Role of Rhodobacter sp. strain PS9, a purple non-sulfur photosynthetic bacterium isolated from an anaerobic swine waste lagoon,in odor remediation

Temporal pigmentation changes resulting from the development of a purple color in anaerobic swine waste lagoons were investigated during a 4-year period. The major purple photosynthetic bacterium responsible for these color changes and the corresponding reductions in odor was isolated from nine photosynthetic lagoons. By using morphological, physiological, and phylogenetic characterization methods we identified the predominant photosynthetic bacterium as a new strain of Rhodobacter, designated Rhodobacter sp. strain PS9. Rhodobacter sp. strain PS9 is capable of photoorganotrophic growth on a variety of organic compounds, including all of the characteristic volatile organic compounds (VOC) responsible for the odor associated with swine production facilities (J. A. Zahn, A. A. DiSpirito, Y. S. Do, B. E. Brooks, E. E. Copper, and J. L. Hatfield, J. Environ. Qual. 30:624-634, 2001). The seasonal variations in airborne VOC emitted from waste lagoons showed that there was a 80 to 93% decrease in the concentration of VOC during a photosynthetic bloom. During the height of a bloom, the Rhodobacter sp. strain PS9 population accounted for 10% of the total community and up to 27% of the eubacterial community based on 16S ribosomal DNA signals. Additional observations based on seasonal variations in meteorological, biological, and chemical parameters suggested that the photosynthetic blooms of Rhodobacter sp. strain PS9 were correlated with lagoon water temperature and with the concentrations of sulfate and phosphate. In addition, the photosynthetic blooms of Rhodobacter sp. strain PS9 were inversely correlated with the concentrations of protein and fluoride.     

Characterization of a new strain of a purple nonsulfur bacterium from a thermal spring

A new budding purple nonsulfur bacterium of the genus Rhodobacter (strain Ku-2) was isolated from a mat of a moderately thermal spring (Baikal rift zone, Buryatia, Russia). The bacterium had lamellar photosynthetic membranes, which are typical of only one Rhodobacter species, Rba. blasticus. The cells contained spheroidene carotenoids and bacteriochlorophyll a (Bchl a). In vivo absorption spectrum of the cells, with the major maximum at 863 nm and an additional peak at 887 nm, is characteristic of the pigment-protein complexes of Bchl a-containing membranes. The previously described Rba. blasticus strains do not exhibit the 887-nm maximum. The new isolate was photoheterotrophic, with optimal growth occurring at 35°C, 3 g/L NaCl, and pH 7–8. The DNA G+C content was 64.4 mol %. The similarity between the 16S rRNA gene sequences of strain Ku-2 and the Rba. blasticus type strain was 98.7%. The PufM amino acid sequences of strain Ku-2 and the earlier studied Rba. blasticus type strain were 89.5 % identical. Thus, strain Ku-2 belongs to the genus Rhodobacter and is phylogenetically close to Rba. blasticus.     

Changes in community structure and photosynthetic activities of total phytoplankton species during the growth,maintenance, and dissipation phases of a Prorocentrum donghaiense bloom

The potential interactions between the bloom-forming dinoflagellates and other phytoplankton during the algal bloom cycle are interesting, while the causes for the phytoplankton community changes were not fully understood. We hypothesized that phytoplankton community structure and photosynthetic activities of total phytoplankton have their special characteristics in different phases of the algal blooms. To test this hypothesis, a survey covering the process of a Prorocentrum donghaiense bloom in coastal waters between Dongtou and Nanji Islands was carried out from 9 to 20 May 2016, and the changes in the phytoplankton community and photosynthetic activities of total phytoplankton were determined. Surface seawater was sampled for microscopic analysis of phytoplankton composition and pulse amplitude modulated (PAM) chlorophyll fluorescence analysis of photosynthetic activities of the total phytoplankton species. A total of 25, 31, and 19 phytoplankton species were identified in its growth (9–12 May), maintenance (13–18 May) and dissipation phases (19–20 May), respectively. Diatoms were dominant in terms of species number while dinoflagellates were predominant at cell abundance. Dinoflagellates were the major dominant species during three phases of the bloom based on the dominance (Y) value, whereas the dominant species extended to dinoflagellates and diatoms including P. donghaiense, Coscinodiscus argus, Gonyaulax spinifera, Cyclotella sp. and Scrippsiella trochoidea in the dissipation phase. In the maintenance phase, the average cell abundances of the total phytoplankton and P. donghaiense were consistent with the chlorophyll a (Chla) concentration in the seawater; for the diversity indices of total phytoplankton species, Simpson index (C) was the highest while Shannon index (H′) and Pielou evenness index (J′) were the lowest. Furthermore, photosynthetic activities of the total phytoplankton species represented by the effective quantum yield (F_q'/F_m') and the maximum relative electron transport rate (rETR_max) in the maintenance phase were higher than those in the growth and dissipation phases. The results indicated that the characteristics of phytoplankton community structure and photosynthetic activities could be regarded as criteria in predicting the phases of algal blooms.     

