INTERACTION BETWEEN BACTERIA, NANNOBACTERIA, AND MINERAL PRECIPITATION IN HOT-SPRINGS OF CENTRAL ITALY

A complex of inorganic and organic factors controls precipitation of c arbonates in hot springs of Lazio, central Italy. A plot of data from this area shows that the main inorganic controls are temperature and M g/Ca ratio of the spring waters. Virtually all springs with waters hot ter than 40-degrees-C precipitate aragonite, and cooler ones form calc ite. Furthermore, even cold-water springs precipitate aragonite if the Mg/Ca ratio exceeds 1:1, except in two cases. To what extent is the p recipitation of travertine inorganic vs. biochemical? Surely, conditio ns in diverse localities can vary between both end-points, but Le Zite lle springs, at the north flank of the caldera of Viterbo, provide a b iochemical extreme. Waters are hot (60-degrees-C), with Mg/Ca of .2, a nd are highly sulfurous. Carbonate precipitation rates can exceed 2 mm /day. Nonetched samples of carbonate crusts, only minutes to a few hou rs old, exhibit aragonite, calcite, and 1- to 5- mum euhedral rhombs o f probable dolomite. Aragonite forms spherical ''pincushions'' of radi al needles, each needle tipped with a nannobacterial body of the same diameter as the needles, 0.1 to 0.4 mum. Each nannobacterium precipita ted its own needle, and was propelled outward by needle growth. As lit tle or no later ''fattening'' of the needle occurred, inorganic precip itation must have been insignificant here. Nonetched calcite crystals are composed of 0.05 mum nannobacterial spheres that were incorporated into each layer of the crystal as it grew. No evidence of bacteria wa s found on the ?dolomite rhomb surfaces. Ironically, aragonite, calcit e, and euhedral ?dolomite rhombs all grew within minutes to an hour of each other in the same solution under the same conditions, savaging a ll the rules exposed at the beginning they remain a baffling problem u nresolved by chemistry, physics, or microbiology.