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The naphthalene-degrading activity of a Pseudomonas sp. strain isolated from a creosote-contaminated soil was shown to be encoded by the IncP9 plasmid pNF142 by transfer to Pseudomonas putida KT2442. The effects of the inoculant strain KT2442 (pNF142) and of naphthalene contamination on the soil bacterial community were studied in microcosms with the following treatments: (I) soil, (II) soil with naphthalene, (III) soil with naphthalene and inoculated with KT2442 (pNF142). The inoculant became the dominant bacterial population in treatment (III) as evidenced by cultivation and denaturing gradient gel electrophoresis (DGGE) analysis. The bacterial DGGE profiles revealed drastically reduced complexity due to the numerical dominance of the inoculant. However, group-specific fingerprints (beta-proteobacteria, actinobacteria) that excluded KT2442 (pNF142) showed less severe changes in the bacterial community patterns. A major effect of naphthalene on the soil bacterial community was observed in treatment (II) after 21 days. Two dominant bands appeared whose sequences showed the highest similarity to those of Burkholderia sp. RP007 and Nocardia vinaceae based on 16S rRNA gene sequencing. These bands were less intense in treatment (III). The increased abundance of RP007-like populations due to naphthalene contamination was also confirmed by PCR amplification of the phnAc gene. The nahAc and nahH genes were detected in DNA and cDNA only in treatment III. Although the inoculant strain KT2442 (pNF142) showed good survival and expression of genes involved in naphthalene degradation, this study suggests that KT2442 (pNF142) suppressed the enrichment of indigenous naphthalene degraders.

Forest ecosystems assimilate more CO 2 from the atmosphere and store more carbon in woody biomass than most nonforest ecosystems, indicating strong potential for afforestation to serve as a carbon management tool. However, converting grasslands to forests could affect ecosystem-atmosphere exchanges of other greenhouse gases, such as nitrous oxide and methane (CH 4 ), effects that are rarely considered. Here, we show that afforestation on a well-aerated grassland in Siberia reduces soil CH 4 uptake by a factor of 3 after 35 years of tree growth. The decline in CH 4 oxidation was observed both in the field and in laboratory incubation studies under controlled environmental conditions, suggesting that not only physical but also biological factors are responsible for the observed effect. Using incubation experiments with 13 CH 4 and tracking 13 C incorporation into bacterial phospholipid fatty acid (PLFA), we found that, at low CH 4 concentrations, most of the 13 C was incorporated into only two PLFAs, 18 : 1x7 and 16 : 0. High CH 4 concentration increased total 13 C incorporation and the number of PLFA peaks that became labeled, suggesting that the microbial assemblage oxidizing CH 4 shifts with ambient CH 4 concentration. Forests and grasslands exhibited similar labeling profiles for the high-affinity methanotrophs, suggesting that largely the same general groups of methanotrophs were active in both ecosystems. Both PLFA concentration and labeling patterns indicate a threefold decline in the biomass of active methanotrophs due to afforestation, but little change in the methanotroph community. Because the grassland consumed CH 4 at a rate five times higher than forest soils under laboratory conditions, we concluded that not only biomass but also cell-specific activity was higher in grassland than in afforested plots. While the decline in biomass of active methanotrophs can be explained by site preparation (plowing), inorganic N (especially NH 4 1 ) could be responsible for the change in cell-specific activity. Overall, the negative effect of afforestation of upland grassland on soil CH 4 uptake can be largely explained by the reduction in biomass and to a lesser extent by reduced cell-specific activity of CH 4 -oxidizing bacteria.

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In a previous study, caulobacteria from a broad range of freshwater, brackish water, marine and soil habitats (Anast & Smit, 1988;MacRae & Smit, 1991;Segers et al., 1994) were studied using a polyphasic approach. As a result, the descriptions of the genera Caulobacter and Brevundimonas were emended and a number of Caulobacter species were transferred to the genus Brevundimonas (Abraham et al., 1999). We report here on three novel species within the genus Brevundimonas which emerged from this study.Strains used in this study were obtained from the American Type Culture Collection (ATCC), the Deutsche Sammlung für Mikroorganismen und Zellkulturen (DSMZ) and the Laboratorium voor Microbiologie, Universiteit Gent, Belgium (LMG), and from one of the authors (J. S.) (CM, FWC and MCS strains) ( Table 1). The strains were grown in freshwater Caulobacter medium PYEM (2 g peptone, 2 g yeast extract and 0.5 g NH 4 Cl per litre MQ water). After autoclaving and cooling, 5 ml sterile-filtered riboflavin (0.2 mg ml 21 ), 2 ml 50 % glucose (sterile), 1 ml 20 % MgSO 4 (sterile) and 1 ml 10 % CaCl 2 (sterile) were added. The strains were grown in 2 l flasks at 30 u C with shaking at 100 r.p.m. and biomass was harvested in the late exponential phase, after 72 h.For the determination of DNA base compositions, genomic DNA was isolated from 2 ml culture using the DNeasy kit (Qiagen). DNA was digested enzymically and mean G+C contents were determined by HPLC (Tamaoka & Komagata, 1984). Calculations were carried out according to Mesbah et al. (1989), with non-methylated lambda phage DNA (Sigma) as a standard. For all strains, G+C contents between 64.6 and 67.0 mol% were found, within the range of those already reported for species of the genus Brevundimonas (Vancanneyt et al., 2005). A 16S rRNA gene sequence-based UPGMA tree and details of phospho-and sulfolipids are available as supplementary material with the online version of this paper.