Department of Microbiology, University of Massachusetts, Amherst, MA, USA.
ISME J. 2010 Feb;4(2):253-66. doi: 10.1038/ismej.2009.115. Epub 2009 Dec 10.
Nutrient limitation is an environmental stress that may reduce the effectiveness of bioremediation strategies, especially when the contaminants are organic compounds or when organic compounds are added to promote microbial activities such as metal reduction. Genes indicative of phosphate-limitation were identified by microarray analysis of chemostat cultures of Geobacter sulfureducens. This analysis revealed that genes in the pst-pho operon, which is associated with a high-affinity phosphate uptake system in other microorganisms, had significantly higher transcript abundance under phosphate-limiting conditions, with the genes pstB and phoU upregulated the most. Quantitative PCR analysis of pstB and phoU transcript levels in G. sulfurreducens grown in chemostats demonstrated that the expression of these genes increased when phosphate was removed from the culture medium. Transcripts of pstB and phoU within the subsurface Geobacter species predominating during an in situ uranium-bioremediation field experiment were more abundant than in chemostat cultures of G. sulfurreducens that were not limited for phosphate. Addition of phosphate to incubations of subsurface sediments did not stimulate dissimilatory metal reduction. The added phosphate was rapidly adsorbed onto the sediments. The results demonstrate that Geobacter species can effectively reduce U(VI) even when experiencing suboptimal phosphate concentrations and that increasing phosphate availability with phosphate additions is difficult to achieve because of the high reactivity of this compound. This transcript-based approach developed for diagnosing phosphate limitation should be applicable to assessing the potential need for additional phosphate in other bioremediation processes.
营养限制是一种环境胁迫,可能会降低生物修复策略的有效性,特别是当污染物是有机化合物时,或者当添加有机化合物以促进微生物活动(如金属还原)时。通过对脱硫弧菌恒化器培养物的微阵列分析,确定了指示磷限制的基因。该分析表明,与其他微生物中高亲和力磷酸盐摄取系统相关的 pst-pho 操纵子中的基因在磷酸盐限制条件下的转录丰度显着更高,其中 pstB 和 phoU 基因的上调最为明显。定量 PCR 分析表明,当从培养基中去除磷酸盐时,G. sulfurreducens 在恒化器中生长时这些基因的表达增加。在原位铀生物修复现场实验中占主导地位的地下 Geobacter 物种的 pstB 和 phoU 转录本比不受磷酸盐限制的 G. sulfurreducens 恒化器培养物更为丰富。向地下沉积物的孵育物中添加磷酸盐并没有刺激异化金属还原。添加的磷酸盐迅速被沉积物吸附。结果表明,即使在经历亚最佳磷酸盐浓度的情况下,Geobacter 物种也可以有效地还原 U(VI),并且由于该化合物的高反应性,通过添加磷酸盐来增加磷酸盐的可用性是难以实现的。这种基于转录本的方法可用于诊断磷酸盐限制,也可用于评估其他生物修复过程中是否需要额外添加磷酸盐。