Changes in physical and chemical properties of pretreated wheat straw during hydrolysis with cellulase

Summary After 5 days of enzymatic hydrolysis, the average wheat straw particle size has decreased by 62% and there is a dramatic shift to particle sizes less than 25 microns in size. Before hydrolysis, all particle size fractions have the same composition. After hydrolysis, the cellulose fraction is reduced in all particles and the decrease is greater for smaller particles.     

Identification of 3-hydroxypalmitic acid methyl ester as a novel autoregulator controlling virulence in Ralstonia solanacearum

Expression of virulence genes in Ralstonia solanacearum , a phytopathogenic bacterium, is controlled by a complex regulatory network that integrates multiple signal inputs. Production of several virulence determinants is co-ordinately reduced by inactivation of phcB , but is restored by growth in the presence of a volatile extracellular factor (VEF) produced by wild-type strains of R. solanacearum . The VEF was purified from spent culture broth by distillation, solvent extraction, and liquid chromatography. Gas chromatography and mass spectroscopy identified 3-hydroxypalmitic acid methyl ester (3-OH PAME) as the major component in the single peak of VEF activity. Authentic 3-OH PAME and the purified VEF were active at ≤1 nM, and had nearly equivalent specific activities for stimulating the expression of eps (the biosynthetic locus for extracellular polysaccharide) in a phcB mutant. Authentic 3-OH PAME also increased the production of three virulence factors by a phcB mutant over 20-fold to wild-type levels, restored normal cell density-associated expression of eps and increased expression of eps when delivered via the vapour phase. Reanalysis of the PhcB amino acid sequence suggested that it is a small-molecule S -adenosylmethionine-dependent methyltransferase, which might catalyse synthesis of 3-OH PAME from a naturally occurring fatty acid. Biologically active concentrations of extracellular 3-OH PAME were detected before the onset of eps expression, suggesting that it is an intercellular signal that autoregulates virulence gene expression in wild-type R. solanacearum . Other than acyl-homoserine lactones, 3-OH PAME is the only endogenous fatty acid derivative shown to be an autoregulator and may be the first example of a new family of compounds that can mediate long-distance intercellular communication.     

Quality control of Utermöhl-based phytoplankton counting and biovolume estimates—an easy task or a Gordian knot?

The most suitable way for standardizing biovolume based assemblage analysis using the Utermöhl technique for counting combined with biomass conversion has not yet been found even though this method has been successfully used in plankton studies for many years. Due to the complexity of the approach easily applicable steps to initially meet primary standard end point or target counts for intra-laboratory standardization tested here seem promising. Examples from count validation and biometric data from the large datasets of three laboratories are given. The first two examples initially intended to quantify the taxon specific scatter of counts by (A) using identical replica of field samples combined with a half-chamber count (scan of every second transect) and the 30 random field approach, respectively, and (B) the replication of transect counts in one sample. Both examples identified relatively low minimum count thresholds to delimit counting errors for single cell counts. The third example identifies shape variability and allometric relationships of the main axes and shows a way to improve taxon specific biomass estimates with special reference to cell thickness. However improved precision of quantitative phytoplankton analysis requires optimization of combined counting strategy and biovolume assessment methods.     

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On the isolation of TI-plasmid from Agrobacterium tumefaciens.

An efficient lysis method for Agrobacterium cells was developed, which allows a reproducible isolation of the tumor inducing (TI)-plasmid. The lysis method is based on the sensitivity of this bacterium to incubation with lysozyme, n-dodecylamine,EDTA, followed by Sarkosyl, after growth in the presence of carbenicillin. We also present a procedure for the isolation of the TI-plasmid on a large scale, that might be used for the mass isolation of other large plasmids which like the TI-plasmid, can not be cleared with earlier described procedures. The purity of the plasmid preparations was determined with DNA renaturation kinetics, which method has the advantage that the plasmid need not to be in the supercoiled or open circular form.