Bacterial community diversity in paper mills processing recycled paper.

Paper mills processing recycled paper suffer from biofouling causing problems both in the mill and final product. The total bacterial community composition and identification of specific taxa in the process water and biofilms at the stock preparation and paper machine areas in a mill with recycled paper pulp was described by using a DNA-based approach. Process water in a similar mill was also analyzed to investigate if general trends can be found between mills and over time. Bacterial community profiles, analyzed by terminal-restriction fragment length polymorphism (T-RFLP), in process water showed that the dominant peaks in the profiles were similar between the two mills, although the overall composition was unique for each mill. When comparing process water and biofilm at different locations within one of the mills, we observed a separation according to location and sample type, with the biofilm from the paper machine being most different. 16S rRNA gene clone libraries were generated and 404 clones were screened by RFLP analysis. Grouping of RFLP patterns confirmed that the biofilm from the paper machine was most different. A total of 99 clones representing all RFLP patterns were analyzed, resulting in sequences recovered from nine bacterial phyla, including two candidate phyla. Bacteroidetes represented 45% and Actinobacteria 23% of all the clones. Sequences with similarity to organisms implicated in biofouling, like Chryseobacterium spp. and Brevundimonas spp., were recovered from all samples even though the mill had no process problems during sampling, suggesting that they are part of the natural paper mill community. Moreover, many sequences showed little homology to as yet uncultivated bacteria implying that paper mills are interesting for isolation of new organisms, as well as for bioprospecting.

Specific interactions between arbuscular mycorrhizal fungi and plant growth-promoting bacteria: as revealed by different combinations.

The interactions between two plant growth-promoting rhizobacteria (PGPR, Pseudomonas fluorescens SBW25 and Paenibacillus brasilensis PB177), two arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Glomus intraradices) and one pathogenic fungus (Microdochium nivale) were investigated on winter wheat (Triticum aestivum cultivar Tarso) in a greenhouse trial. PB177, but not SBW25, had strong inhibitory effects on M. nivale in dual culture plate assays. The results from the greenhouse experiment show very specific interactions; for example, the two AM fungi react differently when interacting with the same bacteria on plants. Glomus intraradices (single inoculation or together with SBW25) increased plant dry weight on M. nivale-infested plants, suggesting that the pathogenic fungus is counteracted by G. intraradices, but PB177 inhibited this positive effect. This is an example of two completely different reactions between the same AM fungus and two species of bacteria, previously known to enhance plant growth and inhibit pathogens. When searching for plant growth-promoting microorganisms, it is therefore important to test for the most suitable combination of plant, bacteria and fungi in order to achieve satisfactory plant growth benefits.

Degradation of PAH in a creosote-contaminated soil. A comparison between the effects of willows (Salix viminalis), wheat straw and a nonionic surfactant.

The degradation of polyaromatic hydrocarbons (PAH) in an aged creosote-contaminated soil in the presence of Salix viminalis was investigated in a greenhouse experiment. Phenanthrene and pyrene were degraded 100% and 80%, respectively, in the presence of plants but only 68% and 63% without plants. The effects of the nonionic surfactant Triton X-100 or the addition of straw, without plants, were also studied. The addition of straw had no effect on PAH degradation compared to the control Pyrene degradation with Triton X-100 at low concentrations (0.06 microl g(-1) DW) was comparable to that with plants but was less for anthracene and phenanthrene. The treatments with plants were, according to SIR measurements, dominated by active microorganisms (98.8% of the biomass), whereas all treatments without plants contained mostly dormant or non-growing microorganisms (1.7-2.0% active). Viable counts and active biomass were highly correlated in all treatments and demonstrated that S. viminalis greatly increased microbial populations. Dominant bacteria were grouped according to Gram, fluorescence and oxidase tests and revealed differences between treatments. The presence of S. viminalis or the surfactant enhanced PAH degradation, primarily by a rhizosphere effect on the microbial activity in the former case and by increased bioavailability in the latter case.