A puddle: an ombrophilic cyano-bacterial community

Sequential stages of formation of an ombrophilic cyano-bacterial community on clay were determined in a laboratory model of a puddle community. In a suspension of washed clay obtained from loamy soil, with montmorillonite as the predominant phase, a bacterial neustonic film is initially formed; it acts as a support for cyanobacterial hormogonia. At the next stage, the upper layer of precipitated clay (about 1 mm) is reinforced by a cyano-bacterial structure of Phormidium sp. trichomes and develops a tissue-like structure. The hormogonia and sheathless cyanobacteria remain free from mineral particles. Subsequently, gas formation results in a separation of a dense cyano-bacterial film from the underlying loose suspension and in formation of gas swellings. The mineral component of the film is differentiated: mineral particles of quartz and feldspar grains are attached to Phormidium sp. trichomes, which act as a factor of mineral selection.