Evaluation of a proposed surface colonization equation usingThermothrix thiopara as a model organism

Abstract

The colonization equation shown below was evaluated usingThermothrix thiopara as a model organism.

$$N = (A/\mu )e^{\mu t} - A/\mu $$

where: N=number of cells on surface (cells field⁻¹); A = attachment rate (cells field⁻¹ h⁻¹); M=specific growth rate (h⁻¹); t=incubation period (h).

Previous studies of microbial surface colonization consider attachment and growth independently. However, the proposed colonization equation integrates the effects of simultaneous attachment and growth. Using this equation, the specific growth rate ofT. thiopara was found to be 0.38±0.3 h⁻¹ during in situ colonization. Estimates ofμ were independent of incubation period after 4 h (2 generations). Shorter incubations were inadequate to produce sufficient microcolonies for accurate determination of specific growth rate. Empirical data for the time course of colonization fell within the 95% confidence interval of predicted values. The attachment rate, although assumed to be constant, was found to continuously increase with time. This increase may have been an artifact due to the continuous deposition of travertine on the surface, or may indicate the need for a function to replace A in the colonization equation. Using the exponential growth equation, the progeny of cells that attach during incubation are considered to be progeny of cells that attach initially. This erroneously inflated the growth rate by 55%.