Characterization of Phototrophic Purple Nonsulfur Bacteria Forming Colored Microbial Mats in a Swine Wastewater Ditch

The community structure of pink-colored microbial mats naturally occurring in a swine wastewater ditch was studied by culture-independent biomarker and molecular methods as well as by conventional cultivation methods. The wastewater in the ditch contained acetate and propionate as the major carbon nutrients. Thin-section electron microscopy revealed that the microbial mats were dominated by rod-shaped cells containing intracytoplasmic membranes of the lamellar type. Smaller numbers of oval cells with vesicular internal membranes were also found. Spectroscopic analyses of the cell extract from the biomats showed the presence of bacteriochlorophyll a and carotenoids of the spirilloxanthin series. Ubiquinone-10 was detected as the major quinone. A clone library of the photosynthetic gene, pufM, constructed from the bulk DNA of the biomats showed that all of the clones were derived from members of the genera Rhodobacter and Rhodopseudomonas. The dominant phototrophic bacteria from the microbial mats were isolated by cultivation methods and identified as being of the genera Rhodobacter and Rhodopseudomonas by studying 16S rRNA and pufM gene sequence information. Experiments of oxygen uptake with lower fatty acids revealed that the freshly collected microbial mats and the Rhodopseudomonas isolates had a wider spectrum of carbon utilization and a higher affinity for acetate than did the Rhodobacter isolates. These results demonstrate that the microbial mats were dominated by the purple nonsulfur bacteria of the genera Rhodobacter and Rhodopseudomonas, and the bioavailability of lower fatty acids in wastewater is a key factor allowing the formation of visible microbial mats with these phototrophs.     

Long term nutrient loads and chlorophyll dynamics in a large temperate Australian lagoon system affected by recurring blooms of cyanobacteria

While rare globally, blooms of the toxic cyanobacteria Nodularia spumigena are a recurring problem in a few estuaries, such as the Baltic Sea and several southern Australian estuaries. Here, we document recurring Nodularia spumigena Mertens blooms in the Gippsland Lakes, S.E. Australia; a temperate lagoon system with episodic, winter-spring dominated catchment inflows. Physico-chemical conditions exerted a strong influence over bloom development, with blooms consistently occurring at surface water salinities between 9 and 20 (average?=?15), inorganic nitrogen concentrations <0.4?μM, and inorganic nitrogen to reactive phosphorus ratios <5. There was a positive correlation between average annual chlorophyll a and total phosphorus (TP) load in years when there was no Nodularia bloom, but this relationship broke down in Nodularia bloom years, even though there was a strong correlation between in-lake TP and chlorophyll a during these years; this highlights the importance of internal sources of phosphorus to bloom development. Large catchment derived nitrate and nitrite (NO_x) inputs following wildfires and floods in 2007, led to high concentrations of NO_x within the surface waters of the Gippsland Lakes through the second half of 2007 and the start of 2008. We hypothesise that these high NO_x concentrations were a key factor leading to an unprecedented Synechococcus sp. bloom that developed in the austral summer of 2007–2008, despite conditions that would otherwise favour a Nodularia bloom.     

