The Spirochetes (2)

Family 1: SPIROCHAETACEAE

Genus 2: Saprospira

The saprospiras are wonderful, versatile microbes. They are not rare, but, perhaps because they apparently include no pathogens, they are still all too little studied. They glide, moving on solid surfaces where they can hope to find potentially nutrient substrates or prey bacteria, but how they move is still under investigation.

The first marine lytic bacteriophage was found in a saprospira, but not all saprospiras succumb to it. All known saprospiras are coloured, due to different kinds of carotenoids.

They are not photosynthetic. They require for growth some or all of the so-called essential amino acids that we animals do, and presumably for the same reason. Many are even more like animals, living by predation on other microbes, including diatoms and  dinoflagellates as well as bacteria. In some, the mucilage tracks that they employ for motility have been pre-adapted to be sticky and thereby to catch bacterial prey, notably species of Vibrio, by their flagella. Then an ixotrophic saprospira can kill them by extracelluar toxins and digest them by extracellular enzymes, thereby liberating the amino acids that it needs for growth. But the natures of that sticky mucilage, and of those toxins and enzymes, need to be further studied.

Scanning electron micrograph of S. grandis Sa g1

Habitat: Saprospiras are marine bacterium. Also found in intestinal tract of oysters. S. thermalis are the only species found in fresh water.

Oxygen Relationships: strictly aerobic

Major character: Spiral portoplasm without an axial filament. Motility is active and rotating. Chemoorganotrophs.

Pathology: S. grandis prey on other bacteria and protists. Unsuspecting bacteria swimming nearby become trapped when the tips of their flagella become stuck in the mucilage on the saprospira filament. No chemotaxis seems to be involved, just approaching too closely. Dozens of live bacteria still spinning on their axes become attached to a single filament, eventually to cover its surface. Extracellular enzymes secreted by the saprospira finish them off. Not all motile bacteria qualify as prey. For example, non-marine but flagellated cells such as E. coli aren't prey, and only 7 out of 25 marine members of the Vibrionaceae could be caught and destroyed.

Significance: S. grandis is useful in preventing harmful algal blooms.

Species: Main species are: S. grandis, S. punctum, S. lepta, S. thermalis.

Phase-contrast micrograph of filaments of a freshwater Saprospira sp.