Search

Traditional methods to combat disease with antimicrobial agents in aquaculture have caused serious concern and alternative approaches using probiotics have been sought. A photosynthetic purple sulfur bacteria Marichromatium purpuratum RuA2 that thrives at salt concentrations of 0.5% to 5.0% and has a more temperate tolerance for oxygen was isolated from a marine fish pond located on the southwestern shore of Qigu, Taiwan. The effects of M. purpuratum RuA2 on the water quality parameters, the occurrence of the sulfonamide resistance gene sul1 and the microbial community were investigated in situ. Supplementation with strain RuA2 resulted in an increased removal rate of total organic carbon and nitrate ions, as well as a lower occurrence of sul1 , in the bacterial community. The abundance and diversity of the bacterial community in the control and M. purpuratum RuA2 -supplemented water samples were investigated. Proteobacteria, Bacteroidetes, Cyanobacteria, Actinobacteria and Planctomycetes were identified to be the top five predominant phyla in the control and M. purpuratum RuA2-supplemented water samples. However, supplementation with M. purpuratum RuA2 increased the diversity of the bacterial community composition. Fourteen unique genera were detected solely in strain RuA2-supplemented water samples and the relative abundance of seven shared genera was associated with supplementation with strain RuA2. In conclusion, M. purpuratum RuA2 showed a desirable capacity for improving water quality, reducing the occurrence of the resistance gene sul1 and advantageous effects on the microbial community structure. Tolerant to salinity and oxygen, M. purpuratum RuA2 exhibits an attractive potential for resolving the challenges facing aquaculture today. [ABSTRACT FROM AUTHOR]

Saline Lake Shira (Southern Siberia, Russia) was meromictic through the observation period 2002–2015. During the under-ice periods of 2015 and 2016, complete mixing of the water column was recorded for the first time, and hydrogen sulphide temporarily disappeared from the water column of the lake; i.e. in those years the lake turned to holomixis. In the summer of 2015, a sharp increase in chlorophyll a , organic carbon, zooplankton, and phytoflagellates was observed in the lake, which was probably due to the release of nutrients from the monimolimnion. Purple sulfur bacteria completely disappeared from the lake after the first mixing in 2015, and did not reappear despite the restoration of meromixis in 2017. Thus, it was demonstrated that purple sulfur bacteria are sensitive to the weakening of the stratification of Lake Shira. Based on the data of the seasonal monitoring of temperature and salinity profiles over the period 2002–2017, it was presumed that the main cause of deep mixing in 2015 was the weakening of the salinity gradient due to strong wind impact and early ice retreat in the spring of 2014. In addition, it was shown that in previous years a significant contribution to the maintenance of meromixis was made by an additional influx of fresh water, which caused a rise in the lake level in the period 2002–2007. Thus, we identified a relationship between the stratification regime of the lake and the change in its level, which provides valuable information both for the forecast of water quality and for reconstruction of the Holocene climate humidity in this region of Southern Siberia from the sediment cores of Lake Shira. [ABSTRACT FROM AUTHOR]

Biogas from anaerobic digestion requires desulfurisation before its intended use due to the corrosive nature of H 2 S. Anaerobic digesters produce biogas continuously and require a continuous process for desulfurisation. Commonly, H 2 S is removed using adsorption to solid media (iron sponge) or absorption and removal through chemical processes (scrubbing), requiring regeneration or replacement of sorbents. As an alternative, a continuous, anaerobic H 2 S removal process, utilising purple phototrophic bacteria was developed. The removal is driven by light as an energy source and potentially reduces the requirement for caustic. A desulfurisation bubble column was fed continuously with a synthetic biogas mixture (2000/5000 ppmV H 2 S, 30% CO 2 , CH 4 balance) at sulfide loading rates ranging from 3.06 to 11.88 mg-S d−1. The liquid was inoculated with purple phototrophic bacteria, nutrients supplied via centrate, an anaerobic digestion residue, and externally irradiated with IR-light. The maximum sulfide removal rate was 10.13 ± 0.06 mg-S (Lh)−1 at a loading rate of 11.83 mg-S (Lh)−1, and the biomass oxidised the sulfide to sulfate utilising electrons for growth. Initially, caustic was dosed to control pH, which was replaced by hydraulic flushing (HRT 4 days), resulting in a mean pH of 6.8 at applied sulfide loading rate of 9.44 mg-S (Lh)−1. A reduction in HRT to 2 days resulted in performance loss. Thus, controlling the biomass inventory was found to be the major challenge of the process. Overall, the process can run caustic-free, and integrate with anaerobic digestion using the centrate as a nutrient source, with light supply limiting feasibility for night-time operation in a scaled process. [Display omitted] • Biogas was continuously desulfurised in a bubble column using mixed culture PPB. • Maximum removal efficiency of 2000 ppmV H 2 S in the biogas was 96.7%. • Maximum sulfide removal rate was 10 mg L−1h−1 in a 2L reactor. • Biogas desulfurised in a single-stage anaerobic process without requiring caustic. [ABSTRACT FROM AUTHOR]

