长江口咸淡水混合水域腐蚀性细菌的筛选及其对文物的腐蚀作用

Screening of corrosive bacteria found in the zone of mixing of fresh and salt water in the Yangtze Estuary,and the impact of these bacteria on cultural relics

近年来,针对文物在海水中的细菌性腐蚀研究主要集中于海域沉积,但关于咸淡水混合水域的腐蚀性细菌研究鲜有报道。河口及近海岸水域是水下文物较为丰富的区域,咸淡水交互作用影响水下文物的埋藏环境和文物遗存。本研究采集长江口北港拦门沙Ⅱ号沉船附近海底不同层次的海泥,通过非定向富集培养基培养,分离纯化得到18株菌,经16S rDNA鉴定出4种具有腐蚀性的细菌:哈夫尼希瓦氏菌(Shewanella hafniensis)、越南芽孢杆菌(Bacillus wiedmannii)、金橙微小杆菌(Exiguobacterium aquaticum)和微小杆菌(Exiguobacterium indicum)。将分离得到的细菌作用于瓷质、陶质和木质等常见文物材料,置于30℃摇床220 r/min转速下培养7 d,喷金干燥,扫描电镜下观察,均可见在材料表面上产生生物膜。生物膜与微生物腐蚀的发生密切相关,除了已报道具有腐蚀性的菌株外,还发现了2株先前并未报道但也在材料表面产生生物膜的菌类:萘醌对希瓦氏菌(Shewanella xiamenensis)和嗜水气单胞菌(Aeromonas hydrophila)。实验结果为揭示海岸带咸淡水混合水域的文物埋藏环境及更好地保护文物提供了科学参考。相比于以往文献,本研究在以下三个方面做出拓展:1)研究了腐蚀性细菌对瓷质、陶质和木质文物材料的腐蚀现象,观察到与微生物腐蚀密切相关的生物膜形成,从而实验证明哈夫尼希瓦氏菌、越南芽孢杆菌、金橙微小杆菌和微小杆菌对于瓷质、陶质和木质材料的腐蚀作用。2)首次发现了两株之前未被报道的潜在腐蚀性的细菌:萘醌对希瓦氏菌和嗜水气单胞菌,它们也能在文物材料表面生成生物膜,初步证明这两株菌也具有腐蚀效果。3)探究了长江口咸淡水混合水域的海泥中的优势菌株为芽孢杆菌,并细分出4株腐蚀性细菌和2株未被报道为腐蚀性细菌但具有腐蚀潜力的细菌,区别于以往微生物腐蚀研究都集中于硫酸盐还原菌这一类菌。本研究发现了更多的腐蚀性细菌,揭示了海岸带咸淡水混合水域微生物的丰富性。本研究着眼于长江口咸淡水混合水域的海泥所富含的腐蚀性细菌与瓷质、陶质和木质文物材料腐蚀的关系,在一定程度上为研究该水域的腐蚀性细菌奠定基础,有助于应用于后期文物保护等相关方面。

Recent studies of bacterial corrosion of cultural relics in seawater have mainly focused on deep-sea salty cement and light cement.However,there are few reports on corrosive bacteria in zones of mixing of fresh and salt water.Estuarine and coastal waters are rich in underwater cultural relics and the interaction of salt and fresh water affects the burial environment and cultural relics.In our study,muddy marine samples were collected at different levels of the sea bed near the No.Ⅱshipwreck at the North Channel of the Yangtze Estuary,and 18 strains of bacteria were isolated using non-directional enrichment medium.Four corrosive bacteria were identified by 16S rDNA sequence analysis:Shewanella hafniensis,Bacillus wiedmannii,Exiguobacterium aquaticum and Exiguobacterium indicum.First,the isolated bacteria were cultured,until they reached their logarithmic growth periods,in a 30℃shaker at a rotational speed of 220 r/min,and then they were allowed to act upon porcelain,pottery,wood and other common cultural relic materials.After a 7-day incubation,those cultural relic materials were sprayed with gold,dried and then observed using scanning electron microscopy(SEM).Biofilms are closely related to the occurrence of microbial corrosion.In addition to the reported corrosive strains,we also found two previously-unreported bacteria—Shewanella xiamenensis and Aeromonas hydrophila—that also produce biofilms on the surface of materials.The experimental results provide scientific reference for explaining the burial environment of cultural relics in the mixture area of fresh water and salt water at estuarine and coastal areas and better understanding of cultural relic conservation.Compared with previous literature,our study expands in the following three aspects:1)the corrosion phenomena of corrosive bacteria on porcelain,pottery and wood cultural relic materials were studied,and the formation of biofilms closely related to microbial corrosion was observed,so as to demonstrate the corrosive effects of Shewanella hafniensis,Bacillus wiedmannii,Exiguobacterium aquaticum and Exiguobacterium indicum on porcelain,pottery and wood materials;2)two previously-unreported corrosive bacteria-Shewanella xiamenensis and Aeromonas hydrophila,which can also form biofilms on the surface of materials-were found for the first time,preliminarily indicating that these two bacteria also have potential corrosive effects;3)Bacillus was explored as the dominant strain in the zone of mixing of fresh water and salt water in the Yangtze Estuary,further revealing the richness of the marine bacterial library because more corrosive bacteria(different from sulfate-reducing bacteria)were found in our study.This study focuses on the relationship between corrosive bacteria abounding in the zone of mixing of fresh water and salt water in the Yangtze Estuary and the corrosion of porcelain,pottery and wood cultural relics,which,to some extent,lays a foundation for the study of corrosive bacteria in the waters.It is conducive to the following application to cultural relic conservation and other related aspects.