Biological Control of Hog Waste Odor through Stimulated Microbial Fe(III) Reduction

Odor control and disposal of swine waste have inhibited expansion of swine production facilities throughout the United States. Swine waste odor is associated primarily with high concentrations of volatile fatty acids (VFAs). Here, we demonstrate that stimulated Fe(III) reduction in hog manure can rapidly remove the malodorous compounds and enhance methane production by 200%. As part of these studies, we enumerated the indigenous Fe(III)-reducing population in swine waste and identified members of the family Geobacteraceae as the dominant species. These organisms were present at concentrations as high as 2 × 10⁵ cells g⁻¹. Several pure cultures of Fe(III) reducers, including Geobacter metallireducens, Geobacter humireducens, Geobacter sulfurreducens, Geobacter grbiciae, Geothrix fermentans, and Geovibrio ferrireducens, readily degraded some or all of the malodorous VFAs found in swine manure. In contrast, Shewanella algae did not degrade any of these compounds. We isolated an Fe(III) reducer, Geobacter strain NU, from materials collected from primary swine waste lagoons. This organism degraded all of the malodorous VFAs tested and readily grew in swine waste amended with Fe(III). When raw waste amended with Fe(III) was inoculated with strain NU, the VFA content rapidly decreased, corresponding with an almost complete removal of the odor. In contrast, the raw waste without Fe(III) or strain NU showed a marked increase in VFA content and a rapid pH drop. This study showed that Fe(III) supplementation combined with appropriate bioaugmentation provides a simple, cost-effective approach to deodorize and treat swine waste, removing a significant impediment to the expansion of pork production facilities.     

Feeding dynamics of the copepod Diacyclops thomasi before, during and following filamentous cyanobacteria blooms in a large, shallow temperate lake

Cyanobacteria blooms are an increasing problem in temperate freshwater lakes, leading to reduced water quality and in some cases harmful effects from toxic cyanobacteria species. To better understand the role of zooplankton in modulating cyanobacteria blooms, from 2008 to 2010 we measured water quality and plankton abundance, and measured feeding rates and prey selectivity of the copepod Diacyclops thomasi before, during and following summertime cyanobacteria blooms in a shallow, eutrophic lake (Vancouver Lake, Washington, USA). We used a combined field and experimental approach to specifically test the hypothesis that copepod grazing was a significant factor in establishing the timing of cyanobacteria bloom initiation and eventual decline in Vancouver Lake. There was a consistent annual succession of zooplankton taxa, with cyclopoid copepods (D. thomasi) dominant in spring, followed by small cladocerans (Eubosmina sp.). Before each cyanobacteria bloom, large cladocerans (Daphnia retrocurva, Daphnia laevis) peaked in abundance but quickly disappeared, followed by brief increases in rotifers. During the cyanobacteria blooms, D. thomasi was again dominant, with small cladocerans abundant in autumn. Before the cyanobacteria blooms, D. thomasi substantially consumed ciliates and dinoflagellates (up to 100% of prey biomass per day), which likely allowed diatoms to flourish. A shift in copepod grazing toward diatoms before the blooms may have then helped to facilitate the rapid increase in cyanobacteria. Copepod grazing impact was the highest during the cyanobacteria blooms both years, but focused on non-cyanobacteria prey; copepod grazing was minimal as the cyanobacteria blooms waned. We conclude that cyclopoid copepods may have an indirect role (via trophic cascades) in modulating cyanobacteria bloom initiation, but do not directly contribute to cyanobacteria bloom decline.     

Bacterial community dynamics during a bloom caused by Akashiwo sanguinea in the Xiamen sea area,China

