The effects of interactions between pseudomonads (Pseudomonas cepacia strains R55 and R85, P. aeruginosa strain R80, P. fluorescens strain R92, and P. putida strain R104) and the arbuscular mycorrhizal fungus Glomus clarum (Nicol. and Schenck) isolate NT4, on spring wheat (Triticum aestivum L. cv. Laura), grown under gnotobiotic and nonsterile conditions, were investigated. Although plant growth responses varied,
positive responses to pseudomonad inoculants generally were obtained under gnotobiotic conditions. Shoot dry weight enhancement
ranged from 16 to 48%, whereas root enhancement ranged from 82 to 137%. Shoot growth in nonsterile soil, however, was unaffected
by pseudomonad inoculants, or reduced by as much as 24%. Shoot growth was unaffected or depressed by G. clarum NT4 whereas early root growth was enhanced by 38%. Significant interactions between the pseudomonad inoculants and G. clarum NT4 were detected. Typically, dual inoculation influenced the magnitude of response associated with any organism applied
alone. The effect of these pseudomonads on G. clarum NT4 spore germination was investigated. Germination was inhibited when spores were incubated either on membranes placed directly
on bacterial lawns of strains R85 and R104 (i.e., direct assay), or on agarose blocks separated from the bacteria by membranes
(i.e., diffusion assay). When the agarose blocks were physically separated from the pseudomonad (i.e., volatile assay), there
was no evidence of inhibition, suggesting that a nonvolatile, diffusible substance(s) produced by both strains R85 and R104
may inhibit G. clarum NT4 spore germination.
Received: 11 December 1995 相似文献
Dried soil samples from many sources have been stored in archives world-wide over the years, but there has been little research on their value for studying microbial populations. Samples collected since 1843 from the Broadbalk field experiment on crop nutrition at Rothamsted have been used to document changes in the structure and composition of soils as agricultural practices evolve, also offering an invaluable record of environmental changes from the pre- to post-industrial era in the UK. To date, the microbial communities of these soils have not been studied, in part due to the well-documented drop in bacterial culturability in dried soils. However, modern molecular methods based on PCR amplification of DNA extracted directly from soil do not require bacterial cells to be viable or intact and may allow investigations into the legacy of bacteria that were present at the time of sample collection.
In a preliminary study, to establish if dried soils can provide a historical record of bacterial communities, samples from the Broadbalk soil archive dating back to 1868 were investigated and plots treated with either farmyard manure (FYM) or inorganic fertilizer (NPK) were compared. As anticipated, the processes of air-drying and milling greatly reduced bacterial viability whilst DNA yields declined less and may be preserved by desiccation. A higher proportion of culturable bacteria survived the archiving process in the FYM soil, possibly protected by the increased soil organic matter. The majority of surviving bacteria were firmicutes, whether collected in 2003 or in 1914, but a wide range of genera was detected in DNA extracted from the samples using PCR and DGGE of 16S rRNA genes. Analysis of DGGE band profiles indicated that the two plots maintained divergent populations. Sequence analysis of bands excised from DGGE gels, from a sample collected in 1914, revealed DNA from - and β-proteobacteria as well as firmicutes. PCR using primers specific for ammonia oxidizing bacteria showed similar band profiles across the two treatments in recently collected samples, however older samples from the NPK plot showed greater divergence. Primers specific for the genus Pseudomonas were designed and used in real-time quantitative PCR to indicate that archived soil collected in 1868 contained 10-fold less pseudomonad DNA than fresh soil, representing around 105 genomes g−1 soil. Prior to milling, dramatically less pseudomonad DNA was extracted from recently collected air-dried soil from the NPK compared to the FYM plot; otherwise, the two plots followed similar trends. Overall bacterial abundance, diversity and survival during the archiving process differed in the two soils, possibly due to differences in clay and soil organic matter content. Nevertheless, the results demonstrate that air-dried soils can protect microbial DNA for more than 150 years and offer an invaluable resource for future research. 相似文献
从全国各地采集豆豉样品,经富集培养并利用纤维蛋白平板法获得一株形态与现存产纤溶酶微生物差异较大的菌株HS9。通过传统方法、化学方法以及16SrRNA序列分析对HS9进行分类鉴定,属于Pseudomonas aeruqinosa,是未见报道的产豆豉纤溶酶菌株。发酵培养HS9获得粗酶,经20%~70%硫酸铵梯度盐析、SephadexG-75凝胶过滤以及CM-Sepharose Fast Flow阳离子交换层析分离纯化后,得到了电泳纯酶。通过SDS-PAGE了解该酶分子量约为34kD,pH8.0~8.5时酶活性最高,最适作用温度48℃,作用方式为直接水解纤维蛋白,胃蛋白酶抑制剂在工作浓度1μmol/L时能完全抑制其活性,推测该酶为天冬氨酸蛋白酶,是一种新型的豆豉纤溶酶。 相似文献
