Hexavalent chromium [Cr(VI)] is a known carcinogen and mutagen; however, the actual mechanisms of Cr toxicity are unknown. Two approaches were used to isolate Cr(VI)-resistant bacteria from metal-contaminated river sediments. Diluted sediments were plated directly onto a peptone-yeast extract (PYE) medium containing 0 to 100 micrograms of Cr(VI) ml-1. Approximately 8.4 x 10(5) CFU g-1 were recovered on 0 microgram of Cr(VI) ml-1, whereas 4.0 x 10(2) CFU g-1 were recovered on PYE plus 100 micrograms of Cr(VI) ml-1. Alternatively, continuous culture enrichment techniques were employed using PYE and 100 micrograms Cr(VI) ml-1 input at dilution rates of 0.02 and 0.10 h-1. After six residence periods, 10(9) CFU were recovered on PYE agar containing 0 microgram of Cr(VI) ml-1 and 10(7) CFU on PYE agar plus 100 micrograms of Cr(VI) ml-1. Of 89 isolates obtained by direct plating onto PYE, 47% were resistant to 100 micrograms of Cr(VI) ml-1, and 29% were resistant to 250 micrograms of Cr(VI) ml-1. When the same isolates were plated onto PYE containing Cr(III), 88% were resistant to 100 micrograms ml-1 but only 2% were resistant to 250 micrograms ml-1. Cr, Co, Sb, and Zn were found in significantly higher concentrations at an industry-related contaminated site than at a site 11 km downstream. Total Cr in the sediments at the contaminated site averaged 586 micrograms (dry weight) g-1, and the downstream site averaged 71 micrograms (dry weight) g-1. The Cr recovered from acid-digested Ottawa River sediment samples was predominantly hexavalent. Five acid digestion procedures followed by atomic absorption spectroscopy were compared and found to be 30 to 70% efficient for recovery of Cr relative to neutron activation analysis. A population of aerobic, heterotrophic bacteria was recovered from sediments containing elevated levels of Cr.(ABSTRACT TRUNCATED AT 250 WORDS)
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机译：六价铬[Cr（VI）]是已知的致癌物和诱变剂。然而，Cr毒性的实际机制尚不清楚。两种方法被用来从金属污染的河流沉积物中分离出抗Cr（VI）的细菌。将稀释的沉积物直接铺板到含有0到100微克Cr（VI）ml-1的蛋白-酵母提取物（PYE）培养基上。在0微克Cr（VI）ml-1上回收大约8.4 x 10（5）CFU g-1，而在PYE加100微克Cr（VI）ml-上回收4.0 x 10（2）CFU g-1。 1。或者，使用PYE和100微克Cr（VI）ml-1输入以0.02和0.10 h-1的稀释率进行连续培养富集技术。六个停留期后，在含有0微克Cr（VI）ml-1的PYE琼脂上回收10（9）CFU，在PYE琼脂上加100微克Cr（VI）ml-1的10（7）CFU。通过直接接种到PYE上获得的89个分离株中，有47％对100微克Cr（VI）ml-1有抵抗力，而29％对250微克Cr（VI）ml-1有抵抗力。当将相同的分离物接种到含有Cr（III）的PYE上时，有88％的细菌对100微克ml-1有抵抗力，但只有2％的细菌对250微克ml-1有抵抗力。在与工业相关的污染场所，发现的Cr，Co，Sb和Zn的浓度明显高于下游11 km。受污染地点沉积物中的总Cr平均为586微克（干重）g-1，而下游地区平均为71微克（干重）g-1。从酸消化的渥太华河沉积物样品中回收的铬主要为六价铬。比较了五种酸消解程序和原子吸收光谱法，发现相对于中子活化分析，Cr的回收效率为30％至70％。从含高水平铬的沉积物中回收了好氧，异养细菌（摘要截短了250字）
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