The sulfur depot in the rhizosphere of a common wetland plant, Juncus effusus, can support long-term dynamics of inorganic sulfur transformations

Impacts of spatial expansion by Phragmites australis on spatiotemporal variation of sulfur fractions in marsh soils of the Min River estuary, Southeast China

To investigate the impacts of spatial expansion by Phragmites australis on spatiotemporal variations of sulfur (S) fractions in marsh soils of the Min River estuary (Southeast China), the contents of total sulfur (TS) and inorganic sulfur (IS) fractions (Water-Soluble-S, W-S-S; Adsorbed-S, A-S; HCl-Soluble-S, H-S-S; and HCl-Volatile-S, H-V-S) were determined in soils of Cyperus malaccensis marsh (before expansion, BE stage), P. australis-C. malaccensis marsh (during expansion, DE stage) and P. australis marsh (after expansion, AE stage) by space-for-time substitution method. Results showed that the expansion of P. australis greatly altered the spatiotemporal variations of TS and IS fractions in marsh soils. The TS contents in soils at AE stage were significantly lower than those at DE and BE stages throughout a year (p < 0.01). Higher levels of W-S-S, A-S, H-S-S and total inorganic sulfur (TIS) generally occurred in soils at DE and AE stages, whereas higher values of H-V-S were observed in soils at BE stage. Although P. australis expansion did not alter the temporal variations of TS stock in soils greatly, the values during autumn and winter were generally higher than those in spring and summer (p < 0.05). The highest TIS stocks in soils of different expansion stages were observed in spring, while the lowest values occurred in summer. The expansion of P. australis significantly increased the IS supply capacity of soils and, compared with the BE stage, stocks of W-S-S, A-S, H-S-S and TIS in soils of all sampling seasons at DE and AE stages increased by 51.40 %, 50.76 %, 63.35 %, 50.52 % and 20.00 %, 31.46 %, 42.93 %, 27.56 %, respectively. It was worth noting that stocks of H-V-S in soils at DE and AE stages showed a decreasing trend compared to the BE stage, implying that the expansion of P. australis might reduce the production of sulfides. This paper found that, compared with C. malaccensis, the increased available IS stocks in soils might be an effective strategy for P. australis to maintain its expansion advantage and the decreased volatile-S in soils might be more favorable for boosting its competitiveness. Our study provided valuable information for understanding the interspecific competition mechanism between P. australis and C. malaccensis. Next step, in order to protect the diversity of marsh vegetations in the Min River estuary, effective measures should be taken to suppress the rapid expansion of P. australis.

Adaptive characteristics of indigenous microflora in an organically contaminated high salinity groundwater

Salinity, a critical factor, could directly or indirectly affect the microbial community structure and diversity. Changes in salinity levels act as environmental filters that influence the transformation of key microbial species. This study investigates the adaptive characteristics of indigenous microflora in groundwater in relation to external organic pollutants under high salinity stress. A highly mineralized shallow groundwater in Northwest China was conducted as the study area, and six representative sampling points were chosen to explore the response of groundwater hydrochemical parameters and microflora, as well as to identify the tolerance mechanisms of indigenous microflora to combined pollution. The results revealed that the dominant genera found in high salinity groundwater contaminated with organic pollutants possess the remarkable ability to degrade such pollutants even under challenging high salinity conditions, including Halomonas, Pseudomonas, Halothiobacillus, Sphingomonas, Lutibacter, Aquabacterium, Thiomicrospira, Aequorivita, etc. The hydrochemical factors, including total dissolved solids (TDS), sulfide, nitrite, nitrate, oxidation reduction potential (ORP), NH3-N, Na, Fe, benzene series, phenols, and halogenated hydrocarbons, demonstrated a significant influence on microflora. High levels of sulphate and sulfide in groundwater can exhibit dual effects on microflora. On one hand, these compounds can inhibit the growth and metabolism of microorganisms. On the other hand, they can also serve as effective electron donors/receptors during the microbial degradation of organic pollutants. Microorganisms exhibit resilience to the inhibitory effects of high salinity and organic pollutants via a series of tolerance mechanisms, such as strengthening the extracellular membrane barrier, enhancing the synthesis of relevant enzymes, initiating novel biochemical reactions, improving cellular self-healing capabilities, responding to unfavorable environmental conditions by migration, and enhancing the S cycle for the microbial metabolism of organic pollutants.

