Occurrence and dynamics of phototrophic purple nonsulphur bacteria compared with other asymbiotic nitrogen fixers in ricefields of Egypt

The occurrence and the dynamics of phototrophic purple nonsulphur bacteria (PPNSB) as well as Azospirillum, Azotobacter, Clostridium, and cyanobacteria at different rice growth stages were studied in two ricefields, at Kafr-El-Shiekh and Al-Fayoum in Egypt.The PPNSB existed in the both rice fields examined, but their numbers varied according to field conditions, habitat and rice growth stage. After transplanting, the number of PPNSB increased gradually, reached its maximum at maximum tillering stage, and thereafter declined toward harvest time. Numbers of PPNSB were generally comparable with that of the heterotrophic N₂-fixers namely Azospirillum, Azotobacter, Clostridium and cyanobacteria, while that of phototrophic purple and green sulphur bacteria were relatively lower.The highest PPNSB numbers were generally found in rhizosphere (10³–10⁶ per g^–1 dw soil) followed by soil (10³–10⁵ per g^–1 dw soil) and floodwater (10–10² per ml). Rice plants showed a positive rhizosphere effect on PPNSB, clostridia, Azotobacter and Azospirillum, negative rhizosphere effect on cyanobacteria and green sulphur bacteria, and no effect on purple sulphur bacteria.     

A modified method for the cultivation of phototrophic bacteria

Simplified anaerobic media and a convenient method for the cultivation of Rhodospirillaceae, Chlorobiaceae, Chloroflexaceae and Chromatiaceae are described. The modified conditions assure almost complete anaerobiosis for media, growth and maintenance.Strains representing several species of Rhodospirillaceae, Chlorobiaceae and Chromatiaceae were successfully grown within relatively short times with full pigmentation, indicating that the new media and cultivation conditions were most suited for photoautotrophic growth.     

北京红篓菌合成聚羟基烷酸的研究

报道从污水处理厂回流池废水中分离到的北京红篓菌 (Rcs.pekingensisstrain 3-p)合成PHAs的研究结果。实验结果表明 ,3 p菌株生长及积累PHAs的最佳培养条件为 :0 0 1 %酵母膏 ,0 0 1 %NH4 Cl,乙酸钠 5g L ;培养基最适pH值为 7 0～ 7 2。在此培养条件下 ,细胞内PHAs积累量达菌体干重的 60 %以上。酶活测定表明菌株 3 p含有与PHAs合成相关的β 酮硫解酶 ,乙酰乙酰CoA还原酶 ,PHA聚合酶 ,初步推断此菌株的代谢途径为     

A possible physiological function of the oxygen-photoreducing system of Rhodospirillum rubrum

Anaerobic suspensions of Rhodospirillum rubrum cells which had been grown in the dark under low oxygen tension showed only a small increase of their ATP content when illuminated for 30 s. The same suspensions failed to start immediate growth in the light. Both high light-induced ATP levels and immediate phototrophic growth were elicited by small amounts of oxygen which were insufficient by themselves to raise the ATP levels or to support growth in the dark. The oxygen requirement for growth disappeared after some time of anaerobic illumination and was not observed in suspensions of cells which had been grown in the light under anaerobiosis. Furthermore, these phototrophic cells reached the maximum levels of ATP when illuminated in the absence of oxygen.Strain F11, a mutant derivative of Rhodospirillum rubrum which lacked the ability to photoreduce oxygen in vitro, needed abnormally high amounts of oxygen to increase its ATP levels and to grow in the light. Besides, KCN inhibited the increase of ATP levels in illuminated mutant cells but not wild type cells. An additional difference between both strains was that the oxygen requirement for growth did not disappear in the mutant after some time of anaerobic incubation in the light.To explain these observations, it is proposed that the photosynthetic system of semiaerobically-grown Rhodospirillum rubrum becomes overreduced under anaerobiosis. The oxygen-photoreducing system, which is impaired in the mutant, is apparently used to oxidize the photosynthetic system to its optimal redox state, carrying electrons to oxygen or to other endogenous acceptors which are formed during incubation in the light. The mutant seems to replace the defective system by a cyanide-sensitive pathway which may reduce oxygen but not the alternative endogenous acceptors.     

