SREL
Reprint #2584
Aquatic
Actinomycete-Fungal Interactions and Their Effects on Organic
Matter Decomposition: A Microcosm Study
D.L.
Wohl, J.V. McArthur
Savannah
River Ecology Laboratory, Institute of Ecology, University
of Georgia, Aiken, SC 29802
Received: 19
June 2000; Accepted: 15 January 2001; Online Publication:
21 June 2001
The role of fungi in the decomposition of organic matter
in streams has been well examined, although the role of
bacterial antagonists in such processes has gained little
attention. To examine bacterial-fungal interactions, experiments
involving pair-wise combinations of four actinomycete isolates
(A1+ and A2+ could remove chitin from chitin-containing
media, and A1- and A2- could not) and two
fungal isolates (F+ a true fungus, F- an oomycote)
were conducted. For each bacterial-fungal combination, 250-ml
microcosms were sampled at 8 day intervals for 32 days.
Microbial biomass and organic matter, as well as the activities
of five extracellular enzymes, were measured. Each experiment
consisted of a control group and four treatment groups.
Controls comprised sterilized stream water and macrophytes.
The first treatment was inoculated with only actinomycetes
(˜103 cells ml-1), the second
treatment was inoculated with only fungi (-10' cells ml-,),
the third group was inoculated simultaneously with actinomycetes
and fungi, and the fourth group was inoculated with actinomycetes
2 days after fungal establishment. For all combinations,
the lowest rates of organic matter decomposition were expected
in the controls, as a result of only physical degradation.
In contrast, the greatest rates of organic matter decomposition
were predicted in treatments inoculated with F+ 2 days prior
to AI - or A2 . Greater than 50% of the organic matter was
decomposed in each of the fungal treatments. Fungal-actinomycete
interactions resulted in reduced fungal biomass relative
to the fungal-only treatments. However, when inoculated
2 days apart, combinations of F- and actinomycetes resulted
in enhanced rates of organic matter decomposition, as well
as greater levels of extracellular enzyme activities. These
results demonstrate that actinomycete-fungal interactions
and their colonization dynamics affect the accumulation
of biomass, extracellular enzyme activities, and rates of
organic matter decomposition.
SREL
Reprint #2584
