Interactions between testate amoebae and saprotrophic microfungi in a Scots pine litter microcosm.

In all terrestrial ecosystems, testate amoebae (TA) encounter fungi. There are strong indications that both groups engage in multiple interactions, including mycophagy and decomposition of TA shells, processes which might be fundamental in nutrient cycling in certain ecosystems. Here, we present the results of an experiment focusing on interactions between TA and saprotrophic microfungi colonizing Scots pine (Pinus sylvestris L.) litter needles. The needles were collected from a temperate pine forest and cultivated in damp chambers. Over a few weeks, melanized mycelium of Anavirga laxa Sutton started to grow out of some needles; simultaneously, the common forest-soil TA Phryganella acropodia (Hertwig and Lesser) Hopkinson reproduced and spread around the mycelium. We investigated whether a potential relationship between TA and saprotrophic microfungi exists by comparing the composition of TA communities on and around the needles and testing the spatial relationship between the A. laxa mycelium and P. acropodia shells in the experimental microcosm. Additionally, we asked whether P. acropodia utilized the A. laxa mycelium as a nutrient source and screened whether P. acropodia shells were colonized by the microfungi inhabiting the experimental microcosm. Our results indicate that saprotrophic microfungi may affect the composition of TA communities and their mycelium may affect distribution of TA individuals in pine litter. Our observations suggest that P. acropodia did not graze directly on A. laxa mycelium, but rather fed on its exudates or bacteria associated with the exudates. The fungus Pochonia bulbillosa (Gams & Malla) Zare & Gams was often found parasitising encysted shells or decomposing already dead individuals of P. acropodia. TA and pine litter microfungi engage in various direct and indirect interactions which are still poorly understood and deserve further investigation. Their elucidation will improve our knowledge on fundamental processes influencing coexistence of soil microflora and microfauna.

The estimation error of skeletal muscle capillary supply is significantly reduced by 3D method.

Capillary supply of individual skeletal muscle fibers is usually evaluated from two-dimensional (2D) images of thin transverse sections by the number of capillary profiles around a fiber (CAF). This method is inherently inaccurate and the resulting capillary length measurement errors can be avoided by using an alternative three-dimensional (3D) approach where the mean length of capillaries around individual muscle fibers per fiber length (Lcap/Lfib) is measured from 3D images acquired by confocal microscopy. We quantified the error of the 2D method and its reduction by using a 3D approach in realistic geometrical models of muscle fiber capillary bed and in true muscle samples. In models we showed that Lcap/Lfib was sensitive to different arrangements of capillaries, while CAF underestimated capillarization since it could not detect the increased length of capillary bed. In true muscle samples, we detected statistically significant differences in the capillary supply of control and denervated rat soleus muscles by both 2D and 3D methods. Lcap/Lfib was larger than CAF in control muscles reflecting their more complicated capillary bed. Thus, 3D approach is more sensitive in agreement with the analysis of geometrical models. We conclude that the 3D method, though technically more demanding than 2D method, represents a more precise approach to evaluation of muscle capillarization. Moreover, the 3D method could be applied to other organs and we suggest potential medical applications.