Sulfide and pH effects on variable fluorescence of photosystem II in two strains of the cyanobacterium Oscillatoria amphigranulata

Changes in fluorescence of photosystem II (PS II) chlorophyll were used to monitor the in vivo effects of sulfide and pH on photosynthesis by the cyanobacterium Oscillatoria amphigranulata. O. amphigranulata is capable of both oxygenic photosynthesis and sulfide dependent anoxygenic photosynthesis. A genetic variant of O. amphigranulata which photosynthesizes oxygenically at normal rates, but is incapable of anoxygenic photosynthesis and cannot tolerate sulfide, was also used to explore the mode of action of sulfide. In vivo fluorescence responses of PS II chlorophyll in the first few seconds of exposure to light (Kautsky transients) reflected the electrochemical states of PS II and associated electron donors and acceptors. Kautsky transients showed a distinct difference between PS II of the wild type and the variant, but sulfide lowered fluorescence in both. Kautsky transients with sulfide were similar to transients with addition of NH₂OH, NH₄ ⁺ or HCN, indicating sulfide interacts with a protein on the donor side of PS II. The fluorescence steady-state (after 2 min) was measured in the presence of sulfide, cyanide and ammonium with pH ranging from 7.2–8.7. Sulfide and cyanide had the most impact at pH 7.2, ammonium at pH 8.7. This suggests that the uncharged forms (HCN, NH₃ and H₂S) had the strongest effect on PS II, possibly because of increased membrane permeability.Abbreviations DCMU 3(3,4-dichlorophenyl)-1,1-dimethyl-urea - Oa-wt Oscillatoria amphigranulata (wild type) - Oa-2 Oscillatoria amphigranulata (genetic variant)     

Adaptation to Hydrogen Sulfide of Oxygenic and Anoxygenic Photosynthesis among Cyanobacteria

Four different types of adaptation to sulfide among cyanobacteria are described based on the differential toxicity to sulfide of photosystems I and II and the capacity for the induction of anoxygenic photosynthesis. Most cyanobacteria are highly sensitive to sulfide toxicity, and brief exposures to low concentrations cause complete and irreversible cessation of CO₂ photoassimilation. Resistance of photosystem II to sulfide toxicity, allowing for oxygenic photosynthesis under sulfide, is found in cyanobacteria exposed to low H₂S concentrations in various hot springs. When H₂S levels exceed 200 μM another type of adaptation involving partial induction of anoxygenic photosynthesis, operating in concert with partially inhibited oxygenic photosynthesis, is found in cyanobacterial strains isolated from both hot springs and hypersaline cyanobacterial mats. The fourth type of adaptation to sulfide is found at H₂S concentrations higher than 1 mM and involves a complete replacement of oxygenic photosynthesis by an effective sulfide-dependent, photosystem II-independent anoxygenic photosynthesis. The ecophysiology of the various sulfide-adapted cyanobacteria may point to their uniqueness within the division of cyanobacteria.     

Physiology of sulfide tolerance in a thermophilic Oscillatoria

Oscillatoria amphigranulata is a fast-growing (3 doublings/day) cyanobacterium isolated from sulfide hot springs in New Zealand. Photosynthesis, as measured by incorporation of [¹⁴C]-HCO ₃ ^- , was initially inhibited by 0.3–1.5 mM sulfide at pH 7.9–8.1. However, conversion to sulfide-dependent anoxygenic photosynthesis occurred in about 2 h or less under light intensities of 3–14 klx. Under the stimulation of higher light intensity (8–14 klx) a partial recovery of oxygenic photosynthesis also occurred. It was concluded that oxygenic photosynthesis was responsible for 21–42% of the total incorporation at sulfide concentrations of 1.0–0.3 mM, respectively. This contribution was suppressed at 1.5 mM sulfide and not elicited under lower light intensities (3–7 klx). As judged by the inhibitory effect of 10 g/ml chloramphenicol protein synthesis was required for attainment of both anoxygenic photosynthesis and photosystem II recovery. Sulfide could not be replaced by thiosulfate, elemental sulfur or dithionite as electron donors in photosynthesis, but elemental sulfur could serve as the sole assimilatory source of sulfur. Oxygenic photosynthesis was inhibited by DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] or DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone), but sulfide relieved the effect of either inhibitor in adapted cells, indicating that electrons derived from sulfide enter the photosynthetic electron transport chain at a point beyond plastoquinone.Uncommon abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - DSPD disalicyclidene propanediamine - DNP-INT 2-4-dinitrophenyl ether of 2-iodo-4-nitrothymol - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - PPO 2,5-diphenyloxazole - POPOP 1,4-bis-2-(5-phenyl oxzolyl) benzene     

