National Food Institute, Technical University of Denmark, Kongens Lyngby, Denmark.
Department of Chemistry and Bioscience, Aalborg University, Aalborg, Denmark.
Microb Biotechnol. 2023 Jun;16(6):1277-1292. doi: 10.1111/1751-7915.14229. Epub 2023 Mar 1.
Lactococcus lactis, a lactic acid bacterium with a typical fermentative metabolism, can also use oxygen as an extracellular electron acceptor. Here we demonstrate, for the first time, that L. lactis blocked in NAD regeneration can use the alternative electron acceptor ferricyanide to support growth. By electrochemical analysis and characterization of strains carrying mutations in the respiratory chain, we pinpoint the essential role of the NADH dehydrogenase and 2-amino-3-carboxy-1,4-naphtoquinone in extracellular electron transfer (EET) and uncover the underlying pathway systematically. Ferricyanide respiration has unexpected effects on L. lactis, e.g., we find that morphology is altered from the normal coccoid to a more rod shaped appearance, and that acid resistance is increased. Using adaptive laboratory evolution (ALE), we successfully enhance the capacity for EET. Whole-genome sequencing reveals the underlying reason for the observed enhanced EET capacity to be a late-stage blocking of menaquinone biosynthesis. The perspectives of the study are numerous, especially within food fermentation and microbiome engineering, where EET can help relieve oxidative stress, promote growth of oxygen sensitive microorganisms and play critical roles in shaping microbial communities.
乳球菌是一种具有典型发酵代谢的乳酸菌，也可以将氧气作为细胞外电子受体。在这里，我们首次证明，NAD 再生受阻的乳球菌可以利用替代电子受体铁氰化物来支持生长。通过对呼吸链突变菌株的电化学分析和表征，我们确定了 NADH 脱氢酶和 2-氨基-3-羧基-1,4-萘醌在细胞外电子传递（EET）中的重要作用，并系统地揭示了潜在的途径。铁氰化物呼吸对乳球菌有意外的影响，例如，我们发现形态从正常的球菌变成了更棒状的外观，并且耐酸性增强。通过适应性实验室进化（ALE），我们成功地增强了 EET 的能力。全基因组测序揭示了观察到的增强的 EET 能力的潜在原因是甲萘醌生物合成的晚期阻断。该研究的视角很多，特别是在食品发酵和微生物组工程中，EET 可以帮助缓解氧化应激，促进对氧气敏感的微生物的生长，并在塑造微生物群落方面发挥关键作用。
