Showing papers by "Peter A. Jumars published in 1998"

A Predictive Model of Bacterial Foraging by Means of Freely Released Extracellular Enzymes

Abstract: Extracellular enzymes are important agents for microbial foraging and material cycling in diverse natural and man-made systems. Their abundance and effects are analyzed empirically on scales much larger than the forager. Here, we use a modelling approach to analyze the potential costs and benefits, to an individual immobile microbe, of freely releasing extracellular enzymes into a fluid-bathed, stable matrix of both inert and food-containing particles. The target environments are marine aggregates and sediments, but the results extend to biofilms, bioreactors, soils, stored foods, teeth, gut contents, and even soft tissues attacked by disease organisms. Model predictions, consistent with macroscopic observations of enzyme activity in laboratory and environmental samples, include: support of significant bacterial growth by cell-free enzymes; preponderance of particle-attached, as opposed to dissolved, cell-free enzymes; solubilization of particulate substrates in excess of resident microbe growth requirements; and constitutive, abundant enzyme release in some environments. Feeding with cell-free enzymes appears to be limited to substrates within a well-defined distance of the enzyme source. Fluxes of dissolved organic material out of pelagic oceanic aggregates and marine sediments, and difficulty detecting dissolved enzymes in such environments, may reflect characteristics of cell-free enzyme foraging and properties of the enzymes. Our calculations further suggest that cell-free enzymes may often be used by microorganisms as the fastest means to search for food.

Constancy of bacterial abundance in surficial marine sediments

Abstract: Controls on bacterial abundance in marine sediments remain poorly understood despite the importance to biogeochemical processes, benthic ecology, and in situ bioremediation. We report an analysis of direct microscopic counts of widely distributed surficial marine sediments, using a new approach of scaling abundance to the fluid volume of pore water within the sediments (bacteria FV -1 ). The analysis identified a greater constancy in benthic bacterial abundance than has been appreciated previously. Whether tested as a combined dataset or separately according to geographic region, less variance was observed when abundance was scaled to fluid volume rather than the traditional dimension of dry sediment mass. The decrease in variance suggests that the primary controls on abundance, such as nutrient acquisition or predator encounter rate, may also scale with porewater fluid volume. With values centered around 10 9 bacteria ml -1 FV, regulation must differ fundamentally from the water column, where values average 10 5 -10 6 bacteria ml -1 FV.

Motion of diatom chains in steady shear flow

Abstract: Information on the motion of phytoplankton in shear flows is essential for predicting or understanding effects of turbulence on processes such as nutrient uptake, aggregate formation, and phytoplankter-herbivore interactions. Of particular interest is the motion of diatom chains because they are expected to benefit most from enhancement of nutrient flux due to turbulence and are often the most abundant components in aggregates. We studied the motion of two chain-forming diatoms, Skeletonema costatum and Thalassiosira nordenskiiildii, in steady shear flow and in the light of available theory for rigid, elongated spheroids. Both species underwent periodic rotation upon exposure to a simple shear flow, as predicted by theory. Whereas the rotational orbits of S. costutum resembled those predicted by theory for rigid spheroids, the rotational motion of T. nordenskiiildii was more like the motion of flexible fibers observed in engineering applications. Periods of rotation of S. costutum increased linearly with increasing axis ratio, whereas no clear relationship was observed between periods of rotation and axis ratios for T. nordenskiiildii. Measured periods of rotation of both species were smaller than predicted by theory for rigid spheroids of similar axis ratios. The diverse behaviors observed imply that fluxes of nutrients and collision frequencies experienced vary greatly with detailed shapes and mechanical properties of chains and their unit cells.