The microbiology of pine bark composting: An Electron-microscope and physiological study

Abstract

An electron microscope study was conducted on samples of pine bark taken from stacks during consecutive stages of composting. It was found using scanning electron microscopy (SEM) that bacteria, actinomycetes and fungi were present in relatively low numbers on the bark surface before composting was initiated. After addition of urea and water to bark heaps, microbial numbers rose, particularly the bacterial fraction. A large number of actinomycetes were seen below the surface of the bark as composting progressed. Transmission electron microscopy (TEM) of bark in the late stages of composting demonstrated the presence of a variety of microbes within the bark cells. The microorganisms were seen, using SEM, to be degrading the surface of the bark chips, and, using TEM, to be attached to the lignified cell walls. Physiological studies on bacteria isolated at different stages of composting showed they had a number of enzymes such as carboxymethyl cellulase that could aid in the degradation of pine bark. The isolates consisted of Gram-negative and Gram-positive strains, some of which were spore formers. Most of the isolates, including some Gram-negative non-sporing bacteria, were able to grow over a wide range of temperatures from 30 to 60°C, and, in some cases, 70°C.