ABSTRACT
Dinitrogen fixation, the biological reduction in N2 gas to ammonia contributes to the supply of new nitrogen in the surface ocean. To understand the diversity and abundance of potentially diazotrophic (N2 fixing) microorganisms associated with marine zooplankton, especially copepods, the nifH gene was studied using zooplankton samples collected in the Pacific Ocean. In total, 257 nifH sequences were recovered from 23 nifH-positive DNA extracts out of 90 copepod samples. The nifH genes derived from cyanobacteria related to Trichodesmium, α- and γ-subdivisions of proteobacteria, and anaerobic euryarchaeota related to Methanosaeta concilii were detected. Our results indicated that Pleuromamma, Pontella, and Euchaeta were the major copepod genera hosting dinitrogen fixers, though we found no species-specific association between copepods and dinitrogen fixers. Also, the digital PCR provided novel data on the number of copies of the nifH gene in individual copepods, which we report the range from 30 to 1666 copies per copepod. This study is the first systematic study of zooplankton-associated diazotrophs, covering a large area of the open ocean, which provide a clue to further study of a possible new hotspot of N2 fixation.
Subject(s)
Alphaproteobacteria/genetics , Betaproteobacteria/genetics , Copepoda/microbiology , Methanosarcinales/genetics , Nitrogen Fixation/genetics , Oxidoreductases/genetics , Trichodesmium/genetics , Zooplankton/microbiology , Alphaproteobacteria/enzymology , Animals , Betaproteobacteria/enzymology , Methanosarcinales/enzymology , Pacific Ocean , Trichodesmium/enzymologyABSTRACT
Formalinized Aeromonas (A.) hydrophila agglutinated loosely with the formalinized American channel catfish erythrocytes (FACCE), while live A. hydrophila agglutinated tightly with the FACCE. There was a significant difference on the number of attaching bacterial cells to the FACCE (p<0.01) (n=40 erythrocytes) between formalinized and live A. hydrophila. The other bacteria such as Salmonella (S.) Typhimurium ST-5, Escherichia (E.) coli V-517 and Staphylococcus (S.) hyicus ATCC1249 used in this experiment did not attach the FACCE.
