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.
hovanecAEM_Jan98
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.
Hovanec_DelongAEM_Aug96