• PPB absorb light at both NIR and VIS wavelengths. • Light scattering did not affect attenuation. • Pigments contributed considerably to attenuation via light absorption. • The proposed model (based on Lambert-Beer) represented PPB growth accurately. • Light penetration of 5 cm in concentrated cultures (≥600 g VS·m−3). Light attenuation in enriched purple phototrophic bacteria (PPB) cultures has not been studied, and its understanding is critical for proper process modelling and reactor design, especially for scaled systems. This work evaluated the effect of different biomass concentrations, reactor configurations, wastewater matrices, and growth conditions, on the attenuation extent of near infra-red (NIR) and ultraviolet-visible (UV–VIS) light spectra. The results show that increased biomass concentrations lead to higher light attenuation, and that PPB absorb both VIS and NIR wavelengths, with both fractions of the spectrum being equally absorbed at biomass concentrations above 1,000 g COD·m−3. A flat plate configuration showed less attenuation compared with cylindrical reactors illuminated from the top, representative for open ponds. Neither a complex wastewater matrix nor the presence of polyhydroxyalkanoates (under nutrient limited conditions) affected light attenuation significantly. The pigment concentration (both bacteriochlorophyll and carotenoids) however, had a strong effect, with significant attenuation in the presence of pigments. Attenuation predictions using the Lambert-Beer law (excluding scattering) and the Schuster model (including scattering) indicated that light scattering had a minimal effect. A proposed mathematical model, based on the Lambert-Beer law and a Monod function for light requirements, allowed effective prediction of the kinetics of photoheterotrophic growth. This resulted in a half saturation coefficient of 4.6 W·m−2. Finally, the results showed that in dense outdoor PPB cultures (≥1,000 g COD·m−3), effective light penetration is only 5 cm, which biases design away from horizontal lagoons, and towards non-incident multi-panel systems such as flat plate reactors. [Display omitted] [ABSTRACT FROM AUTHOR]

The greatest mass extinction on Earth occurred 252 million years ago during the latest Permian. Complete biotic recovery, characterized by a return to pre-extinction diversity levels, took an extraordinarily long time (ca. 5 × 106 yr), probably because harsh conditions developed repeatedly during the Early Triassic. Here, we show the recurrence of euxinic conditions during the Early Triassic and the development of especially severe such conditions during the late Early Triassic, just prior to full biotic recovery from the mass extinction. Dibenzothiophenes and carotenoids accumulated in upper Lower Triassic sediments from South China, located on the western margin of the Paleotethys Ocean. Among these, chlorobactane, a biomarker for green-pigmented green sulfur bacteria, and okenane, a biomarker for purple sulfur photosynthetic bacteria, were identified in upper Early Triassic samples. Both compounds were detected in limestone (micrite) and we therefore infer that planktonic green and purple sulfur bacteria were the sources of these carotenoids, and that their presence indicates photic zone euxinia at the time of deposition. Concentrations of redox sensitive elements (M, V, and U), relative to that of Al, and the U/Th ratio, progressively increased during the late Early Triassic. The euxinic conditions represented by the carotenoids and the elements were likely caused by a combination of locally shallow restricted conditions and global environmental oscillations, such as those related to global warming, during the late Early Triassic. The presence of these biomarkers, together with the increase in the abundance of redox sensitive elements relative to Al and the U/Th, suggests that euxinic conditions could be one of the causes for the delayed recovery of marine communities in the Paleotethys Ocean after the latest Permian mass extinction event. [ABSTRACT FROM AUTHOR]

