On this page are reprints of peer-reviewed research papers written or co-authored by Dr. Timothy A. Hovanec.

Peer-reviewed means that before the paper was published in a scientific journal it was first anonymously reviewed by other researchers not connected with the lab. These reviewers judged the paper for content and scientific worthiness. Only papers determined to meet sufficient scientific criteria are accepted for publication. This is part of the self-policing of scientists.

The abstract of each paper is presented to give you a quick review of the paper. All the articles are copyrighted and may not be reprinted or copied in any fashion without the written consent of the copyright holder.

Paul C. Burrell, Carol M. Phalen, and Timothy A. Hovanec. Identification of Bacteria Responsible for Ammonia Oxidation in Freshwater Aquaria. Applied and Environmental Microbiology, Dec. 2001, p. 5791-5800

Abstract: Culture enrichments and culture-independent molecular methods were employed to identify and confirm the presence of novel ammonia-oxidizing bacteria (AOB) in nitrifying freshwater aquaria. Reactors were seeded with biomass from freshwater nitrifying systems and enriched for AOB under various conditions of ammonia concentration. Surveys of cloned rRNA genes from the enrichments revealed four major strains of AOB which were phylogenetically related to the Nitrosomonas marina cluster, the Nitrosospira cluster, or the Nitrosomonas europaea-Nitrosococcus mobilis cluster of the subdivision of the class Proteobacteria. Ammonia concentration in the reactors determined which AOB strain dominated in an enrichment. Oligonucleotide probes and PCR primer sets specific for the four AOB strains were developed and used to confirm the presence of the AOB strains in the enrichments. Enrichments of the AOB strains were added to newly established aquaria to determine their ability to accelerate the establishment of ammonia oxidation. Enrichments containing the Nitrosomonas marina-like AOB strain were most efficient at accelerating ammonia oxidation in newly established aquaria. Furthermore, if the Nitrosomonas marina-like AOB strain was present in the original enrichment, even one with other AOB, only the Nitrosomonas marina-like AOB strain was present in aquaria after nitrification was established. Nitrosomonas marina-like AOB were 2% or less of the cells detected by fluorescence in situ hybridization analysis in aquaria in which nitrification was well established.
hovanec AEM_Dec01

Hovanec, T. A., L. T. Taylor, A. Blakis and E. F. DeLong. 1998. Nitrospira- Like Bacteria Associated with Nitrite Oxidation in Freshwater Aquaria. Applied and Environmental Microbiology Vol. 64, No. 1: 258-264.

Abstract: Oxidation of nitrite to nitrate in aquaria is typically attributed to bacteria belonging to the genus Nitrobacter which are members of the alpha subdivision of the Proteobacteria. In order to identify bacteria responsible for nitrite-oxidation in aquaria, clone libraries of rRNA genes were developed from biofilms of several freshwater aquaria. Analysis of the rDNA libraries, along with results from denaturing gradient gel electrophoresis (DGGE) on frequently sampled biofilms, indicated the presence of a putative nitrite-oxidizing bacteria closely related to the genus Nitrospira. Nucleic acid hybridization experiments with rRNA from biofilms of freshwater aquaria demonstrated that Nitrospira-like rRNA comprised nearly 5% of the rRNA extracted from the biofilms during the establishment of nitrification. Nitrite-oxidizing bacteria belonging to the alpha Proteobacteria subdivision (e. g., Nitrobacter spp.) were not detected in same samples. Aquaria which received a commercial preparation containing Nitrobacter species did not show evidence of Nitrobacter growth and development but did develop substantial populations of Nitrospira-like species. Time series analysis of rDNA phylotypes on aquaria biofilms by DGGE, combined with nitrite and nitrate analysis, showed a correspondence between the appearance of Nitrospira-like bacterial ribosomal DNA, and the initiation of nitrite oxidation. In total, the data suggest that Nitrobacter winogradskyi and close relatives were not the dominant nitrite-oxidizing bacteria in freshwater aquaria. Instead, nitrite oxidation in freshwater aquaria appeared to be mediated by bacteria closely related to Nitrospira moscoviensis and Nitrospira marina.

Hovanec, T. A. and E. F. DeLong. 1996. Comparative Analysis of Nitrifying Bacteria Associated with Freshwater and Marine Aquaria. Applied and Environmental Microbiology Vol. 62, No. 8: 2888-2896.

Abstract: Three nucleic acid probes, two for autotrophic ammonia-oxidizing bacteria of the beta subdivision of the class Proteobacteria and one for alpha subdivision nitrite-oxidizing bacteria, were developed and used to study nitrifying bacterial phylotypes associated with various freshwater and seawater aquarium biofilters. Nitrosomonas europaea and related species were detected in all nitrifying seawater systems, and accounted for as much as 20% of the total eubacterial rRNA. In contrast, nitrifying bacteria belonging to the beta Proteobacterial subdivision were detected in only two samples from freshwater aquaria showing vigorous nitrification rates. rRNA originating from nitrite-oxidizing alpha subdivision Proteobacteria was not detected in samples from either aquarium environment. The data obtained indicates that chemolithotrophic ammonia oxidation in the freshwater aquaria was not due to beta Proteobacterial phylotypes related to the genus Nitrosomonas, and their close relatives, the organisms usually implicated in freshwater nitrification. It is likely that nitrification in natural environments is even more complex than nitrification in these simple systems and is less well characterized with regard to the microorganisms responsible.