Project description:Propionate is an abundant carboxylic acid in nature. Microorganisms metabolize propionate aerobically via the 2-methylcitrate pathway. This pathway depends on a series of three reactions in the citric acid cycle that leads to the conversion of succinate to oxaloacetate. Interestingly, the gamma-proteobacterium Escherichia coli can use propionate as a carbon and electron source under oxic but not under anoxic conditions. The typical downregulation of the citric acid cycle under anoxic conditions is only partially responsible for the inability to use propionate under anoxic conditions since an arcA mutant shows very limited growth on propionate. RT-PCR and transcriptomic analysis revealed a post-transcriptional regulation of the prp-genecluster encoding the necessary enzymes for propionate metabolism. The polycistronic mRNA was hydrolyzed in the 3`-5` direction under anoxic conditions. This regulatory strategy is highly constructive because the last gene of the operon encodes the first enzyme of the propionate metabolism. Further analysis revealed that RNase R catalyzes the hydrolysis of the prp transcripts. Consequently, an rnr-deletion strain could metabolize propionate under anoxic conditions. To the best of our knowledge, this is the first study describing the influence of RNase R on the anaerobic metabolism of E. coli.
Project description:Polyethylene terephthalate (PET) biodegradation is regarded as an environmentally friendly degradation method. In this study, an artificial microbial consortium composed of Rhodococcus jostii, Pseudomonas putida and two metabolically engineered Bacillus subtilis was constructed to degrade PET. First, a two-species microbial consortium was constructed with two engineered B. subtilis that could secrete PET hydrolase (PETase) and monohydroxyethyl terephthalate hydrolase (MHETase), respectively; it could degrade 13.6% (weight loss) of the PET film within 7 days. A three-species microbial consortium was further obtained by adding R. jostii to reduce the inhibition caused by terephthalic acid (TPA), a breakdown product of PET. The weight of PET film was reduced by 31.2% within 3 days, achieving about 17.6% improvement compared with the two-species microbial consortium. Finally, P. putida was introduced to reduce the inhibition caused by ethylene glycol (EG), another breakdown product of PET, obtaining a four-species microbial consortium. With the four-species consortium, the weight loss of PET film reached 23.2% under ambient temperature. This study constructed and evaluated the artificial microbial consortia in PET degradation, which demonstrated the great potential of artificial microbial consortia in the utilization of complex substrates, providing new insights for biodegradation of complex polymers.
Project description:Granular activated carbon (GAC) could promote methane production from organic wastes, but a wide range of dosages has been reported. In present study, different GAC dosages of 0, 0.5, 5 and 25?g/L were supplemented into anaerobic digesters and the methanogenic degradation kinetics of acetate, propionate and butyrate were characterized, respectively. At high organic load of 5?g/L, the degradation rates of propionate and butyrate increased by 1.5-4.7 and 2.5-7.0 times at varied GAC dosages. The methane production rates (Rmax) from propionate and butyrate were significantly elevated when increasing GAC dosage up to 5?g/L. However, only a minor increment was found for acetate degradation either at 1?g/L or 5?g/L. The stimulatory mechanism of GAC for accelerated syntrophic degradation of propionate and butyrate can be primarily attributed to the triggering effect on acetogenesis, as evidenced by the enrichment of syntrophic bacteria e.g. Thermovirga, Synergistaceae, and Syntrophomonas etc.
Project description:Purpose: To understand the adaptive mechanisms of Methanocellales to low H2 and syntrophic growth. Methods: We analyzed the transcriptomes of M. conradii and P. thermopropionicum under monoculture and syntrophic coculture conditions by strand specific mRNA sequencing using Illumina Hiseq 2000. Four biological replicates were sequenced. The sequence reads that passed quality filters were analyzed by Burrows–Wheeler Aligner (BWA) followed by HTSeq and DESeq2. qRT–PCR validation was performed using SYBR Green assays Results: The results showed that M. conradii and P. thermopropionicum interacted closely and synchronized their gene transcription during the syntrophic growth. In coculture, M. conradii and P. thermopropionicum significantly enhanced the transcription of genes related to energy conservation processes, including methanogenesis, propionate degradation and electron bifurcation. By contrast, the genes coding for biosynthesis steps were downregulated in both M. conradii and P. thermopropionicum during the syntrophic growth. The physiology experiment showed that formate but not H2 inhibited syntrophic oxidation of propionate. Accordingly, formate dehydrogenase-encoding genes in both M. conradii and P. thermopropionicum were markedly upregulated, indicating that formate plays an important role in the interspecies electron transfer between M. conradii and P. thermopropionicum in coculture. Conclusions: our study provides abundant transcriptome data indicating the adaptations of Methanocella spp. to H2 limitation and suggests that flavin based electron bifurcations are critical to the syntrophic growth in both M. conradii and P. thermopropionicum.