MEPS 128:109-120 (1995)  -  doi:10.3354/meps128109

The contribution of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA) and ammonium to the C and N requirements of bacterioplankton was examined in batch cultures enriched with various sources of C and N. DFAA sustained up to 14 and 34% of the C and N requirements, respectively, during exponential growth. DCAA constituted less than 10% of the C demand in all cultures during exponential growth and up to 24% of the N demand in N-limited cultures. In C-limited cultures DFAA, DCAA, and NH₄⁺ constituted 37 to 62%, 4 to 10% and 27 to 59% of total N uptake (DFAA + DCAA + NH₄⁺) during exponential growth. In nitrogen-limited cultures the corresponding values were 78, 14, and 8% of total N uptake. During the stationary phase the importance of DCAA as a C and N source increased as DFAA and NH₄⁺ concentrations decreased. In addition to allowing us to examine the contribution of various compounds to supporting bacterial production, our data on uptake and concentrations suggest that bacteria release free and combined amino acids, especially during the stationary phase.

DCAA . DFAA . Ammonium . Bacterial utilization . C- and N-limitation