title: Response of Nitrobacter spp. ribosomal gene and transcript abundance following nitrite starvation and exposure to mechanistically distinct inhibitors.
abstract: The Nitrobacter spp. rRNA gene (rDNA) and relative rRNA transcript abundance (rRNAt/rDNA ratio) were evaluated in response to sudden changes in the nitrite oxidation rate. The rDNA abundance poorly indicated sudden transitions in the rate, whereas the relative rRNAt abundance usually varied quickly and significantly. In response to changes in nitrite concentration, 8 h were required for the rRNAt/rDNA ratio to transition from a minimum value at nitrite starvation (approximately 0.07) to a maximum value with excess nitrite present (approximately 4), and 5 h were required for this metric to return to the minimum value after nitrite starvation re-ensued. Generally, the relative rRNAt abundance dropped significantly after 4.5 h of exposure to three different inhibitors. A sharp decline in the rRNAt/rDNA ratio occurred during exposure to 3,5-DCP (from 4 down to 0.2) even as the fractional inhibition level remained low (< 0.10); the minimum ratio value was observed when nitrite oxidation was completely inhibited. The ratio decreased significantly during exposure to azide (from 4 to 0.5) and H+ (from 2 to 0.2), but only when the fractional inhibition levels were high (> 0.8). Interestingly, when the pH was suddenly changed to 4.5, inhibiting nitrite oxidation completely, the rRNAt/rDNA metric did not decline suggesting that rRNAt processing was inhibited. This effect was not observed during severe inhibition with 3,5-DCP and azide. Overall, the findings indicate the relative rRNAt abundance can be used to closely track in situ Nitrobacter spp. activity and in most instances will reveal inhibition events with the potential to impact treatment performance in reactors where Nitrobacter spp. are dominant.
authors.affiliation: Department of Biosystems Engineering, The University of Tennessee, Knoxville, Tennessee 37996, USA. shawkins@utk.edu
authors.forename: Shawn A
authors.initials: SA
authors.lastname: Hawkins
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Robinson
authors.forename: Alice C
authors.initials: AC
authors.lastname: Layton
authors.forename: Gary S
authors.initials: GS
authors.lastname: Sayler
mesh_terms: D001386:Azides / Q000494:pharmacology*; D018533:Biomass; D002733:Chlorophenols / Q000494:pharmacology*; D004275:DNA, Ribosomal / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D005798:Genes, Bacterial; D009573:Nitrites / Q000378:metabolism*; D009576:Nitrobacter / Q000187:drug effects / Q000235:genetics*; D010101:Oxygen Consumption / Q000187:drug effects; D011522:Protons; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects / Q000235:genetics*
chemical_list: D001386:Azides; D002733:Chlorophenols; D004275:DNA, Ribosomal; D009573:Nitrites; D011522:Protons; D012333:RNA, Messenger; C116190:3,5-dichlorophenol