Dynamics of microbial growth in surface layers of a coastal marine sediment ecosystem

Abstract

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.

Growth of Enterococci in Unaltered, Unseeded Beach Sands Subjected to Tidal Wetting

“…There are limitations to using microcosms to study microbial processes, as natural field conditions (such as temperature, moisture, and concentration of predators) are difficult to maintain. However, microcosms are commonly used for studying microbial growth and transformations in environmental media (15,24). Using this technique, the present study shows that the intermittent wetting of sands by seawater stimulates the transient replication of enterococci at rates of 0.20 to 0.63 per day (equivalent to doubling times of 1.1 to 3.5 days).…”

Aerobic growth at nanomolar oxygen concentrations

“…We chose these doubling times because in Earthsurface environments, organisms must be able to respond to changing temperatures, moisture, and energy supply, which are dynamic on time scales of days to months. Such doubling times are also typical for prokaryotes in surface marine sediments and in the marine water column (26,27). Model results show that for a 1-μm cell, an oxygen concentration of 0.2 nM would be sufficient to allow a doubling time of 30 d, and for a cell as small as 0.5 μm [which is small for a prokaryote cell (11)], 0.050 nM O 2 would suffice (Table 1).…”

Bacterial recolonization of deposit‐feeder egesta: In situ regrowth or immigration?

“…Thus, naturally incubated feces could have become enriched in some growth-stimulating solutes as they aged, relative to feces on latrines. It is highly unlikely that a rapid equilibration of solute concentration could have led to the numerical responses observed within our 2-h incubations, however, given that doubling times in porewaters of sandy intertidal sediments generally are on the order of days (e.g., Fallon et al 1983;Karl and Novitsky 1988;Deming and Baross 1993 and references within). Outward diffusion of metabolic byproducts would also be inhibited on latrines.…”