Loss of sulfide adaptation ability in a thermophilic Oscillatoria

A spontaneous variant incapable of anoxygenic photosynthesis was derived from a fully competent strain of Oscillatoria amphigramulata which was originally isolated from a high sulfide-containing hot spring of New Zealand. Although the variant (Oa-2) acquired a slight ability to photosynthesize in the presence of 0.3–0.4 mM sulfide, this was only after a 24 h exposure to sulfide and represented oxygenic photosynthesis only. Unlike the parent strain, the incompetent variant never grew in the presence of sulfide >0.05 mM, nor was there any relief of the inhibition by DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] of CO₂ photoincorporation when sulfide was present. The variant strain has retained all of these characteristics over a 4 year period with monthyl transfers in non-sulfide medium. The wild type, under identical conditions, has retained all of its competence with respect to sulfide.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Anaerobic heterotrophic dark metabolism in the cyanobacterium Oscillatoria limnetica: Sulfur respiration and lactate fermentation

The cyanobacterium Oscillatoria limnetica, capable of anoxygenic photosynthesis in the light with sulfide as electron donor can anaerobically break down its intracellular polyglucose in the dark. In the absence of elemental sulfur, the organism carries out lactate fermentation; in its presence, anaerobic respiration occurs in which sulfur is reduced to sulfide. Induction of anoxygenic photosynthesis or synthesis of new proteins is not necessary for either process. Cells adapted in the dark to sulfur reduction are capable of anoxygenic photosynthesis during a subsequent light period, unless protein synthesis has been inhibited during the dark incubation period.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - FCCP Carbonylcyanide p-trifluoromethoxyphenylhydrazone - mgat milligramatom - OD optical density     

Adaptation to sulfide and to the underwater light field in three cyanobacterial isolates from Lake Arcas (Spain)

Abstract: Three strains of cyanobacteria isolated from karstic Lake Arcas were tested for photosynthetic adaptations to soluble sulfide. One of them, AO11, was identified as Oscillatoria cf. ornata , and forms dense populations in the sulfide-rich anoxic hypolimnion of this lake. This cyanobacterium was able to perform sulfide-dependent anoxygenic photosynthesis and its oxygenic photosynthesis was relatively insensitive to sulfide. The other strains studied were AP1 and AO21, identified respectively as Pseudanabaena sp. and Oscillatoria cf. tenuis , populations of which were present only in epilimnetic waters at low population densities. Pseudanabaena sp. also carried out anoxygenic photosynthesis, but oxygenic photosynthesis was totally inhibited by 0.5 mM sulfide. Oscillatoria cf. tenuis lost most of its oxygenic photosynthetic capacity when submitted to 0.1 mM sulfide and anoxygenic photosynthesis accounted for less than 20% of sulfide-free controls. In addition to different photosynthetic capabilities, the three cyanobacteria exhibited differences in light-harvesting photosynthetic accessory pigments. Pigment analysis of cultures grown under different light conditions showed the capacity of Oscillatoria cf. ornata AO11 to produce phycoerythrin under low light intensity or under predominantly green light, while neither Pseudanabaena sp. AP1 nor Oscillatoria cf. tenuis AO21 produced this pigment. The complementary chromatic adaptation of Oscillatoria cf. ornata correlates well with its summertime distribution under the dim light field of the hypolimnion. The distribution and abundance of specific cyanobacterial populations in Lake Arcas can thus be explained by the interplay of light regime and presence of sulfide as some of the most determinant ecological parameters.     