Phytoplankton blooms are a worldwide ecological problem and one of the major algae that cause phytoplankton blooms is Akashiwo sanguinea. Though much research has addressed the abiotic causes (e.g. growth condition) of A. sanguinea blooms, few studies have examined the dynamics of microbial communities associated with these blooms. In this study, polymerase chain reaction (PCR)-based denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA genes was used to document changes in the phylogenetic diversity of microbial communities associated with an A. sanguinea bloom that occurred in the Xiamen sea in May 2010. Surface sea water was sampled once a day within five consecutive days at four sites, and the microbial community composition was determined using DGGE. Sea water concentrations of chlorophyll a, nitrate and phosphate were also measured. The results indicated that the A. sanguinea bloom was probably stimulated by low salinity (26–30‰) and ended probably because inorganic nutrients were consumed and resulted in a N/P ratio unfavorable for this alga. Gammaproteobacteria populations increased significantly during bloom declines and then decreased post-bloom. Divergences in the microbial community composition during different bloom periods were the result of changes in Candidatus, Pelagibacter, Alteromonas, Rhodobacteraceae, Vibrio and Pseudoalteromonas populations. Sediminimonas qiaohouensis was the first bacterium shown to be significantly negatively correlated with A. sanguinea concentration. This study indicated that bacteria may play an important role in A. sanguinea–bloom regulation and provides a deeper insight into bacterial community succession during and after an A. sanguinea–bloom.     

<Emphasis Type="Italic">Rhodobaca barguzinensis</Emphasis> sp. nov., a new alkaliphilic purple nonsulfur bacterium isolated from a soda lake of the Barguzin Valley (Buryat Republic,Eastern Siberia)

A novel strain, alga-05, of alkaliphilic purple nonsulfur bacteria was isolated from sediments of a small saline (60 g/l) soda lake near Lake Algin (Barguzin Valley, Buryat Republic, Russia). These bacteria contain bacteriochlorophyll a and carotenoids of the alternative spirilloxanthin group with predominating demethylspheroidenone. They are facultative anaerobes; their photosynthetic structures are of the vesicular type and arranged along the cell periphery. Growth of this strain is possible in a salinity range of 5–80 g/l NaCl, with an optimum at 20 g/l NaCl. Best growth occurred at 20–35°C. Analysis of the 16S rRNA gene sequences demonstrated that the studied isolate is closely related to the alkaliphilic purple nonsulfur bacterium Rhodobaca bogoriensis (99% similarity) isolated from soda lakes of the African Rift Zone. According to the results of DNA-DNA hybridization, strain alga-05 has a 52% similarity with the type species of the genus Rhodobaca. On the basis of the obtained genotypic data and some phenotypic properties (dwelling in a hypersaline soda lake of Siberia, moderate halophily, ability to grow at relatively low temperatures, etc.), the isolated strain of purple bacteria was described as a new species of the genus Rhodobaca, Rca. barguzinensis sp. nov.     

Algicidal Effects of a Novel Marine Pseudoalteromonas Isolate (Class Proteobacteria,Gamma Subdivision) on Harmful Algal Bloom Species of the Genera Chattonella,Gymnodinium, and Heterosigma

