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A novel strain of fluorescent pseudomonad (PB-St2) was isolated from surface-sterilized stems of sugarcane grown in Pakistan. The bacterium was identified as Pseudomonas aurantiaca on the basis of 16S rRNA gene sequence analysis and results from physiological and biochemical characteristics carried out with API50 CH and QTS 24 bacterial identification kits. Assays using substrate specific media for enzymes revealed lipase and protease activities but cellulase, chitinase, or pectinase were not detected. The bacterium was unable to solubilize phosphate or produce indole acetic acid. However, it did produce HCN, siderophores, and homoserine lactones. In dual culture assays on agar, the bacterium showed antifungal activity against an important pathogen of sugarcane in Pakistan, namely Colletotrichum falcatum, as well as for pathogenic isolates of Fusarium oxysporium, F. lateritium but not against F. solani. The antifungal metabolites were identified using thin-layer chromatography, UV-spectra, and MALDI-TOFF spectra and shown to be phenazine-1-carboxylic acid (PCA), 2-hydroxyphenazine (2-OH-PHZ), and N-hexanoyl homoserine lactone (HHL) (assessed using only TLC data). The capacity of this bacterium to produce HCN and 2-OH-PHZ, as well as to inhibit the growth of C. falcatum, has not been previously reported.

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Copyright of Canadian Journal of Microbiology is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Alcohol production from corn is gaining importance in Ontario, Canada, and elsewhere. A major cost of corn production is the cost of chemical fertilizers and these continue to increase in price. The competitiveness of alcohol with fossil fuels depends on access to low-cost corn that allows growers to earn a sustainable income. In this study we set out to determine if we can identify root-associated microorganisms from Ontario-grown corn that can enhance the nutrient flow to corn roots, directly or indirectly, and help minimize the use of extraneous fertilizer. Bacteria were isolated from corn rhizosphere and screened for their capacity to enhance corn growth. The bacteria were examined for their ability to fix nitrogen, solubilize phosphate, and produce indole acetic acid (IAA) and antifungal substances on potato dextrose agar. Bacterial suspensions were applied to pregerminated seed of four corn varieties (39D82, 39H84, 39M27, and 39T68) planted in sterilized sand and unsterilized cornfield soil. The plants were grown under greenhouse conditions for 30 days. Three isolates were identified as having growth-promoting effect. These bacteria were identified as to species by biochemical tests, fatty acid profiles, and 16S rDNA sequence analysis. Corn rhizosphere isolates, Gluconacetobacter azotocaptans DS1, Pseudomonas putida CQ179, and Azospirillum lipoferum N7, provided significant plant growth promotion expressed as increased root/shoot weight when compared to uninoculated plants, in sand and/or soil. All strains except P. putida CQ179 were capable of nitrogen fixation and IAA production. Azospirillum brasilense, however, produced significantly more IAA than the other isolates. Although several of the strains were also able to solubilize phosphate and produce metabolites inhibitory to various fungal pathogens, these properties are not considered as contributing to growth promotion under the conditions used in this study. These bacteria will undergo field tests for their effect on corn growth. [ABSTRACT FROM AUTHOR]

Abstract: Fertilizer costs are a major component of corn production. The use of biofertilizers may be one way of reducing production costs. In this study we present isolation and identification of three plant growth promoting bacteria that were identified as Enterobacter cloacae (CR1), Pseudomonas putida (CR7) and Stenotrophomonas maltophilia (CR3). All bacterial strains produced IAA in the presence of 100mgl−1 of tryptophan and antifungal metabolites to several soilborne pathogens. S. maltophilia and E. cloacae had broad spectrum activity against most Fusarium species. The only strain that was positive for nitrogen fixation was E. cloacae and it, and P. putida, were also positive for phosphate solubilization. These bacteria and the corn isolate Sphingobacterium canadense CR11, and known plant growth promoting bacterium Burkholderia phytofirmans E24 were used to inoculate corn seed to examine growth promotion of two lines of corn, varieties 39D82 and 39M27 under greenhouse conditions. When grown in sterilized sand varieties 39M27 and 39D82 showed significant increases in total dry weights of root and shoot of 10–20% and 13–28% and 17–32% and 21–31% respectively. Plants of the two varieties grown in soil collected from a corn field had respective increases in dry weights of root and shoot of 10–30% and 12–35% and 11–19% and 10–18%. In sand, a bacterial mixture was highly effective whereas in soil individual bacteria namely P. putida CR7 and E. cloacae CR1 gave the best results with 39M27 and 39D82 respectively. These isolates and another corn isolate, Azospirillum zeae N7, were tested in a sandy soil with a 55 and 110kgha−1 of nitrogen fertility at the Delhi research Station of Agriculture and Agri-Food Canada over two years. Although out of seven bacterial treatments, no treatment provided a statistically significant yield increase over control plots but S. canadense CR11 and A. zeae N7 provided statistically significant yield increase as compared to other bacteria. The 110kg rate of nitrogen provided significant yield increase compared to the 55kg rate in both years. [Copyright &y& Elsevier]

This study describes the biocontrol potential of rhizobacteria against a range of fungal phytopathogens. Out of 227 bacteria isolated from the rhizosphere of maize, rice, wheat, potato, sunflower and soybean crops cultivated in different agro-ecological regions of Pakistan, 48 exhibited >60 % antifungal activity against Fusarium oxysporum, Fusarium moniliforme, Rhizoctonia solani, Colletotrichum gloeosporioides, Colletotrichum falcatum, Aspergillus niger, and Aspergillus flavus. The rhizobacteria inhibiting >65 % pathogen growth were selected for detailed molecular and in planta studies most of which were identified as Pseudomonas and Bacillus species based on 16S rRNA gene sequence analysis. Antifungal metabolites produced by these rhizobacteria analyzed through LCMS were identified as antibiotics (iturin, surfactins, fengycin, DAPG, Phenazine, etc.), cell wall degrading enzymes (protease, chitinase, and cellulase), plant growth promotion enzymes and hormones (indole-3-acetic acid, ACC-deaminase, phosphates, nitrogen fixation), N-acyl-homoserine lactones and siderophores. The growth room experiment validated the potential of these bacteria as biofertilizer and biopesticide agents. Of all, P. aeruginosa strain FB2 and B. subtilis strain RMB5 showed significantly higher potential as antagonistic plant-beneficial bacteria effective against a range of fungal phytopathogens. Both these bacteria can be used to develop a dual-purpose bacterial inoculum as biopesticide and biofertilizer. Rest of the antagonistic PGPR may be exploited for disease control in less-infested soils. [ABSTRACT FROM AUTHOR]