The interaction between peat moss and cyanobacteria plays an important role in the terrestrial carbon and nitrogen cycle. Understanding the metabolites exchanged, the associated physiological processes, and the environmental conditions under which symbioses develop is important to better understand the mechanisms behind these interactions. In April 2022, Alyssa A. Carrell and other teams from the Oak Ridge National Laboratory in the United States published an article titled "Novel metabolic interactions and environmental conditions mediate the boreal peatmoss-cyanobacteria mutualism " in the ISME Journal (IF 11.217). This paper uses a cross-feeding approach to characterize the symbiotic relationship between Sphagnum moss (Sphagnum) and Nostoc cyanobacteria (Nostoc cyanobacteria) through spatial metabolomics, untargeted metabolomics, and macro-transcriptomics , elucidating the widespread existence The environmental, metabolic and physiological basis of the plant-cyanobacterial symbiosis has important implications for predicting the basis of carbon and nitrogen cycling in peatland ecosystems and general host-microbe interactions.
Research materials
cells, culture medium
technical route
Step 1: Effects of different pH conditions on the symbiotic relationship between Sphagnum- Nodida ;
Step 2: Metabolic cross-feeding study;
Step 3: Spatial metabolomics study;
Step 4: Metatranscriptomic study.
Research results
1. Effects of different pH conditions on the symbiotic relationship between Sphagnum moss and Nodida
The author selected a strain with symbiotic ability from various strains of the genus N. UTEX 1037 for follow-up research, in Sterile S. angustifolium and N. muscorum UTEX 1037 were cultured at pH 3.5, 5.5 and 8.5. Symbiosis outcomes were assessed by comparing the growth of the S. It was found that in low pH (3.5) environments, symbiosis has clear benefits: when species grow together under these conditions, the change in weight is greater than the sum of individual growth. However, no growth benefit was clearly observed when had a pH of of 5.5 or 8.5 (Figure 1).
Figure 1 Analysis of dry weight growth of Sphagnum moss and Nodida under different pH conditionsFigure 1 Analysis of dry weight growth of Sphagnum moss and Nodida under different pH conditions
2. Metabolic cross-feeding study
Observed under low pH conditions The growth benefits of S. We therefore assessed metabolites released by each partner of the symbiont when grown in fresh liquid medium, as well as changes in the abundance of exometabolites released in spent medium when cross-fed to other partners.The results showed that 225 exometabolites were identified from the spent culture medium of a single partner, among which N. muscorum UTEX 1037 consumed 53% of the S. Consumed N. muscorum UTEX 28% of 1037 exometabolites (Figure 2).
Figure 2 Experimental design and methods
In order to further characterize the metabolite exchange, the exometabolites with significant (p 0.05) changes in abundance before and after feeding were divided into amino acids, carbohydrates , fatty acids and their conjugates, lipids, Nucleotides and nucleosides and six categories of organic acids, N. muscorum UTEX 1037 consumes S. angustifolium exometabolites with a larger percentage of each chemical class, such as 75% of amino acids and 77% of carbohydrates. compounds, 50% fatty acids, etc. S. angustifolium consumed 30% of the amino acids, 54% of the carbohydrates, and 76% of the nucleosides in the UTEX 1037 exometabolites of N. muscorum (Fig. 3).
Figure 3 Distribution display of companion metabolites consumed by Sphagnum moss and Nodida
3. Spatial metabolomics study
The authors further investigated the results of the cross-feeding study using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). It was found that N. muscorum UTEX 1037 and S. angustifolium produced small amounts of xanthine nucleosides when grown alone. However, when grown close to each other, N. muscorum UTEX 1037 increased xanthine nucleoside production, while S. angustifolium did not. Cross-feeding experiments showed that S. 3S. xanthine nucleosides provided by angustifolium. Similar results were observed for adenine . MALDI-MSI imaging found that N. muscorum UTEX 1037 was present, and S. angustifolium produced choline sulfate. Cross-feeding results showed that 98% of the choline sulfate provided by S. gustifolium was consumed by N. muscorum UTEX 1037 (Fig. 4).
Figure 4 Cross-feeding and MALDI-MSI results of sulfated choline, xanthine and adenine
Figure 5 Cross-feeding and MALDI-MSI results of trehalose exchange
4. Metatranscriptomic study
N. UTEX 1037 Transcription The group results showed that except for glutamine synthetase, genes related to N2 fixation showed a downward trend. The expression of N. muscorum UTEX 1037 gene involved in photosynthesis in photosystems I and II was generally reduced when supplemented with S. The expression of photosystem I genes is increasing trend. Enrichment analysis identified genes involved in S. angustifolium host defense as downregulated when the host was cocultured with N. muscorum UTEX 1037.In addition, when S. angustifolium was fed N. muscorum UTEX 1037 exometabolite, the expression of the plant defense-related gene phenylalanine ammonia lyase was induced, but when co-cultured, the expression of the gene was not changed (Fig. 6, Figure 7).
Figure 6 Study on the gene expression profile of Sphagnum moss co-cultured with Sphagnum moss or the external metabolites it produces
Figure 7 Research on the gene expression profile of Sphagnum moss co-cultured with Sphagnum moss or its external metabolites produced
Editor's summary
Summary As mentioned above, the Sphagnum-Nodida symbiosis is driven by pH value, and the symbiotic relationship only occurs at low pH values. Metabolic cross-feeding studies as well as mass spectrometry imaging analysis identified trehalose as the main carbohydrate source released by Sphagnum moss, which is consumed by Nodida along with taurine, and sulfoacetic acid. In exchange, Nodida increases the secretion of purine and amino acids. Metatranscriptomic analysis showed that host defenses in Sphagnum moss were downregulated when in symbiosis with Nodida and not simply as a result of chemical exposure (Fig. 8).
Figure 8 Conceptual model of Sphagnum-Nostida symbiosis based on MALDI-MSI, cross-feeding and metatranscriptomic analysis
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