A cDNA library generated from seeds of Cassia obtusifolia was sequenced using Illumina/Solexa platform. More than 12,968,231 high quality reads were generated, and have been deposited in NCBI SRA (SRR 1012912). A total of 40,102 unigenes (>200 bp) were obtained with an average sequence length of 681 bp by de novo assembly. About 34,089 (85%) unique sequences were annotated and 8694 of the unique sequences were assigned to specific metabolic pathways by the Kyoto Encyclopedia of Genes and Genomes. Among them, 131 unigenes, which are involved in the biosynthesis and (or) regulation of anthraquinone, carotenoid, flavonoid, and lipid, the 4 best known active metabolites, were identified from cDNA library. In addition, three lipid transfer proteins were obtained, which may contribute to the lipid molecules transporting between biological membranes. Meanwhile, 30 cytochrome P450, 12 SAM-dependent methyltransferases, and 12 UDP-glucosyltransferase unigenes were identified, which could also be responsible for the biosynthesis of active metabolites.
Microbial consortia consisting of cooperational strains exhibit biodegradation performance superior to that of single microbial strains and improved remediation efficiency by relieving the environmental stress. Tetrahydrofuran (THF), a universal solvent widely used in chemical and pharmaceutical synthesis, significantly affects the environment. As a refractory pollutant, THF can be degraded by some microbial strains under suitable conditions. There are often a variety of stresses, especially pH stress, that inhibit the THF-degradation efficiency of microbial consortia. Therefore, it is necessary to study the molecular mechanisms of microbial cooperational degradation of THF. In this study, under conditions of low pH (initial pH = 7.0) stress, a synergistic promotion of the THF degradation capability of the strain Rhodococcus ruber YYL was found in the presence of a non-THF degrading strain Bacillus cereus MLY1. Metatranscriptome analysis revealed that the low pH stress induced the strain YYL to up-regulate the genes involved in anti-oxidation, mutation, steroid and bile acid metabolism, and translation, while simultaneously down-regulating the genes involved in ATP production. In the co-culture system, strain MLY1 provides fatty acids, ATP, and amino acids for strain YYL in response to low pH stress during THF degradation. In return, YYL shares the metabolic intermediates of THF with MLY1 as carbon sources. This study provides the preliminary mechanism to understand how microbial consortia improve the degradation efficiency of refractory furan pollutants under environmental stress conditions.
Cassia obtusifolia, belonging to legume family, is important in many fields with high pharmaceutical, economic, and ecological values. These interests of C. obtusifolia triggered in-depth and fundamental genetic and molecular research. Therefore, the stable reference gene is necessary for normalization of the gene expression studies. In this study, 10 candidate reference genes were subjected to expression analysis in 12 different tissues and under different stresses by qRT-PCR. The expression stability was evaluated using geNorm, NormFinder, and BestKeeper software. In conclusion, different suitable reference genes were selected in different tissues and under different stress. CYP1, EF1α2, ACT2, UBQ1 were the most stable reference genes in all samples. The relative expression levels of WRKY gene were detected to confirm the reliability of the selected reference genes. These results provided suitable reference genes that could be used for normalization in C. obtusifolia tissues and under different stress.
Bacterial consortia are among the most basic units in the biodegradation of environmental pollutants. Pollutant-degrading strains frequently encounter different types of environmental stresses and must be able to survive with other bacteria present in the polluted environments. In this study, we proposed a noncontact interaction mode between a tetrahydrofuran (THF)-degrading strain, Rhodococcus ruber YYL, and a non-THF-degrading strain, Bacillus cereus MLY1. The metabolic interaction mechanism between strains YYL and MLY1 was explored through physiological and molecular studies and was further supported by the metabolic response profile of strain YYL, both monocultured and cocultured with strain MLY1 at the optimal pH (pH 8.3) and under pH stress (pH 7.0), through a liquid chromatography-mass spectrometry-based metabolomic analysis. The results suggested that the coculture system resists pH stress in three ways: (i) strain MLY1 utilized acid metabolites and impacted the proportion of glutamine, resulting in an elevated intracellular pH of the system; (ii) strain MLY1 had the ability to degrade intermediates, thus alleviating the product inhibition of strain YYL; and (iii) strain MLY1 produced some essential micronutrients for strain YYL to aid the growth of this strain under pH stress, while strain YYL produced THF degradation intermediates for strain MLY1 as major nutrients. In addition, a metabolite cross-feeding interaction with respect to pollutant biodegradation is discussed. IMPORTANCE Rhodococcus species have been discovered in diverse environmental niches and can degrade numerous recalcitrant toxic pollutants. However, the pollutant degradation efficiency of these strains is severely reduced due to the complexity of environmental conditions and limitations in the growth of the pollutant-degrading microorganism. In our study, Bacillus cereus strain MLY1 exhibited strong stress resistance to adapt to various environments and improved the THF degradation efficiency of Rhodococcus ruber YYL by a metabolic cross-feeding interaction style to relieve the pH stress. These findings suggest that metabolite cross-feeding occurred in a complementary manner, allowing a pollutant-degrading strain to collaborate with a nondegrading strain in the biodegradation of various recalcitrant compounds. The study of metabolic exchanges is crucial to elucidate mechanisms by which degrading and symbiotic bacteria interact to survive environmental stress.
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