Dark Sulfate Uptake and Bacterial Productivity in a Subalpine Lake

Abstract

Dark uptake of 35SO4 was investigated as a possible method for estimating bacterial production rates in Castle Lake, California. Assuming a fixed cellular sulfur; carbon ratio, bacterial productivities determined in this manner ranged from 2.5 to 28 mg C°m.—3°day—1 in 48 in situ measurements in the summer of 1972. Average production rates increased throughout the sampling period and corresponded in part to increasing levels of dissolved organic carbon. Production rates were stimulated by addition of NH4Cl and vitamin B12 to water samples, but not by thiamine, biotin, SO4, NO3, PO4 or a trace metal mix. Further studies on the sulfur content of bacteria and the role of phytoplankton in SO4 uptake are required before dark 35SO4 uptake is used for routine field measurements.

Assimilatory sulfur metabolism in marine microorganisms

“…Whole cell sulfate uptake has been used in freshwater ecosystems in the hope of finding a method for estimating bacterial carbon production for inclusion in carbon budgets (Campbell and Baker, 1978;Jassby, 1975;Jordan and Peterson, 1978;Monheimer, 1974b). However, laboratory studies demonstrated a 65-fold range in C:S uptake ratios (Monheimer, 1978b), preventing unambi guous interpretation of carbon ass imil at i on va lues derived from sulfate uptake studies (Monheimer, 1978a).…”

“…However, laboratory studies demonstrated a 65-fold range in C:S uptake ratios (Monheimer, 1978b), preventing unambi guous interpretation of carbon ass imil at i on va lues derived from sulfate uptake studies (Monheimer, 1978a). Indeed, the C:S ratio for ~ halodurans (Table 4-30) spans the range of purportedly con--251-stant C:S ratios of 50:1 (Jassby, 1975) to 500:1 (Monheimer, 1974b) during exponential growth. A much smaller range is observed for A. luteovi olaceus because ce 11 growth and protei n synthes i s are more tightly coupled.…”

“…In the open ocean, animals capable of filter-feeding on particles in the bacterial size range (0.2-2 l.m) have been repeatedly observed, often in large numbers (Harbison and McAlister, 1979;Wiebe et aL., 1979), and knowledge of the potential transfer of microbial biomass No attempts have been made to measure sulfate metabol ism by marine bacteria, in part due to the large isotope dilution barrier posed by the nearly 30mM sulfate concentration. A sulfate uptake method used in freshwater (Jassby, 1975;Jordan and Peterson, 1978;Monheimer, 1974a) met with frustration due to the lack of correlation between sulfate uptake -258-and bacterial carbon production (Monheimer, 1978b). Consideration of the physiology of unbalanced bacterial growth with respect to carbon and sulfur metabolism argues against a close correlation between whole cell carbon and sulfur assimilation (Chapters 1 and 4).…”

“…The application of com~etitive inhibition, by sulfate analogs to natural populations may be of practical value in the case of thiosulfate (S203)' The use of sulfate 'uptake by bacteria as a measure of bacterial production has been attempted in freshwater habitats (Jassby, 1975;Monheimer, 1974a) but met with 1 ittle success due to low rates of sulfate uptake combined with high isotope adsorption blanks . Although no constant relationship was found between microbial carbon assimilation and sulfate uptake (Monheimer, 1978b), evidence derived from the data of Datko et ale (1978b) A possible means for circumventing the problem of isotope dilution is to outcompete sulfate for uptake and metabolism using a competitive inhibitor which can replace sulfate in assimilatory sulfur metabolism.…”

Improved filtration procedures for freshwater [35S]SO4 uptake studies 1

“…A similar technique for estimating bacterial production based on dark [35S]S0, uptake was proposed by Jassby (1975 and rinsed with 50 ml of filtered lake water. When we followed similar procedures for oligotrophic lakes in New Hampshire, Ontario, and British Columbia, we obtained control (sample killed with Lugol's preservative) filter values from 4,000 cpm (at 0.2 &i [35s]so 4 ml-l) to 50,000 cpm (at 1.0 &i ml-l).…”