Change in the H2 photoproduction capability in a synchronously grown aerobic nitrogen-fixing cyanobacterium,Synechococcus sp. Miami BG 043511

Synchronously growing cells of nitrogen-fixing Synechococcus sp. Miami BG 043511 were harvested periodically and the capability for hydrogen photoproduction in closed vessels was measured under hydrogen production conditions. The capability for hydrogen photoproduction in cells was correlated with that of cellular carbohydrate content. Cells with a high carbohydrate content exhibited a high capacity for hydrogen production and those with low carbohydrate content exhibited low capacity for hydrogen production. Nitrogenase activity at the onset of incubation did not coincide with a capability for the cells to produce hydrogen during the subsequent incubation period. Interestingly, when cells with a high capacity for hydrogen photoaccumulation were incubated, alternate periods of hydrogen and oxygen accumulation were observed at 12 hour intervals. About 0.5 ml of hydrogen per ml of cell suspension was accumulated in flasks during the initial 12-h incubation period. These observations indicate that the use of synchronous culture can be one of the ways of provide materials suitable not only for basic studies but also for applied aspects of hydrogen photoproduction.     

Denitrifying population dynamic and evolution of nitrogen gas during a composting process

Abstract Little information exists about nitrogen losses through microbial activity during treatment of solid urban waste (SUW) by processes such as composting. In the present study, in addition to evaluating the pattern of nitrogen losses by denitrification at different stages of the process, a comparison between the method of Pochon and Tardieux, and an improved gas chromatographic method for estimating denitrifying populations was undertaken, Though the MPN (Most Probable Number) enumerations were higher using the colorimetric method than the gas chromatographic one, the patterns of the two graphs showing numbers of denitrifiers during composing were the same. The highest numbers were revealed immediately after loading the reactor (10⁷–10⁸/g d.w.), lower numbers of denitrifiers were found in the second sampling corresponding to the thermophilic phase (10³–10⁴/g d.w.). These numbers increased gradually as the waste material stabilized (10th to 123rd day of composting) to again reach values of 10⁷–10⁸/g d.w.     

Senescence and N release from clover roots following permanent excision of the shoot

Six to seven week old red clover plants (Trifolium pratense L. cv Merviot) were used to investigate the time-course of root senescence following complete and permanent excision from the shoot. Plants were grown in sand culture watered with nutrient solution. After excision of the shoots, roots were left in situ and sampled over a period of up to 42 days. Respiration rate began to decrease immediately after excision, reaching 50% of its initial value after 24 h. The decline involved a reduction in the capacity of the respiratory pathways as measured in the presence of an uncoupler (FCCP) and exogenous glucose. The reduction in respiration could be prevented by supplying 100 mM sucrose to excised roots incubated in nutrient solution at the time of excision, but not 4–5 days after excision. There was a steady reduction in the protein and soluble sugar concentrations from the time of excision and a smaller reduction in starch. Free amino acid concentrations increased immediately after excision, but the temporal dynamics differed between individual amino acids. The total concentration of free amino acids rose to a maximum value 6–13 days after excision, before declining. Under these conditions roots survived for a remarkably long period of time. Depending on the experiment, cell viability, measured as the percentage of cells with positive turgor, was unchanged for at least 20 days, and complete loss of viability was not observed until 34–42 days after excision. There was no appreciable loss of N from the roots until cell viability declined significantly. The potential implications of these results for modelling and management of N cycling in cropping systems is discussed briefly.     

Identification of iron-regulated outer membrane proteins in uropathogenic Proteus mirabilis and its relationship with heme uptake

The effect of iron deprivation on the expression of outer membrane proteins and the ability to use heme as an iron source by uropathogenic Proteus mirabilis , Pr 6515, was studied. Examination of iron-restricted bacteria showed three outer membrane proteins ranging from 66 to 75 kDa to be affected by iron restriction, as well as a newly expressed 64-kDa protein. These proteins were induced within 15 minutes of iron-deprivation. The strain grew in the presence of ferric citrate, hemin and hemoglobin as iron sources, but could not use transferrin, lactoferrin or siderophores from exogenous sources. The 64- and 66-kDa proteins showed hemin-binding activity by affinity chromatography, and both reacted in Western blots with sera from mice transurethrally infected with the same strain. We suggest that P. mirabilis expresses iron-regulated outer membrane proteins that could be involved in heme uptake and may have a role in pathogenesis.     

Piscivory and prey selection of four predator species in a whitefish dominated subarctic lake

According to logistic regressions derived for pike Esox lucius and burbot Lota lota , the probability of ingesting fishes in Lake Muddusjärvi, northern Finland, was 50% at 19·3 and 22·1 cm L _T, whereas Arctic charr Salvelinus alpinus and brown trout Salmo trutta shifted to piscivory at the lengths of 25·7 and 26·4 cm L _T. The specialist piscivores, pike and burbot, consumed more prey species and took a wider range of prey sizes than Arctic charr and brown trout. The prey length for all predators increased in relationship to predator length. Whitefish Coregonus lavaretus was the dominant prey species in the lake and in the diet of all the piscivorous species. The whitefish population was divided into three forms, of which the slow-growing, and the most numerous densely rakered whitefish form (DR), was selected by all predator species. This form also had the smallest average size and widest habitat range, utilizing both pelagic and epibenthic habitats. Two sparsely rakered whitefish forms (LSR and SSR) occupied only epibenthic habitats and had lower relative densities than DR. These forms, LSR and SSR, had a minor importance in the diet of predator species.     

A further extension of the method for independently measuring the amount of nitrogen fixed by a legume crop

Summary The combination of using¹⁵N for determining the amount of nitrogen fixed by a legume crop in field experiments and the labelling of only one treatment at a time in each treatment combination is shown to be conceptually and experimentally valid for determining the effect of cultural practices on the amount of nitrogen fixed by a legume crop.     

Response of lentil to VA Mycorrhizal inoculation and plant available P levels of unsterile soils

Summary Responses of lentil in unsterile soils at low, medium and high levels of plant available soil P toGlomus fasciculatum inoculation were evaluated. It was observed that growth, dry matter accumulation, nodulation, and nitrogen fixation were considerably improved in VAM inoculated plants over uninoculated control at low and medium levels of plant available soil P.