Summary The plant growth‐promoting effect of Pseudomonas putida S‐313 is associated with its ability to desulfurize arylsulfonates. To understand this further, other plant‐associated bacteria able to desulfurize a range of arylsulfonates were isolated from the rhizospheres of winter and spring barley. The isolates belonged to the β‐proteobacteria, including bacteria from the Variovorax paradoxus group and from the Acidovorax genus. They desulfurized toluenesulfonate to p‐ cresol, and were found to contain orthologues of the P. putida S‐313 asfA gene (> 70% sequence identity to AsfA), which is required for aryldesulfonation in this species. Further putative asfA orthologues were identified in several bacteria and cyanobacteria whose genomes have been sequenced, but of these only Cupriavidus ( Ralstonia ) metallidurans was able to utilize arylsulfonates as sulfur source. Cultivation of V. paradoxus , C. metallidurans or P. putida S‐313 with toluenesulfonate as sulfur source led to a 100‐fold increase in expression of the asfA homologues, which was largely repressed when sulfate was added. Polymerase chain reaction with degenerate primers was used to generate asfAB clone libraries from spring‐ and winter‐barley rhizosphere DNA. Cluster analysis of 76 sequenced AsfA fragments revealed a broad diversity, with the majority of the sequences clustered together with AsfA from bacteria that are able to utilize toluenesulfonate as sulfur source. The diversity of asfA in barley rhizosphere underlines the importance of the desulfonation process for bacteria that inhabit the plant rhizosphere.
Bacterial communities in rhizospheres of transgenic maize (Zea mays, with the pat-gene conferring resistance to the herbicide glufosinate; syn. l-phosphinothricin) were compared to its isogenic, non-transgenic cultivar. Total DNA was extracted from bacterial cell consortia collected from rhizospheres of plants grown in an agricultural field. With the use of three different primer pairs binding to evolutionarily conserved regions of the bacterial 16S rRNA gene, partial sequences were amplified by polymerase chain reaction (PCR). The PCR products were subjected to single-strand conformation polymorphism (SSCP) to generate genetic profiles which corresponded to the diversity of the amplified sequences. Genetic profiles of rhizospheres consisted of 40-60 distinguishable bands depending on the chosen primer pairs, and the variability between independent replicates was very low. Neither the genetic modification nor the use of the herbicide Liberty (syn. Basta; active ingredient: glufosinate) affected the SSCP profiles as investigated with digital image analysis. In contrast, PCR-SSCP profiles of bacterial communities from rhizospheres of sugar beet, grown in the same field as a control crop, were clearly different. A less pronounced but significant difference was also observed with rhizosphere samples from fine roots of maize plants collected 35 and 70 days after sowing. Sequencing of the dominant 30 products from one typical SSCP profile generated from transgenic maize rhizospheres indicated the presence of typical soil and rhizosphere bacteria: half of the bands could be attributed to Proteobacteria, mainly of the alpha- and beta-subgroups. Other SSCP bands could be assigned to members of the following phylogenetic groups: Cytophaga-Flavobacterium-Bacteroides, Chlamydiales-Verrucomicrobium, Planctomyces, Holophaga and to Gram-positive bacteria with a high G+C DNA content.
Plants rely on microorganisms to mobilize organically and inorganically bound sulfur (S) and phosphorus (P) in which the plant can then readily utilize. The aim of this study was to investigate the role of S- and P-mobilizing bacteria in plant growth promotion in biochar-amended soil, which has been rarely investigated so far. Pot experiments of Lolium perenne were established on S and P limited soil with 1% or 2% biochar (Miscanthus×giganteus) or without biochar (control) for a period of 126 days. Both biochar amendments resulted in significant plant growth promotion. Rhizobacteria capable of growing with (1) S from aromatic sulfonates, (2) P from phosphate esters, (3) P from phosphonates, and (4) P from tri-calcium phosphates as sole source of S or P, respectively, were significantly more abundant in the biochar treatments. 16S rRNA gene-based rhizobacteria community analysis revealed a significant biochar treatment effect. Abundance of nematodes feeding on bacteria was also significantly increased in the biochar treatments. Diversity analysis of rhizospheric asfA and phnJ genes revealed broad sequence diversities in bacterial sulfonate and phosphonate-mineralizing capabilities. These findings suggest that biochar amendment enhances microbially mediated nutrient mobilization of S and P resulting in improved plant growth. Significant increases in sulfonate, calcium-phosphate, phosphate-ester and phosphonate mobilizing bacteria, bacterial feeding nematodes and plant growth were identified alongside changes in bacterial community structure upon soil amendment with biochar. Significant increases in sulfonate, calcium-phosphate, phosphate-ester and phosphonate mobilizing bacteria, bacterial feeding nematodes and plant growth were identified alongside changes in bacterial community structure upon soil amendment with biochar.
