Abstract

PENA-ZUNIGA, Pedro; SAMPERIO-RAMOS, Guillermo A  and  PAJARES-MORENO, Silvia. Distribution and potential activity of aerobic denitrifying bacteria isolated from sediments of a coastal lagoon system in northwestern Mexico. Cienc. mar [online]. 2024, vol.50, e3459.  Epub Jan 24, 2025. ISSN 0185-3880.  https://doi.org/10.7773/cm.y2024.3459.

Denitrification is the primary pathway by which fixed nitrogen is lost from marine systems and consists of the sequential respiration of nitrate into molecular nitrogen by diverse heterotrophic microorganisms. Since estuarine sediments serve as important niches for denitrification, this study assessed the distribution and potential activity of aerobic denitrifying bacteria isolated from sediments at 2 depths and 2 habitats (with Zostera marina seagrass and without seagrass) along a transect in Bahía de San Quintín (Mexico), and their relationship with various environmental parameters. A total of 1,611 bacteria were isolated, of which 85.1% carried denitrifying genes (nirK, nirS, or nosZ). Their distribution was heterogeneous in the bay and was primarily influenced by sediment texture, pH, total organic carbon, and total nitrogen, with the highest abundance of denitrifying bacteria in surface sediments (66.2%). The denitrifying isolates were classified into 23 species belonging to γ-Proteobacteria (82.4% of isolates), α-Proteobacteria (7.9%), Bacilli (5.7%), and Actinobacteria (4%). Denitrifying activity in aerobic conditions was confirmed in 7 species of bacteria carrying denitrifying genes: Paracoccus marcusii, Planococcus maritimus, Planococcus rifietoensis, Pseudomonas songnenensis, Psychrobacter alimentarius, Psychrobacter celer, and Psychrobacter piscatorii. The results suggest that these sediments harbor a high abundance of culturable bacteria with nirK, nirS, or nosZ genes, although denitrification activity in aerobic conditions could not be confirmed in most cases, possibly due to the inactivity of these genes or those involved in nitrate reduction (nas, nar, or nap). This study represents the first step towards understanding the ecology of microorganisms involved in aerobic denitrification in Bahía de San Quintín and in coastal lagoons in general.

Keywords : aerobic denitrification; estuary; sediments; isolation; denitrifying genes.

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