Strains Of Purple Nonsulfur Bacteria Research Articles

Selecting Phosphorus-Solubilizing Strains of Purple Nonsulfur Bacteria Isolated From Pineapple Cultivated Acid Sulfate Soils

The presence of acid sulfate soils is such an obstacle for pineapple cultivation in Vietnam due to their low pH, high toxicity and poor nutrient availability, especially phosphorus (P), which is immobilized by cations in the soils. Therefore, the study occurred to select purple nonsulfur bacteria (PNSB) strains that can solubilize P under toxic and acidic conditions. There were 33 strains that can tolerate the acidic condition, and they were selected and tested for viability and P solubilization under conditions containing Al3+, Fe2+, and Mn2+ toxins. Four strains, including W15, W39, W42 and W48 suffered from growth inhibition by Al3+, Fe2+ and Mn2+ less than the other strains under both microaerobic light and aerobic dark conditions (ML and AD conditions). In addition, there were four strains (W15, W25, W42 and W48) solubilizing Al-P well (21.4-25.2 mg L-1), two strains (W23 and W42) solubilizing Fe-P well (15.9-17.3 mg L-1), and two strains (W17 and W42) solubilizing Ca-P well (23.0-36.4 mg L-1) under both ML and AD conditions. Ultimately, there were five strains selected (W17, W23, W25, W42 and W48) and identified as Rhodopseudomonas palustris strain W17 and W23, Cereibacter sphaeroides strain W23, W42 and W48 based on the 16S rRNA technique. The selected strains also produced ALA, EPS and siderophores at 1.31-2.19 mg L-1, 0.78-1.89 mg L-1, and 16.2-55.6%, respectively. Therefore, these strains were promising in providing nutrients for pineapples in the form of biofertilizer.

Phylogenetic Analysis for Molecular Characterization and Identification of Rhodopseudomonas Spp.

The BLAST analysis is a fast method for identifying likely microbial species. However, it is not always able to definitively determine closely related genera or taxa because there may be numerous similar or identical scores from homologous sequences. In order to overcome this constraint, the utilization of phylogenetic tree construction and analysis is employed to get a more accurate molecular characterization of microorganisms. This study utilized the 16S rDNA sequence of BRSSOU1, which formed a cluster with a particular strain in the phylogenetic tree and exhibited a 99.92% alignment with Rhodopseudomonas sp. according to the NCBI-BLAST results. Therefore, BRSSOU1 was determined to be Rhodopseudomonas palustris. Our deduction is that BRSSOU1 is a variant of Rhodopseudomonas palustris. The strains were obtained from water samples collected at the source of the Jhelum River near Verinag, Kashmir. In addition, samples of wastewater were obtained from several rivers, namely Arpath, Lidder, Neelum, Sind, Kunhar, and Pohru. PNSB strains were isolated and identified using both traditional bacterial culture techniques and molecular approaches. The identification technique effectively uncovered these strains of Purple Non-sulfur Bacteria (PNSB).

Nitrogen-Fixing Purple Nonsulfur Bacteria Originating from Acid Saline Soils of a Rice-Shrimp Farm

The study was conducted to (i) isolate, select, and identify strains of purple nonsulfur bacteria (PNSB), which can fix nitrogen (N), from soil and water in a rice-shrimp integrated system, (ii) to determine the capacity of the selected potent PNSB strains in producing plant growth promoting substances. The isolation resulted in 57 pure PNSB strains from 36 soil samples and 36 water samples of rice-shrimp paddy fields in Thanh Phu - Ben Tre. Among them, 49 strains survived under pH 5.0 conditions, 24 of which grew well under microaerobic light (ML) and aerobic dark (AD) conditions in a basic isolation medium (BIM) containing NaCl 5‰. Two strains (S01 and S06) with the greatest N fixation were identified by 16S rRNA techniques as Rhodobacter sphaeroides. Their N production was 16.9 mg L-1 under the ML condition and 32.1 mg L-1 under the AD condition. Moreover, two R. sphaeroides S01 and S06 strains performed P solubilization at 0.382-2.954 mg L-1 from Al-P, 3.81-4.28 mg L-1 from Fe-P, and 3.87-4.74 mg L-1 from Ca-P, and production of plant growth promoting substances, such as IAA (12.3-15.5 mg L-1), EPS (1.09-1.58 mg L-1), siderophores (10.7-53.6%) and ALA (1.68-2.82 mg L-1) under both the incubating conditions.

Isolation and characterization of novel potassium-solubilizing purple nonsulfur bacteria from acidic paddy soils using culture-dependent and culture-independent techniques.

