Microbial succession on a chitinous substrate in a woodland stream

Plate counts, scanning electron microscopy, and direct observations were utilized to determine successional trends of different groups of microorganisms onProcambarus versutus (Hagen) exoskeletons incubatedin situ in a second-order, acidic woodland stream in Northwest Florida. Plate counts and SEM observations indicated a definite successional pattern dominated in numbers initially by the nonbranching bacteria, followed by the actinomycetes. The greatest number of fungal propagules coincided with the least number of bacterial colony-forming units. Chitinoclastic bacterial colonizers increased on the substrate throughout the study, comprising as much as 88% of the total bacterial community during the final stages of chitin decomposition. Scanning electron micrographs taken over the duration of the study revealed the abundance of an actinomycete, identified as a species ofStreptomyces, on the exoskeleton. Enumeration of microorganisms in the stream sediment was also performed in conjunction with the exoskeleton analysis. Relatively constant numbers of bacteria and fungi were observed, with chitinoclastic bacteria comprising between 3 and 11% of the total sediment bacterial community.