Despite the high potential for oxidative stress stimulated by reduced iron, contemporary iron-depositing hot springs with circum-neutral pH are intensively populated with cyanobacteria. Therefore, studies of the physiology, diversity, and phylogeny of cyanobacteria inhabiting iron-depositing hot springs may provide insights into the contribution of cyanobacteria to iron redox cycling in these environments and new mechanisms of oxidative stress mitigation. In this study the morphology, ultrastructure, physiology, and phylogeny of a novel cyanobacterial taxon, JSC-1, isolated from an iron-depositing hot spring, were determined. The JSC-1 strain has been deposited in ATCC under the name Marsacia ferruginose, accession number BAA-2121. Strain JSC-1 represents a new operational taxonomical unit (OTU) within Leptolyngbya sensu lato. Strain JSC-1 exhibited an unusually high ratio between photosystem (PS) I and PS II, was capable of complementary chromatic adaptation, and is apparently capable of nitrogen fixation. Furthermore, it synthesized a unique set of carotenoids, but only chlorophyll a. Strain JSC-1 not only required high levels of Fe for growth (>40 M), but it also accumulated large amounts of extracellular iron in the form of ferrihydrite and intracellular iron in the form of ferric phosphates. Collectively, these observations provide insights into the physiological strategies that might have allowed cyanobacteria to develop and proliferate in Fe-rich, circum-neutral environments.Cyanobacteria inhabiting ferrous iron-rich hot springs with circum-neutral pH represent unique models for examining the mechanisms by which early organisms evolved to cope with such habitats common on early Earth. Such organisms have previously been shown to be resistant to Fe 2ϩ (37) or Fe 3ϩ (6, 7) at concentrations in the micromolar to millimolar range. Moreover, high Fe concentrations (apparent optimum of ϳ0.5 mM) stimulated the growth of these cyanobacteria, which were described as siderophilic (having an affinity for iron) cyanobacteria (7).The cyanobacteria inhabiting the Chocolate Pots hot springs in Yellowstone National Park, Wyoming, were shown to have played at least a passive role in contributing to iron deposition by serving as nucleation sites for the accumulation of iron minerals and associated silica deposits (36, 38). The precipitation of external iron that encrusts the cyanobacterial cells inhabiting this hot spring appears to be dependent on the species composition and chemistry of the mat (36, 38); however, multiple anoxygenic phototrophs found in the Chocolate Pots hot springs (8) could also contribute to the formation of Fe oxides (21, 49). Therefore, only iron mineralization experiments with model cyanobacterial strains can demonstrate the role of siderophilic cyanobacteria in the formation of specific, iron-bearing minerals.An additional common feature of circum-neutral irondepositing hot springs is elevated concentrations of hydrogen peroxide (50). Shcolnick and coauthors (41) showed that a wild type of Synech...

Studies directed at cyanobacteria inhabiting iron-depositing hot springs may provide insights into the role of both ancient and contemporary cyanobacteria mediated iron transformations. Here we phylogenetically, morphologically and physiologically characterize a novel cyanobacterium isolated from an iron-depositing hot spring. Phylogenetic analyses indicate that the bacterium is a representative of a new genus, exhibiting a maximum 95.2% homology to database sequences. The isolate is a unicellular cyanobacterium with bladder-like cells typically packed as duplexes, or in extracellular polymeric substance covered clumps and small chains without the ability to produce baeocystes. No growth without added combined nitrogen occurred. While requiring relatively large amounts of iron for growth (>40microM), the isolate was shown to facilitate removal of iron from culture media. These results suggest that the isolate may be an important component of an iron-depositing microbial community. The name "Chroogloeocystis siderophila" for this cyanobacterium is proposed.

Surface translocation has been described in a large variety of microorganisms, including some gramnegative enteric bacteria. Here, we describe the novel observation of the flagellum-independent migration of Vibrio cholerae and Escherichia coli on semisolid surfaces with remarkable speeds. Important aspects of this motility are the form of inoculation, the medium composition, and the use of agarose rather than agar. Mutations in several known regulatory or surface structure proteins, such as ToxR, ToxT, TCP, and PilA, did not affect migration, whereas a defect in lipopolysaccharide biosynthesis prevented translocation. We propose that the observed surface migration is an active process, since heat, protease, or chloramphenicol treatments of the cells have strong negative effects on this phenotype. Furthermore, several V. cholerae strains strongly expressing the hemagglutinin/protease but not their isogenic hap-negative mutants, lacked the ability of surface motility, and the treatment of migrating strains with culture supernatants from hap strains but not hap-null strains prevented surface translocation.Bacterial translocation is arguably one of the most impressive features in the bacterial life. Perhaps the planktonic or free-swimming bacterial phase is primarily a mechanism of translocation from one surface to another, since in nature microbial activity is probably mostly associated with surfaces (4). Surface translocation enables the bacteria to establish symbiotic and pathogenic associations with plants and animals, and potential benefits of translocation include increased access to nutrients, avoidance of toxic substances, access to preferred colonization sites within hosts, and increased efficiency of transmission. The study of bacterial interactions with various surfaces is a newly emerging field and especially the remarkable ability of bacteria to form surface-associated structured and cooperative consortia, called biofilms, has received increasing attention in recent years (30).Movement in aqueous environments by swimming or along surfaces by using different modes of translocation has been classified into several distinct forms. Six different types of translocation have been recognized by Hendrichsen (13) as (i) swarming, dependent on excessive development of flagella and partly on cell-to-cell interaction; (ii) swimming, dependent on flagella and fluid; (iii) gliding, dependent on intrinsic motive force and partly on cell-to-cell interactions; (iv) twitching, dependent on intrinsic motive force and, as we know now, type IV pili; (v) sliding, dependent on growth and reduced friction (i.e., spreading by expansion); and (vi) darting, dependent on growth of capsulated aggregates (i.e., spreading by ejection). All of these different modes of translocation require special surface structures or components, such as flagella, pili, surfactants, slime, or capsules. The flagellum-independent surface spreading of Serratia marcescens can be classified as sliding since it was dependent on growth and the production of...