During a bacterial survey of the Huon Estuary in southern Tasmania, Australia, we isolated a yellow-pigmented Pseudoalteromonas strain (class Proteobacteria, gamma subdivision), designated strain Y, that had potent algicidal effects on harmful algal bloom species. This organism was identified by 16S rRNA sequencing as a strain with close affinities to Pseudoalteromonas peptidysin. This bacterium caused rapid cell lysis and death (within 3 h) of gymnodinoids (including Gymnodinium catenatum) and raphidophytes (Chattonella marina and Heterosigma akashiwo). It caused ecdysis of armored dinoflagellates (e.g., Alexandrium catenella, Alexandrium minutum, and Prorocentrum mexicanum), but the algal cultures then recovered over the subsequent 24 h. Strain Y had no effect on a cryptomonad (Chroomonas sp.), a diatom (Skeletonema sp.), a cyanobacterium (Oscillatoria sp.), and two aplastidic protozoans. The algicidal principle of strain Y was excreted into the seawater medium and lost its efficacy after heating. Another common bacterial species, Pseudoalteromonas carrageenovora, was isolated at the same time and did not have these algicidal effects. The minimum concentrations of strain Y required to kill G. catenatum were higher than the mean concentrations found in nature under nonbloom conditions. However, the new bacterium showed a chemotactic, swarming behavior that resulted in localized high concentrations around target organisms. These observations imply that certain bacteria could play an important role in regulating the onset and development of harmful algal blooms.Historically, the dynamics of marine bacterial and algal populations have been studied largely in isolation. Increasing evidence is now pointing toward a close spatial and temporal association between the two and recently attention has been focused on phagocytosis of bacteria by photosynthetic flagellates (21, 28, 30). In contrast, the importance of inhibitory or predatory bacteria in regulating populations of different algal species has received relatively little attention (9, 11). Some bacteria may selectively promote bloom formation by algal species (13), while other bacteria have algicidal effects and are involved in the termination and decomposition of algal blooms (12). The latter finding has raised the possibility of bacterial control of harmful algal blooms (19). There is little data on the occurrence of marine algicidal bacteria outside Japan, where toxic blooms are frequent events (20), and algicidal bacteria have been isolated during toxic blooms of naked dinoflagellates and raphidophytes (9).Gymnodinium catenatum (a causative organism of paralytic shellfish poisoning) is thought to have been introduced into southern Tasmania via ballast water after 1973, and in some years it has a severe negative impact on the shellfish industry (16). Previous efforts to understand and predict the seasonal and interannual variability of harmful algal blooms have largely focused on the environmental factors that affect dinoflagellate growth in the water column, notably water temperature, rainfall, and water column stability (16). Rainfall and estuarine flow patterns also largely determine the allochthonous input of dissolved organic matter (DOM), which is a source of organic carbon for bacteria (27) and is possibly involved in micronutrient dynamics that promote G. catenatum growth (3, 6). As part of a study investigating DOM, bacteria, and algal interactions in the Huon Estuary (24), we isolated two bacterial strains that we tested for possible alga-bacterium interactions by using cultures of G. catenatum. Both bacteria appeared to be Pseudoalteromonas species, which are extremely common, slightly halophilic, gram-negative bacteria found in many marine ecosystems. Preliminary observations indicated that one of the strains was extremely toxic towards G. catenatum, while the other was more benign. The aims of this study were (i) to determine the taxonomic identity of the bacteria, (ii) to document by light microscopy the sequence of algal cell lysis after exposure to an algicidal Pseudoalteromonas strain and compare this lysis to the effect of the more benign Pseudoalteromonas species, (iii) to define the minimum bacterial concentrations required for algicidal effects and compare these concentrations to concentrations in natural water samples, and (iv) to investigate the range of potential target organisms for the bacterium.     

Expression of yellow tail (Seriola quinqueradiata) fish growth hormone cDNA in the marine photosynthetic bacterium Rhodobacter SP NKPB 0021

Summary A full length cDNA encoding yellow tail (Seriola quinqueradiata) growth hormone has been cloned into an expression vector, pUK319, which contains a Rhodobacter specific replicon. The resulting plasmid, pKGH319 was introduced by transformation into the marine photosynthetic bacterium Rhodobacter sp. strain NKPB0021. The plasmid was maintained as an autonomous replicon and showed good stability in the absence of antibiotics. Fish growth hormone was purified by HPLC from yellow tail pituitary glands and used to raise polyclonal antibodies for immuno blot analysis of Rhodobacter recombinants. Recombinant growth hormone was immunoreactive to mouse antiserum against natural yellow tail hormone. Our results suggest that the fish growth hormone gene was expressed under the lac promoter of Escherichia coli to levels suitable for the use of recombinant photosynthetic bacteria as a marine fish feed supplement.     

Isolation and Properties of New Photosynthetic Bacteria Isolated from Seawater

Three strains of purple nonsulfur photosynthetic bacteria were isolated from seawater. They showed the characteristic properties of Rhodobacter species. Their biochemical, physiological, and chemotaxonomical properties were different from those of previously known species.     

