title: Physiology and behaviour of marine Thioploca.
abstract: Among prokaryotes, the large vacuolated marine sulphur bacteria are unique in their ability to store, transport and metabolize significant quantities of sulphur, nitrogen, phosphorus and carbon compounds. In this study, unresolved questions of metabolism, storage management and behaviour were addressed in laboratory experiments with Thioploca species collected on the continental shelf off Chile. The Thioploca cells had an aerobic metabolism with a potential oxygen uptake rate of 1760 micromol O2 per dm(3) biovolume per h, equivalent to 4.4 nmol O2 per min per mg protein. When high ambient sulphide concentrations (approximately 200 microM) were present, a sulphide uptake of 6220+/-2230 micromol H2S per dm(3) per h, (mean+/-s.e.m., n=4) was measured. This sulphide uptake rate was six times higher than the oxidation rate of elemental sulphur by oxygen or nitrate, thus indicating a rapid sulphur accumulation by Thioploca. Thioploca reduce nitrate to ammonium and we found that dinitrogen was not produced, neither through denitrification nor through anammox activity. Unexpectedly, polyphosphate storage was not detectable by microautoradiography in physiological assays or by staining and microscopy. Carbon dioxide fixation increased when nitrate and nitrite were externally available and when organic carbon was added to incubations. Sulphide addition did not increase carbon dioxide fixation, indicating that Thioploca use excess of sulphide to rapidly accumulate sulphur rather than to accelerate growth. This is interpreted as an adaptation to infrequent high sulphate reduction rates in the seabed. The physiology and behaviour of Thioploca are summarized and the adaptations to an environment, dominated by infrequent oxygen availability and periods of high sulphide abundance, are discussed.
authors.affiliation: Department of Biological Sciences, University of Aarhus, Aarhus, Denmark.
authors.forename: Signe
authors.initials: S
authors.lastname: Høgslund
authors.forename: Niels Peter
authors.initials: NP
authors.lastname: Revsbech
authors.forename: J Gijs
authors.initials: JG
authors.lastname: Kuenen
authors.forename: Bo Barker
authors.initials: BB
authors.lastname: Jørgensen
authors.forename: Victor Ariel
authors.initials: VA
authors.lastname: Gallardo
authors.forename: Jack
authors.initials: J
authors.lastname: van de Vossenberg
authors.forename: Jeppe Lund
authors.initials: JL
authors.lastname: Nielsen
authors.forename: Lars
authors.initials: L
authors.lastname: Holmkvist
authors.forename: Esther T
authors.initials: ET
authors.lastname: Arning
authors.forename: Lars Peter
authors.initials: LP
authors.lastname: Nielsen
mesh_terms: D000332:Aerobiosis; D000641:Ammonia / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002677:Chile; D019015:Geologic Sediments / Q000382:microbiology*; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D011122:Polyphosphates / Q000378:metabolism; D013440:Sulfides / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism; D041962:Thiotrichaceae / Q000302:isolation & purification* / Q000378:metabolism*
chemical_list: D009566:Nitrates; D009573:Nitrites; D011122:Polyphosphates; D013440:Sulfides; D002245:Carbon Dioxide; D013455:Sulfur; D000641:Ammonia; D010100:Oxygen