Impact of varying electron donors on the molecular microbial ecology and biokinetics of methylotrophic denitrifying bacteria

Abstract

The goal of this study was to identify bacterial populations that assimilated methanol in a denitrifying sequencing batch reactor (SBR), using stable isotope probing (SIP) of (13)C labeled DNA and quantitatively track changes in these populations upon changing the electron donor from methanol to ethanol in the SBR feed. Based on SIP derived (13)C 16S rRNA gene clone libraries, dominant SBR methylotrophic bacteria were related to Methyloversatilis spp. and Hyphomicrobium spp. These methylotrophic populations were quantified via newly developed real-time PCR assays. Upon switching the electron donor from methanol to ethanol, Hyphomicrobium spp. concentrations decreased significantly in accordance with their obligately methylotrophic nutritional mode. In contrast, Methyloversatilis spp. concentrations were relatively unchanged, in accordance with their ability to assimilate both methanol and ethanol. Direct assimilation of ethanol by Methyloversatilis spp. but not Hyphomicrobium spp. was also confirmed via SIP. The reduction in methylotrophic bacterial concentration upon switching to ethanol was paralleled by a significant decrease in the methanol supported denitrification biokinetics of the SBR on nitrate. In sum, the results of this study demonstrate that the metabolic capabilities (methanol assimilation and metabolism) and substrate specificity (obligately or facultatively methylotrophic) of two distinct methylotrophic bacterial populations contributed to their survival or washout in denitrifying bioreactors.

Sulfur-based mixotrophic denitrification corresponding to different electron donors and microbial profiling in anoxic fluidized-bed membrane bioreactors

“…Compared with methanol-fed R1, the lower sulfate generation and residual TOC concentration were observed in the ethanol-fed R2. This can be explained by the fact that denitrifying bacteria are more accessible to ethanol than methanol (Baytshtok et al, 2009). Some researchers also reported that ethanol fostered higher specific denitrification rates than methanol (Martin et al, 2009;Mokhayeri et al, 2008;Lu and Chandran, 2010;Salminen et al, 2014).…”

“…Nitrite and nitrous oxide concentrations for the ethanol-fed mixotrophic denitrification peaked before the methanol-fed process, and relatively lower nitrite and nitrous oxide accumulations were observed in the ethanol-fed process, indicating ethanol-fed mixotrophic denitrification had higher denitrification biokinetics than methanol. In fact, many commercially available carbon sources induce higher denitrification activity than methanol (Baytshtok et al, 2009;Bodík et al, 2009;Lu et al, 2014;Nyberg et al, 2004). Nitrogen balances were determined to further elucidate the removal mechanisms of sulfur-based denitrification.…”

“…These suggest that the addition of methanol or ethanol had a clear effect on the microbial community structure. For a given system, the carbon source has a remarkable potential impact on the denitrifying community structure than others, as organic carbon determines various metabolic pathways of heterotrophic bacteria (Baytshtok et al, 2009;Lu et al, 2014;Hallin et al, 2006;Wan et al, 2011;Lu et al, 2012).…”

Comparative Analysis of Denitrifying Activities of Hyphomicrobium nitrativorans, Hyphomicrobium denitrificans, and Hyphomicrobium zavarzinii

“…Some strains have been characterized by their denitrification capacities (2)(3)(4)(5). They have often been identified as major players in denitrification systems supplemented with methanol (4,(6)(7)(8), and their presence has been associated with high denitrification rates (9,10).…”

Insights into Denitrification in Methylotenera mobilis from Denitrification Pathway and Methanol Metabolism Mutants

“…M ethanol-enhanced denitrification as part of sewage treatment is a well-described phenomenon (1), and a number of methylotrophs have been implicated in this process, carried out by mixed cultures (2)(3)(4)(5). However, the role of denitrification and its connection to methylotrophy in natural systems is not well understood, and data from studies involving pure cultures of methylotrophs are sparse.…”