Five strains of Trichoderma with known biocontrol activities were assessed for their effect upon pea growth and their antagonistic activity against large Pythium ultimum inocula. The effect of Trichoderma inocula upon the indigenous soil microflora and soil enzyme activities in the presence and absence of Pythium is assessed. In the absence of Pythium, Trichoderma strain N47 significantly increased the wet shoot weight by 15% but did not significantly affect the dry weight, whilst strains T4 and N47 significantly increased the root weights by 22% and 8% respectively. Strains TH1 and N47 resulted in significantly greater root lengths. Pythium inoculation significantly reduced the root length and the number of lateral roots and nodules, and significantly increased the root and rhizosphere soil fungal populations. Pythium inoculation significantly reduced the plant wet and dry shoot weights and significantly increased the wet and the dry shoot/root ratio. All the Trichoderma strains reduced the number of lesions caused by Pythium and increased the number of lateral roots. The effect of the Pythium on emergence and shoot growth was significantly reduced by all the Trichoderma strains except strain To10. Inoculation with Trichoderma strains TH1 and T4 resulted in significantly greater wet root weights (62% and 57%, respectively) in the presence of Pythium compared to the Pythium control. Strain N47 significantly increased the shoot/root ratio compared to the Pythium control. Inoculation with Trichoderma strains T4, T12 and N47 significantly reduced Pythium populations. Pythium increased the activity of C, N and P cycle enzymes, whilst four Trichoderma strains reduced this effect, indicating reduced plant damage and C leakage. Overall, strains T4 and N47 had the greatest beneficial characteristics, as both these strains improved plant growth in the absence of Pythium and reduced plant damage in the presence of Pythium. The dual properties of these strains improve the commercial application, giving them an advantage over single action inocula, especially in the absence of plant pathogens.

Original article can be found at: http://www.sciencedirect.com/science/journal/00380717 Copyright Elsevier Ltd. DOI : 10.1016/S0038-0717(97)00061-8Comparative assays for determining chitobiosidase, N-acetyl glucosaminidase, acid phosphatase, alkaline phosphatase, phosphodiesterase, aryl 2 sulfatase and urease activities from small samples of soil were developed. The enzyme assays and ATP biomass assessments were used to monitor perturbations caused by the presence of Pseudomonas fluorescens in the rhizosphere of wheat. Microbial biomass as well as the measured enzyme activities decreased with depth, except for acid phosphatase activity which was similar at all depths. A combined substrate mix addition of urea, colloidal chitin and glycerophosphate significantly increased N-acetyl glucosaminidase, chitobiosidase, aryl sulfatase and urease activities but did not cause a significant difference in acid and alkaline phosphatase and phosphodiesterase activities. Inoculation of seeds with P. fluorescens resulted in significant increases in rhizosphere chitobiosidase and urease activities at 5-20 cm depth and a significant decrease in alkaline phosphatase activity. Inoculation with the bacterium in the presence of substrate mix gave opposing effects to those treatments without substrate mix addition: chitobiosidase, aryl sulfatase and urease activities were significantly lower and alkaline phosphatase was significantly higher at the 5-20cm depth interval with inoculation of bacteria. Biomass values for the combined bacteria and substrate mix treatment were significantly higher than the substrate mix alone treatment

Aims: Four well-described strains of Pseudomonas¯uorescens were assessed for their effect on pea growth and their antagonistic activity against large Pythium ultimum inocula. Methods and Results: The effect of Pseudomonas strains on the indigenous soil micro¯ora, soil enzyme activities and plant growth in the presence and absence of Pythium was assessed. Pythium inoculation reduced the shoot and root weights, root length, and the number of lateral roots. The effect of Pythium was reduced by the Pseudomonas strains. Strains F113, SBW25 and CHAO increased shoot weights (by 20%, 22% and 35%, respectively); strains Q2-87, SBW25 and CHAO increased root weights (14%, 14% and 52%). Strains SBW25 and CHAO increased root lengths (19% and 69%) and increased the number of lateral roots (14% and 29%). All the Pseudomonas strains reduced the number of lesions and the root and soil Pythium populations, while SBW25 and CHAO increased the number of lateral roots. Pythium inoculation increased root and soil microbial populations but the magnitude of this effect was Pseudomonas strain-speci®c. Pythium increased the activity of C, N and P cycle enzymes, while the Pseudomonas strains reduced this effect, indicating reduced plant damage. Conclusions: Strains SBW25 and CHAO had the greatest bene®cial characteristics, as these strains produced the greatest reductions in the side effects of Pythium infection (microbial populations and enzyme activities) and resulted in signi®cantly improved plant growth. Strain SBW25 does not produce antifungal metabolites, and its biocontrol activity was related to a greater colonization ability in the rhizosphere. Signi®cance and Impact of the Study: This is the ®rst critical comparison of such important strains of Ps.¯uorescens showing disease biocontrol potential.

