Coexistence of microaerophilic Fe(II)-oxidizers and anaerobic Fe(III)-reducers in environments with fluctuating redox conditions is a prime example of mutualism, in which both partners benefit from the sustained Fe-pool. Consequently, the Fe-cycling machineries (i.e., metal-reducing or –oxidizing pathways) should be most affected during co-cultivation. However, contrasting growth requirements impeded systematic elucidation of their interactions. To disentangle underlying interaction mechanisms, we established a suboxic co-culture system of Sideroxydans sp. CL21 and Shewanella oneidensis. We showed that addition of the partner’s cell-free supernatant enhanced both growth and Fe(II)-oxidizing or Fe(III)-reducing activity of each partner. Metabolites of the exometabolome of Sideroxydans sp. CL21 are generally upregulated if stimulated with the partner´s spent medium, while S. oneidensis exhibits a mixed metabolic response in accordance with a balanced response to the partner. Surprisingly, RNA-seq analysis revealed genes involved in Fe-cycling were not differentially expressed during co-cultivation. Instead, the most differentially upregulated genes included those encoding for biopolymer production, lipoprotein transport, putrescine biosynthesis, and amino acid degradation suggesting a regulated inter-species biofilm formation. Furthermore, the upregulation of hydrogenases in Sideroxydans sp. CL21 points to competition for H₂ as electron donor. Our findings reveal that a complex metabolic and transcriptomic response, but not accelerated formation of Fe-end products, drive interactions of Fe-cycling microorganisms.

微生氧Fe（II）-氧化剂和厌氧Fe（III）-还原剂在氧化还原条件变化的环境中并存是互惠的主要例子，双方都受益于持续的铁池。因此，在联合培养期间，铁循环设备（即金属还原或氧化途径）应受到最大影响。但是，不同的增长要求阻碍了系统性地阐明它们之间的相互作用。为了弄清潜在的相互作用机制，我们建立了Sideroxydans sp。的亚氧共培养系统。CL21和希瓦氏菌。我们显示，添加伴侣的无细胞上清液可增强每个伴侣的生长和Fe（II）氧化或Fe（III）还原活性。代谢的代谢Sideroxydans sp。如果用伴侣的用过的培养基刺激，CL21通常会被上调，而沙门氏菌根据对伴侣的平衡反应表现出混合的代谢反应。出乎意料的是，RNA-seq分析显示，在共培养过程中，参与铁循环的基因没有差异表达。取而代之的是，差异最大的上调基因包括编码生物聚合物生产，脂蛋白转运，腐胺生物合成和氨基酸降解的基因，表明物种间生物膜形成受到调节。此外，Sideroxydans sp中的加氢酶的上调。CL21指出了对H _2的竞争作为电子供体。我们的发现表明，复杂的代谢和转录组反应（但未加速铁最终产物的形成）驱动铁循环微生物的相互作用。