title: Water and temperature relations of soil Actinobacteria.
abstract: Actinobacteria perform essential functions within soils, and are dependent on available water to do so. We determined the water-activity (aw ) limits for cell division of Streptomyces albidoflavus, Streptomyces rectiviolaceus, Micromonospora grisea and Micromonospora (JCM 3050) over a range of temperatures, using culture media supplemented with a biologically permissive solute (glycerol). Each species grew optimally at 0.998 aw (control; no added glycerol) and growth rates were near-optimal in the range 0.971-0.974 (1 M glycerol) at permissive temperatures. Each was capable of cell division at 0.916-0.924 aw (2 M glycerol), but only S. albidoflavus grew at 0.895 or 0.897 aw (3 M glycerol, at 30 and 37°C respectively). For S. albidoflavus, however, no growth occurred on media at ≤ 0.870 (4 M glycerol) during the 40-day assessment period, regardless of temperature, and a theoretical limit of 0.877 aw was derived by extrapolation of growth curves. This level of solute tolerance is high for non-halophilic bacteria, but is consistent with reported limits for the growth and metabolic activities of soil microbes. The limit, within the range 0.895-0.870 aw , is very much inferior to those for obligately halophilic bacteria and extremely halophilic or xerophilic fungi, and is inconsistent with earlier reports of cell division at 0.500 aw . These findings are discussed in relation to planetary protection policy for space exploration and the microbiology of arid soils.
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, BT9 7BL, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Stevenson
authors.forename: John E
authors.initials: JE
authors.lastname: Hallsworth
mesh_terms: D039903:Actinobacteria / Q000254:growth & development* / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology; D013696:Temperature; D014867:Water / Q000032:analysis* / Q000378:metabolism
chemical_list: D003470:Culture Media; D012987:Soil; D014867:Water