Accumulation of ambient phosphate into the periplasm of marine bacteria is proton motive force dependent.

Bacteria acquire phosphate (Pi) by maintaining a periplasmic concentration below environmental levels. We recently described an extracellular Pi buffer which appears to counteract the gradient required for Pi diffusion. Here, we demonstrate that various treatments to outer membrane (OM) constituents do not affect the buffered Pi because bacteria accumulate Pi in the periplasm, from which it can be removed hypo-osmotically. The periplasmic Pi can be gradually imported into the cytoplasm by ATP-powered transport, however, the proton motive force (PMF) is not required to keep Pi in the periplasm. In contrast, the accumulation of Pi into the periplasm across the OM is PMF-dependent and can be enhanced by light energy. Because the conventional mechanism of Pi-specific transport cannot explain Pi accumulation in the periplasm we propose that periplasmic Pi anions pair with chemiosmotic cations of the PMF and millions of accumulated Pi pairs could influence the periplasmic osmolarity of marine bacteria.

Diel changes and diversity of pufM expression in freshwater communities of anoxygenic phototrophic bacteria.

The anoxygenic phototrophic bacteria (APB) are an active component of aquatic microbial communities. While DNA-based studies have delivered a detailed picture of APB diversity, they cannot provide any information on the activity of individual species. Therefore, we focused on the expression of a photosynthetic gene by APB communities in two freshwater lakes (Cep lake and the Rímov Reservoir) in the Czech Republic. First, we analyzed expression levels of pufM during the diel cycle using RT-qPCR. The transcription underwent a strong diel cycle and was inhibited during the day in both lakes. Then, we compared DNA- (total) and RNA-based (active) community composition by sequencing pufM amplicon libraries. We observed large differences in expression activity among different APB phylogroups. While the total APB community in the Rímov Reservoir was dominated by Betaproteobacteria, Alphaproteobacteria prevailed in the active library. A different situation was encountered in the oligotrophic lake Cep where Betaproteobacteria (order Burkholderiales) dominated both the DNA and RNA libraries. Interestingly, in Cep lake we found smaller amounts of highly active uncultured phototrophic Chloroflexi, as well as phototrophic Gemmatimonadetes. Despite the large diversity of APB communities, light repression of pufM expression seems to be a common feature of all aerobic APB present in the studied lakes.

Shining light on the alphaproteobacterial general stress response: Comment on: Fiebig et al., Mol Microbiol, 2019.

The general stress response (GSR) allows many bacterial species to react to myriad different stressors. In Alphaproteobacteria, this signaling pathway proceeds through the partner-switching PhyR-EcfG sigma-factor mechanism and is involved in multiple life processes, including virulence in Brucella abortus. To date, details of the alphaproteobacterial GSR signaling pathway have been determined using genetic and biochemical work on a diverse set of species distributed throughout the clade. Fiebig and co-workers establish Erythrobacter litoralis DSM 8509 as a genetically tractable lab strain and use it to both directly and indirectly delineate photoresponsive GSR pathways mediated by multiple HWE/HisKA_2 histidine kinases. The existence of a new phototrophic lab strain allows researchers to compare the GSR across different Alphaproteobacteria, as well as study the interplay between the GSR and phototrophy. Additionally, the discovery of new HWE/HisKA_2 kinases regulating the GSR poses new questions about how different stimuli feed into this widespread stress pathway.

Fingerprints of partial oxidation of biogenic magnetite from cultivated and natural marine magnetotactic bacteria using synchrotron radiation.

Magnetotactic bacteria are a multi-phyletic group of bacteria that synthesize membrane-bound magnetic minerals. Understanding the preservation of these minerals in various environments (e.g., with varying oxygen concentrations and iron supply) is important for understanding their role as carriers of primary magnetizations in sediments and sedimentary rocks. Here we present X-ray near edge structure (XANES) spectra for Fe in magnetotactic bacteria samples from recent sediments to assess surface oxidation and crystal structure changes in bacterial magnetite during early burial. Our results are compared with a XANES spectrum of cultivated Magnetofaba australis samples, and with magnetic properties, and indicate that oxidation of magnetite to maghemite increases with depth in the sediment due to longer exposure to molecular oxygen. These results are relevant to understanding magnetic signatures carried by magnetofossils in oxic sediments and sedimentary rocks of different ages.

[Diversity and Physiological and Biochemical Properties of Heterotrophic Bacteria. Isolated from Lake Baikal Neuston.]

