Marine bacteria (Beggiatoa spp.)

Description

Beggiatoa spp. are large, colorless sulfur bacteria that include both colonial and filamentous forms, and they can dominate microbial communities associated with marine sediments. Beggiatoa spp. appear white due to the reflection of light against their sulfur inclusions and may form mats on marine sediments ranging in size from a few millimeters to several meters (Fenchel and Bernard 1995a).

Background

Distribution. Beggiatoa spp. are found throughout the world’s oceans from shallow nearshore areas to hydrothermal vents and the deep sea (Fenchel and Bernard 1995a). Mats have been observed below productive upwelling zones and productive shallow water areas. In general, their presence in shallow water areas is considered an indication of environmental deterioration.

Biology. Fenchel and Bernard (1995a) provide a brief overview of Beggiatoa biology. Beggiatoa spp. oxidize sulfide into elemental sulfur or sulfate, and can use nitrate in the absence of oxygen. Mat communities can include photosynthetic microorganisms, and in areas where sulfide and oxygen concentrations overlap at the sediment surface, the sulfur bacteria perform diurnal vertical migrations, appearing at the sediment surface during darkness. Beggiatoa spp. mats are porous, though they appear dense, with bacteria filaments comprising approximately 7 percent of mat volume (Fenchel and Bernard 1995b). Typically, mats are 0.6 millimeters thick, but coverage area varies with water movement; mat size is inversely related to flow rate.

Environmental Influences

Predation. Some protozoan (ciliates, amoebas) and meiofaunal (nematodes) species consume sulfur bacteria, including Beggiatoa spp., but the role of these interactions in food web dynamics is relatively unstudied (Fenchel and Bernard 1995a).

Pollution. Formation of Beggiatoa spp. mats has been considered a sign of environmental degradation. Since they are tolerant of anoxic conditions, they are good indicators of oxygen-depleted environments (C. Bernard, pers. comm.).

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