Root-associated microbial communities are very important for biogeochemical cycles in wetland ecosystems and help to elaborate the mechanisms of plant invasions. In the estuary of Jiulong River (China), Spartina alterniflora has widely invaded Kandelia obovata-dominated habitats, offering an opportunity to study the influence of root-associated bacteria. The community structures of endophytic and rhizosphere bacteria associated with selected plant species were investigated using the barcoded Illumina paired-end sequencing technique. The diversity indices of bacteria associated with the roots of S. alterniflora were higher than those of the transition stands and K. obovata monoculture. Using principal coordinate analysis with UniFrac metrics, the comparison of β-diversity showed that all samples could be significantly clustered into 3 major groups, according to the bacteria communities of origin. Four phyla, namely Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes, were enriched in the rhizoplane of both salt marsh plants, while they shared higher abundances of Cyanobacteria and Proteobacteria among endophytic bacteria. Members of the phyla Spirochaetes and Chloroflexi were found among the endophytic bacteria of S. alterniflora and K. obovata, respectively. One of the interesting findings was that endophytes were more sensitive in response to plant invasion than were rhizosphere bacteria. With linear discriminate analysis, we found some predominant rhizoplane and endophytic bacteria, including Methylococcales, Pseudoalteromonadacea, Clostridium, Vibrio, and Desulfovibrio, which have the potential to affect the carbon, nitrogen, and sulfur cycles. Thus, the results provide clues to the isolation of functional bacteria and the effects of root-associated microbial groups on S. alterniflora invasions.

The self-assembly of Ag(I) ions with 3,5-dimethyl-4-amino-1,2,4-triazole (L1) and 4-salicylideneamino-1,2,4-triazole (L2) gave two novel complexes, [Ag4(mu2-L1)6][Ag4(mu2-L1)6(CH3CN)2](ClO4)8.2H2O (1) and [Ag4(mu2-L2)6(CH3CN)2](AsF6)4.2H2O (2), both of which contain tetranuclearic clusters constructed via Ag(I) ions and six N1,N2-bridged triazoles with a Ag4N12 core. When 4-(6-amino-2-pyridyl)-1,2,4-triazole (L3) was employed, {[Ag4(mu2-L3)4(mu3-L3)2](CF3SO3)4.H2O}n (3), {[Ag4(mu2-L3)4(mu3-L3)2](ClO4)4}n (4), and {[Ag4(mu2-L3)2(mu3-L3)4](PF6)4.CH3CN.0.75H2O}n (5) were isolated. 3 and 4 are 1D polymers, while 5 is a 2D polymer. 1D and 2D coordination polymers are constructed via the self-assembly of Ag4N12 cores as secondary building units (SBUs). The connection of these SBUs can be represented as a ladderlike structure for 1D polymers and a 4.8(2) net for 2D polymers. Electrospray ionization mass spectrometry measurements and NMR (1H and 13C) studies demonstrate that the tetranuclear SBU retains its integrity and the coordination polymers decompose into the tetranuclear Ag4N12 core in solution. 2 exhibits blue emission in the solid state and green emission in solution at ambient temperature. Strong blue fluorescence for complexes 3-5 in the solid state can be assigned to the intraligand fluorescent emission.

No abstract

These pot experiments aimed to investigate the effects of polycyclic aromatic hydrocarbons (PAHs) on plant uptake, rhizophere, endophytic bacteria, and phytoremediation potentials of contaminated sediments. Salt marsh plant Spartina alterniflora was selected and cultivated in phenanthrene (PHE)- and pyrene (PYR)-contaminated sediments (for 70 days). The results indicated that the amount of PHE removed from the sediments ranged from 13 to 36 %, while PYR ranged from 11 to 30 %. In rhizophere sediment, dehydrogenase activities were significantly (P < 0.05) enhanced by higher concentration of PHE treatments, while polyphenol oxidase activities were prohibited more than 10 % in non-rhizophere sediment. Compared with the control, PHE treatments had also significantly (P < 0.05) lower total microbial biomass; especially for gram-negative bacteria, this decrease was more than 24 %. However, the PYR treatments had little effect on the dehydrogenase, polyphenol oxidase, and total phospholipid fatty acid analysis (PLFA) biomass. The greatest abundance of PAH-ring hydroxylating dioxygenases isolated from gram-negative bacteria (PAH-RHDα-GN) of rhizoplane and endophyte in roots were found at high concentration of PHE treatments and increased by more than 100- and 3-fold, respectively. These results suggested that PAH pollution would result in the comprehensive effect on S. alterniflora, whose endophytic bacteria might play important roles in the phytoremediation potential of PAH-contaminated sediments.

Purpose Plants and their root-associated microbes play important roles in the remediation of polycyclic aromatic hydrocarbons (PAHs) present in the sediments of contaminated coastal wetlands. The detailed information about the effects of PAHs on root-associated bacterial communities could help to isolate PAH-degrading bacteria and optimize the process of phytoremediation. Materials and methods The community structures of rhizospheric (RB) and endophytic bacteria (EB) of salt marsh plant (Spartina alterniflora) grown in phenanthrene (PHE)-and pyrene (PYR)-contaminated sediments (for 70 days) were investigated using the barcoded Illumina paired-end sequencing technique. Results and discussion The diversity and community structure of EB and RB were more sensitive to PHE and PYR contamination as compared to those in the sediments. All samples were strongly clustered according to EB, RB, and sediments, suggesting the niche-specific influence of PAHs on bacterial communities. Potential PAH-degrading bacteria (Pseudomonas sp., Paenibacillus sp., and Flavobacterium sp.) in EB and RB were stimulated by PAH contamination. The results revealed an increase prevalence of specific bacteria which may be responsible for PAH degradation. PHE contamination increased the abundance of Proteobacteria in EB but decreased the number of Firmicutes, Bacteroidetes, and Chloroflexi. The numbers of Proteobacteria and Firmicutes in EB were enhanced by PYR treatment. However, both PHE and PYR treatment showed similar effects on the bacterial communities in RB.Conclusions The results suggested that PAH pollution could alter root-associated bacterial communities of S. alterniflora, whose EB might play an important role in the phytoremediation of PAH-contaminated sediments.