title: Inactivation of photosynthetic electron flow during desiccation of desert biological sand crusts and Microcoleus sp.-enriched isolates.
abstract: Filamentous cyanobacteria, the main primary producers in biological sand crusts, survive harsh environmental conditions including diurnal desiccation/rehydration cycles. Here we describe the inactivation of photosystem II during dehydration of native crusts (NC) and Microcoleus sp. isolates grown on nitrocellulose filters (NCF). The morphology of NCF cells, visualized by scanning-transmission and atomic-force microscopy, disclosed long bacterial filaments encapsulated in extracellular polysaccharides (EPS) tubes consisting of parallel fibrils (100-400 nm wide and 50-100 nm high) oriented mostly perpendicular to the tube length. Presence of empty EPS tubes indicated a gliding capability of the cells. Desiccation of NC resulted in a rapid decline of F(o) and complete loss of F(v). These changes were accompanied by a decrease of 77 K PSII fluorescence emission relative to that of PSI, when excited at 430 nm, and a significant decrease of energy transfer from phycobilisomes to PSII. Lowering the turgor pressure through the addition of 1.5 M trehalose to natural crusts, reduced F(v)/F(m) by over 50% and was accompanied by a decrease of 77 K PSI fluorescence induced by chlorophyll excitation. Excitation of phycobilisomes resulted in a downshift of the PSI emission wavelength by 8 nm, indicative of reduced energy transfer from LHCI to the core PSI. Decline of F(v)/F(m) in trehalose-incubated NCF cells did not induce significant changes in 77 K fluorescence emission. These results suggest that alterations in energy transfer from antennae to reaction centers may be part of the survival strategy of Microcoleus.
authors.affiliation: Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Itzhak
authors.initials: I
authors.lastname: Ohad
authors.forename: Reinat
authors.initials: R
authors.lastname: Nevo
authors.forename: Vlad
authors.initials: V
authors.lastname: Brumfeld
authors.forename: Ziv
authors.initials: Z
authors.lastname: Reich
authors.forename: Tom
authors.initials: T
authors.lastname: Tsur
authors.forename: Michael
authors.initials: M
authors.lastname: Yair
authors.forename: Aaron
authors.initials: A
authors.lastname: Kaplan
mesh_terms: D000458:Cyanobacteria / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism* / Q000648:ultrastructure; D003889:Desert Climate; D003890:Desiccation; D004579:Electron Transport; D004789:Enzyme Activation; D007700:Kinetics; D018625:Microscopy, Atomic Force; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism; D012822:Silicon Dioxide / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014867:Water
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D012822:Silicon Dioxide