The removal efficiency of a nanoalumina depth filter (Disruptor™) was tested using raw seawater from the North Sea in a laboratory scale filtration unit and reverse osmosis (RO) test unit. Permeate flux was measured against time using untreated and pre-filtered seawater. Untreated seawater exhibited a rapid permeate flux decline. Seawater pre-filtered through the DisruptorTM showed showed high flux that declined only slightly after 120 min of operation due to increasing of osmotic pressure and formation of scaling on the membrane surface. The surface morphologies of clean and fouled RO membranes were examined using scanning electron microscope (SEM). The surface of the membrane fouled by untreated seawater was completely covered by a fouling layer, while the membrane surfaces exposed to Disruptor™ pre-filtered seawater were clean and only scaling was detected. The functional groups on clean and fouled RO membrane samples were investigated by attenuated total reflection — Fourier transform infrared spectroscopy (ATR–FTIR). The spectra of the RO membrane fouled by untreated seawater showed absorption bands at 1025, 1006 and 915 cm–1, indicating that the fouling materials were polysaccharides and silica clay materials. The spectrum on the RO membrane exposed to pre-filtered seawater through the Disruptor™ was indistinguishable from that of the clean RO membrane. The involvement of transparent exopolymer particles (TEP) in the establishment of biofouling and development of biofilm was investigated. Results showed that TEP size increased as well as the number of bacteria with time of incubation. However, the number of TEP decreased by about 80% in seawater pre-filtered through the DisruptorT™.
Organically bound sulfur makes up about 90% of the total sulfur in soils, with sulfonates often the dominant fraction. Actinobacteria affiliated to the genus Rhodococcus were able to desulfonate arylsulfonates in wheat rhizospheres from the Broadbalk long-term field wheat experiment, which includes plots treated with inorganic fertilizer with and without sulfate, with farmyard manure, and unfertilized plots. Direct isolation of desulfonating rhizobacteria yielded Rhodococcus strains which grew well with a range of sulfonates, and contained the asfAB genes, known to be involved in sulfonate desulfurization by bacteria. Expression of asfA in vitro increased >100-fold during growth of the Rhodococcus isolates with toluenesulfonate as sulfur source, compared with growth with sulfate. By contrast, the closely related Rhodococcus erythropolis and Rhodococcus opacus type strains had no desulfonating activity and did not contain asfA homologues. The overall actinobacterial community structure in wheat rhizospheres was influenced by the sulfur fertilization regime, as shown by specific denaturing gradient gel electrophoresis of PCR amplified 16S rRNA gene fragments, and asfAB clone library analysis identified nine different asfAB genotypes closely affiliated to the Rhodococcus isolates. However, asfAB-based multiplex restriction fragment length polymorphism (RFLP)/terminal-RFLP analysis of wheat rhizosphere communities revealed only slight differences between the fertilization regimes, suggesting that the desulfonating Rhodococcus community does not specifically respond to changes in sulfate supply.
Bacterial communities in rhizospheres of transgenic maize (Zea mays, with the pat-gene conferring resistance to the herbicide glufosinate; syn. l-phosphinothricin) were compared to its isogenic, non-transgenic cultivar. Total DNA was extracted from bacterial cell consortia collected from rhizospheres of plants grown in an agricultural field. With the use of three different primer pairs binding to evolutionarily conserved regions of the bacterial 16S rRNA gene, partial sequences were amplified by polymerase chain reaction (PCR). The PCR products were subjected to single-strand conformation polymorphism (SSCP) to generate genetic profiles which corresponded to the diversity of the amplified sequences. Genetic profiles of rhizospheres consisted of 40–60 distinguishable bands depending on the chosen primer pairs, and the variability between independent replicates was very low. Neither the genetic modification nor the use of the herbicide Liberty (syn. Basta; active ingredient: glufosinate) affected the SSCP profiles as investigated with digital image analysis. In contrast, PCR–SSCP profiles of bacterial communities from rhizospheres of sugar beet, grown in the same field as a control crop, were clearly different. A less pronounced but significant difference was also observed with rhizosphere samples from fine roots of maize plants collected 35 and 70 days after sowing. Sequencing of the dominant 30 products from one typical SSCP profile generated from transgenic maize rhizospheres indicated the presence of typical soil and rhizosphere bacteria: half of the bands could be attributed to Proteobacteria, mainly of the α- and β-subgroups. Other SSCP bands could be assigned to members of the following phylogenetic groups: Cytophaga–Flavobacterium–Bacteroides, Chlamydiales–Verrucomicrobium, Planctomyces, Holophaga and to Gram-positive bacteria with a high G+C DNA content.
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