The metabolic impact of extracellular nitrite on aerobic metabolism of Paracoccus denitrificans

Abstract

Nitrite, in equilibrium with free nitrous acid (FNA), can inhibit both aerobic and anaerobic growth of microbial communities through bactericidal activities that have considerable potential for control of microbial growth in a range of water systems. There has been much focus on the effect of nitrite/FNA on anaerobic metabolism and so, to enhance understanding of the metabolic impact of nitrite/FNA on aerobic metabolism, a study was undertaken with a model denitrifying bacterium Paracoccus denitrificans PD1222. Extracellular nitrite inhibits aerobic growth of P. denitrificans in a pH-dependent manner that is likely to be a result of both nitrite and free nitrous acid (pKa = 3.25) and subsequent reactive nitrogen oxides generated from the intracellular passage of FNA into P. denitrificans. Increased expression of a gene encoding a flavohemoglobin protein (Fhp) (Pden_1689) was observed in response to extracellular nitrite. Construction and analysis of a deletion mutant established Fhp to be involved in endowing nitrite/FNA resistance at high extracellular nitrite concentrations. Global transcriptional analysis confirmed nitrite-dependent expression of fhp and indicated that P. denitrificans expressed a number of stress response systems associated with protein, DNA and lipid repair. It is therefore suggested that nitrite causes a pH-dependent stress response that is due to the production of associated reactive nitrogen species, such as nitric oxide from the internalisation of FNA.

Tuning the modular Paracoccus denitrificans respirome to adapt from aerobic respiration to anaerobic denitrification

“…Levels of the periplasmic ‐reductase ( napAB , Pden_4719‐4723) (Ellington et al ., ), involved in redox balancing during aerobic metabolism remained unchanged and absolute expression levels were low. However, a gene encoding a flavohemoglobin‐dependent nitric oxide dioxygenase (nodA ; Pden_1869) involved in nitrosative stress (Hartop et al ., ) is highly expressed in anaerobic‐denitrifying conditions along with the adjacent gene (Pden_1690) that encodes a putative nitric oxide responsive repressor of the NsrR family (Spiro, ; Vine and Cole, ). This observation is consistent with the cells experiencing a degree of nitrosative stress during denitrification, most probably associated with production of intracellular reactive nitrogen species such as the NO radical.…”

Enhancing sludge biodegradability through free nitrous acid pre-treatment at low exposure time

“…FNA pre-treatment has been demonstrated to cause a strong biocidal impact on microorganisms, to increase sludge biodegradability and SMP at FNA concentrations in the range of 0.36-2.13 mg N-HNO 2 /L [6,7, 12,13]. FNA exists in equilibrium with nitrite and the mechanisms by which nitrite and FNA have been reported to act as cytotoxins include the following [16,17]: (i) FNA can lead to the formation of reactive nitrogen and oxygen species in the cytoplasm including nitric oxide (NO), nitrogen dioxide (NO 2 ), peroxynitrite (ONOO -), hydroxide ion (OH -) and hydrogen peroxide (H 2 O 2 ), all of which exhibit toxicity towards bacterial cells, causing cell death; (ii) FNA has been suggested to act as an uncoupler acting to circumvent the ATP synthesis as a result of a short-circuit formed by FNA transporting protons across the inner membrane and back into the cell and so increasing the conductance of the cytoplasmic membrane; and (iii) FNA may be able to directly inhibit electron carriers.…”

Trace metal availability affects greenhouse gas emissions and microbial functional group abundance in freshwater wetland sediments

“…Following NO 2 reduction, the production and consumption of 238 NO is an important denitrification intermediate. Although we didn't measure NO in our experiments, we 239 assume that it was quickly utilized or reduced to N 2 O due to its potent cytotoxicity at μM levels (Chaudhari 240 et al, 2017;Hartop et al, 2017). In contrast, we saw a dramatic effect of Cu addition.…”

“…Other well-known environmental factors controlling denitrification are O 2 , NH 4 + , NO 3 -/NO 2 -, and C (Thomson 337 et al, 2012). Synthesizing the findings from other chemostat (Baumann et al, 1996;Felgate et al, 338 2012;Giannopoulos et al, 2017;Hartop et al, 2017;Conthe et al, 2018) and incubation (Koike and Hattori, 339 1975;Okereke, 1993;Morley et al, 2008) studies, it appears that the relative importance of the 340 aforementioned factors in control of denitrification is O 2 > NH 4 + , NO 3/2 -> C/N or C quality, with trace metal 341 bioavailability exerting an additional effect on each factor. The present results suggest that the effect Cu 342 exerts on N 2 and N 2 O emissions from the environment may be more extensive than previously thought.…”