Eva Eklund

Rhizobium nodulation inProsopis juliflora seedlings at different irrigation levels in eastern Kenya

The field phase of the present study was carried out at Bura, eastern Kenya. The introduced, drought resistantProsopis juliflora seedlings were watered at four different irrigation levels. 43 sample trees with 1772 root nodules were dug up and investigated. Several trees lacked viable root nodules especially in nonirrigated plots. Regression analysis indicated significant negative correlation between the mortality of the root nodules and the level of irrigation. Rhizobium strains, which were isolated from the sample trees, were capable of nodulating indigenousAcacia senegal.

Acid Hydrolysis of Sunflower Seed Husks for Production of Single Cell Protein

SummarySunflower seed husks were chosen as a typical lignocellulosic waste product of low value. This model substrate was hydrolyzed with sulphuric acid at 120°C. The hydrolysis was carried out in two steps: hydrolysis of the pentosan fraction and subsequent hydrolysis of the cellulose fraction. The pentosan fraction was nearly quantitatively hydrolyzed. For the cellulose hydrolysis the yield was 79% of the theoretical yield. The hydrolyzates were neutralized to pH 5 with solid calcium hydroxide and used for preparation of growth media forCandida yeasts andPaecilomyces variotii. For the pentosan hydrolyzates the yields of yeast biomass were 35–36 g per 100 g available reducing sugars (supplied to the medium). In cellulose hydrolyzates the corresponding yields were 45–48 g withCandida utilis andC. tropicalis and about 30 g withC. pseudotropicalis. P. variotii was noticeably superior to the yeasts. In pentosan hydrolyzates it produced 63 g dry mycelium from 100 g reducing sugars supplied; in cellulose hydrolyzates, 94 g. This suggests that it must be an effective utilizer of a wide range of compounds, for example, organic acids in the medium.

Establishment and disappearance of introduced pseudomonads in the rhizoplane of peat grown cucumber plants

SummarySeeds of cucumber were inoculated with two different fluorescent Pseudomonas cultures and grown in peat. The establishment of the introduced pseudomonads as well as of spontaneously developing Pseudomonas populations in the rhizoplane was studied. It was found that the pseudomonads were able to compete successfully in the rhizoplane of young cucumber plants. However, they did not keep their position in the predominating populations for more than a restricted, comparatively short period. After eight weeks, at the flowering stage of the cucumber plants, they were hardly detectable among other bacteria in the rhizoplane.

Behaviour of Selected Finnish Red Clover Rhizobium Inoculants under Field Conditions

The effect on red clover dry weight and crude protein production of six Finnish red clover Rhizobium inoculants was studied in field experiments carried out at nine geographical sites in Finland. The ability of the inoculants to compete with the native Rhizobium populations was studied in three of these field experiments.

Extracellular proteases from soil actinomycetes. II. The hydrolytic features of the extracellular protease of an actinomycete, isolated from peat.

Summary The ammo acids, set free from casein, haemoglobin, and egg albumin by crude fractions of the extracellular protease of a soil actinomycete (labelled AIV17) have been examined and compared with the amino acids liberated by promise, subtilisin, and trypsin under the same conditions. Of the enzymes included in the investigation, pronase showed the widest range of activity in the cleavage of peptide bounds. However, particularly fraction I of AIV17-protease (molecular weight ≥ 30.000) also liberated a wide spectrum of amino acids, especially from casein and haemoglobin. Metal chelating agents like EDTA do not inhibit the caseolytic activity of either un-fractionated AIV17-protease or of fraction I of it. Therefore, neutral metallo-proteinases obviously do not play an important role in the protease complex, produced by the strain AIV17. The activity of AIV17-protease seems to be subjected to the release (a) of alkaline amino acids like lysine, and arginine (b) of hydrophobic amino acids, particularly leucine, and the aromatic acids tyrosine and phenylalanine. The comparatively high amounts of free amino acids released may be due to the simultaneous action of several alkaline serine proteinases in combination with traces of exopeptidases. In the liberation of particularly acid amino acids, glutamic and aspartic acid from haemoglobin, fraction II of AIV17-protease (Mw 10.000–30.000) showed some relationship to subtilisin. The fraction mentioned differed from subtilisin in its pronounced affinity to peptide bounds adjacent to lysine. As a whole, the proteinases of AIV17 seem to possess a higher hydrolytic capacity than the alkaline proteinases of Bacillus subtilis.

Extracellular Proteases from Soil Aetinomycetes: III. Effect of Growth Medium and Temperature on the Protease Production by an Actinomycete, Isolated from Peat

Summary The ability of an actinomycete, isolated from peat (labelled A IV 17), to produce extracellular protease in various low-cost media has been examined. It has been found that for protease production with the strain A IV 17 glucose can be replaced as energy source by xylose or glycerol. Horn meal, representing a cheap slaughtery waste product, has been found to be a favourable nitrogen source for the production of A IV 17-protease. With small changes in the composition of the medium, used for protease production, the productivity of the organism in question has been more than doubled, as compared with the protease yields achieved in the skim-milk medium, originally used for the screening of extracellular proteases produced by actinomycetes, isolated from soil.