Author(s): Jrgensen NO, Kroer N, Coffin RB
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Abstract The significance of dissolved combined amino acids (DCAA), dissolved free amino acids (DFAA), and dissolved DNA (D-DNA) as sources of C and N for marine bacteria in batch cultures with variable substrate C/N ratios was studied. Glucose, ammonium, alanine, and phosphate were added to the cultures to produce C/N ratios of 5, 10, and 15 and to ensure that phosphorus was not limiting. Maximum bacterial particulate organic carbon production (after 25 h of incubation) was inversely correlated with the C/N ratio: with the addition of identical amounts of carbon, the levels of production were 9.0-, 10.0-, and 11.1-fold higher at C/N ratios of 15, 10, and 5, respectively, relative to an unamended control. The bacterial growth efficiency increased from 22\% (control cultures) to 44 to 53\% in the cultures with manipulated C/N ratios (C/N-manipulated cultures). Net carbon incorporation from DCAA, DFAA, and D-DNA supported on average 19, 4, and 3\% (control cultures and cultures to which only phosphate was added [+P cultures]) and 5, 4, and 0.3\% of the particulate organic carbon production (C/N-manipulated cultures), respectively. In the C/N-manipulated cultures, a 2.6- to 3.4-fold-higher level of incorporation of DCAA, relative to that in the control cultures, occurred. Incorporation of D-DNA increased with the substrate C/N ratio, suggesting that D-DNA mainly was a source of N to the bacteria. Organic N (DCAA, DFAA, and D-DNA) sustained 14 to 49\% of the net bacterial N production. NH(4) was the dominant N source and constituted 55 to 99\% of the total N uptake. NO(3) contributed up to 23\% to the total N uptake but was released in two cultures. The studied N compounds sustained nearly all of the bacterial N demand. Our results show that the C/N ratio of dissolved organic matter available to bacteria has a significant influence on the incorporation of individual compounds like DCAA and D-DNA.
This article was published in Appl Environ Microbiol
and referenced in Journal of Aquaculture Research & Development