RETICULATED FILAMENTS IN CAVE POOLSPELEOTHEMS: MICROBE OR MINERAL?

摘要

We report on a reticulated filament found in modern and fossil cave samplesthat cannot be correlated to any known microorganism or organism part. Thesefilaments were found in moist environments in five limestone caves (four in New Mexico,U.S.A., one in Tabasco, Mexico), and a basalt lava tube in the Cape Verde Islands. Mostof the filaments are fossils revealed by etching into calcitic speleothems but two are onthe surface of samples. One hundred eighty individual reticulated filaments were imagedfrom 16 different samples using scanning electron microscopy. The filaments are up to75 (average 12 pm) long, but all filaments appear broken. These reticulated filamentsare elongate, commonly hollow, tubes with an open mesh reminiscent of a fish net orhoneycomb. Two different cross-hatched patterns occur; 77% of filaments havehexagonal chambers aligned parallel to the filament and 23% of filaments havediamond-shaped chambers that spiral along the filament. The filaments range from300 nm to 1000 nm in diameter, but there are two somewhat overlapping populations;one 200-400 nm in size and the other 500-700 nm. Individual chambers range from 40 to100 nm with 30-40 nm thick walls. Similar morphologies to the cave reticulatedfilaments do exist in the microbial world, but all can be ruled out due to the absence ofsilica (diatoms), different size (diatoms, S-layers), or the presence of iron (Leptothrix sp.).Given the wide range of locations that contain reticulated filaments, we speculate thatthey are a significant cave microorganism albeit with unknown living habits.