hill and Keller 1980: Chen and Wallender 1984; Gohring and Wallender 1987). the joint effects of uniformity and quantity of applied water on irrigation system selection or on economical sprinkler spacing were investigated. The dependence of the irrigation system cost on the uniformity was derived by varying the sprinkler spacing and calculating the resulting changes in the uniformity and in the cost. However, the spatial variation of the irrigation water was regarded as deterministic. uncertainty was not accounted for in the economic application. and the attitude of the decision maker' toward risk was ignored. Seginer (1 987) presented a comprehensive review describing a general approach to economic optimisation of the irrigation system considering the quantity of T h i s research has been financed in part by the United States Agency for International Development. in concert with the US Department of Agriculture. Office of International Cooperation and Development.