Soil and Water Science Department, University of Florida, Gainesville, 32601, USA.
Can J Microbiol. 2010 Mar;56(3):236-46. doi: 10.1139/w10-005.
Arsenic hyperaccumulator fern Pteris vittata L. produces large amounts of root exudates that are hypothesized to solubilize arsenic and maintain a unique rhizosphere microbial community. Total heterotrophic counts on rich or defined media supplemented with up to 400 mmol/L of arsenate showed a diverse arsenate-resistant microbial community from the rhizosphere of P. vittata growing in arsenic-contaminated sites. Twelve bacterial isolates tolerating 400 mmol/L of arsenate in liquid culture were identified. Selected bacterial isolates belonging to different genera were tested for their resistance to osmotic and oxidative stresses. Results showed that growth was generally better under osmotic stress generated by arsenic than under that generated by NaCl or PEG 6000, demonstrating that arsenic detoxification metabolism also cross-protected bacterial isolates from arsenic-induced osmotic stress. After 32 h of growth, all arsenate at 1 mmol/L was reduced to arsenite by strains Naxibacter sp. AH4, Mesorhizobium sp. AH5, and Pseudomonas sp. AH21, but arsenite at 1 mmol/L remained unchanged. Sensitivity to hydrogen peroxide was similar to that in broad-host pathogen Salmonella enterica sv. Typhimurium wild type, except strain AH4. The results suggested that these arsenic-resistant bacteria are metabolically adapted to arsenic-induced osmotic or oxidative stresses in addition to the specific bacterial system to exclude cellular arsenic. Both these adaptations contribute to the high arsenic resistance in the bacterial isolates.
砷超富集蕨类植物蜈蚣草会产生大量的根系分泌物，这些分泌物被认为可以溶解砷，并维持独特的根际微生物群落。在富含营养或特定培养基中添加高达 400mmol/L 的砷酸盐进行总异养计数，结果显示，在砷污染地区生长的蜈蚣草根际存在着多样化的砷酸盐抗性微生物群落。从液体培养中耐受 400mmol/L 砷酸盐的 12 个细菌分离株被鉴定出来。对属于不同属的选定细菌分离株进行耐渗透压和耐氧化应激测试。结果表明，在由砷产生的渗透压下，生长情况通常优于由 NaCl 或聚乙二醇 6000 产生的渗透压，这表明砷解毒代谢也能使细菌分离株免受砷诱导的渗透压。在 1mmol/L 的砷酸盐存在下，菌株 Naxibacter sp. AH4、Mesorhizobium sp. AH5 和 Pseudomonas sp. AH21 能在 32 小时内将 1mmol/L 的砷酸盐还原为亚砷酸盐，但 1mmol/L 的亚砷酸盐保持不变。对过氧化氢的敏感性与广泛宿主病原体鼠伤寒沙门氏菌野生型相似，除了菌株 AH4。结果表明，这些砷抗性细菌除了具有特定的细菌系统来排除细胞内的砷外，还适应了由砷诱导的渗透压或氧化应激。这两种适应都有助于提高细菌分离株的砷抗性。
