Oceans high bacterial abundance

Fig. 8.3 Comparative bacterial community analysis (based on 16S rRNA gene clone libraries) of two species of Palinurid lobster larvae sampled directly from wild plankton of tropical ocean environment (R ornatus 1, R ornatus 2, R penicillatus) or from a hatchery environment (cultured R ornatus). Distinct community differences were detected between wild and aquaculture reared larvae. Also note the relatively high overall abundance of bacteria represented by single operational...

Additional evidence for a bacterial contribution to HMW DOM proteins comes from molecular-level analyses of dissolved amino acids. Hydrolysis of HMW DON releases 11-29% of the nitrogen as amino acids (McCarthy et al., 1996). Specific amino acids include common protein amino acids, as well as /3-alanine and y-aminobutyric acid which are nonprotein amino acid degradation products. The distribution of amino acids is similar to that of fresh plankton cells, suspended particulate matter, and total dissolved amino acids. However, stereochemical analyses show HMW DOM amino acids to be elevated in the D-enantiomer, with d/l ratios for alanine, aspartic acid, glutamic acids, and serine ranging from 0.1 to 0.5 (McCarthy et al., 1998). Racemization of phytoplankton-derived L-amino acids is too slow at ocean temperatures to yield such high D/L ratios, but bacteria can synthesize D-amino acids, and it is likely that the D-amino acids in HMW DOM result from bacterial bioploymers rich in these particular amino acids. The high dA ratios of some amino acids and the abundance of amide nitrogen in HMW DOM N-NMR spectra led McCarthy et al. (1998) to... 

---