Patterns of Microbial Heterotrophy Through Changing Environments in a Marine Sediment

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.

Microbial activity at the sediment-water interface in Halifax Harbor, Canada

“…However, since the amount of nutrient added is equal to VOL. 45,1983 the amount used in the measurement of heterotrophic activity by the single substrate concentration technique of Griffiths et al (6) used in this and other studies (13,14), the rates obtained here should correspond to previous measurements. However, the glutamate uptake rate calculated for the interface with the whole-core technique (12.8 ng g [dry weight]-1 h-1; Table 3) is almost an order of magnitude less than that measured (113.5 ng g [dry weight]-1 h-1; Table 2) with the previous technique, using shaken subsamples diluted in filtered seawater.…”

“…The sampling site used in this study was the area of Halifax Harbor known as Eastern Passage, which was also the site of previous studies (8,9,13,14,16 …”

“…Standard heterotrophic activity measurements were made on the interface as previously described (13,14), using [U-t4Cjglutamic acid (specific activity, 267 mCi/ mmol). Heterotrophic activity measurements conducted with undisturbed cores were made by adding, [ Additions were made so that the final concentration of labeled substrate in the overlying water was equal to that used for the described heterotrophic activity measurement, 0.01 ,XCi/ml.…”

Heterotrophic activity throughout a vertical profile of seawater and sediment in Halifax Harbor, Canada

“…Two sampling sites were used in this study. The primary site, known as the Eastern Passage site, has been used in previous studies (7,8,11,13). It is within Halifax Harbor and is characterized as a 22-m water column overlying a mud bottom.…”

“…Two sampling sites were used in this study. The primary site, known as the Eastern Passage site, has been used in previous studies (7,8,11,13 mmol). Ten-milliliter portions of the water samples were placed into 50-ml serum bottles, labeled substrate (0.1 ,uCi) was added to each, the bottles were capped, and the head space within was flushed with the appropriate air-N2 mixture to simulate the in situ 02 concentration at that particular depth.…”