Noncyclic electron transport in chromatophores from photolithotrophically grown Rhodobacter sulfidophilus

Chromatophores isolated from the marine phototrophic bacterium Rhodobacter sulfidophilus were found to photoreduce NAD with sulfide as the electron donor. The apparent K _m for sulfide was 370 M and the optimal pH was 7.0. The rate of NAD photoreduction in chromatophore suspensions with sulfide as the electron donor (about 7–12 M/h·mol Bchl) was approximately onetenth the rate of sulfide oxidation in whole cell suspensions. NAD photoreduction was inhibited by rotenone, carbonyl cyanide-m-chlorophenylhydrazone, and antimycin A. Sulfide reduced ubiquinone in the dark when added to anaerobic chromatophore suspensions. These results suggest that electron transport from sulfide to NAD involves an initial dark reduction of ubiquinone followed by reverse electron transport from ubiquinol to NAD mediated by NADH dehydrogenase.Abbreviations Bchl bacteriochlorophyll - CCCP carbonyl cyanide-m-chlorophenylhydrazone - MOPS 3(N-morpholino)-propane sulfonate - Uq ubiquinone     

In vivo inhibition of nitrogenase by hydroxylamine in Rhodospirillaceae Role of nitric oxide

Rhodobacter capsulatus strains E1F1 and B10 and Rhodobacter sphaeroides DSM 158 did not use hydroxylamine as nitrogen source for growth but metabolized it mainly through the glutamine synthetase reaction. Hydroxylamine had a high toxicity for cells growing either under phototrophic or dark-aerobic conditions. l-methionine-d,l-sulfoximine partially inhibited hydroxylamine uptake and increased the inhibition time of nitrogenase activity by this nitrogen compound. Nitric oxide was also a powerful inhibitor of nitrogenase in intact cells of R. capsulatus. Since low amounts of NO were produced from hydroxylamine, short-term inhibition of nitrogenase in the presence of this compound could be mediated in vivo by nitric oxide.Abbreviations GS glutamine synthetase - MSX l-methionine-d,l-sulfoximine - MTA mixed alkyltrimethylammonium bromide     

Degradation of p-nitrophenol by the phototrophic bacterium Rhodobacter capsulatus

The phototrophic bacterium Rhodobacter capsulatus detoxified p-nitrophenol and 4-nitrocatechol. The bacterium tolerated moderate concentrations of p-nitrophenol (up to 0.5 mM) and degraded it under light at an optimal O₂ pressure of 20 kPa. The bacterium did not metabolize the xenobiotic in the dark or under strictly anoxic conditions or high O₂ pressure. Bacterial growth with acetate in the presence of p-nitrophenol took place with the simultaneous release of nonstoichiometric amounts of 4-nitrocatechol, which can also be degraded by the bacterium. Crude extracts from R. capsulatus produced 4-nitrocatechol from p-nitrophenol upon the addition of NAD(P)H, although at a very low rate. A constitutive catechol 1,2-dioxygenase activity yielding cis,cis-muconate was also detected in crude extracts of R. capsulatus. Further degradation of 4-nitrocatechol included both nitrite- and CO₂-releasing steps since: (1) a strain of R. capsulatus (B10) unable to assimilate nitrate and nitrite released nitrite into the medium when grown with p-nitrophenol or 4-nitrocatechol, and the nitrite concentration was stoichiometric with the 4-nitrocatechol degraded, and (2) cultures of R. capsulatus growing microaerobically produced low amounts of ¹⁴CO₂ from radiolabeled p-nitrophenol. The radioactivity was also incorporated into cellular compounds from cells grown with uniformly labeled ¹⁴C-p-nitrophenol. From these results we concluded that the xenobiotic is used as a carbon source by R. capsulatus, but that only the strain able to assimilate nitrite (E1F1) can use p-nitrophenol as a nitrogen source. Received: 30 December 1996 / Accepted: 3 September 1997     

Membrane Biochemistry : by E. Sim Chapman and Hall; London, 1982

Adenine, cytidine and guanosine nucleotides were supplied to cultures of Rhodopseudomonas capsulata under aerobic heterotrophic and phototrophic growth conditions. Aerobic growth is not affected by exogenous nucleotides (up to 10 mM) whereas phototrophic growth is strongly inhibited by adenine but not by guanosine or cytidine nucleotides. During phototrophic growth there is an inverse relationship between the concentration of exogenous adenine nucleotides and photopigment synthesis. There are no statistically significant differences between the inhibitory effect of AMP, ADP and ATP on the growth rate and bacteriochlorophyll synthesis since adenine nucleotides are incorporated into the cell as AMP by means of the phosphoribosyl transferase system.     

