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Salter I.,University Pierre and Marie Curie | Bottjer D.,SOEST | Bottjer D.,Center for Microbial Oceanography | Christaki U.,University Pierre and Marie Curie | Christaki U.,University of Lille Nord de France
Environmental Microbiology | Year: 2011

The effect of inorganic particle concentrations on bacteria-virus-nanoflagellate dynamics in an oligotrophic coastal system was investigated using a model aluminosilicate, kaolinite, with a modal size of 2.1μm. Virus-only, bacteria-only and bacteria-virus-nanoflagellate incubations were carried out at increasing kaolinite concentrations to elucidate the microbial response. The sorption of bacteria and viruses to kaolinite particles was negligible over a concentration range of 1-50mgl -1. In contrast, the abundance of heterotrophic nanoflagellates was negatively correlated with kaolinite concentrations following both 48 and 96h incubations. Calculated nanoflagellate bacterial ingestion rates were reduced by 5-35% depending on kaolinite particle concentration. In the bacteria-virus-nanoflagellate incubations viral production increased by 56×10 3 to 104×10 3VLPsml -1h -1 as a function of kaolinite particle concentration. Our results demonstrate for the first time that the interaction of microbial populations with inorganic particles can shift the balance between protist and virally mediated mortality of marine heterotrophic prokaryotes. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd. Source

Wilson S.T.,Center for Microbial Oceanography | Wilson S.T.,University of Hawaii at Manoa | Tozzi S.,Center for Microbial Oceanography | Tozzi S.,University of California at Santa Cruz | And 12 more authors.
Applied and Environmental Microbiology | Year: 2010

The hydrogen (H 2) cycle associated with the dinitrogen (N 2) fixation process was studied in laboratory cultures of the marine cyanobacterium Crocosphaera watsonii. The rates of H 2 production and acetylene (C 2H 2) reduction were continuously measured over the diel cycle with simultaneous measurements of fast repetition rate fluorometry and dissolved oxygen. The maximum rate of H 2 production was coincident with the maximum rates of C 2H 2 reduction. Theoretical stoichiometry for N 2 fixation predicts an equimolar ratio of H 2 produced to N 2 fixed. However, the maximum rate of net H 2 production observed was 0.09 nmol H 2 μg chlorophyll a (chl a) -1 h -1 compared to the N 2 fixation rate of 5.5 nmol N 2 μg chl a -1 h -1, with an H 2 production/N 2 fixation ratio of 0.02. The 50-fold discrepancy between expected andobserved rates of H 2 production was hypothesized to be a result of H 2 reassimilation by uptake hydrogenase. This was confirmed by the addition of carbon monoxide (CO), a potent inhibitor of hydrogenase, which increased net H 2 production rates ∼40-fold to amaximumrate of 3.5 nmol H 2 μg chl a -1 h -1. We conclude that the reassimilation of H 2 by C. watsonii is highly efficient (>98%) and hypothesize that the tight coupling between H 2 production and consumption is a consequence of fixing N 2 at nighttime using a finite pool of respiratory carbon and electrons acquired from daytime solar energy capture. The H2 cycle provides unique insight into N 2 fixation and associated metabolic processes in C. watsonii. © 2010 American Society for Microbiology. Source

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