Spore germination inCylindrospermum sp.: Influence of gases and growth conditions

Influence of different gases on spore germination ofCylindrospermum sp. revealed that acetylene and ethylene suppressed the germination which was more pronounced at their higher concentrations. Germination was completely inhibited under the atmosphere of hydrogen and argon even when supplied with 1% CO₂. Carbon dioxide, both in air and in N₂, stimulated the process. However, higher concentrations of CO₂ inhibited the germination in a concentration-dependent manner, possibly due to a decrease in pH. Germination was completely arrested in the absence of light and nutrients. The energetic requirement for germination was not efficiently fulfilled by photosystem I (PS II was blocked by 3-(3,4-dichlorophenyl)-1,1-dimethylurea) or under conditions of anoxygenic photosynthesis (medium supplemented with sodium sulfide).     

The genetic basis of anoxygenic photosynthetic arsenite oxidation

‘Photoarsenotrophy’, the use of arsenite as an electron donor for anoxygenic photosynthesis, is thought to be an ancient form of phototrophy along with the photosynthetic oxidation of Fe(II), H₂S, H₂ and . Photoarsenotrophy was recently identified from Paoha Island's (Mono Lake, CA) arsenic‐rich hot springs. The genomes of several photoarsenotrophs revealed a gene cluster, arxB2AB1CD, where arxA is predicted to encode for the sole arsenite oxidase. The role of arxA in photosynthetic arsenite oxidation was confirmed by disrupting the gene in a representative photoarsenotrophic bacterium, resulting in the loss of light‐dependent arsenite oxidation. In situ evidence of active photoarsenotrophic microbes was supported by arxA mRNA detection for the first time, in red‐pigmented microbial mats within the hot springs of Paoha Island. This work expands on the genetics for photosynthesis coupled to new electron donors and elaborates on known mechanisms for arsenic metabolism, thereby highlighting the complexities of arsenic biogeochemical cycling.     

Reduced sulfur and nitrogen compounds and molecular hydrogen as electron donors for anaerobic CO2 photoreduction in Anacystis nidulans

Photosynthesis by Anacystis nidulans was studied in presence of reduced sulfur or nitrogen compounds, or of hydrogen. O₂ evolution and CO₂ fixation were depressed by sulfide, sulfite, cysteine, thioglycollate, hydroxylamine and hydrazine. Sulfite, cysteine and hydrazine inhibited O₂ evolution much more strongly than CO₂ fixation, indicating ability to supply electrons for CO₂ photoreduction; DCMU suppressed these photoreductions. In contrast, some anoxygenic photosynthetic CO₂ fixation insensitive to DCMU was found with sulfide, thiosulfate and hydrogen. Emerson enhancement studies confirmed that sulfite, cysteine and hydrazine acted on photosystem II, while photoreduction supported by sulfide, thiosulfate and hydrogen needed photosystem I only.Sulfite was photooxidized to sulfate, sulfide to elemental sulfur, and thiosulfate to sulfate plus elemental sulfur; the sulfur accumulated inside the cells. Results on the stoichiometries of the photoreductions were consistent with the photooxidation products determined. Inhibitor studies suggested photosynthetic CO₂ fixation through the Calvin cycle.While photoreduction by all reductants used was found to be constitutive in Anacystis, the process was stimulated by anaerobic preincubation with the reductants only in the cases of hydrogen and thiosulfate; this adaptation was prevented by chloramphenicol and by O₂. Anaerobic photoautotrophic growth of Anacystis was, however, not observed; the increase in dry weight with H₂ and thiosulfate was not accompanied by cell multiplication or by an increase in chlorophyll content. Parallel short-term experiments with Chlorella did not reveal any constitutive photoreduction in this eukaryotic alga.Abbreviations CAP chloramphenicol - CCCP carbonyl cyanide m-chlorophenylhydrazone - DBMIB dibromothymoquinone - DCMU dichlorophenyl dimethyl urea - DSPD disalicylidenepropane diamine-(1,3) - EDAC 1-ethyl-3(3-dimethylaminopropyl-) carbodiimide     