Abstract: Purple sulfur phototrophic bacteria accumulate various storage materials, such as sulfur globules, glycogen or polyhydroxy alkanoates (PHAs) under appropriate conditions. The formation of these materials requires reducing power which might be recovered upon their breakdown. This work aims at the understanding of the metabolism of PHA and its link to the nitrogenase mediated in vivo H2 evolution in Thiocapsa roseopersicina BBS. The strain could accumulate 30% of the dry cell weight in the form of PHAs. Analysis of the genome sequence revealed the loci involved in PHAs synthesis and degradation. Phylogenetic analysis indicated independent evolution of the anabolic and catabolic proteins. A mutant carrying deleted PHA biosynthesis genes has been created in a host containing nitrogenase but none of the hydrogenases. Determination of the H2 evolving capacity of the mutant revealed significantly reduced H2 production in PHA deficient cells. Addition of excess electron sources such as thiosulfate stimulated the H2 production via multiple effects. [Copyright &y& Elsevier]

Abstract: Coastal photosynthetic microbial mats are highly structured microbial communities that populate a variety of shallow environments such as estuaries, sheltered sandy beaches, intertidal flats, salt marshes and hypersaline salterns. In soft sediments, most of these microbial mats are formed of vertically stratified, multicolored cohesive thin layers, of several functional groups of microorganisms, such as cyanobacteria, colorless sulfur bacteria, purple sulfur bacteria and sulfate-reducing bacteria, distributed along vertical microgradients of oxygen, sulfide and light. These microbial communities are highly productive and significant contributors to carbon, nitrogen and sulfur cycles and to sediment stability in shallow-water habitats. Many examples of these communities have been cited in the past, but comparatively few microbial mats have been presented for which mass developments of anoxygenic purple bacteria have been observed. Yet, application of molecular approaches has provided fresh insight into the ecology, diversity and evolution of microbial mats. In situ measurements using electrochemical and optical microprobes led to detailed characterization of their physical and chemical environment, whereas reflectance measurements revealed the spatial and temporal heterogeneity of microbial mat surfaces. We hereby report the main discoveries due to introduction of these powerful techniques and we point out the potential insight to be gained from the study of anoxygenic purple bacterial mats. [Copyright &y& Elsevier]

Summary: A 991bp DNA fragment, consisting of a 225 amino acid reading frame homologous to outer membrane protein coding ompA gene, was cloned from a purple sulfur bacterium Allochromatium vinosum. The homology analysis revealed up to 51% similarity to other bacterial species. The absence of branching within diazotrophs or other taxonomically related groups shows the structural importance of the protein regardless of the metabolism and evolution of the species. [Copyright &y& Elsevier]

Abstract: An unusual purple sulfur bacterium present in the pink layer of the Ebro Delta microbial mats has been identified through the study of its ultrastructural features. As pure cultures of this bacterium have not been obtained, due to its inability to grow in axenic conditions, only enrichment cultures where it reached at least 90% of total biomass have been considered. In enrichment cultures, the cells are rods that are 5.4±0.6μm wide and 11.0±2.1μm long. The color of the cell suspensions is pink to pinkish-red. Cells are motile by means of a polar tuft of flagella and multiply by binary fission. This bacterium possesses an extensive internal photosynthetic membrane system consisting of stacks of lamellae, contains bacteriochlorophyll a and carotenoids of normal spirilloxanthin series and deposits sulfur intracellularly. In natural samples, the most abundant phototrophic purple sulfur bacterium developing in this ecosystem has the same kind of intracytoplasmic membrane system, but the cells differ slightly in size and arrangement, in that they are ovoid, 4.2±0.5μm wide and 6.0±1.4μm long, and can be seen forming irregular non-motile clumps which are embedded in slime. Differences observed between field samples and enrichment cultures suggest that environmental conditions may bring about changes in the phenotypic characteristics of the cells. The morphological characteristics of the described bacterium resemble those of large Chromatia. However, this bacterium differs from known species in this group, particularly in terms of its photosynthetic membrane system and in its light absorption properties. [Copyright &y& Elsevier]