The hypothesis that Na' and K + gradients have an energy storing function [V. FEBS Lett. 87,171 -1761 has been tested in experiments with Escherichia coli, the marine bacterium Vibrio harveyi, an extremely halophilic Halobaclerium halobium and a fresh-water cyanobacterium Phormidium uncinatum from Lake Baikal living at an extremely low salt concentration. The capability of these microorganisms to maintain A pH was compared using motility as a AD,-supported function. It was found that in all cases the gradient of monovalent cations is competent to prolong the period of active motility after other energy sources are exhausted. Maximal prolongation was found in H . halobium, which in a Na+ medium was still motile when light was switched off for 9 h under anaerobic conditions. In V. harveyi the motility was maintained for 1 h, in E. coli for about 10 min and in Ph. uncinatum for about 2 min. Thus the ApH buffer capacity of the monovalent cation gradient is proportional to the content of these cations in the habitat. It was also found that in Ph. uncinatum only A pKis effective, whereas in E. coli and V. harveyi both ApK and ApNa are.In E. coli when the K C release is completed and the cells become motionless, motility can be temporarily restored by adding NaCl which initiates an H + efflux.Under conditions of exhaustion of energy sources, the Na' and K + gradient was shown to stabilize potential in H. halobium cells, measured with a tetraphenylphosphonium probe.In H . halobium and E. coli, the anaerobic ATP level was found to stabilize when the Na+ and K + gradients were present. Addition of N,N-dicyclohexylcarbodiimide destabilized this level, which indicated that Na+ and K + gradients could support de novo ATP synthesis.It is concluded that the data obtained are in agreement with the concept of the energy storing by the Na' and K + gradients. Other functions of these gradients and the mechanisms of their formation are discussed.

Light-dependent Na+ and H+ transports, membrane potential (A Y) and motility have been studied in the cells of the marine cyanobacterium Oscillutoriu brevis. In the presence of a protonophorous uncoupler, carbonyl cyanide-m-chlorophenylhydrazone, the intracellular Na+ level is shown to increase in the dark and decrease in the light. The Na+/H+ antiporter, monensin, stimulates the dark CCCP-dependent [Na+]in increase and abolishes the light-dependent [Na+]in decrease. Na+ ions are necessary for the fast light-induced AY generation and H+ uptake by the cells. This uptake is inhibited by monensin being resistant to CCCP. Monensin sensitizes the AY' level and the motility rate to low CCCP concentrations.The obtained data are consistent with the assumption that 0. brevis possesses a primary Na+ pump which utilizes (directly or indirectly) the light energy.

Arthrospira (Spirulina) platensis (A. platensis) is a model organism for investigation of adaptation of photosynthetic organisms to extreme environmental conditions: the cell functions in this cyanobacterium are optimized to high pH and high concentration (150-250 mM) of Na+. However, the mechanism of the possible fine-tuning of the photosynthetic functions to these extreme conditions and/or the regulation of the cellular environment to optimize the photosynthetic functions is poorly understood. In this work we investigated the effect of Na-ions on different photosynthetic activities: linear electron transport reactions (measured by means of polarography and spectrophotometry), the activity of photosystem II (PS II) (thermoluminescence and chlorophyll a fluorescence induction), and redox turnover of the cytochrome b6f complex (flash photolysis); and measured the changes of the intracellular pH (9-aminoacridine fluorescence). It was found that sodium deprivation of cells in the dark at pH 10 inhibited, within 40 min, all measured photosynthetic reactions, and led to an alkalinization of the intracellular pH, which rose from the physiological value of about 8.3-9.6. These were partially and totally restored by readdition of Na-ions at 2.5-25 mM and about 200 mM, respectively. The intracellular pH and the photosynthetic functions were also sensitive to monensin, an exogenous Na+/H+ exchanger, which collapses both proton and sodium gradients across the cytoplasmic membrane. These observations explain the strict Na+-dependency of the photosynthetic electron transport at high extracellular pH, provide experimental evidence on the alkalization of the intracellular environment, and support the hypothesized role of an Na+/H+ antiport through the plasma membrane in pH homeostasis (Schlesinger et al. (1996). J. Phycol. 32, 608-613). Further, we show that (i) the specific site of inactivation of the photosynthetic electron transport at alkaline pH is to be found at the water splitting enzyme; (ii) in contrast to earlier reports, the inactivation occurs in the dark and, for short periods, without detectable damage in the photosynthetic apparatus; and (iii) in contrast to high pH, Na+ dependency in the neutral pH range is shown not to originate from PSII, but from the acceptor side of PSI. These data permit us to conclude that the intracellular environment rather than the machinery of the photosynthetic electron transport is adjusted to the extreme conditions of high pH and high Na+ concentration.

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The siderophilic, thermophilic Leptolyngbyaceae cyanobacterium JSC-12 was isolated from a microbial mat in an iron-depositing hot spring. Here, we report the high-quality draft genome sequence of JSC-12, which may help elucidate the mechanisms of resistance to extreme iron concentrations in siderophilic cyanobacteria and lead to new remediation biotechnologies.