Aquatic detritivores, fungi and bacteria, were tested in microcosms in the lab to elucidate whether synergistic or antagonistic relationships prevailed between the two and whether or not community composition plays a role during leaf decomposition. Microbial interactions were examined in communities of pre-determined compositions using two different communities each of fungi and bacteria. Communities consisted of three identified strains (different species) each per community totaling six bacterial and six fungal species tested. Medium renewal occurred every fourth day to avoid nutrient depletion and toxic build-up. After 72 days of decomposition no significant differences in leaf mass loss had occurred between communities containing fungi, either in the presence (47.6±4.9%) or absence (48.3±4.0%) of bacteria. Bacteria only communities (23.1±6.9%) mimicked those of the controls (23.7±4.5%). Bacteria tended to negatively influence production of fungal biomass and spores whereas fungi generally increased bacterial CFU counts. Community composition did not influence overall leaf decomposition, but affected reproductive performances for both fungal spore production (-24.6%) and bacterial CFU counts (6.1%) between core and mixed communities. An organic matter budget revealed that abiotic decomposition processes (23.7±4.5%) dominated over biotic decomposition processes (16.3±1.2%). Microbial interactions within communities led to two fungal species (Flagellospora curvula and Articulospora tetracladia) to dominate in communities and probably leaf mass loss, FPOM and fungal production, while two bacterial strains Pseudomonas sp. 28-2 and Pseudomonas sp. 28-18 dominated bacterial production. A creamy bacterium in B1 communities and a bright orange bactrium in mixed B2 communities appeared and became dominant midway through the experiment. This suggests complex interactions between fungi and bacteria.