Food poisoning laboratories identify Bacillus cereus using routine methods that may not differentiate all Bacillus cereus group species. We recharacterized Bacillus food-poisoning strains from 39 outbreaks and identified B. cereus in 23 outbreaks, B. thuringiensis in 4, B. mycoides in 1, and mixed strains of Bacillus in 11 outbreaks. (16,19,22). They are difficult to discern using standard biochemical schemes, chemotaxonomic methods, or phylogenetically relevant target genes (1, 2), and many distinguishing pathogenicity markers in this group can be attributed to mobile plasmids (18,21,22,23). B. cereus sensu stricto carries the plasmid-borne emetic toxin cereulide (ces) (7,13,14), and B. thuringiensis carries insecticidal crystal protein (ICP) (cry) genes on one or more plasmids (3, 5, 6). The differentiation of B. cereus group members using molecular techniques is not routine in food-poisoning diagnostic methods and may cause underreporting of species such as B. thuringiensis (1,8 DNA was extracted by lysing pure culture in a heating block at 102°C for 10 min. Microcentrifuged supernatant was frozen at Ϫ80°C until required. Pathogenicity genes for emetic cereulide toxin (nonribosomal peptide synthetase [NRPS]) and ICP (cry1 or cry2) were detected in multiplex PCR assays (7, 10) shown in Fig. 1. Each master mix contained 0.8 M of each primer, hot start master mix, diethyl pyrocarbonate water (20 l), and 5 l of DNA. The PCR products were loaded onto 2% agarose gels made with 0.5ϫ Tris-borate-EDTA buffer and ethidium bromide (1 g ml Ϫ1 ). The gels were electrophoresed at 120 V for 30 min and then visualized on a Bio-Rad Gel Doc 2000.Strains positive for NRPS were designated as B. cereus, those positive for ICP (by microscopy or PCR) as B. thuringiensis, those with rhizoidal growth on nutrient agar as B. mycoides, and all other strains with the typical B. cereus phenotype as B. cereus NRPS Ϫ ICP Ϫ . PCR-negative isolates were further examined for ICP crystals using transmission electron microscopy (TEM) since B. thuringiensis strains may carry one to six cry genes and there is no universal method available to detect all cry genes (there are currently more than 150 cry1 toxins) (17; Bacillus thuringiensis toxin nomenclature [http: //www.lifesci.sussex.ac.uk/Home/Neil_Crickmore/Bt/]). Samples of B. cereus group bacteria were prepared for electron microscopy by fixation with 2% glutaraldehyde and 1% para-

The aim of this study was to determine the impact of wild‐type along with functionally and nonfunctionally modified Pseudomonas fluorescens strains in the rhizosphere. The wild‐type F113 strain carried a gene encoding the production of the antibiotic 2,4‐diacetylphloroglucinol (DAPG) useful in plant disease control, and was marked with a lacZY gene cassette. The first modified strain was a functional modification of strain F113 with repressed production of DAPG, creating the DAPG‐negative strain F113 G22. The second paired comparison was a nonfunctional modification of wild‐type (unmarked) strain SBW25, constructed to carry marker genes only, creating strain SBW25 EeZY‐6KX. Significant perturbations were found in the indigenous bacterial population structure, with the F113 (DAPG+) strain causing a shift towards slower growing colonies (K strategists) compared with the nonantibiotic‐producing derivative (F113 G22) and the SBW25 strains. The DAPG+ strain also significantly reduced, in comparison with the other inocula, the total Pseudomonas populations but did not affect the total microbial populations. The survival of F113 and F113 G22 were an order of magnitude lower than the SBW 25 strains. The DAPG+ strain caused a significant decrease in the shoot‐to‐root ratio in comparison to the control and other inoculants, indicating plant stress. F113 increased soil alkaline phosphatase, phosphodiesterase and aryl sulphatase activities compared to the other inocula, which themselves reduced the same enzyme activities compared to the control. In contrast to this, the β‐glucosidase, β‐galactosidase and N‐acetyl glucosaminidase activities decreased with the inoculation of the DAPG+ strain. These results indicate that soil enzymes are sensitive to the impact of inoculation with genetically modified microorganisms (GMMs).