Protein content and protein synthesis rates of planktonic marine bacteria

Abstract

Bacterial carbon production is an important parameter in understanding the flows of carbon and energy in aquatic ecosystems, but has been difficult to measure. Present methods are based on measuring the rate of cell production, and thus require a knowledge of cellular carbon content of the growing bacteria to convert cell production into carbon production. We have examined the possibility that protein synthesis rate of pelagic bacteria might serve as the basis for directly estimating bacterial carbon production. We measured bacterial protein content and protein production of pelagic bacteria. Bacterial protein content was measured as amino acids by high performance liquid chromatography of cell hydrolysates of bacterial assemblages of mean diameters from 0.026 to 0.4 km. Cellular protein:volume (w/v) in the largest bacteria was 15.2 '10 (similar to cultured Escherichia coli] but increased with decreasing cell size to 46.5 % in 0.026 pm bacteria. Protein per bacterium was correlated with cell volume by the power function y = 8 8 .~2~' (r2 = 0.67; p C 0.01; n = 25). An inventory of major bacterial macromolecular pools revealed that cell protein:dry weight and cell protein:carbon were essentially constant (63 % and 54 %. respectively) for the entire cell size range although cell protein:volume increased with decreasing cell size. Thus, the smaller cells in the size range were rich in carbon and dry weight and poor in water compared with larger cells. We established the experimental conditions for estimating protein synthesis on the basis of 3H leucine incorporation by bacteria, and determined the necessary parameters (including the intracellular isotope dilution by HPLC) for converting 3~ leucine incorporation into protein synthesis rate. In samples from Scripps Institution of Oceanography pier the intracellular isotope dilution was only 2-fold. In a field study in Southern California Bight bacterial protein production and %I-thymidine incorporation methods yielded comparable rates of bacterial production. Bacterial protein production method was an order of magnitude more sensitive and yielded bacterial carbon production directly without the need to know the cell size of the part of the assemblage in growth state.

From image analysis to chemical analysis of bacteria: A long-term study?

“…Recently, the measurement of the C content of natural freshwater and marine bacteria (Table 1) was done by HPLC of hydrolyzed amino acids (Simon and Azam 1989), X-ray analysis of single cells in the scanning electron microscope (Norland et al 1987) and CHN analysis of bacteria on glass-fiber filters (Lee and Fuhrman 1987). Each method for determining bacterial C and size has advantages and drawbacks.…”

“…By X-ray analysis, carbon and volume data for single cells are obtained, but calibration is very diffi- (Lee and Fuhrman 1987). A ratio of carbon to dry matter of 55% was assumed for curve 2; 1 - Simon and Azam 1989;2-Norland et al 1987;3-Lee and Fuhrman 1987. Cell volume (pm3) cult.…”

“…Both HPLC and CHN analysis deliver averaged carbon values for a narrow size range of bacterial cell volumes (see Table I), yet must be extrapolated to natural populations ranging from -0.00 1 pm3 to -1 pm3 (Bjornsen et al 1989;Krambeck and von Montigny 1988). The formulas derived from the data of Simon and Azam (1989), Norland et al ( 198 7) and Lee and Fuhrman ( 198 (2) C = 14 vol-0.15 (Lee and Fuhrman 1987).…”

“…1 and 3 differs by almost one order of magnitude (3.7 and 28.7 fg C cell-l). The formula of Simon and Azam (1989) generates a more even carbon distribution of -26%, 34%, and 40% for small (0.00 l-0.0 1 pm3), medium-sized (0.0 1-O. 1 hm3), and large cells (0.1-0.5 pm"), with an average C content of 8.4 fg cell-1 (Table 2).…”

Mesure de la biomasse et de l'activité bactérienne dans l'eau de distribution

“…Des méthodes permettant des mesures d'activité bactérienne ont été dévelop-pées pour l'étude des milieux aquatiques naturels, elles sont principalement basées sur l'emploi de traceurs radioactifs. Parmi celles-ci, l'incorporation de thymidine tritiée dans le matériel génétique bactérien (FUHRMAN et AZAM, 1980SERVAIS, 1988) est actuellement la plus couramment utilisée, mais l'incorporation de leucine tritiée dans les protéines (KIRCHMAN étal., 1985) semble une voie tout à fait intéressante et complémentaire (SIMON et AZAM, 1989 ;SERVAIS, 1990 ;SERVAIS etGARNiER, 1990). Ces deux méthodes ont été sélectionnées, d'une part, pour leur spécificité vis-à-vis des bactéries, d'autre part, pour leur sensibilité nécessaire à la mesure d'activité dans les conditions d'un réseau de distribution.…”