Unsaturated fatty acid composition and biosynthesis in Oscillatoria limnetica and other cyanobacteria

A number of cyanobacteria showing a high degree of adaptation to life under reduced oxygen tensions as witnessed by their potency of facultative anoxygenic CO₂ photoassimilation with sulfide as electron donor were found to lack polyunsaturated fatty acids in their lipids. Lack of polyunsaturated fatty acids was found in representatives of different taxonomic groups. One of the strains lacking polyenoic acids was Oscillatoria limnetica, which can alternatively grow acrobically or anaerobically with sulfide as electron donor. This organism was found to synthesize monounsaturated fatty acids by desaturation of their saturated counterparts, in the presence as well as in the absence of molecular oxygen.Abbreviations ACP Acyl carrier protein - DCMU 3(3,4-dichlorophenyl)-1,1-dimethylurea     

Nitrogen supply as a factor influencing photoinhibition and photosynthetic acclimation after transfer of shade-grown Solanum dulcamara to bright light

We have compared the ability of shadegrown clones of Solamum dulcamara L. from shade and sun habitats to acclimate to bright light, as a function of nitrogen nutrition before and after transfer to bright light. Leaves of S. dulcamara grown in the shade with 0.6 mM NO ₃ ^- have similar photosynthetic properties as leaves of plants grown with 12.0 mM NO ₃ ^- . When transferred to bright light for 1–2 d the leaves of these plants show substantial photoinhibition which is characterized by about 50% decrease in apparent quantum yield and a reduction in the rate of photosynthesis in air at light saturation. Photoinhibition of leaf photosynthesis is associated with reduction in the variable component of low-temperature fluorescence emission, and with loss of in-vitro electron transport, especially of photosystem II-dependent processes.We find no evidence for ecotypic differentiation in the potential for photosynthetic acclimation among shade and sun clones of S. dulcamara, or of differentiation with respect to nitrogen requirements for acclimation. Recovery from photoinhibition and subsequent acclimation of photosynthesis to bright light only occurs in leaves of plants provided with 12.0 mM NO ₃ ^- . In these, apparent quantum yield is fully restored after 14 d, and photosynthetic acclimation is shown by an increase in light-saturated photosynthesis in air, of light-and CO₂-saturated photosynthesis, and of the initial slope of the CO₂-response curve. The latter changes are highly correlated with changes in ribulose-bisphosphate-carboxylase activity in vitro. Plants supplied with 0.6 mM NO ₃ ^- show incomplete recovery of apparent quantum yield after 14 d, but CO₂-dependent leaf photosynthetic parameters return to control levels.Symbols and abbreviations F_o initial level of fluorescence at 77 K - F_m maximum level of fluorescence at 77 K - F_v variable components of fluorescence at 77 K (F_v=F_m-F_o) - PSI, PSII photosystem I and II, respectively - RuBP ribulose-1,5-bisphosphate - RuBPCase ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39)     

Toxic and non-toxic Nodularia strains can be distinguished from each other and from eukaryotic algae with chlorophyll fluorescence fingerprinting

Chlorophyll fluorescence induction curves of toxic and non-toxic strains of the cyanobacterium Nodularia were measured and compared with fluorescence curves measured from four species of eukaryotic algae. Both cyanobacteria and algae were isolated from the Baltic Sea. The results show that Nodularia strains can be distinguished from the eukaryotes by applying a pattern recognition procedure to the fluorescence induction curves, suggesting that the fluorescence fingerprinting technique might be useful in environmental monitoring of marine algae. The six studied Nodularia strains could not be distinguished from each other from their fluorescence induction kinetics. However, their fluorescence curves fell into two clear categories, the toxic and the non-toxic Nodularia. Emission spectroscopy and differences in the fluorescence induction curves showed that the ratio of the intensity of the Photosystem I emission peak to the Photosystem II peak is higher in non-toxic Nodularia than in the toxic strains, suggesting that the toxicity affects the structure of the photosynthesis machinery. The effect on photosynthesis may be related to the ability of the microcystins to chelate iron.     