Expression and characterization of the assimilatory NADH-nitrite reductase from the phototrophic bacterium Rhodobacter capsulatus E1F1

A nas gene region from Rhodobacter capsulatus E1F1 containing the putative nasB gene for nitrite reductase was previously cloned. The recombinant His₆-NasB protein overproduced in E. coli showed nitrite reductase activity in vitro with both reduced methyl viologen and NADH as electron donors. The apparent K _m values for nitrite and NADH were 0.5 mM and 20 μM, respectively, at the pH and temperature optima (pH 9 and 30°C). The optical spectrum showed features that indicate the presence of FAD, iron-sulfur cluster and siroheme as prosthetic groups, and nitrite reductase activity was inhibited by sulfide and iron reagents. These results indicate that the phototrophic bacterium R. capsulatus E1F1 possesses an assimilatory NADH-nitrite reductase similar to that described in non-phototrophic organisms.     

Simultaneous phototrophic and chemotrophic growth in the purple sulfur bacterium Thiocapsa roseopersicina M1

Abstract The anoxygenic phototrophic purple sulfur bacterium Thiocapsa roseopersicina was grown in illuminated continuous cultures with thiosulfate as growth limiting substrate. Aeration resulted in completely colorless cells growing chemotrophically, whereafter the conditions were changed to a 23 h oxic/1 h anoxic regime. After 11 volume changes at a dilution rate of 0.031 h⁻¹ (35% of μ_max) a time dependent equilibrium was established. During the 23 h oxic periods bacteriochlorophyll a synthesis (BChl a ) was not observed, whereas during the 1 h anoxic periods synthesis was maximal (i.e. 1.1 μg (mg protein)⁻¹ h⁻¹). As a result the BChl a concentration gradually increased from zero to an average value over 24 h of 1.9 μg (mg protein)⁻¹. Concomitantly, the protein concentration increased from 13.9 mg 1⁻¹ during continuous oxic conditions to 28.8 mg 1⁻¹. For comparison, the protein concentration during fully phototrophic growth at an identical thiosulfate concentration in the inflowing medium was 53.7 mg 1⁻¹. The specific respiration rate was 8 μmol O₂ (mg protein)⁻¹ h⁻¹ during full chemotrophic growth and gradually decreased to 3.5 μmol O₂ (mg protein)⁻¹ h⁻¹ after 11 volume changes at the regime employed. These data show that T. rosepersicina is able to simultaneously utilize light and aerobic respiration of thiosulfate as sources of energy. The ecological relevance of the data is discussed.     

Two halophilic Ectothiorhodospira strains with unusual morphological,physiological and biochemical characters

Two strains belonging to the genus Ectothiorhodospira were isolated from enrichment cultures inoculated with sulfide-containing samples from the saltern of Trapani. Cells are motile short spirilla with internal stacks of membranes. During sulfide utilization they produce external globules of sulfur that are then completely oxidized to sulfate. These halophilic microorganisms need NaCl concentrations of 11% and 18% and a slightly alkaline pH. They are typical photoautotrophic bacteria, utilizing sulfide, sulfur and, only one of them, thiosulfate as photosynthetic electron donors; growth is stimulated by organic compounds. Neither of the two strains is capable of assimilatory sulfate reduction and neither grows in the dark. Pigments of the two strains are bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series subgroup 1B. Quinones are Q8 and MK8 in a strain and Q8 and MK7 in the other one: the latter situation, with quinone side chains of different lengths, is atypical within phototrophic bacteria. For morphological, physiological and biochemical characters, at least one of these strains clearly stays apart from the six Ectothiorhodospira species described until now.List of abbreviations HPLC high performance liquid chromatography - TLC thin layer chromatography - Qn ubiquinone—number of isoprenoid units of the side chain - MKn menaquinone—number of isoprenoid units of the side chain - R_t retention time - R_f retention factor Dedicated to the memory of Professor Gino Florenzano who inspired this work     

Chromatium glycolicum sp. nov., a moderately halophilic purple sulfur bacterium that uses glycolate as substrate

From the microbial mats that develop in Solar Lake, a new purple sulfur bacterium was isolated. This strain (Chromatium strain SL 3201) was morphologically similar to Chromatium gracile and Chromatium minutissimum. Chromatium SL 3201 was found to be a moderate halophile with a growth range between 2 and 20% NaCl (optimum 4–5% NaCl) and was able to grow photo-organotrophically using glycolate and glycerol. It is the first described phototrophic sulfur bacterium able to use glycolate. According to NaCl requirements and utilization of organic compounds, the strain is not related to any known species of the genus Chromatium. On the basis of its 16S rRNA gene sequence, it clusters with other Chromatium species and is most similar to Chromatium salexigens and Chr. gracile, but it is sufficiently separated to be considered as a new species of the genus. It is, therefore, described as Chromatium glycolicum sp. nov. Received: 17 June 1996 / Accepted: 4 November 1996     

