Impact
of Heavy Metals on Transcriptional and Physiological
Activity of Nitrifying Bacteria
- Publication date
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Abstract
Heavy
metals can
inhibit nitrification, a key process for nitrogen
removal in wastewater treatment. The transcriptional responses of <i>amoA</i>, <i>hao</i>, <i>nirK</i>, and <i>norB</i> were measured in conjunction with specific oxygen uptake
rate (sOUR) for nitrifying enrichment cultures exposed to different
metals (Ni(II), Zn(II), Cd(II), and Pb(II)). There was significant
decrease in sOUR with increasing concentrations for Ni(II) (0.03–3
mg/L), Zn(II) (0.1–10 mg/L), and Cd(II) (0.03–1 mg/L)
(<i>p</i> < 0.05). However, no considerable changes in
sOUR were observed with Pb(II) (1–100 mg/L), except at a dosage
of 1000 mg/L causing 84% inhibition. Based on RT-qPCR data, the transcript
levels of <i>amoA</i> and <i>hao</i> decreased
when exposed to Ni(II) dosages. Slight up-regulation of <i>amoA</i>, <i>hao</i>, and <i>nirK</i> (0.5–1.5-fold)
occurred after exposure to 0.3–3 mg/L Zn(II), although their
expression decreased for 10 mg/L Zn(II). With the exception of 1000
mg/L Pb(II), stimulation of all genes occurred on Cd(II) and Pb(II)
exposure. While overall the results show that RNA-based function-specific
assays can be used as potential surrogates for measuring nitrification
activity, the degree of inhibition inferred from sOUR and gene transcription
is different. We suggest that variations in transcription of functional
genes may supplement sOUR based assays as early warning indicators
of upsets in nitrification