Functional analysis of thioredoxin from the desert lichen-forming fungus, Endocarpon pusillum Hedwig, reveals its role in stress tolerance

Mixed and membrane-separated culturing of synthetic cyanobacteria-yeast consortia reveals metabolic cross-talk mimicking natural cyanolichens

Metabolite exchange mediates crucial interactions in microbial communities, significantly impacting global carbon and nitrogen cycling. Understanding these chemically-mediated interactions is essential for elucidating natural community functions and developing engineered synthetic communities. This study investigated membrane-separated bioreactors (mBRs) as a novel tool to identify transient metabolites and their producers/consumers in mixed microbial communities. We compared three co-culture methods (direct mixed, 2-chamber mBR, and 3-chamber mBR) to grow a synthetic binary community of the cyanobacterium Synechococcus elongatus PCC 7942 and the fungus Rhodotorula toruloides NBRC 0880, as well as axenic S. elongatus. Despite not being natural lichen constituents, these organisms exhibited interactions resembling those in cyanolichens. S. elongatus fixed CO2 into sugars as the primary shared metabolite, while R. toruloides secreted various biochemicals, predominantly sugar alcohols, mirroring the metabolite exchange observed in natural lichens. The mBR systems successfully captured metabolite gradients and revealed rapidly consumed compounds, including TCA cycle intermediates and amino acids. Our approach demonstrated that the 2-chamber mBR optimally balanced metabolite exchange and growth dynamics. This study provides insights into cross-species metabolic interactions and presents a valuable tool for investigating and engineering synthetic microbial communities with potential applications in biotechnology and environmental science.

Synergistic effect of thioredoxin and its reductase from Kluyveromyces marxianus on enhanced tolerance to multiple lignocellulose-derived inhibitors

BACKGROUND

Multiple lignocellulose-derived inhibitors represent great challenges for bioethanol production from lignocellulosic materials. These inhibitors that are related to the levels of intracellular reactive oxidative species (ROS) make oxidoreductases a potential target for an enhanced tolerance in yeasts.

RESULTS

In this study, the thioredoxin and its reductase from Kluyveromyces marxianus Y179 was identified, which was subsequently achieved over-expression in Saccharomyces cerevisiae 280. In spite of the negative effects by expression of thioredoxin gene (KmTRX), the thioredoxin reductase (KmTrxR) helped to enhance tolerance to multiple lignocellulose-derived inhibitors, such as formic acid and acetic acid. In particular, compared with each gene expression, the double over-expression of KmTRX2 and KmTrxR achieved a better ethanol fermentative profiles under a mixture of formic acid, acetic acid, and furfural (FAF) with a shorter lag period. At last, the mechanism that improves the tolerance depended on a normal level of intracellular ROS for cell survival under stress.

CONCLUSIONS

The synergistic effect of KmTrxR and KmTRX2 provided the potential possibility for ethanol production from lignocellulosic materials, and give a general insight into the possible toxicity mechanisms for further theoretical research.

Two new species of Endocarpon (Verrucariaceae, Ascomycota) from China

Endocarpon species are key components of biological soil crusts. Phenotypic and systematic molecular analyses were carried out to identify samples of Endocarpon collected from the southeast edge of the Tengger Desert in China. These morphological and molecular analyses revealed two previously undescribed species that form highly supported independent monophyletic clades within Endocarpon. The new taxa were named Endocarpon deserticola sp. nov. and E. unifoliatum sp. nov. Furthermore, our results indicated that the newly developed protein coding markers adenylate kinase (ADK) and ubiquitin-conjugating enzyme h (UCEH) are useful for assessing species boundaries in phylogenic analyses.

Enhanced fermentative performance under stresses of multiple lignocellulose-derived inhibitors by overexpression of a typical 2-Cys peroxiredoxin from Kluyveromyces marxianus

BACKGROUND

Bioethanol from lignocellulosic materials is of great significance to the production of renewable fuels due to its wide sources. However, multiple inhibitors generated from pretreatments represent great challenges for its industrial-scale fermentation. Despite the complex toxicity mechanisms, lignocellulose-derived inhibitors have been reported to be related to the levels of intracellular reactive oxygen species (ROS), which makes oxidoreductase a potential target for the enhancement of the tolerance of yeasts to these inhibitors.

RESULTS

A typical 2-Cys peroxiredoxin from Kluyveromyces marxianus Y179 (KmTPX1) was identified, and its overexpression was achieved in Saccharomyces cerevisiae 280. Strain TPX1 with overexpressed KmTPX1 gene showed an enhanced tolerance to oxidative stresses. Serial dilution assay indicated that KmTPX1 gene contributed to a better cellular growth behavior, when the cells were exposed to multiple lignocellulose-derived inhibitors, such as formic acid, acetic acid, furfural, ethanol, and salt. In particular, KmTPX1 expression also possessed enhanced tolerance to a mixture of formic acid, acetic acid, and furfural (FAF) with a shorter lag period. The maximum glucose consumption rate and ethanol generation rate in KmTPX1-expressing strain were significantly improved, compared with the control. The mechanism of improved tolerance to FAF depends on the lower level of intracellular ROS for cell survival under stress.

CONCLUSION

A new functional gene KmTPX1 from K. marxianus is firstly associated with the enhanced tolerance to multiple lignocellulose-derived inhibitors in S. cerevisiae. We provided a possible detoxification mechanism of the KmTPX1 for further theoretical research; meanwhile, we provided a powerful potential for application of the KmTPX1 overexpressing strain in ethanol production from lignocellulosic materials.

Transcriptional Responses in Root and Leaf of Prunus persica under Drought Stress Using RNA Sequencing

Prunus persica L. Batsch, or peach, is one of the most important crops and it is widely established in irrigated arid and semi-arid regions. However, due to variations in the climate and the increased aridity, drought has become a major constraint, causing crop losses worldwide. The use of drought-tolerant rootstocks in modern fruit production appears to be a useful method of alleviating water deficit problems. However, the transcriptomic variation and the major molecular mechanisms that underlie the adaptation of drought-tolerant rootstocks to water shortage remain unclear. Hence, in this study, high-throughput sequencing (RNA-seq) was performed to assess the transcriptomic changes and the key genes involved in the response to drought in root tissues (GF677 rootstock) and leaf tissues (graft, var. Catherina) subjected to 16 days of drought stress. In total, 12 RNA libraries were constructed and sequenced. This generated a total of 315 M raw reads from both tissues, which allowed the assembly of 22,079 and 17,854 genes associated with the root and leaf tissues, respectively. Subsets of 500 differentially expressed genes (DEGs) in roots and 236 in leaves were identified and functionally annotated with 56 gene ontology (GO) terms and 99 metabolic pathways, which were mostly associated with aminobenzoate degradation and phenylpropanoid biosynthesis. The GO analysis highlighted the biological functions that were exclusive to the root tissue, such as "locomotion," "hormone metabolic process," and "detection of stimulus," indicating the stress-buffering role of the GF677 rootstock. Furthermore, the complex regulatory network involved in the drought response was revealed, involving proteins that are associated with signaling transduction, transcription and hormone regulation, redox homeostasis, and frontline barriers. We identified two poorly characterized genes in P. persica: growth-regulating factor 5 (GRF5), which may be involved in cellular expansion, and AtHB12, which may be involved in root elongation. The reliability of the RNA-seq experiment was validated by analyzing the expression patterns of 34 DEGs potentially involved in drought tolerance using quantitative reverse transcription polymerase chain reaction. The transcriptomic resources generated in this study provide a broad characterization of the acclimation of P. persica to drought, shedding light on the major molecular responses to the most important environmental stressor.