Exploiting the symbiotic interaction between crops and nitrogen-fixing bacteria is a simple and ecological method to promote plant growth in prospective extraterrestrial human outposts. In this study, we performed an RNA-seq analysis to investigate the adaptation of the legume symbiont Paraburkholderia phymatum STM815^T to simulated microgravity (s0-g) at the transcriptome level. The results revealed a drastic effect on gene expression, with roughly 23% of P. phymatum genes being differentially regulated in s0-g. Among those, 951 genes were upregulated and 858 downregulated in the cells grown in s0-g compared to terrestrial gravity (1 g). Several genes involved in posttranslational modification, protein turnover or chaperones encoding were upregulated in s0-g, while those involved in translation, ribosomal structure and biosynthesis, motility or inorganic ions transport were downregulated. Specifically, the whole phm gene cluster, previously bioinformatically predicted to be involved in the production of a hypothetical malleobactin-like siderophore, phymabactin, was 20-fold downregulated in microgravity. By constructing a mutant strain (ΔphmJK) we confirmed that the phm gene cluster codes for the only siderophore secreted by P. phymatum as assessed by the complete lack of iron chelating activity of the P. phymatum ΔphmJK mutant on chrome azurol S (CAS) agar plates. These results not only provide a deeper understanding of the physiology of symbiotic organisms exposed to space-like conditions, but also increase our knowledge of iron acquisition mechanisms in rhizobia.

利用农作物和固氮细菌之间的共生相互作用是一种简单且生态的方法，可以促进未来的外星人类前哨基地的植物生长。在本研究中，我们进行了 RNA-seq 分析，以研究豆科植物共生体Paraburkholderia phymatum STM815 ^T在转录组水平上对模拟微重力 (s0-g)的适应。结果揭示了对基因表达的巨大影响，大约 23% 的P. phymatum基因在 s0-g 中受到差异调节。其中，与地球重力（1 g）相比，在 s0-g 中生长的细胞中有 951 个基因上调，858 个基因下调。 s0-g 中涉及翻译后修饰、蛋白质周转或分子伴侣编码的几个基因上调，而涉及翻译、核糖体结构和生物合成、运动或无机离子运输的基因下调。具体来说，之前生物信息学预测整个phm基因簇参与假想的 Malleobactin 样铁载体 phymabactin 的产生，但在微重力下下调了 20 倍。通过构建突变菌株 (Δ phmJK )，我们确认phm基因簇编码由P. phymatum分泌的唯一铁载体，通过P. phymatum Δ phmJK突变体对铬天青 S (CAS ）琼脂平板。这些结果不仅让我们更深入地了解暴露于类太空条件下的共生生物的生理学，而且还增加了我们对根瘤菌铁获取机制的了解。