The distribution of bacteria in Sitka spruce stumps between one and ten years old was investigated by dilution plating wood chips taken from seven sampling positions up to 55 mm from the stump surface. The same wood chips were used to determine the presence Basidiomycotina within the stump wood. The number of bacterial colony forming units in the wood samples decreased in stumps between one and five years old, reaching a minimum after six years, before increasing in stumps up to ten years old. There was also a decline in numbers of bacteria isolated with increasing distance from the stump surface and the stump edge. A similar trend was detected in the diversity of the bacterial community. The size of the bacterial population was also correlated with stump moisture content. The presence of Basidiomycotina was associated with the presence of bacteria within the sample. However, the number of bacteria isolated from samples containing Basidiomycotina did not differ from that where no Basidiomycotina were isolated. Interactions between wood-decay fungi, including Heterobasidion annosum, and bacterial isolates were studied in vitro. The growth medium, timing of inoculations, and bacterial and fungal species tested were fund to significantly affect the outcome of the interaction. Bacterial isolates degraded cellulose, pectin and starch, cellulolytic ability increased with increasing stump age. Siderophores and chitinase, potential antifungal compounds, were produced by 29% and 2% of isolates respectively, however, these isolates had no effect on the distribution of Basidiomycotina in the stumps. Four groups of bacteria were identified from cluster analysis of 13 phenotypic characteristics. Different groups of bacteria were found to dominate bacteria isolated from stumps of different ages indicating that bacterial successions occur in decaying Sitka spruce stumps.

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Dans les écosystèmes forestiers, la décomposition du bois est un processus majeur, notamment impliqué dans le cycle du carbone et des nutriments. Les champignons basidiomycètes saprotrophes, incluant les pourritures blanches, sont les principaux agents de cette décomposition dans les forêts tempérées. Bien que peu étudiées, des communautés bactériennes sont également présentes dans le bois en décomposition et cohabitent avec ces communautés fongiques. L'impact des interactions bactéries-champignons sur le fonctionnement d'une niche écologique a été décrit dans de nombreux environnements. Cependant, leur rôle dans le processus de décomposition du bois n'a été que très peu investigué. A partir d'expériences en microcosme et en utilisant une approche non cultivable, il a été démontré que la présence du champignon Phanerochaete chrysosporium influençait significativement la structure et la diversité des communautés bactériennes associées au processus de décomposition du hêtre (Fagus sylvatica). Par une approche cultivable, cet effet mycosphère a été confirmé, se traduisant par une augmentation de la densité des communautés bactériennes en présence du champignon ainsi que par une modification de la diversité fonctionnelle de ces communautés. Enfin, une approche polyphasique a été développée, combinant l'analyse des propriétés physico-chimiques du bois et des activités enzymatiques extracellulaires. Les résultats de cette expérience ont révélé que l'association de P. chrysosporium avec une communauté bactérienne issue de la mycosphère de ce dernier aboutissait à une dégradation plus importante du matériau bois par rapport à la dégradation par le champignon seul, démontrant pour la première fois des interactions bactéries-champignons synergiques dans le bois en décomposition / Wood decomposition is an important process in forest ecosystems in terms of their carbon and nutrient cycles. In temperate forests, saprotrophic basidiomycetes such as white-rot fungi are the main wood decomposers. While they have been less studied, bacterial communities also colonise decaying wood and coexist with these fungal communities. Although the impact of bacterial-fungal interactions on niche functioning has been highlighted in a wide range of environments, little is known about their role in wood decay. Based on microcosm experiments and using a culture-independent approach, we showed that the presence of the white-rot fungus Phanerochaete chrysosporium significantly modified the structure and diversity of the bacterial communities associated with the degradation of beech wood (Fagus sylvatica). Using a culture-dependent approach, it was confirmed that in the presence of the fungus the mycosphere effect resulted in increased bacterial abundance and modified the functional diversity of the fungal-associated bacterial communities. Lastly, a polyphasic approach simultaneously analysing wood physicochemical properties and extracellular enzyme activities was developed. This approach revealed that P. chrysosporium associated with a bacterial community isolated from its mycosphere was more efficient in degrading wood compared to the fungus on its own, highlighting for the first time synergistic bacterial-fungal interactions in decaying wood