Douglas E. Caldwell

Fine structure of in situ microbial iron deposits

The fine structure of iron deposits produced by Leptothrix spp. from two caverns and a surface spring were observed. In the case of Leptothrix pseudovacuolata, the iron occurred as an amorphous deposit within the cell sheath and the cells contained gas vesicles. In the case of the other Leptothrix spp., the iron was deposited within the cell sheath either as a hexagonal or fibrillar matrix. In the case of fibrillar iron deposits, fibrils resembling those of the sheath were found within the cytoplasm of the cells. This suggests that the deposition of iron could have occurred within the cells as well as at the cell surface. In some cases, the fine structure of microbial iron deposits could provide a means of distinguishing biological from abiological iron deposition.

Derivation of a Growth Rate Equation Describing Microbial Surface Colonization

AbstractA surface growth rate equation is derived which describes simultaneous growth and attachment during microbial surface colonization. The equation simplifies determination of attachment and growth rate, and does not require a computer program for solution. This rate equation gives the specific growth rate (Μ) as a function of the number of cells on the surface (N), the incubation period (t), and the number of colonies (Ci) containing either one cell, two cells, four cells, etc, as shown below.

Chemostat and in‐situ colonization kinetics of thermothrix thiopara on calcite and pyrite surfaces

\mu = \frac{{\ln (\frac{N}{{C_i }} + 1)}}{t}

Weathering of calcite, pyrite, and sulfur by Thermothrix thiopara in a thermal spring

The attachment rate (A) is given by the following relationship:

Multicellular organization in a degradative biofilm community.

A = \mu C_i

Bioaccumulation of the herbicide diclofop in extracellular polymers and its utilization by a biofilm community during starvation

The proposed colonization kinetics are compared with exponential growth kinetics using 3-dimensional computer plots. Colonization kinetics diverged most from exponential kinetics when the growth rate was low or the attachment rate was high. Using these kinetics, it is possible to isolate the effects of growth and attachment on microbial surface colonization.