For heterotrophic microorganisms (44 strains) isolated-from the surface film of Lake Baikal, iden- tification was carried out and their. physiological and biochemical characteristics were determined. Com- pared to the water column, diversity of cultured heterotrophs was low, indicating formation of stable micro- bial communities at the air-water interphase interface. Heterotrophic bacteria isolated from the surface mi- crolayer exhibited the enzymatic activity comparable to that for strains form other biofilm associations. Deinococcusfi6us strain NA202 'vas the most active component of the community, capable of utilization of the broadest spectrum of mono- and disaccharides,'sugars, and amino acids. This strain possessed the highest diversity of extracellular enzymes and was the most resistant to UV radiation. The physiological and bio- chemical properties of this strain may-be responsible for its adaptation to survival in extreme conditions of the surface microlayer. Our results improve our understanding of occurrence of UV-resistant strains in freshwater ecosystems.

Growth of Dunaliella tertiolecta and associated bacteria in photobioreactors.

The aim of this study was to test three flat-plate photobioreactor configurations for cultivation of marine green alga Dunaliella tertiolecta under non-axenic growth conditions and to characterize and quantify the associated bacteria. The photobioreactor cultivations were conducted using tap water-based media. Static mixers intended to enhance mixing and light utilization did not generally increase algal growth at the low light intensities used. The maximum biomass concentration (measured as volatile suspended solids) and maximum specific growth rate achieved in the flat plate with no mixer were 2.9 g l⁻¹ and 1.3 day⁻¹, respectively. Based on quantitative polymerase chain reaction, bacterial growth followed the growth of D. tertiolecta. Based on 16S rDNA amplification and denaturing gradient gel electrophoresis profiling, heterotrophic bacteria in the D. tertiolecta cultures mainly originated from the non-axenic algal inocula, and tap water heterotrophs were not enriched in high chloride media (3 % salinity). Bacterial communities were relatively stable and reproducible in all flat-plate cultivations and were dominated by Gammaproteobacteria, Flavobacteria, and Alphaproteobacteria.

The photosynthetic apparatus and photoinduced electron transfer in the aerobic phototrophic bacteria Roseicyclus mahoneyensis and Porphyrobacter meromictius.

Photosynthetic electron transfer has been examined in whole cells, isolated membranes and in partially purified reaction centers (RCs) of Roseicyclus mahoneyensis, strain ML6 and Porphyrobacter meromictius, strain ML31, two species of obligate aerobic anoxygenic phototrophic bacteria. Photochemical activity in strain ML31 was observed aerobically, but the photosynthetic apparatus was not functional under anaerobic conditions. In strain ML6 low levels of photochemistry were measured anaerobically, possibly due to incomplete reduction of the primary electron acceptor (Q(A)) prior to light excitation, however, electron transfer occurred optimally under low oxygen conditions. Photoinduced electron transfer involves a soluble cytochrome c in both strains, and an additional reaction center (RC)-bound cytochrome c in ML6. The redox properties of the primary electron donor (P) and Q(A) of ML31 are similar to those previously determined for other aerobic phototrophs, with midpoint redox potentials of +463 mV and -25 mV, respectively. Strain ML6 showed a very narrow range of ambient redox potentials appropriate for photosynthesis, with midpoint redox potentials of +415 mV for P and +94 mV for Q(A). Cytoplasm soluble and photosynthetic complex bound cytochromes were characterized in terms of apparent molecular mass. Fluorescence excitation spectra revealed that abundant carotenoids not intimately associated with the RC are not involved in photosynthetic energy conservation.

Microbial oxidation of CH(4) at different temperatures in landfill cover soils.

Biological oxidation of CH(4) is an important constraint on the emission of this gas from areas, such as landfills to the atmosphere. We studied the effect of temperature on methanotrophic bacteria in three different landfill cover soils, incubated in the laboratory. In samples of a young cover, consisting of wood chips and sewage sludge, the phospholipid fatty acids (PLFAs), regarded as biomarkers for type I methanotrophs (16:1omega5t, 16:1omega6c, 16:1omega8c), primarily increased at low temperatures (5-10 degrees C). On the other hand, the PLFA marker for type II methanotrophs (18:1omega8c) was highly elevated only at 20 degrees C. These results suggest that temperature can determine the selection of methanotroph populations.

Maximization of hydrogen production ability in high-density suspension of Rhodovulum sulfidophilum cells using intracellular poly(3-hydroxybutyrate) as sole substrate.

