Comparison of the numerical grazing response of two marine heterotrophic nanoflagellates fed with different bacteria

The numerical grazing responses of two marine heterotrophic nanoflagellates (HNF), Jakoba libera strain 5(2) and Cafeteria sp. strain 5(3) fed with three bacterial strains (Alteromonas sp., Flavobacterium sp., and Pseudomonas sp.) and mixed bacterial communities (MBC) were compared. J. libera-5(2) had different numerical grazing responses to food bacteria. The net HNF cellular production, maximum specific growth rate (μmax) and maximum clearance rate (Fmax) values of J. libera-5(2) were highest with Pseudomonas sp., followed by Flavobacterium sp., MBC and Alteromonas sp. In contrast, Cafeteria sp.-5(3) showed the same numerical response to the food bacteria, and attained a 57-fold higher net stationary phase population, a 9-fold higher μmax, and a 5-fold higher Fmax than J. libera-5(2) with Alteromonas sp. as food bacteria. These differences in numerical grazing response of HNF may be important in structuring both the bacterial and protozoan species composition and succession in the marine environments.