Zecher Karsten, Hayes Kristiane Rebecca, Philipp Bodo
Institute for Molecular Microbiology and Biotechnology, University of Münster, Münster, Germany.
Front Microbiol. 2020 Oct 6;11:533894. doi: 10.3389/fmicb.2020.533894. eCollection 2020.
Dissolved organic nitrogen (DON) compounds such as methylamines (MAs) and glycine betaine (GBT) occur at detectable concentrations in marine habitats and are also produced and released by microalgae. For many marine bacteria, these DON compounds can serve as carbon, energy, and nitrogen sources, but microalgae usually cannot metabolize them. Interestingly though, it was previously shown that sp. strain KarMa-a member of the marine -can cross-feed ammonium such that the ammonium it produces upon degrading monomethylamine (MMA) then serves as nitrogen source for the diatom ; thus, these organisms form a mutual metabolic interaction under photoautotrophic conditions. In the present study, we investigated whether this interaction plays a broader role in bacteria-diatom interactions in general. Results showed that cross-feeding between strain KarMa and was also possible with di- and trimethylamine as well as with GBT. Further, cross-feeding of strain KarMa was also observed in cocultures with the diatoms and with MMA as the sole nitrogen source. Regarding cross-feeding involving other strains, the analysis of MA and GBT degradation pathways indicated that algae-associated -type strains likely interact with in a similar manner as the strain KarMa does. For these types of strains (such as , , , , and ), ammonium cross-feeding after methylamine degradation showed species-specific patterns, whereas bacterial GBT degradation always led to diatom growth. Overall, the degradation of DON compounds by the family and the subsequent cross-feeding of ammonium may represent a widespread, organism-specific, and regulated metabolic interaction for establishing and stabilizing associations with photoautotrophic diatoms in the oceans.
溶解有机氮（DON）化合物，如甲胺（MAs）和甘氨酸甜菜碱（GBT），在海洋生境中以可检测的浓度存在，并且也是由微藻产生和释放的。对于许多海洋细菌来说，这些DON化合物可以作为碳、能量和氮源，但微藻通常不能代谢它们。然而，有趣的是，先前的研究表明，海洋中的 sp. 菌株KarMa能够交叉供应铵，使得它在降解一甲胺（MMA）时产生的铵随后作为硅藻的氮源；因此，这些生物体在光合自养条件下形成了一种相互的代谢相互作用。在本研究中，我们调查了这种相互作用是否在细菌 - 硅藻相互作用中普遍发挥更广泛的作用。结果表明，KarMa菌株与 之间也可以以二甲胺和三甲胺以及GBT进行交叉供应。此外，在以MMA作为唯一氮源与硅藻 和 的共培养物中也观察到了KarMa菌株的交叉供应。关于涉及其他 菌株的交叉供应，对MA和GBT降解途径的分析表明，与藻类相关的 型菌株可能与 的相互作用方式与KarMa菌株类似。对于这些类型的菌株（如 、 、 、 和 ），甲胺降解后的铵交叉供应呈现出物种特异性模式，而细菌对GBT的降解总是导致硅藻生长。总体而言， 家族对DON化合物的降解以及随后的铵交叉供应可能代表了一种广泛存在的、生物体特异性的和受调控的代谢相互作用，用于在海洋中与光合自养硅藻建立和稳定共生关系。