Tackling codon usage bias for heterologous expression in Rhodobacter sphaeroides by supplementation of rare tRNAs

The photosynthetic Rhodobacter species are promising alternative expression hosts in bioproduction and biorefinery due to their unique metabolic capacities. With prominent inner membrane areas and efficient endogenous translocation machineries, they are especially attractive for membrane protein expression. However, codon usage bias could be a limitation in the engineering of Rhodobacter species and has seldom been investigated. In this study, we tackled the codon bias of Rhodobacter by functionally expressing 8 rare tRNAs of Rhodobacter sphaeroides with a multi-copy vector. The impact of tRNA supplementation was evaluated through monitoring expression levels of two heterologous proteins with different phylogenetic origins, a membrane subunit of the riboflavin transporter, RibU, from Lactobacillus acidophilus La-14 and a decaheme cytochrome, MtrA, from Shewanella oneidensis. Our results showed that the performances were closely related to medium composition and rare codon percentages of raw DNA sequences. Provision of rare tRNAs has increased RibU production by 7.7-folds and 2.86-fold in minimal medium and rich medium, respectively, while MtrA levels were increased by 1-fold in minimal medium. The present study confirms the presence of codon bias in R. sphaeroides and offers a facile tool for improving heterologous expression of rare-codon containing genes. We anticipate that this tRNA supplementation system can be further extended to other species of Rhodobacter, and thus will facilitate the engineering of purple bacteria for interesting applications in microbial technology.     

Selective expression of light-harvesting complexes alters phospholipid composition in the intracytoplasmic membrane and core complex of purple phototrophic bacteria

Phospholipid–protein interactions play important roles in regulating the function and morphology of photosynthetic membranes in purple phototrophic bacteria. Here, we characterize the phospholipid composition of intracytoplasmic membrane (ICM) from Rhodobacter (Rba.) sphaeroides that has been genetically altered to selectively express light-harvesting (LH) complexes. In the mutant strain (DP2) that lacks a peripheral light-harvesting (LH2) complex, the phospholipid composition was significantly different from that of the wild-type strain; strain DP2 showed a marked decrease in phosphatidylglycerol (PG) and large increases in cardiolipin (CL) and phosphatidylcholine (PC) indicating preferential interactions between the complexes and specific phospholipids. Substitution of the core light-harvesting (LH1) complex of Rba. sphaeroides strain DP2 with that from the purple sulfur bacterium Thermochromatium tepidum further altered the phospholipid composition, with substantial increases in PG and PE and decreases in CL and PC, indicating that the phospholipids incorporated into the ICM depend on the nature of the LH1 complex expressed. Purified LH1–reaction center core complexes (LH1–RC) from the selectively expressing strains also contained different phospholipid compositions than did core complexes from their corresponding wild-type strains, suggesting different patterns of phospholipid association between the selectively expressed LH1–RC complexes and those purified from native strains. Effects of carotenoids on the phospholipid composition were also investigated using carotenoid-suppressed cells and carotenoid-deficient species. The findings are discussed in relation to ICM morphology and specific LH complex–phospholipid interactions.     

Native architecture of the photosynthetic membrane from Rhodobacter veldkampii

The photosynthetic membrane in purple bacteria contains several pigment–protein complexes that assure light capture and establishment of the chemiosmotic gradient. The bioenergetic tasks of the photosynthetic membrane require the strong interaction between these various complexes. In the present work, we acquired the first images of the native outer membrane architecture and the supramolecular organization of the photosynthetic apparatus in vesicular chromatophores of Rhodobacter (Rb.) veldkampii. Mixed with LH2 (light-harvesting complex 2) rings, the PufX-containing LH1–RC (light-harvesting complex 1 – reaction center) core complexes appear as C-shaped monomers, with random orientations in the photosynthetic membrane. Within the LH1 fence surrounding the RC, a remarkable gap that is probably occupied (or partially occupied) by PufX is visualized. Sequence alignment revealed that one specific region in PufX may be essential for PufX-induced core dimerization. In this region of ten amino acids in length all Rhodobacter species had five conserved amino acids, with the exception of Rb. veldkampii. Our findings provide direct evidence that the presence of PufX in Rb. veldkampii does not directly govern the dimerization of LH1–RC core complexes in the native membrane. It is indicated, furthermore, that the high membrane curvature of Rb. veldkampii chromatophores (Rb. veldkampii features equally small vesicular chromatophores alike Rb. sphaeroides) is not due to membrane bending induced by dimeric RC–LH1–PufX cores, as it has been proposed in Rb. sphaeroides.     

