Differential expression of clade I and II N2O reductase genes in denitrifying Thauera linaloolentis 47LolT under different nitrogen conditions

Nitrous oxide (N2O) is a potent greenhouse gas and its reduction to dinitrogen gas by the N2O reductase (encoded by the nosZ gene) is the only known biological N2O sink. Within the nosZ phylogeny there are two major clades (I and II), which seem to have different ecological niches. However, physiological differences of nosZI and nosZII expression that may impact emissions of N2O are not well understood. Here, we evaluated the differential expression of nosZI and nosZII, both present in Thauera linaloolentis strain 47LolT, in response to N2O concentration and the presence of the competing electron acceptor nitrate (NO3−). Different N2O levels had a negligible effect on the expression of both nosZ clades. Interestingly, nosZII expression was strongly upregulated in the absence of NO3−, while nosZI expression remained constant across the conditions tested. Thus, NO3− possibly inhibited nosZII expression, which suggests that N2O mitigation mediated by nosZII can be restricted due to the presence of NO3− in the environment. This is the first study demonstrating differential expression of nosZI and nosZII genes under the same physiological conditions and their implications for N2O emission under varying environmental conditions in terms of NO3− availability.

Ecological and physiological implications of nitrogen oxide reduction pathways on greenhouse gas emissions in agroecosystems

ABSTRACT Microbial reductive pathways of nitrogen (N) oxides are highly relevant to net emissions of greenhouse gases (GHG) from agroecosystems. Several biotic and abiotic N-oxide reductive pathways influence the N budget and net GHG production in soil. This review summarizes the recent findings of N-oxide reduction pathways and their implications to GHG emissions in agroecosystems and proposes several mitigation strategies. Denitrification is the primary N-oxide reductive pathway that results in direct N2O emissions and fixed N losses, which add to the net carbon footprint. We highlight how dissimilatory nitrate reduction to ammonium (DNRA), an alternative N-oxide reduction pathway, may be used to reduce N2O production and N losses via denitrification. Implications of nosZ abundance and diversity and expressed N2O reductase activity to soil N2O emissions are reviewed with focus on the role of the N2O-reducers as an important N2O sink. Non-prokaryotic N2O sources, e.g. fungal denitrification, codenitrification and chemodenitrification, are also summarized to emphasize their potential significance as modulators of soil N2O emissions. Through the extensive review of these recent scientific advancements, this study posits opportunities for GHG mitigation through manipulation of microbial N-oxide reductive pathways in soil.

Effects of Some Hill Reaction-Inhibiting Herbicides on Nitrous Oxide Emission from Nitrogen-Input Farming Soil

Nitrous oxide (N2O) emission-suppressing activity of some electron-transport inhibitors of the Hill reaction system was investigated. The Hill reaction inhibitors—paraquat, isouron, bromacil, diquat, and simazine—all of which have been or are currently being used as herbicides in farming activity are expected to inhibit the electron-transporting pathways of nitrate respiration in denitrifying bacteria. Using N2O-emitting soil bed (5.0 g of fresh weight) from a continuously manured Andisol corn farmland in Hokkaido, Japan, which was autoclaved and further supplemented with an active N2O-emitter, Pseudomonas sp. 5CFM15-6D, and 1 mL of 100 mM NH4NO3 or (NH4)2SO4 solution as the sole nitrogen source (final concentration, 0.2 mM) in a 30 mL gas-chromatography vial, the effects of the five herbicides on N2O emission were examined. Paraquat and isouron (each at 50 µM) showed a statistically significant suppression of N2O emission in both the nitrification and the denitrification processes after a 7-day-incubation, whereas diquat at the same concentration accelerated N2O emission in the presence of NO3−. These results suggest that paraquat and isouron inhibited both the nitrification and the denitrification processes for N2O generation, or its upstream stages, whereas diquat specifically inhibited N2O reductase, an enzyme that catalyzes the reduction of N2O to N2 gas. Incomplete denitrifiers are the key players in the potent emission of N2O from Andisol corn farmland soil because of the missing nosZ gene. The electron relay system-inhibiting herbicides—paraquat and isouron—possibly contribute to the prevention of denitrification-induced nitrogen loss from the farming soil.

Correlation Between Wastewater Treatment Performances and Sludge Characteristics

The balance between biotechnological useful microorganisms species, as well as the aerobic sludge granules morphology influences the treatment plant performance. This paper presents an attempt to correlate the experimental results on wastewater treatment performance with aerobic granular sludge structural community. The experiments were conducted in two lab scale bioreactors operated in parallel at different retention times. Treatment performances achieved in both systems lead to an effluent that complies NTPA001 limits, both systems being able of simultaneous nitrification / denitrification and phosphorus removal. For qualitative and quantitative analysis of aerobic granular sludge specific microorganisms, DNA has been succeesfully isolated and purifyied from sludge samples, thus obtaining bacterial DNA extracts in concentrations of up to 56 ng/mL and 78% purity. The resulted DNA extracts were used for qPCR amplification. Amplification was carried out in the presence of a series of 10 pairs of primers for the detection / quantification of specific bacteria and genes involved in the treatment process: universal bacteria; Micotrix parvicella; Ammonia oxidizing archaea; Ammonium monooxigenase; Nitrobacter Sp.; nitrite reductase; N2O reductase; phosphorus accumulating microorganisms. The experimental results showed a qualitative and quantitative improvement of the sludge quality in terms of species distribution and share of biotechnologically useful bacteria.