Utilization of reducing power in light-limited cultures of Chromatiumvinosum DSM 185

This study describes how the phototrophic organism Chromatium vinosum, when grown under different degrees of light limitation, distributes the reducing power initially present in the medium as hydrogen sulfide. Under all the conditions of illumination tested, sulfur was the major store of reducing power. Glycogen, which was virtually absent under light limitation, accounted for 31.6% of the stored reducing power at saturating irradiances. Analysis of the electron budget showed that under light-limiting conditions, an important fraction of reducing power did not appear in storage products or in structural cell material. Analysis of dissolved organic carbon in the supernatant of the culture indicated the excretion of organic compounds. Received: 16 January 1998 / Accepted: 7 September 1998     

A new method for liquid nitrogen storage of phototrophic bacteria under anaerobic conditions

A simple, effective and economical method for the long-term preservation of bacteria in liquid nitrogen under anaerobic conditions is described. As a case example anaerobic photosynthetic bacteria were successfully preserved. Gas tight small screw-cap glass ampoules with butyl rubber septa were used for freezing the specimen anaerobically. During experimental manipulations no anaerobic chamber or glove boxes were required. All teste cultures yielded high recoveries after repeated thawing and during storage. After freezing, survival recoveries of Rhodospirillaceae range from 70–100%, whereas with strict anaerobic strains of Chlorobiaceae and Chromatiaceae a maximum loss of 1–2 log₁₀ counts was observed. No further loss in viability occurred after 1–2 years of storage.The small size of the ampoules and the use of single ampoule for 15–20 repeated retrievals proved economical with respect to storage space and costs.The system is compact and suitable for the preservation of anaerobic phototropic bacteria and other fragile anaerobic microorganisms.     

Rates of sulfate reduction and thiosulfate consumption in a marine microbial mat

Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 10⁸ cells of sulfate reducers cm⁻³ sediment, 2.0 × 10⁹ cells of chemolithoautotrophs cm⁻³ sediment, and 4.0 × 10⁷ cells of anoxygenic phototrophs cm⁻³ sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm⁻³ d⁻¹ in the absence of oxygen, and 123 nmol cm⁻³ d⁻¹ in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm⁻³ d⁻¹). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate.     

Isolation and growth of the phototrophic bacterium Rhodopseudomonas palustris strain B1 in sago-starch-processing wastewater

An indigenous strain of the purple non-sulphur phototrophic bacterium, Rhodopseudomonas palustris strain B1, was selected for the utilization and treatment of wastewater from a sago-starch-processing decanter. Growth of Strain B1 under anaerobic–light conditions in the carbohydrate-rich effluent was optimized by using 50% (v/v) effluent diluted in a basal minimal mineral medium with the addition to 0.1% (w/v) yeast extract. The optimum level of nitrogen source supplement, ammonium sulphate, was 1.0g/l. Highest cell mass concentration was achieved by using tungsten lamps as the light source with a light intensity of 4 klux. Under these optimal conditions, a maximum biomass of about 2.5g dry cell/l with a pigment content of about 1.1mg carotenoid/g dry weight cell was achieved after 96h of anaerobic cultivation. There was a 77% reduc n the chemical oxygen demand (COD) of the effluent. A cell yield of about 0.59g dry weight cell/g COD was obtained.     

Sedimentary photosynthetic pigments of algae and phototrophic bacteria in Lake Hamana,Japan: temporal changes of anoxia in its five basins

We analyzed photosynthetic pigments of algae and bacteria (phototrophic sulfur bacteria: Chromatium and brown Chlorobium) in sediment cores and water samples obtained from five basins of Lake Hamana, a brackish, eutrophic, holomictic lake in Japan, and discussed our findings in relation to the distribution of the phototrophs. The four outer basins are connected to the central basin by narrow inlets. The prevalence of anoxia in Lake Hamana was demonstrated by the widespread presence of bacterial pigments in each core. The construction of training walls in 1954–1956 to direct tidal currents into the lake via Imagire-guchi Channel, the sole inlet for seawater, increased the lake water circulation, suppressed the development of anoxia, and caused Chromatium to disappear. Strong correlations (r ² 0.7) between total algal carotenoid (TAC) and total bacterial carotenoid (TBC) contents in each core were found in four basins. We ascribe this to the induction of anoxia by water stratification and algal proliferation, which precede the growth of phototrophic sulfur bacteria in the deeper layers of the water column. The slopes of the TBC–TAC correlations in the sediment cores, indicating the extent and stability of anoxia at each site, differed among basins (0.23–0.67) and were inversely related to the exchange rate of water by seawater intrusion in each basin.