A novel deltaproteobacterial, mesophilic, hydrogen-oxidizing, and sulfate-reducing bacterium (strain KaireiS1) was highly enriched from an inactive chimney located in the active zone of the Kairei hydrothermal vent field (Central Indian Ridge) in the Indian Ocean. Based on 16S rRNA gene analyses, strain KaireiS1 is the currently only cultured representative of a cluster of uncultured Deltaproteobacteria, positioned within the Desulfobulbaceae family, between the Desulfobulbus genus and the “Cable Bacteria.” A facultative autotrophic lifestyle of KaireiS1 is indicated by its growth in the absence of organic compounds, measurements of CO₂-fixation rates, and activity measurements of carbon monoxide dehydrogenase, the key enzyme of the reductive Acetyl-CoA pathway. Apart from hydrogen, strain KaireiS1 can also use propionate, lactate, and pentadecane as electron donors. However, the highest cell numbers were reached when grown autotrophically with molecular hydrogen. Hydrogen uptake activity was found in membrane and soluble fractions of cell-free extracts and reached up to 2,981±129 nmol H₂*min⁻¹*mg⁻¹ of partially purified protein. Commonly, autotrophic sulfate-reducing bacteria from the Deltaproteobacteria class, thriving in hydrothermal vent habitats are described as thermophiles. Given its physiological characteristics and specific isolation source, strain KaireiS1 demonstrates a previously unnoticed potential for microbial sulfate reduction by autotrophs taking place at moderate temperatures in hydrothermal vent fields.

从位于印度洋 Kairei 热液喷口场（中印度洋脊）活动区的非活动烟囱中高度富集了一种新型的 deltaproteobacterial、嗜温性、氧化性和硫酸盐还原菌（KaireiS1 菌株）。根据 16S rRNA 基因分析，菌株 KaireiS1 是目前唯一培养的未培养 Deltaproteobacteria 群的代表，位于 Desulfobulbaceae 家族内，介于脱硫球属和“电缆细菌”。KaireiS1 的兼性自养生活方式通过其在没有有机化合物的情况下的生长、CO ₂固定率的测量以及一氧化碳脱氢酶（还原乙酰辅酶 A 途径的关键酶）的活性测量来表明。除了氢之外，KaireiS1 菌株还可以使用丙酸盐、乳酸盐和十五烷作为电子供体。然而，当用分子氢自养生长时，细胞数量达到最高。在无细胞提取物的膜和可溶级分中发现了氢吸收活性，并且达到了部分纯化蛋白质的高达 2,981±129 nmol H ₂ *min ^-1 *mg ^-1。通常，自养硫酸盐还原菌来自变形杆菌类，在热液喷口栖息地蓬勃发展被描述为嗜热菌。鉴于其生理特征和特定的隔离源，菌株 KaireiS1 展示了以前未被注意到的通过自养生物在热液喷口场中等温度下进行微生物硫酸盐还原的潜力。