Cross-species investigation of the functions of the Rhodobacter PufX polypeptide and the composition of the RC–LH1 core complex

In well-characterised species of the Rhodobacter (Rba.) genus of purple photosynthetic bacteria it is known that the photochemical reaction centre (RC) is intimately-associated with an encircling LH1 antenna pigment protein, and this LH1 antenna is prevented from completely surrounding the RC by a single copy of the PufX protein. In Rba. veldkampii only monomeric RC–LH1 complexes are assembled in the photosynthetic membrane, whereas in Rba. sphaeroides and Rba. blasticus a dimeric form is also assembled in which two RCs are surrounded by an S-shaped LH1 antenna. The present work established that dimeric RC–LH1 complexes can also be isolated from Rba. azotoformans and Rba. changlensis, but not from Rba. capsulatus or Rba. vinaykumarii. The compositions of the monomers and dimers isolated from these four species of Rhodobacter were similar to those of the well-characterised RC–LH1 complexes present in Rba. sphaeroides. Pigment proteins were also isolated from strains of Rba. sphaeroides expressing chimeric RC–LH1 complexes. Replacement of either the Rba. sphaeroides LH1 antenna or PufX with its counterpart from Rba. capsulatus led to a loss of the dimeric form of the RC–LH1 complex, but the monomeric form had a largely unaltered composition, even in strains in which the expression level of LH1 relative to the RC was reduced. The chimeric RC–LH1 complexes were also functional, supporting bacterial growth under photosynthetic conditions. The findings help to tease apart the different functions of PufX in different species of Rhodobacter, and a specific protein structural arrangement that allows PufX to fulfil these three functions is proposed.     

Examination of Ulva bloom species richness and relative abundance reveals two cryptically co-occurring bloom species in Narragansett Bay,Rhode Island

Blooms caused by the green macroalga Ulva pose a serious threat to coastal ecosystems around the world. Despite numerous studies of the causes and consequences of these blooms, we still have a limited understanding of Ulva bloom species richness and abundance due to difficulties in identifying Ulva species using morphological features. Along the northeastern U.S. coastline, all blooms of distromatic Ulva blades were previously identified as Ulva lactuca. Recent molecular sequencing, however, discovered the presence of additional distromatic Ulva species. Therefore, in order to determine the relative abundance of Ulva species within blooms, we conducted monthly surveys at four Narragansett Bay, RI, sites representing a gradient of bloom severity. We found that the biomass of Ulva within blooms was a mix of Ulva compressa and Ulva rigida, not U. lactuca as previously reported. In contrast, sites not impacted by blooms that were located near the mouth of Narragansett Bay were dominated by U. lactuca. We also observed spatial and temporal differences in Ulva and total macroalgal diversity between bloom-impacted sites, indicating that Ulva bloom composition can be radically different between similar sites within close proximity. We discuss our results in the context of Ulva blooms worldwide, highlighting the need to definitively determine bloom species composition in order to fully understand bloom dynamics.     

Interactions of Algae within the Community of <Emphasis Type="Italic">Gracilaria gracilis</Emphasis> (Rhodophyta)

Interactions among the unattached red alga Gracilaria gracilis, the dominant species of an algal community, and associated algal species Chaetomorpha linum, Enteromorpha prolifera f. prolifera, and Polysiphonia sp. were studied during and after an algal bloom. It was shown that during their bloom the associated algae Enteromorpha and Polysiphonia sp. significantly decreased the photosynthetic rate of G. gracilis but did not affect its growth rate. It is suggested that the inhibition of Gracilaria gracilis photosynthesis is connected to the impact of extracellular metabolites excreted by Chaetomorpha linum, Enteromorpha prolifera f. prolifera, and Polysiphonia sp. In laboratory experiments, the photosynthetic rate of the associated species was enhanced in the presence of Gracilaria. However, no significant alterations were observed in the content of chlorophyll a, growth, and the dark respiration rates of associated algae when they were kept together with Gracilaria. It was suggested that allelopathic interactions observed among algal species during the formation of the monospecific Gracilaria community, as well as during algal blooms, are not determinative.