Growth of and hydrogen production by wild-type (WT) Rhodovulum sulfidophilum were compared with those by one of its mutants lacking the poly(3-hydroxybutyrate) (PHB) biosynthesis ability (PNM2). During phototrophic growth under aerobic conditions with fixed illumination, changes in the extinction coefficient and PHB content of WT and PNM2 cells revealed interference of light penetration by PHB. WT cells synthesized PHB at an early stage of the cultivation. PHB degradation after exhaustion of acetate during the cultivation of WT resulted in a decrease of the extinction coefficient. The hydrogen production rate under anaerobic conditions with fixed illumination was examined in WT and PNM2 cell suspensions at different densities. The hydrogen production rate was determined not by the light penetration but by the kinds of hydrogen donors and the density of suspension. The highest value of the rate of hydrogen production from PHB, 33.0 ml/l/h, was improved compared with 26.6 ml/l/h, which was the highest value in hydrogen production from succinate. Under the same illumination, conversion to hydrogen from PHB is more efficient than that from succinate, which is one of the best substrates for hydrogen production. These results suggest that the hydrogen production rate can be maximized in the hydrogen production system based on PHB degradation, which is achieved in high-density suspension under external-substrate-depleted conditions after aerobic cultivation in the presence of an excess amount of acetate.

Effect of light and oxygen and adaptation to changing light conditions in a photosynthetic mutant in which the LHII complex of Rhv. sulfidophilum was heterologously expressed in a strain of Rb. capsulatus whose puc operon was deleted.

In this paper we show the effect of oxygen and light on the expression of the photosynthetic apparatus of a mutant heterologously expressing the puc operon. This mutant was obtained by introducing in trans an expression plasmid, bearing the puc A, B, and C genes of Rhv. sulfidophilum, as well as its own promoter, in an LHII(-) mutant of Rb. capsulatus. The results showed that oxygen and light repressed LHII expression. Even low-light intensities lowered the LHII content to undetectable levels by spectrophotometry or by SDS-PAGE. In high-light grown cells, where the relative ratios of LHI and LHII complexes were significantly diminished, we were able to detect LHII complexes. Under the latter condition, the absorption spectrum showed that some pigment accumulated in the membrane even in the absence of cell division. These pigments were used in a later step to assemble LHII complexes, when the high-light grown cells were transferred to semiaerobiosis in the dark. Transition of high-light grown cells to low-light conditions allowed us to study the adaptability of these heterologous mutant cells. We observed that adaptation never occurred, in part probably owing to energy limitation.

Time-dependent changes in the carotenoid composition and preferential binding of spirilloxanthin to the reaction center and anhydrorhodovibrin to the LH1 antenna complex in Rhodobium marinum.

Carotenoids were isolated from the cells of Rhodobium marinum, and their structures were determined by mass spectrometry and 1H nuclear magnetic resonance spectroscopy; the carotenoids include lycopene, rhodopin, anhydrorhodovibrin, rhodovibrin and spirilloxanthin. Time-dependent changes in the carotenoid composition in the reaction center (RC) and the light-harvesting complex 1 (LH1) were traced by high-performance liquid chromatography analysis of the extracts. The carotenoid composition changed according to the spirilloxanthin biosynthetic pathway. However, spirilloxanthin having the longest conjugated chain was always preferentially bound to the RC, and anhydrorhodovibrin and other precursors to the LH1.

Swimming characteristics of magnetic bacterium, Magnetospirillum sp. AMB-1, and implications as toxicity measurement.

To develop a novel toxicity measurement system using the persistent swimming property of magnetic bacteria along an externally applied magnetic field, certain characteristics of Magnetospirillum sp. AMB-1 cells were examined, including their growth pattern, motility, magnetosensitivity, swimming speed, and cell length distribution. In addition, the effect of toxic compounds on the swimming speed was assessed relative to application as a toxicity sensor. With an inoculum of 1.0 x 10(8) cells/mL, the cells reached the stationary phase with a concentration of about 5 x 10(8) cells/mL after 20 h, under both aerobic and anaerobic conditions. The distribution of the cell length did not vary significantly during the growth period, and both aerobically and anaerobically growing cells showed a similar cell length distribution. Although the cells showed similar growth patterns under both conditions, the anaerobically grown cells exhibited higher motility and magnetosensitivity. Actively growing cells under anaerobic conditions had an average swimming speed of 49 microm/s with a standard deviation of 20 microm/s. When the anaerobically growing cells were exposed to various concentrations of toxic compounds, such as 1-propanol and acetone, the swimming speed decreased with an increased concentration of the toxic compound. Accordingly, the relationship between swimming speed and toxicity can be used as an effective quantitative toxicity measurement; furthermore, the relative sensitivity of the proposed system was comparable to Microtox, which is commercially available.