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. 2013 Oct 31;8(10):e78275.
doi: 10.1371/journal.pone.0078275. eCollection 2013.

Diversity and spatial distribution of hydrazine oxidoreductase (hzo) gene in the oxygen minimum zone off Costa Rica

Liangliang Kong  1 , Hongmei Jing, Takafumi Kataoka, Carolyn Buchwald, Hongbin Liu
Affiliations

Diversity and spatial distribution of hydrazine oxidoreductase (hzo) gene in the oxygen minimum zone off Costa Rica

Liangliang Kong et al. PLoS One. .

Abstract

Anaerobic ammonia oxidation (anammox) as an important nitrogen loss pathway has been reported in marine oxygen minimum zones (OMZs), but the community composition and spatial distribution of anammox bacteria in the eastern tropical North Pacific (ETNP) OMZ are poorly determined. In this study, anammox bacterial communities in the OMZ off Costa Rica (CRD-OMZ) were analyzed based on both hydrazine oxidoreductase (hzo) genes and their transcripts assigned to cluster 1 and 2. The anammox communities revealed by hzo genes and proteins in CRD-OMZ showed a low diversity. Gene quantification results showed that hzo gene abundances peaked in the upper OMZs, associated with the peaks of nitrite concentration. Nitrite and oxygen concentrations may therefore colimit the distribution of anammox bacteria in this area. Furthermore, transcriptional activity of anammox bacteria was confirmed by obtaining abundant hzo mRNA transcripts through qRT-PCR. A novel hzo cluster 2x clade was identified by the phylogenetic analysis and these novel sequences were abundant and widely distributed in this environment. Our study demonstrated that both cluster 1 and 2 anammox bacteria play an active role in the CRD-OMZ, and the cluster 1 abundance and transcriptional activity were higher than cluster 2 in both free-living and particle-attached fractions at both gene and transcriptional levels.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Location of sampling stations in Costa Rica Dome (CRD).
Figure 2
Figure 2. Hydrographic conditions of the sampling stations.
Shadow layers indicate the core of the oxygen minimum zones (OMZs) characterized by dissolved oxygen concentration lower than 1.0 μM.
Figure 3
Figure 3. Vertical distributions of nitrite (NO2 -) and ammonium (NH4 +) in the water columns of the sampling stations in Costa Rica Dome (CRD).
Figure 4
Figure 4. Neighbor-joining phylogenetic tree constructed with anammox bacteria hzo-deduced amino acid sequences from the oxygen minimum zone (OMZ) in Costa Rica Dome (CRD).
The sequences in bold were obtained in the present study. The sequences were grouped at a 1% cutoff value using DOTUR and only one sequence was selected to represent the operational taxonomic unit (OTU). The number in the brackets followed the sequence name indicated the number of the clones recovered. Bootstrap resampling was performed 1000 times and only its values higher than 50% are shown. The scale bar presents the number of amino acid substitutions per site.
Figure 5
Figure 5. Vertical profiles of hzo cluster 1 and cluster 2x gene abundances in the smaller size fraction (0.2-2.0 μm) among different stations in Costa Rica Dome (CRD).
Shadow layers show the core of the oxygen minimum zone (OMZ) characterized by dissolved oxygen concentration lower than 1.0 μM.
See this image and copyright information in PMC

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