High abundance of diazotrophic picocyanobacteria (< 3 mu m) in a Southwest Pacific coral lagoon

• Published in: Aquatic Microbial Ecology
• Main Authors: Biegala, Isabelle C., Raimbault, Patrick
• Other Authors: Caractérisation et modélisation des échanges dans des lagons soumis aux influences terrigènes et anthropiques (CAMELIA), Institut de Recherche pour le Développement (IRD Nouvelle-Calédonie )-Institut de Recherche pour le Développement (IRD Guyane )
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: diazotrophs; picoplankton; FISH; Pacific; coral lagoon; symbiosis; 16S RIBOSOMAL-RNA; TARGETED OLIGONUCLEOTIDE PROBES; TROPICAL NORTH-ATLANTIC; IN-SITU IDENTIFICATION; NITROGEN-FIXATION; CONFOCAL MICROSCOPY; COMMUNITY STRUCTURE; N-2 FIXATION; OCEAN; CYANOBACTERIA; envir; socio; North Atlantic
• Online Access: https://doi.org/10.3354/ame01185; https://hal.archives-ouvertes.fr/hal-00727031

In the present study we detected unicellular diazotrophic cyanobacteria along a nutrient gradient in New Caledonia's coral lagoon (24 000 km(2)) using whole-cell hybridization of specific Nitro821 probes (TSA-FISH, Tyramide Signal Amplification of Fluorescent In Situ Hybridization). The specificity of this probe was confirmed on cultures and in the natural environment, Surprisingly, the community of Nitro821-targeted cells was numerically dominated by picocyanobacteria (97%, 1 to 1.5 mu m). These organisms were either free living (63%), recovered with the 0.2 to 3 mu m size fraction or associated (37%) to particles or planktonic dinoflagellates from larger size fractions (3 to 10 mu m and >10 mu m). Diazotrophic picocyanobacterial abundance ranged from 3 to 140 cells ml(-1) along the nutrient gradient and was highest at the oligotrophic lagoonal station. These cells may contribute to N-2 fixation from the 10 mu m size fraction (0 to 1.9 nmol N-1 24 h(-1)). In addition, in the middle of the lagoon daylight N-15(2) fixation could explain 78% of N-15(2) fixation over 24 h. The results presented in the present study reveal for the first time a significant concentration of photosynthetic diazotrophs within the marine picoplankton community.