Molecular
Characterization of Denitrifying Bacterial Communities in the Cape Fear River
Estuary,
ABSTRACT
Denitrifying
bacteria are ubiquitously distributed in various ecological niches. Under anaerobic conditions, denitrifying
bacteria use available nitrate and nitrite in place of oxygen to fuel
respiratory systems. Denitrification
is an important microbial process that removes excess nitrogen, which may cause
eutrophication and fish kills in aquatic
environments. To understand how
denitrifying community composition is shaped by environmental parameters,
denitrifying communities in the Cape Fear River Estuary, North Carolina were
examined using molecular techniques to detect and examine the presence of
nitrite reductases (nirS and nirK),
the functional genes responsible for denitrification,
and to understand the genetic diversity that exists within this group of
bacteria. In addition, community
structures of denitrifying bacteria were compared along environmental gradients
in the Cape Fear River Estuary. DNA
extracted from the sediment samples at each site was used as a template for PCR
amplification of nirS genes, and the
amplified products were cloned and subsequently sequenced for further
analysis. Phylogenetic
analysis of the nirS genes showed the presence
of diverse denitrifying bacteria at the Cape Fear River Estuary. Genetic diversity was highest at the site
with lowest salinity and highest nitrate concentration, and lowest at the site
of highest salinity and lowest nitrate concentration. Statistical analysis of nirS
gene sequences performed with Distance Based OTU and Richness Determination
(DOTUR) and Molecular Evolutionary Genetics Analysis (MEGA) indicated close
relationships exist between denitrifying community diversity and salinity and
nitrate concentration in the estuary.
Therefore, this study provides the first insights into the diversity and
structure of denitrifying bacterial communities at the Cape Fear River Estuary,