New communities of large filamentous sulfur bacteria in the eastern South Pacific.

New complex communities of morphologically diverse and sometimes abundant large, multicellular, filamentous bacteria were discovered in the oxygen-deficient, organically laden, shelf sediments under the oxygen minimum zone off the coast of the eastern Pacific, i.e., off the coasts of central and northern Chile; central and northern Perú; Roca Redonda, Galápagos Archipielago, Ecuador; and off the Pacific coasts of Panamá and Costa Rica. Similar microbial communities were also observed in the reduced layer of a muddy-sand beach adjacent to a mangrove swamp on Coiba Island, Pacific Panamá, and in the organically laden bottom underneath a salmon culture pen in southern Chile (region X). Of varying morphology, the diameters of the bacteria range from 1 to 10 mum, and their lengths from around 10 mum to usually several hundreds but at times several thousands of micrometers. The new filamentous bacterial component is at least one order of magnitude smaller than the also multicellular "megabacteria" Thioploca spp. and Beggiatoa spp., and is collectively referred to as "macrobacteria". A recent review only mentioned a few of these free-living filamentous bacteria, remarking on their scarcity despite the obvious advantages of a large size. This prokaryote size-window has been rarely investigated optically by researchers; thus, assemblages that appear to have had world-wide distribution probably since pre-Cambrian times have been overlooked.