Intraspecific variation in the response of the cyanobacterium Nodularia spumigena to moderate UV-B radiation

Floating and nodularin-producing strains of Nodularia spumigena from the Baltic Sea are regarded as belonging to one species. However, intraspecific variation in the response of N. spumigena to environmental factors has been commonly overlooked. As blooms of N. spumigena occur in late summer, a period with strong light and stable water-column stratification, the cells can be expected to also be exposed to ultraviolet-B radiation (UV-B, 280–320 nm). The UV-B tolerance of four different strains of N. spumigena, isolated from the Baltic Sea, was investigated in the laboratory for 8 days, by measuring photosynthesis, growth and pigment composition. Variables included maximum quantum yield of photosynthesis (F_v/F_m, PAM fluorometry), growth rate (cell counts) and photosynthetic pigments, as well as mycosporine-like amino acids (HPLC). Intraspecific differences regardless of treatment were found for cell dimension, growth rate, F_v/F_m and pigment concentrations. UV-B related effects differed between strains. By Day 8 one of the four strains showed a lower F_v/F_m when treated with UV-B; in another strain the growth rate and cell numbers were lower. In three strains, UV-B exposure resulted in higher cell concentrations of carotenoids and chlorophyll a. In all strains, the concentrations of total mycosporine-like amino acids were 60–130% higher in the UV-B treated samples compared with samples shielded from UV-B. Although strain-specific differences in UV-B tolerance were observed, it is concluded that N. spumigena is a species that is not generally negatively affected by moderate levels of UV-B radiation.     

Isolation and characterization of<Emphasis Type="Italic"> Erythrobacter</Emphasis> sp. strains from the upper ocean

Seven strains of marine aerobic anoxygenic phototrophs belonging to the genus Erythrobacter were isolated. The strains were characterized regarding their physiological and biochemical properties, 16S rDNA and pufM gene sequences, morphological features, substrate preference, as well as pigment and lipid composition. All strains had functional type-2 reaction centers containing bacteriochlorophyll, served by small, light-harvesting complex 1, and were photosynthetically competent. In addition, large pools of carotenoids were found, but only some of the accessory pigments transfer energy to the reaction centers. All of the isolates were facultative photoheterotrophs. They required an organic carbon substrate for growth; however, they are able to supplement a significant fraction of their metabolic requirements with photosynthetically derived energy.Abbreviations BChl Bacteriochlorophyll - Chl Chlorophyll - Erb. Erythrobacter - Erm. Erythromicrobium - FAMEs Fatty acid methyl esters - IRFRR Infrared fast repetition rate - LH1, LH2 Light-harvesting complex 1 and 2, respectively - Por. Porphyrobacter - PUFAs Polyunsaturated fatty acids - Rsb. Roseobacter - RubisCO Ribulose-1,5-bisphosphate carboxylase/oxygenase - µ Growth rate - ₄₇₀ Functional cross-section of the photosynthetic unit at 470 nm     

Structure-function relationship in hemoproteins: The role of cytochrome c 3 in the reduction of colloidal sulfur by sulfate-reducing bacteria

Cytochromes c ₃ of different strains of sulfatereducing bacteria have been purified and tested for their capacity to reduce colloidal sulfur to hydrogen sulfide. The results are in good agreement with the activities reported for the whole cells. Cytochrome c ₃ is the sulfur reductase of some strains of sulfate-reducing bacteria such as Desulfovibrio desulfuricans Norway 4 and sulfate-reducing bacterium strain 9974 from which the sulfur reductase activity can be purified with the cytochrome c ₃. In contrast, Desulfovibrio vulgaris Hildenborough cytochrome c ₃ is inhibited by the product of the reaction namely hydrogen sulfide. Chloramphenicol has no effect on the sulfur reductase activity of D. desulfuricans Norway 4 when resting cells grown on lactate-sulfate medium are put in the presence of colloidal sulfur. This shows that the sulfur reductase activity is constitutive and corresponds to the fact that colloidal sulfur grown cells do not contain more cytochrome c ₃ (or another sulfur reductase) than lactate-sulfate-grown cells.     

