DISSOLVED FREE AMINO-ACIDS, COMBINED AMINO-ACIDS, AND DNA AS SOURCES OF CARBON AND NITROGEN TO MARINE-BACTERIA

Utilization of naturally-occurring dissolved free and combined amino a cids (DFAA and DCAA) and dissolved DNA (D-DNA) was studied in batch cu ltures of bacteria from 2 shallow marine environments, Santa Rosa Soun d (SRS), Florida, USA, and Flax Pond (FP), Long Island, New York, USA. In addition to control experiments, cultures were enriched with vario us sources of C and N. In the SRS cultures, net C assimilation of DCAA , DFAA and D-DNA made up from 42 to 60 % of net bacterial C production . The average, relative incorporation of C from DCAA, DFAA and D-DNA w as 0.13, 0.77 and 0.10, respectively. The corresponding values of N we re 0.10, 0.81 and 0.09. Addition of NH4+, DFAA, or both, increased the incorporation of DCAA, DFAA and D-DNA. Incorporation of N from DCAA, DFAA and D-DNA equaled 111 to 219 % of the bacterial N production. Inc luding incorporation of NH4+ and release of NO3-, calculated net bacte rial N incorporation made up 48 and 290 % of bacterial N production. I n the FP experiment, net assimilation of DCAA, DFAA and D-DNA equaled 66 to 91 % (average 77 %) of net bacterial C production. Largely all C incorporation was due to assimilation of DFAA. Enrichment of the cult ures with NH4+, glucose, methylamines, and high-molecular-weight disso lved organic matter all increased bacterial production. Net N incorpor ation of DCAA, DFAA and D-DNA corresponded to between 100 and 180 % of net bacterial N production. In 3 cultures DFAA were the dominant (> 5 0 %) bacterial N source. In the other cultures, DFAA and NH4+ were sim ilar in importance as an N source, and together they accounted for 80 to 99 % of bacterial N incorporation. Including uptake of NH4+ and upt ake or release of NO3- in the N budgets, bacterial N incorporation equ aled 155 to 413 % of bacterial N production. The reason for this appar ently excessive N uptake in both sets of cultures may be the release o f organic nitrogen compounds.