Smith Jessica A, Holmes Dawn E, Woodard Trevor L, Li Yang, Liu Xinying, Wang Li-Ying, Meier David, Schwarz Ingrid A, Lovley Derek R
Department of Microbiology, University of Massachusetts Amherst, Morrill IV N Science Center , Amherst, Massachusetts, USA.
Department of Biomolecular Sciences, Central Connecticut State University , New Britain, Connecticut, USA.
Microbiol Spectr. 2023 Aug 31;11(5):e0094123. doi: 10.1128/spectrum.00941-23.
Direct interspecies electron transfer (DIET) is important in anaerobic communities of environmental and practical significance. Other than the need for close physical contact for electrical connections, the interactions of DIET partners are poorly understood. Type VI secretion systems (T6SSs) typically kill competitive microbes. Surprisingly, highly expressed T6SS genes when DIET-based co-cultures were initiated with . T6SS gene expression was lower when the electron shuttle anthraquinone-2,6-disulfonate was added to alleviate the need for interspecies contact. Disruption of , the gene for the main T6SS needle-tube protein subunit, and the most highly upregulated gene in DIET-grown cells eliminated the long lag periods required for the initiation of DIET. The mutation did not aid DIET in the presence of granular-activated carbon (GAC), consistent with the fact that DIET partners do not make physical contact when electrically connected through conductive materials. The -deficient mutant also established DIET quicker with . However, the mutant also reduced Fe(III) oxide faster than the wild-type strain, a phenotype not expected from the loss of the T6SS. Quantitative PCR revealed greater gene transcript abundance for key components of extracellular electron transfer in the -deficient mutant versus the wild-type strain, potentially accounting for the faster Fe(III) oxide reduction and impact on DIET. The results highlight that interspecies interactions beyond electrical connections may influence DIET effectiveness. The unexpected increase in the expression of genes for extracellular electron transport components when was deleted emphasizes the complexities in evaluating the electromicrobiology of highly adaptable species. IMPORTANCE Direct interspecies electron transfer is an alternative to the much more intensively studied process of interspecies H transfer as a mechanism for microbes to share electrons during the cooperative metabolism of energy sources. DIET is an important process in anaerobic soils and sediments generating methane, a significant greenhouse gas. Facilitating DIET can accelerate and stabilize the conversion of organic wastes to methane biofuel in anaerobic digesters. Therefore, a better understanding of the factors controlling how fast DIET partnerships are established is expected to lead to new strategies for promoting this bioenergy process. The finding that when co-cultured with initially expressed a type VI secretion system, a behavior not conducive to interspecies cooperation, illustrates the complexity of establishing syntrophic relationships.
直接种间电子转移（DIET）在具有环境和实际意义的厌氧群落中很重要。除了需要紧密的物理接触来建立电连接外，DIET伙伴之间的相互作用还知之甚少。VI型分泌系统（T6SSs）通常会杀死竞争性微生物。令人惊讶的是，当基于DIET的共培养物开始时，T6SS基因高度表达。当添加电子穿梭体蒽醌-2,6-二磺酸盐以减少对种间接触的需求时，T6SS基因表达降低。主要T6SS针管蛋白亚基的基因以及DIET生长细胞中上调程度最高的基因的缺失消除了DIET启动所需的长时间延迟期。在存在颗粒活性炭（GAC）的情况下，该突变对DIET没有帮助，这与DIET伙伴通过导电材料进行电连接时不进行物理接触的事实一致。缺乏该基因的突变体与另一种菌建立DIET的速度也更快。然而，该突变体还原氧化铁的速度也比野生型菌株快，这一表型并非T6SS缺失所预期的。定量PCR显示，与野生型菌株相比，缺乏该基因的突变体中细胞外电子转移关键成分的基因转录丰度更高，这可能是氧化铁还原更快以及对DIET产生影响的原因。结果表明，除电连接外的种间相互作用可能会影响DIET的效率。当该基因缺失时，细胞外电子传输成分基因表达意外增加，这凸显了评估高度适应性微生物的电微生物学的复杂性。重要性直接种间电子转移是一种替代研究更为深入的种间氢转移过程的机制，作为微生物在能源协同代谢过程中共享电子的一种方式。DIET是厌氧土壤和沉积物中产生甲烷（一种重要的温室气体）的重要过程。促进DIET可以加速并稳定厌氧消化池中有机废物向甲烷生物燃料的转化。因此，更好地理解控制DIET伙伴关系建立速度的因素有望带来促进这种生物能源过程的新策略。与另一种菌共培养时最初表达VI型分泌系统这一不利于种间合作的行为的发现，说明了建立互生关系的复杂性。
