Abstract
Lithoautotrophic nitrite-oxidizing bacterial populations from moving-bed biofilters of brackish recirculation aquaculture systems (RAS; shrimp and barramundi) were tested for their metabolic activity and phylogenetic diversity. Samples from the biofilters were labeled with 13C-bicarbonate and supplemented with nitrite at concentrations of 0.3, 3 and 10 mM, and incubated at 17 and 28°C, respectively. The biofilm material was analyzed by fatty acid methyl ester - stable isotope probing (FAME-SIP). High portions of up to 45% of Nitrospira-related labeled lipid markers were found confirming that Nitrospira is the major autotrophic nitrite oxidizer in these brackish systems with high nitrogen loads. Other nitrite-oxidizing bacteria such as Nitrobacter or Nitrotoga were functionally not relevant in the investigated biofilters. Nitrospira-related 16S rRNA gene sequences were obtained from the samples with 10 mM nitrite and analyzed by a cloning approach. Sequence studies revealed four different phylogenetic clusters within the marine sublineage IV of Nitrospira, though most sequences clustered with the type strain of Nitrospira marina and with a strain isolated from a marine RAS. Three lipids dominated the whole fatty acid profiles of nitrite-oxidizing marine and brackish enrichments of Nitrospira sublineage IV organisms. The membranes included two marker lipids (16∶1 cis7 and 16∶1 cis11) combined with the non-specific acid 16∶0 as major compounds and confirmed these marker lipids as characteristic for sublineage IV species. The predominant labeling of these characteristic fatty acids and the phylogenetic sequence analyses of the marine Nitrospira sublineage IV identified organisms of this sublineage as main autotrophic nitrite-oxidizers in the investigated brackish biofilter systems.
Highlights
In biofilters of recirculation aquaculture systems (RAS), nitrite oxidation by lithoautotrophic bacteria (NOB) is the most important process to prevent the cultivated organisms from intoxication with nitrite [1]
Nitrite is formed by ammoniaoxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) during the first process of aerobic nitrification
Recirculation aquaculture systems are increasing worldwide [4], we still lack a detailed understanding of the process of bacterial nitrification, and especially nitrite oxidation, in marine RAS [5]
Summary
In biofilters of recirculation aquaculture systems (RAS), nitrite oxidation by lithoautotrophic bacteria (NOB) is the most important process to prevent the cultivated organisms from intoxication with nitrite [1]. Nitrite is formed by ammoniaoxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) during the first process of aerobic nitrification. Recirculation aquaculture systems are increasing worldwide [4], we still lack a detailed understanding of the process of bacterial nitrification, and especially nitrite oxidation, in marine RAS [5]. The guild of NOB is phylogenetically heterogeneous and comprises bacteria of at least five different genera: Nitrobacter, Nitrospina, Nitrococcus, Nitrospira and the recently discovered Nitrotoga. NOB grow slowly due to the low energy yield during oxidation of nitrite [13]. NOB cultures have only rarely been established in the laboratory [14]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.