Iron is an essential nutrient for all microorganisms in the marine environment. Iron limitation of primary production has been well documented across a significant portion of the global surface ocean, but much less is known regarding the potential for iron limitation of the marine heterotrophic microbial community. In this work, we characterize the transcriptomic response of the heterotrophic bacterial community to iron additions in the California Current System, an eastern boundary upwelling system, to detect in situ iron stress of heterotrophic bacteria. Changes in gene expression in response to iron availability by heterotrophic bacteria were detected under conditions of high productivity when carbon limitation was relieved but when iron availability remained low. The ratio of particulate organic carbon to dissolved iron emerged as a biogeochemical proxy for iron limitation of heterotrophic bacteria in this system. Iron stress was characterized by high expression levels of iron transport pathways and decreased expression of iron-containing enzymes involved in carbon metabolism, where a majority of the heterotrophic bacterial iron requirement resides. Expression of iron stress biomarkers, as identified in the iron-addition experiments, was also detected in situ. These results suggest iron availability will impact the processing of organic matter by heterotrophic bacteria with potential consequences for the marine biological carbon pump.

中文翻译：

---

加州当前系统中异养细菌的铁限制追踪有机碳和铁的相对可用性

铁是海洋环境中所有微生物的必需营养素。在全球表层海洋的很大一部分地区，初级生产的铁限制已得到充分记录，但对于海洋异养微生物群落的铁限制潜力却知之甚少。在这项工作中，我们描述了加州海流系统（东部边界上升流系统）中异养细菌群落对铁添加的转录组反应，以检测异养细菌的原位铁胁迫。当碳限制解除但铁可用性仍然较低时，在高生产力条件下检测到异养细菌响应铁可用性的基因表达变化。颗粒有机碳与溶解铁的比率成为该系统中异养细菌铁限制的生物地球化学指标。铁胁迫的特点是铁转运途径的高表达水平和参与碳代谢的含铁酶的表达减少，而碳代谢是异养细菌铁需求的大部分所在。还原位检测了在添加铁实验中鉴定的铁应激生物标志物的表达。这些结果表明铁的可用性将影响异养细菌对有机物的处理，并对海洋生物碳泵产生潜在影响。