Spatial characterization of microbial sulfur cycling in horizontal-flow constructed wetland models

Constructed wetlands (CWs) are a cost-effective technology for wastewater treatment in which plant-microorganism relationships play a key role in transforming pollutants. However, there is little knowledge about the spatial organization of microbial metabolic processes in CWs. Here we show the structuring of microbial transformation of inorganic sulfur compounds (ISCs) in two horizontal subsurface-flow CW models fed with sulfate-rich artificial wastewater. One model was fully planted with Juncus effusus, while the other was planted only in the middle to investigate further the influence of the plant on ISC transformations. Chemical analyses revealed that sulfate reduction and re-oxidation of sulfide/sulfur occurred simultaneously along the flow paths, with net reduction at the beginning of the CWs, where organic carbon from the influent was still present, and predominant re-oxidation in the downstream sections. Porewater ISC concentrations hardly differed between the two CWs. However, analysis of the bacterial communities showed that sulfur cycling in the fully planted CW was much higher. Total bacterial abundances were about 50 times and 3-4 orders of magnitude higher in the rhizoplane than in porewater and on gravel, respectively, as quantified by qPCR determination of the 16S rRNA gene. Sequencing of 16S rRNA gene amplicons revealed that bacterial communities on the roots and in the porewater differed substantially, apparently a consequence of the fluxes of oxygen and exudates from the roots. Furthermore, we observed partitioning of ISC transforming bacteria into different niches of the CWs. The results of the chemical and microbial analyses collectively support that extensive sulfur cycling occurred in the rhizospheres of the CW models. The study is relevant to the treatment of sulfur-containing wastewater and the elucidation of microbial communities involved in biogeochemical activities to improve water quality.

RNA-Seq analysis of soft rush (Juncus effusus): transcriptome sequencing, de novo assembly, annotation, and polymorphism identification

BACKGROUND

Juncus effusus L. (family: Juncaceae; order: Poales) is a helophytic rush growing in temperate damp or wet terrestrial habitats and is of almost cosmopolitan distribution. The species has been studied intensively with respect to its interaction with co-occurring plants as well as microbes being involved in major biogeochemical cycles. J. effusus has biotechnological value as component of Constructed Wetlands where the plant has been employed in phytoremediation of contaminated water. Its genome has not been sequenced.

RESULTS

In this study we carried out functional annotation and polymorphism analysis of de novo assembled RNA-Seq data from 18 genotypes using 249 million paired-end Illumina HiSeq reads and 2.8 million 454 Titanium reads. The assembly comprised 158,591 contigs with a mean contig length of 780 bp. The assembly was annotated using the dammit! annotation pipeline, which queries the databases OrthoDB, Pfam-A, Rfam, and runs BUSCO (Benchmarking Single-Copy Ortholog genes). In total, 111,567 contigs (70.3%) were annotated with functional descriptions, assigned gene ontology terms, and conserved protein domains, which resulted in 30,932 non-redundant gene sequences. Results of BUSCO and KEGG pathway analyses were similar for J. effusus as for the well-studied members of the Poales, Oryza sativa and Sorghum bicolor. A total of 566,433 polymorphisms were identified in transcribed regions with an average frequency of 1 polymorphism in every 171 bases.

CONCLUSIONS

The transcriptome assembly was of high quality and genome coverage was sufficient for global analyses. This annotated knowledge resource can be utilized for future gene expression analysis, genomic feature comparisons, genotyping, primer design, and functional genomics in J. effusus.