Anaerobic phototrophic nitrite oxidation by Thiocapsa sp. strain KS1 and Rhodopseudomonas sp. strain LQ17

Abstract

In anaerobic enrichment cultures for phototrophic nitrite-oxidizing bacteria from different freshwater sites, two different cell types, i.e. non-motile cocci and motile, rod-shaped bacteria, always outnumbered all other bacteria. Most-probable-number (MPN) dilution series with samples from two freshwater sites yielded only low numbers (¡3¾10 3 cm "3 ) of phototrophic nitrite oxidizers. Slightly higher numbers (about 10 4 cm "3 ) were found in activated sewage sludge. Anaerobic phototrophic oxidation of nitrite was studied with two different isolates, the phototrophic sulfur bacterium strain KS1 and the purple nonsulfur bacterium strain LQ17, both of which were isolated from activated sludge collected from the municipal sewage treatment plant in Konstanz, Germany. Strain KS1 converted 1 mM nitrite stoichiometrically to nitrate with concomitant formation of cell matter within 2-3 days, whereas strain LQ17 oxidized only up to 60 % of the given nitrite to nitrate within several months with the concomitant formation of cell biomass. Nitrite oxidation to nitrate was strictly light-dependent and required the presence of molybdenum in the medium. Nitrite was oxidized in both the presence and absence of oxygen. Nitrite inhibited growth at concentrations higher than 2 mM. Hydroxylamine and hydrazine were found to be toxic to the phototrophs in the range 5-50 mM and did not stimulate phototrophic growth. Based on morphology, substrate-utilization pattern, in vivo absorption spectra, and 16S rRNA gene sequence similarity, strain KS1 was assigned to the genus Thiocapsa and strain LQ17 to the genus Rhodopseudomonas. Also, Thiocapsa roseopersicina strains DSM 217 and DSM 221 were found to oxidize nitrite to nitrate with concomitant growth. We conclude that the ability to use nitrite phototrophically as electron donor is widespread in nature, but low MPN counts indicate that its contribution to nitrite oxidation in the studied habitats is rather limited.

Coexistence of nitrifying, anammox and denitrifying bacteria in a sequencing batch reactor

“…Recent research reported the ability of non-nitrifying bacteria related to the Rhodopseudomonas spp. (purple non-sulfur bacteria -strain LQ17) to use nitrite phototrophically as an electron donor as well (Schott et al, 2010). In addition, in our study, five of the remaining clone sequences (SNAD_16SrRNA_NOB(1_5, 2_5), SNAD_16SrRNA_NOB(1_6, 1_9, 2_2) and SNAD_16SrRNA_NOB_1_8) were closely related to Nitrobacter spp.…”

Nitrification expanded: discovery, physiology and genomics of a nitrite-oxidizing bacterium from the phylum Chloroflexi

“…This hypothesis gained strong support from the recent isolation of extant phototrophic NOB in the genera Rhodopseudomonas and Thiocapsa , which are closely affiliated with Nitrobacter and Nitrococcus , respectively (Schott et al , 2010). The NXR of Nitrobacter and Nitrococcus is oriented toward the cytoplasm (see also above).…”

“…This hypothesis gains support from analyses of the genes upstream and downstream of nxr (Supplementary Text S1 and Supplementary Figures S4a, S4c and d). Whether this evolutionary scenario supports or contrasts a phototrophic origin of nitrite oxidation in Nitrobacter and Nitrococcus (Teske et al , 1994) is a fascinating question that might be better illuminated once first sequences of nxr loci from the proteobacterial phototrophic NOB (Schott et al , 2010) become available.…”

“…Occasionally, new NOB enrichments or isolates are reported (for example, Lebedeva et al , 2011), but these strains usually belong to one of the already established groups. The only exceptions in the past 25 years were the description of Nitrotoga (Alawi et al , 2007) as a new nitrite-oxidizing genus in the Betaproteobacteria and the discovery of anoxygenic phototrophic NOB from the Alpha - and Gammaproteobacteria (Griffin et al , 2007; Schott et al , 2010). Thus, the diversity of NOB still appears to be restricted to a few phylogenetic groups, most of which are Proteobacteria .…”

The Genome of Nitrospina gracilis Illuminates the Metabolism and Evolution of the Major Marine Nitrite Oxidizer

“…Since these ICM resemble those of related phototrophic proteobacteria (purple bacteria), Teske et al (1994) hypothesized that Nitrobacter and Nitrococcus evolved from phototrophic ancestors where nitrite was used as electron donor for anoxygenic photosynthesis. Indeed, phototrophic nitrite oxidizers from the genera Rhodopseudomonas and Thiocapsa , which are closely related to Nitrobacter and Nitrococcus , were discovered recently (Schott et al, 2010). In contrast, Nitrospira lack ICM.…”