N2-fixation in Erwinia herbicola

Four from 18 strains of Erwinia herbicola tested had nitrogenase activity and grew with N₂ as sole source of nitrogen under strict anaerobic conditions with a doubling time of 20–24 h. Nitrogenase activity started only 96–120 h after transfer to a special medium maintained under anaerobic conditions. A ten fold increase in protein per culture found after the maximum nitrogenase activity of 80–130 nmol C₂H₄. mg protein^-1·min^-1 was accompanied by a fall in pH of the medium (20 mM phosphate buffer and in 125 mM Tris-buffer) from pH 7.2 to 5.4 or less, but only to 6.8 in 100 mM phosphate buffer. In all cases we found a sharp curtailing of nitrogenase activity 48 h after the maximum. The bacteria utilized only 35–50% of the nitrogen fixed for growth. Erwinia herbicola strains differed from two strains of Enterobacter agglomerans in being unable to fix nitrogen on agar surfaces exposed to air. Specific nitrogenase activity in Erwinia herbicola is compared with data reported for other Enterobacteriaceae and is found to be higher than that reported for Klebsiella pneumoniae, Enterobacter cloacae or Citrobacter freundii.     

Occurrence of facultative anoxygenic photosynthesis among filamentous and unicellular cyanobacteria.

Eleven of 21 cyanobacteria strains examined are capable of facultative anoxygenic photosynthesis, as shown by their ability to photoassimilate CO2 in the presence of Na2S, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 703-nm light. These include different cyanobacterial types (filamentous and unicellular) of different growth histories (aerobic, anaerobic, and marine and freshwater). Oscillatoria limnetica, Aphanothece halophytica (7418), and Lyngbya (7104) have different optimal concentrations of Na2S permitting CO2 photoassimilation, above which the rate decreases: 3.5, 0.7, and 0.1 mM, respectively. In A. halophytica, for each CO2 molecule photoassimilated two sulfide molecules are oxidized to elemental sulfur, which is excreted from the cells.The ecological and evolutionary significance of anoxygenic photosynthesis in the cyanobacteria is discussed.     

Effects of low and elevated CO2 on C3 and C4 annuals

Abutilon theophrasti (C₃) and Amaranthus retroflexus (C₄), were grown from seed at four partial pressures of CO₂: 15 Pa (below Pleistocene minimum), 27 Pa (pre-industrial), 35 Pa (current), and 70 Pa (future) in the Duke Phytotron under high light, high nutrient, and wellwatered conditions to evaluate their photosynthetic response to historic and future levels of CO₂. Net photosynthesis at growth CO₂ partial pressures increased with increasing CO₂ for C₃ plants, but not C₄ plants. Net photosynthesis of Abutilon at 15 Pa CO₂ was 70% less than that of plants grown at 35 Pa CO₂, due to greater stomatal and biochemical limitations at 15 Pa CO₂. Relative stomatal limitation (RSL) of Abutilon at 15 Pa CO₂ was nearly 3 times greater than at 35 Pa CO₂. A photosynthesis model was used to estimate ribulose-1,5-bisphosphate carboxylase (rubisco) activity (Vc_max), electron transport mediated RuBP regeneration capacity (J _max), and phosphate regeneration capacity (PiRC) in Abutilon from net photosynthesis versus intercellular CO₂ (A–C _i) curves. All three component processes decreased by approximately 25% in Abutilon grown at 15 Pa compared with 35 Pa CO₂. Abutilon grown at 15 Pa CO₂ had significant reductions in total rubisco activity (25%), rubisco content (30%), activation state (29%), chlorophyll content (39%), N content (32%), and starch content (68%) compared with plants grown at 35 Pa CO₂. Greater allocation to rubisco relative to light reaction components and concomitant decreases in J _max and PiRC suggest co-regulation of biochemical processes occurred in Abutilon grown at 15 Pa CO₂. There were no significant differences in photosynthesis or leaf properties in Abutilon grown at 27 Pa CO₂ compared with 35 Pa CO₂, suggesting that the rise in CO₂ since the beginning of the industrial age has had little effect on the photosynthetic performance of Abutilon. For Amaranthus, limitations of photosynthesis were balanced between stomatal and biochemical factors such that net photosynthesis was similar in all CO₂ treatments. Differences in photosynthetic response to growth over a wide range of CO₂ partial pressures suggest changes in the relative performance of C₃ and C₄ annuals as atmospheric CO₂ has fluctuated over geologic time.     