Halorhodospira halophila is a halophilic photosynthetic bacterium classified as a purple sulfur bacterium. We found that H. halophila generates hydrogen gas during photoautotrophic growth as a byproduct of a nitrogenase reaction. In order to consider the applied possibilities of this photobiological hydrogen generation, we cloned and characterized the structural and regulatory genes encoding the nitrogenase, nifH, nifD and nifA, from H. halophila. This is the first description of the nif genes for a purple sulfur bacterium. The amino-acid sequences of NifH and NifD indicated that these proteins are an Fe protein and a part of a MoFe protein, respectively. The important residues are conserved completely. The sequence upstream from the nifH region and sequence similarities of nifH and nifD with those of the other organisms suggest that the regulatory system might be a NifL-NifA system; however, H. halophila lacks nifL. The amino-acid sequence of H. halophila NifA is closer to that of the NifA of the NifL-NifA system than to that of NifA without NifL. H. halophila NifA does not conserve either the residue that interacts with NifL or the important residues involved in NifL-independent regulation. These results suggest the existence of yet another regulatory system, and that the development of functional systems and their molecular counterparts are not necessarily correlated throughout evolution. All of these Nif proteins of H. halophila possess an excess of acidic residues, which acts as a salt-resistant mechanism. [Copyright &y& Elsevier]

Thiocapsa bogorovii BBS (former name Thiocapsa roseopersicina) contains HydSL hydrogenase belonging to 1e subgroup of NiFe hydrogenases (isp-type). The operon of these hydrogenases contains gene for small subunit (hydS), gene for large subunit (hupL), and genes isp1 and isp2 between them. It is predicted that last two genes code electron transport careers for electron transfer from/to HydSL hydrogenase. However, the interaction between them is unclear. The aim of this study was to determine structural and functional role of T. bogorovii HydS C-terminal end. For this purpose, we modelled all subunits of the complex HydS-HydL-Isp1-Isp2. Hydrophobicity surface analysis of the Isp1 model revealed highly hydrophobic helices suggesting potential membrane localization, as well as the hydrophilic C-terminus, which is likely localized outside of membrane. Isp1 model was docked with models of full length and C-terminal truncated HydSL hydrogenases and results illustrate the possibility of HydSL membrane anchoring via transmembrane Isp1 with essential participation of C-terminal end of HydS in the interaction. C-terminal end of HydS subunit was deleted and our studies revealed that the truncated HydSL hydrogenase detached from cellular membranes in contrast to native hydrogenase. It is known that HydSL hydrogenase in T. bogorovii performs the reaction of elemental sulfur reduction (S 0 + H 2 = ≥H 2 S). Cells with truncated HydS produced much less H 2 S in the presence of H 2 and S 0. Thus, our data support the conclusion that C-terminal end of HydS subunit participates in interaction of HydSL hydrogenase with Isp1 protein for membrane anchoring and electron transfer. • The role of C-terminus of HydS subunit of HydSL hydrogenase of Thiocapsa bogorovii was studied • Modelling of all subunits with following docking of HydSL with Isp1 showed important role of C-terminus of HydS in docking. • Cells with C-terminal truncated hydrogenase reduced S 0 to H 2 S under H 2 atmosphere with lower rate. • Cells with C-terminal truncated hydrogenase contained hydrogenase in soluble fraction in contrast to full length hydrogenase. • C-terminus of HydS subunit participates in interaction of HydSL with Isp1 protein for membrane anchoring and electron transfer. [ABSTRACT FROM AUTHOR]

