Search

Isovalerate is one of the key intermediates during anaerobic digestion treating protein-containing waste/wastewater. Investigating the effect of different kinds of inhibitors on isovalerate-degrading microbial community is necessary to develop measures for improving the effectiveness of the treatment plants. In the present study, dynamic changes in the isovalerate-degrading microbial community in presence of inhibitors (ammonium, sulfide, mixed ammonium and sulfide, and chlortetracycline (CTC)) were investigated using high-throughput sequencing of 16S rRNA gene. Our observations showed that the isovalerate-degrading microbial community responded differently to different inhibitors and that the isovalerate degradation and gas production were strongly repressed by each inhibitor. We found that sulfide inhibited both isovalerate oxidation followed by methanogenesis, while ammonium, mixed ammonium and sulfide, and CTC mainly inhibited isovalerate oxidation. Genera classified into Proteobacteria and Chloroflexi were less sensitive to inhibitors. The two dominant genera, which are potential syntrophic isovalerate oxidizers, exhibited different responses to inhibitors that the unclassified_Peptococcaceae_3 was more sensitive to inhibitors than the unclassified_Syntrophaceae. Upon comparison to acetoclastic methanogen Methanosaeta, hydrogenotrophic methanogens Methanoculleus and Methanobacterium were less sensitive to inhibitors.

This study evaluated the performance of an upflow anaerobic filter (UAF) reactor in the thermophilic methane fermentation of hypersaline molasses wastewater. The high salinity (~ 45 mS/cm) of the undiluted wastewater completely inhibited the biogas production. An acclimation strategy involving gradient dilution of the molasses wastewater was implemented to gradually increase the salt stress. Consequently, the biogas production was recovered, inhibited only slightly by the high salinity of the undiluted wastewater. The reactor steadily achieved a high total organic carbon (TOC) loading rate of 5 g/L/day, with approximately 60% TOC removal efficiency. Acclimation to the gradually increased salt stress leads to a relative abundance of some halotolerant microbes, such as bacteria from Arcobacter, Tissierella, and Ruminococcaceae, which increased as their hydrolytic and acidogenic abilities adjusted to the incremental increase in salinity. Additionally, hydrogenotrophic methanogens, especially Methanoculleus, showed greater resistance to hypersalinity than aceticlastic methanogens. These results suggest that acclimation of the fermentation microbial community to hypersalinity is an effective strategy to improve methane production from hypersaline molasses wastewater in thermophilic UAF reactors.

A heterologous xylose utilization pathway, either xylose reductase-xylitol dehydrogenase (XR-XDH) or xylose isomerase (XI), is usually introduced into Saccharomyces cerevisiae to construct a xylose-fermenting strain for lignocellulosic ethanol production. To investigate the molecular basis underlying the effect of different xylose utilization pathways on the xylose metabolism and ethanol fermentation, transcriptomes of flocculating industrial strains with the same genetic background harboring different xylose utilization pathways were studied. A different source of xylA did not obviously affect the change of the strains transcriptome, but compared with the XR-XDH strain, several key genes in the central carbon pathway were downregulated in the XI strains, suggesting a lower carbon flow to ethanol. The carbon starvation caused by lower xylose metabolism in XI strains further influenced the stress response and cell metabolism of amino acid, nucleobase, and vitamin. Besides, the downregulated genes mostly included those involved in mitotic cell cycle and the cell division-related process. Moreover, the transcriptomes analysis indicated that the after integrate xylA in the δ region, the DNA and chromosome stability and cell wall integrity of the strains were affected to some extent. The aim of this was to provide some reference for constructing efficient xylose-fermenting strains.

Propionate is a crucial intermediate during methane fermentation. Investigating the effects of different kinds of inhibitors on the propionate-degrading microbial community is necessary to develop countermeasures for improving process stability. In the present study, under inhibitory conditions (acetate, propionate, sulfide, and ammonium addition), the dynamic changes of the propionate-degrading microbial community from a mesophilic chemostat fed with propionate as the sole carbon source were investigated using high-throughput sequencing of 16S rRNA. Sulfide and/or ammonia inhibited specific species in the microbial community. Compared with Syntrophobacter, Smithella was more resistant to inhibition by sulfide and/or ammonia. However, Syntrophobacter demonstrated greater tolerance than Smithella under acid inhibition conditions. Some genera that had close phylogenetic relationships and similar functions showed similar responses to different inhibitors.

A combined biological (augmented membrane bioreactor (MBR)) and photochemical (photocatalysis and ozonation) treatment has been proposed for bromoamine acid (BAA) removal in dyeing wastewater. It was demonstrated that the color and chemical oxygen demand removal in the sequential augmented MBR was about 90% and 50%, respectively. By ribosomal intergenic spacer analysis, it was found that the introduced strain QYY was maintained as the predominant species and the diversity of the system was relatively low throughout the operation. Photocatalysis and ozonation processes were efficient to treat the effluents from MBR with high color and total organic carbon removal more than 90% within 120 min. Therefore, the hybrid treatment system is a possible way to achieve the complete mineralization of BAA.

A salt-tolerant bacterium was isolated from the surface soil of a pharmaceutical factory, which could efficiently decolorize azo dyes. The strain was identified as Exiguobacterium sp. according to its morphological characteristics and 16S rRNA gene sequence analysis. Decolorization of X-3B with resting cells of this strain, which were catalyzed by redox mediator (anthraquinone), was studied, and the conditions were optimized. For color removal and cells growth, the optimal inoculation amount, pH, temperature, salinity, and metal ions were 6% (v/v), 5.4-7.0, 30-40 degrees C, 15% (w/v) NaCl, and 1 mmol L(-1) Mg(2+) or Ca(2+), respectively. It was exhibited that decolorization process proceeded primarily by enzymatic reduction associated with a minor portion of bio-adsorption to inactivated microbial cells. Anthraquinone could really accelerate the decolorization of X-3B under the optimal conditions.