Heliobacterium sulfidophilum sp. nov. andHeliobacterium undosum sp. nov.: Sulfideoxidizing heliobacteria from thermal sulfidic springs

Two new species of heliobacteria isolated from cyanobacterial mats of two alkaline sulfidic hot springs are formally described. Strains BR4 and BG29 are assigned to anoxygenic phototrophic bacteria of the familyHeliobacteriaceae, since they possess the unique properties of this taxon: strict anaerobiosis, formation of bacteriochlorophyllg, the lack of extensive intracytoplasmic membranes and chlorosomes, an unusual cell wall structure, and phylogenetic relatedness to the low G+C gram-positive eubacteria. Based on the 16S rDNA sequence similarity, strains BR4 and BG29 are assigned to the genusHeliobacterium and described as two new species of this genus:Heliobacterium sulfidophilum sp. nov. andHeliobacterium undosum sp. nov. The G+C content of the DNA is 51.3 mol % inHbt. sulfidophilum and 57.2-57.7 mol % inHbt. undosum. The cells ofHbt. sulfidophilum are rods, and the cells ofHbt. undosum are slightly twisted spirilla or short rods. Both new bacteria are motile by peritrichous flagella.Hbt. sulfidophilum produces endospores. The new bacteria are strict anaerobes growing photoheterotrophically on a limited range of organic compounds. In the dark, they can switch from photosynthesis to the slow fermentation of pyruvate. Biotin is required as a growth factor. Both species are highly tolerant to sulfide (up to 2 mM at pH 7.5) and oxidize it photoheterotrophically to elemental sulfur; photoautotrophic growth was not observed. The temperature optimal for growth ofHbt. sulfidophilum andHbt undosum is 30–35‡C, and the optimal pH is 7–8.     

THE EFFECT OF SULFIDE ON THE BLUEGREEN ALGAE OF HOT SPRINGS. I. NEW ZEALAND AND ICELAND1

The concentration of soluble sulfide (H₂S, HS^?, S⁼)² in hot springs of New Zealand and Iceland has a “species-determining” effect which appears to override the effect of all other chemical factors excepting hydrogen ion concentration. The cosmopolitan high-temperature form (HTF) of Mastigocladus laminosus (Ag.) Cohn appears to be sensitive to concentrations of S⁼ over 0.15 mg·l^?1 in New Zealand and 0.25 mg·l^?1 in Iceland. It was absent in thermal streams where S⁼ level was high enough to exceed this concentration at a point below its optimal temperature range (i.e., below ca. 50 C). In low or non-S⁼ springs in these regions this alga formed mats to an upper temperature limit of 63–64 C. In contrast, one bluegreen alga (Oscillatoria amphigranulata van Goor) occurred abundantly only in moderate to high S⁼ springs of New Zealand; this was a species with an upper temperature limit of about 57 C. Field ¹⁴C-HCO₃^? incorporation experiments with various levels of added S⁼ confirmed the sensitivity of HTF Mastigocladus and the great tolerance of O. amphigranulata. In the latter, the photosynthetic incorporation of ¹⁴C-HCO₃^? was sustained or enhanced by the additions of S⁼ in the presence of 5 × 10^?5m DCMU, an inhibitor of photoelectron transport on the reducing side of photosystem II. It is possible, but not proven, that S⁼ may act as a photoreductant in this species.