• Photoheterotrophic growth was suppressed in the presence of oxygen. • PPB were outcompeted by aerobic heterotrophs under aerobic conditions. • The out-competition is explained by lower aerobic growth rates of PPB. • PPB are resilient to oxygen due to their chemoheterotrophic capabilities. There is an ongoing debate around the effect of microaerobic/aerobic conditions on the wastewater treatment performance and stability of enriched purple phototrophic bacteria (PPB) cultures. It is well known that oxygen-induced oxidative conditions inhibit the synthesis of light harvesting complexes, required for photoheterotrophy. However, in applied research, several publications have reported efficient wastewater treatment at high dissolved oxygen (DO) levels. This study evaluated the impact of different DO concentrations (0-0.25 mg·L−1, 0-0.5 mg·L−1 and 0-4.5 mg·L−1) on the COD, nitrogen and phosphorus removal performances, the biomass yields, and the final microbial communities of PPB-enriched cultures, treating real wastewaters (domestic and poultry processing wastewater). The results show that the presence of oxygen suppressed photoheterotrophic growth, which led to a complete pigment and colour loss in a matter of 20-30 h after starting the batch. Under aerobic conditions, chemoheterotrophy was the dominant catabolic pathway, with wastewater treatment performances similar to those achieved in common aerobic reactors, rather than those corresponding to phototrophic systems (i.e. considerable total COD decrease (45-57% aerobically vs. ± 10% anaerobically). This includes faster consumption of COD and nutrients, lower nutrient removal efficiencies (50-58% vs. 72-99% for NH 4 +-N), lower COD:N:P substrate ratios (100:4.5-5.0:0.4-0.8 vs. 100:6.7-12:0.9-1.2), and lower apparent biomass yields (0.15-0.31 vs. 0.8-1.2 g COD biomass ·g COD removed −1)). The suppression of photoheterotrophy inevitably resulted in a reduction of the relative PPB abundances in all the aerated tests (below 20% at the end of the tests), as PPB lost their main competitive advantage against competing aerobic heterotrophic microbes. This was explained by the lower aerobic PPB growth rates (2.4 d−1 at 35 °C) when compared to common growth rates for aerobic heterotrophs (6.0 d−1 at 20 °C). Therefore, PPB effectively outcompete other microbes under illuminated-anaerobic conditions, but not under aerobic or even micro-aerobic conditions, as shown by continuously aerated tests controlled at undetectable DO levels. While their aerobic heterotrophic capabilities provide some resilience, at non-sterile conditions PPB cannot dominate when growing chemoheterotrophically, and will be outcompeted. [Display omitted] [ABSTRACT FROM AUTHOR]

Sustainable development is driving a rapid focus shift in the wastewater and organic waste treatment sectors, from a "removal and disposal" approach towards the recovery and reuse of water, energy and materials (e.g. carbon or nutrients). Purple phototrophic bacteria (PPB) are receiving increasing attention due to their capability of growing photoheterotrophically under anaerobic conditions. Using light as energy source, PPB can simultaneously assimilate carbon and nutrients at high efficiencies (with biomass yields close to unity (1 g COD biomass ·g COD removed −1)), facilitating the maximum recovery of these resources as different value-added products. The effective use of infrared light enables selective PPB enrichment in non-sterile conditions, without competition with other phototrophs such as microalgae if ultraviolet-visible wavelengths are filtered. This review reunites results systematically gathered from over 177 scientific articles, aiming at producing generalized conclusions. The most critical aspects of PPB-based production and valorisation processes are addressed, including: (i) the identification of the main challenges and potentials of different growth strategies, (ii) a critical analysis of the production of value-added compounds, (iii) a comparison of the different value-added products, (iv) insights into the general challenges and opportunities and (v) recommendations for future research and development towards practical implementation. To date, most of the work has not been executed under real-life conditions, relevant for full-scale application. With the savings in wastewater discharge due to removal of organics, nitrogen and phosphorus as an important economic driver, priorities must go to using PPB-enriched cultures and real waste matrices. The costs associated with artificial illumination, followed by centrifugal harvesting/dewatering and drying, are estimated to be 1.9 , 0.3–2.2 and 0.1–0.3 $·kg dry biomass −1. At present, these costs are likely to exceed revenues. Future research efforts must be carried out outdoors, using sunlight as energy source. The growth of bulk biomass on relatively clean wastewater streams (e.g. from food processing) and its utilization as a protein-rich feed (e.g. to replace fishmeal, 1.5–2.0 $·kg−1) appears as a promising valorisation route. Unlabelled Image • PPB-enriched cultures and real waste matrices should be used in future studies. • Treatment efficiencies and product value are main economic drivers. • Natural illumination is required for large-scale economic feasibility. • Biomass utilization as protein-rich feed appears to be most promising. [ABSTRACT FROM AUTHOR]