No abstract

Heterotrophic activity was measured through a vertical profile in Halifax Harbor sediments using 14C labeled glucose, glutamate, and lactate as substrates. A modified heterotrophic potential method was used to detect the amount of label that was converted to low molecular weight metabolites as well as the amounts respired to CO, and incorporated into cellular material. For all three substrates, total uptake was greatest at the transit~on from aerobic to anerobic sediments (40 cm subbottom). The percentage of the total uptake respired reflected the predominant type of heterotrophic metabolism at the various horizons with the highest values occurring above (aerobic respiration) and below (sulfate reduction) the 40 cm horizon. Incorporation of the substrates into cellular matenal was low for both glutamate and lactate (< 5 % ) but averaged approximately 30 % for glucose. For all three substrates tested, low molecular weight metabolites represented a significant portion of the substrate uptake at many horizons (approximately 50 % at 40 cm). Data are presented indicating that the observed increase in heterotroph~c activity at 40 cm sub-bottom may be due to chemoautotrophic organic carbon production at this horizon.

No abstract

Microbial biomass, metabolic activity, and nucleic acid synthesis were measured throughout a vertlcal profile of a coastal sub-tropical marine sediment. Heterotrophic activity, as measured by the uptake and respiration of 14C-glutamic acid, varied between individual sediment cores but generally was constant with depth for a given sample. Blomass (as determined by ATP concentrations) and DNA and RNA synthesis rates (as measured by the incorporation of 3H-adenine) were consistently higher at the sediment-water interface and decreased with depth. Consequently, the biomass(ATP)-specific rate of heterotrophic uptake increased sharply wlth depth while the biomassspecific rates of RNA and DNA synthesis remained constant These data indicate the presence of a large microbial biomass associated with the sediment-water interface and a smaller but equally competent population deeper within the sediment. Furthermore, cell divis~on (DNA synthesis) does not appear to b e directly correlated with heterotrophic activity; however, data from both methods yield important and independent information concerning the metabolism of the mlcrob~al population as a whole.

ABSTRACT. Growth kinehcs of the microbial community of a coastal, sub-tropical sediment were studied by following uptake of 3~-a d e n i n e .3~-a d e n i n e was incorporated into RNA and DNA, thus providing a measure of both cell metabolism and growth. Extrapolation from measured values of isotope dilution of the ATP pool at isotopic equhbrium (i.e. SA,,, parameter) indicated that a large portion of the adenine required for community nucleic acid synthesis was derived from uptake of exogenous supplies. Microbial community doubling times, estimated from adenine nucleotide pool labeling kinetics, ranged from 26 h at the seawater-sediment interface to 47 to 92 h for samples beneath the interface. RNA synthesis rate consistently exceeded DNA synthesis rate by 1 to 2 orders of magnitude for all horizons examined, in spite of these relatively slow growth rates. The newly synthesized RNA was found to be stable with less than 10% being degraded during a period equivalent to the mean population doubling time. Our results indicate a sediment microbial community with growth rates and metabolism distinctly different from water-column communities. The results strongly suggest net, but unbalanced growth in these sediment communities.