胞外呼吸菌Exiguobacterium sp. PY14的分离鉴定及其异化铁还原特性

Isolation of extracellular respiratory strain Exiguobacterium sp.PY14 and its dissimilatory iron reduction characteristic

胞外呼吸菌广泛分布于自然生境中,是驱动铁等元素地球化学循环的重要因素,已成为各种有机污染物降解和重金属污染去除的研究热点.为了挖掘具有环境修复应用前景的胞外呼吸菌,从鄱阳湖湿地土壤中筛选具有胞外异化铁还原能力的菌株,通过形态、生理生化和遗传分析进行菌种鉴定,并对其最优生长条件、异化铁还原特性及胞外电子传递机制进行研究.结果显示,分离得到的菌株PY14具有较高的异化铁还原能力,细菌形态、生理生化特征及16S rRNA基因系统发育分析鉴定其为革兰氏阳性的微小杆菌属(Exiguobacterium);具有嗜碱耐盐生长特性,最适生长pH值为8.0,在NaCl浓度高达50g/L条件下生长良好;能够利用葡萄糖、丙酮酸、乙酸和乳酸等多种小分子碳源(电子供体)进行厌氧呼吸,5 d内5 mmol/L水铁矿的还原率高达80%,添加电子穿梭(蒽醌-2,6-二磺酸盐)可显著增强其异化还原水铁矿、针铁矿和赤铁矿的速率;可通过自身分泌腐殖酸类电子穿梭体实现介导异化铁还原过程.本研究获得了一株有望在盐碱土壤或水体等环境中高效驱动铁还原的胞外呼吸菌,为进一步认识革兰氏阳性细菌胞外电子传递机制提供新依据.

Extracellular respiratory bacteria exist widely in natural habitats and are important driving factors in the geochemical cycles of various elements,such as Fe.Thus,they have become a research hotspot for organic pollutant degradation and heavy metal removal.This study aimed to explore new extracellular respiratory bacteria with great potential for use in environmental remediation.The wetland soil of Poyang Lake was sampled to isolate bacterial strains capable of extracellular dissimilatory iron reduction using the ferrihydrite reduction ratio as the evaluation criterion.The selected strain was identified based on morphological,physiological,and biochemical characteristics and 16S rRNA gene phylogenetic analysis.The optimal growth conditions,dissimilatory iron reduction behavior,and extracellular electron transport mechanisms were subsequently analyzed.Strain PY14 has a high dissimilatory iron reduction ability and belongs to the gram-positive Exiguobacterium.The optimal pH was 8.0,and the tolerated NaCl concentration was 50 g/L.The strain can use various low-molecular-weight organic matter,such as glucose,pyruvate,acetate,and lactate,as carbon sources(electron donors)for anaerobic respiration.The reduction ratio of 5 mmol/L ferrihydrite reached 80%within 5 d,and the addition of an electron shuttle(anthraquinone-2,6-disulfonate)greatly promoted the dissimilatory reduction rate of ferrihydrite,goethite,and hematite.It has an indirect extracellular electron transfer pathway characterized by endogenous electron shuttle secretion,similar to that of humic acid.This study not only identified an extracellular respiratory bacterium that could efficiently drive iron reduction in saline-alkali soil or water environments but also provided a new basis for further understanding the unknown extracellular electron transport mechanism of gram-positive bacteria.