Figure 4
Low pH in etching filopodia in sponge excavated pit exposed after detachment of a piece of bioeroded calcite from the “mother sponge”. (a)Transmitted light image showing etching filopodia carving out chips on the leading edge of a bored channel in the substratum. (b) Z-stack imaging of the same area; red fluorescence represents pH below neutral. (c) Processed image using the fluorescence intensity/pH calibration (Fig. 9) showing low pH in etching filopodia that are carving chips from an excavation pit. Due to the detachment from the “mother sponge”, most tissue around the pit was removed, however, a large fraction of cells within etched crevices remained, enabling exclusive visualization of the etching filopodia. The high fluorescence levels in the centre of the pit are due to the superposition of cells causing additive fluorescence and were therefore dismissed from further analysis.
