Metaproteomics, Heterotrophic Growth, and Distribution of Nitrosomonas europaea and Nitrobacter winogradskyi after Long-Term Operation of an Autotrophic Nitrifying Biofilm Reactor

Abstract

Bioregenerative life support systems (BLSS) are currently in development to tackle low recovery efficiencies, high energy demands, as well as food, water, and oxygen production challenges through the regeneration of nutrients from waste streams. The MELiSSA pilot plant has been developed as a testbed for regenerative life support system bioreactor operation and characterization. As nitrogen is a vital resource in such systems, we studied the functional composition of a new packed-bed nitrifying bioreactor inoculated with a co-culture of Nitrosomonas europaea (ATCC 25978) and Nitrobacter winogradskyi (ATCC 25391). After 840 days of autotrophic continuous cultivation, the packed-bed was sampled at five vertical positions, each with three horizontal positions, and the biomass at each position was characterized via qPCR, 16S amplicon sequencing, and liquid chromatography tandem mass spectrometry. The total number of cells within the different sections fluctuated around 8.95 ± 5.10 × 107 cells/mL of beads. Based on 16S amplicons and protein content, N. europaea and N. winogradskyi constituted overall 44.07 ± 11.75% and 57.53 ± 12.04% of the nitrifying bioreactor, respectively, indicating the presence of a heterotrophic population that, even after such a long operation time, did not affect the nitrification function of the bioreactor. In addition, DNA-based abundance estimates showed that N. europaea was slightly more abundant than N. winogradskyi, whereas protein-based abundance estimates indicated a much higher abundance of N. europaea. This highlights that single-method approaches need to be carefully interpreted in terms of overall cell abundance and metabolic activity.

Whole transcriptome analysis highlights nutrient limitation of nitrogen cycle bacteria in simulated microgravity

“…N. europaea and N. winogradskyi grew in a ratio of ~15:1 across all three conditions. In a previous chemostat co-culture study, the ammonia and nitrite oxidizers were present in a ratio of 4:1, while in a biofilm reactor, the relative abundance varied from 9:1 to 3:7 along the height of the bioreactor 40 – 42 . In the bioreactor, NH 4 + at the inlet was consumed by a high population density of N. europaea .…”

“…Due to high NH 4 + concentrations, N. europaea in the lower regions was very active and likely outcompeted N. winogradskyi for O 2 , since N. europaea possesses a lower half saturation constant ( K m ) (1–15 µM O 2 ) than N. winogradskyi (22–166 µM O 2 ) 43 . Gradually, N. winogradskyi abundance increases due to heightened NO 2 − availability and lower NH 4 + levels through NH 3 oxidation by N. europaea 41 , 42 . In the current study, it is possible that N. europaea outcompeted N. winogradskyi for all O 2 in SMG and NG in a batch configuration, as suggested by Ilgrande et al 4 .…”

Radiotolerance of N-cycle bacteria and their transcriptomic response to low-dose space-analogue ionizing irradiation

“… 73 N/A 1141 RV: TTGTCACCGGCAGTCTCTCTAG Mastroleo et al. 73 N/A urea FW: AGCGCCTTTGTGATGGAA This paper N/A urea RV: GATCTGGATGTCGGGAATCATC This paper N/A amoA FW: ACACCCGAGTATGTTCGTCA Perez et al. 66 N/A amoA RV: TGCGATGTACGATACGACCT Perez et al.…”