Macromolecules & Molecular Size Distributions

The study of the microbial breakdown of macromolecules is an important area of research for natural and engineered systems. The largest pool of organic carbon on the planet is the dissolved organic matter (DOM) in the ocean. Understanding the fate of this material can help us to understand global carbon cycling and the dynamics of natural systems. In engineered systems, such as water and wastewater treatment systems, the efficiency of removal of DOM in both abiotic and microbially-based systems is a function of the molecule size.

When is a organic matter a "molecule" or a "particle"? There is no one accepted size classification of DOM. For example, marine chemists define colloids as DOM greater than 1000 Daltons (1 kDa), and particles as material larger than 0.2 um. Water treatment engineers characterize colloids as particles less than 0.2 um but larger than 100 kDa, defining macromolecules as any DOM that cannot be classified (typically with a molecular weight of > 1 kDa).

Bacteria must degrade molecules larger than approximately 1 kDa before they can be taken into the cell and oxidized for energy. The breakdown of macromolecules, defined here as all material larger than 1 kDa, is a relatively unexamined area of research. It is difficult to conduct such research as the changes in size distributions of these molecules must be monitored during degradation experiments. Our laboratory has contributed to analysis of molecule sizes by developing a permeation coefficient model (Logan and Jiang, 1990) for analyzing particle size distributions.

Research into this area has gone on for many years in the Logan laboratory, primarily in the following areas: 1- characterizing molecular size distributions using ultrafiltration (UF) separation techniques; 2- microbial degradation of macromolecules; 3- removal of macromolecules in water and wastewater treatment processes. This work is described in a series of papers-- see the publications link in the menu to the left. Additional detail on the permeation coefficient model can be found in Chapter 3 of my book Environmental Transport Processes, and the powerpoint presentation listed above (see UF-method).