The current research as aimed (i) to isolate and select the purple nonsulfur bacteria (PNSB) possessing the potassium-solubilizing ability from acid paddy fields and (ii) to evaluate the ability to release the plant growth-promoting substances (PGPS) of selected PNSB. A total of 35 acid sulfate (AS) soil samples were collected in An Giang province, Vietnam. Then, 70 PNSB strains were isolated from the AS soil samples. In the current study, the isolated strains were screened and selected according to their tolerability to acidic conditions, ability to solubilize potassium, and characteristics of a plant growth promoter on basic isolation media with various incubation conditions. Therein, three strains, TT07.4, AN05.1, and AC04.1, presented the highest potassium solubilization under the microaerobic light (11.8-17.7 mg L-1) and aerobic dark (16.4-24.7 mg L-1) conditions and stresses from Al3+, Fe2+, and Mn2+ toxicity. The selected strains were identified as Rhodopseudomonas pentothenatexigens by the 16S rDNA sequence, with 99% similarity. The selected acidic-resistant strains possessed the traits of biofertilizers under both microaerobic light and aerobic dark conditions, with abilities to fix nitrogen (0.17-6.24; 7.93-11.2 mg L-1); solubilize phosphorus from insoluble compounds with 3.22-49.9 and 9.49-11.2 mg L-1 for Al-P, 21.9-25.8 and 20.2-25.1 mg L-1 for Ca-P, and 10.1-29.8 and 18.9-23.2 mg L-1 for Fe-P; produce 5-aminolevulinic acid (0.63-3.01; 1.19-6.39 mg L-1), exopolymeric substances (0.14-0.76; 0.21-0.86 mg L-1), indole-3-acetic acid (12.9-32.6; 13.6-17.8 mg L-1), and siderophores (28.4-30.3; 6.15-10.3%). The selected potassium-solubilizing strains have a great potential to apply in liquid form into rice seed and solid form in AS soils to supply nutrients and PGPS for enhancing rice growth and grain yield.

Potential of Phosphorus Solubilizing Purple Nonsulfur Bacteria Isolated from Acid Sulfate Soil in Improving Soil Property, Nutrient Uptake, and Yield of Pineapple (Ananas comosus L. Merrill) under Acidic Stress

This study aimed to (i) evaluate purple nonsulfur bacteria (PNSB) strains possessing the highest phosphorus (P) solubilizing capacity in field and (ii) determine the efficacy of PNSB biofertilizers in improving soil quality, P uptake, growth, and yield of pineapple cultivated in acid sulfate soil (ASS). A field experiment was conducted in a completely randomized block design with two factors, including the first factor as P fertilizer levels (0, 50, 75, and 100% P) based on recommended fertilizer formula (RFF) and the second factor as supplementation of biofertilizers containing P solubilizing PNSB (no inoculated PNSB, Rhodobacter sphaeroides W48, R. sphaeroides W42, and a mixture of R. sphaeroides W48 and W42). The results indicated that the supplementation of PNSB biofertilizers led to an increase of 25.3–33.9% in soluble P concentration in soil compared to control treatment. Among the selected PNSB strains, R. sphaeroides W42 and a mixture of the PNSB in biofertilizers solubilized all insoluble P fractions (Fe-P, Al-P, and Ca-P) and strain W48 in biofertilizers for Fe-P and Al-P. Furthermore, the supplementation of biofertilizers from R. sphaeroides W48 and W42 individually and their mixture raised plant height by 3.56–4.10% and available P concentration by 25.3–33.9%. Total P uptake in pineapple treatments with biofertilizers from mixed PNSB was 42.9% higher than that in the control treatment ( p < 0.05 ). Application of mixed PNSB strains can reduce 25% P of chemical fertilizer, but the pineapple yield rose over 12.1%. Both R. sphaeroides W48 and W42 are potent for use as crop yield enhancers to obtain the sustainable pineapple cultivation under acidic stress.

Effects of Seed Bio-Priming by Purple Non-Sulfur Bacteria (PNSB) on the Root Development of Rice.

The effects of seed bio-priming (seed soaking) with purple non-sulfur bacteria (PNSB) on the grain productivity and root development of rice were examined by a field study and laboratory experiments, respectively. Two PNSB strains, Rhodopseudomonas sp. Tsuru2 and Rhodobacter sp. Tsuru3, isolated from the paddy field of the study site were used for seed bio-priming. For seed bio-priming in the field study, the rice seeds were soaked for 1 day in water containing a 1 × 105 colony forming unit (cfu)/mL of PNSB cells, and the rice grain productivities at the harvest time were 420, 462 and 504 kg/are for the control, strain Tsuru2-primed, and strain Tsuru3-primed seeds, respectively. The effects of seed priming on the root development were examined with cell pot cultivation experiments for 2 weeks. The total root length, root surface area, number of tips and forks were evaluated with WinRhizo, an image analysis system, and strains Tsuru2- and Tsuru3-primed seeds showed better root development than the control seeds. The effects of seed priming with the dead (killed) PNSB cells were also examined, and the seed priming with the dead cells was also effective, indicating that the effects were attributed to some cellular components. We expected the lipopolysaccharide (LPS) of PNSB as the effective component of PNSB and found that seed priming with LPS of Rhodobacter sphaeroides NBRC 12203 (type culture) at the concentrations of 5 ng/mL and 50 ng/mL enhanced the root development.

Potential of potent purple nonsulfur bacteria isolated from rice-shrimp systems to ameliorate rice (Oryza sativa L.) growth and yield in saline acid sulfate soil

In rice-shrimp farming systems, the high level of sodium that shrimps are able to grow in may create an adverse environment for rice. This research aimed to isolate purple nonsulfur bacteria (PNSB) from rice-shrimp fields and select strains that were resistant to H+, Al3+, Fe2+ and Mn2+, that can produce plant growth promoting substances such as 5-aminolevulinic acid, exopolymeric substances, indole-3-acetic acid and siderophores. The selected bacteria were applied in a soil pot experiment to determine their ability to enhance rice growth and yield. From 63 PNSB isolated from 21 paddy fields of rice-shrimp systems, four strains were selected for their properties as biofertilizers and plant growth promoters (PGP). They were all identified as strains of Luteovulum sphaeroides. A randomized complete block design incorporating six treatments was used to investigate the ability of the four PNSB strains to ameliorate rice growth and yield in saline acidic soil with saline water irrigation at 4‰. PNSB cultures at 1.90 × 105 CFU g−1 dry soil weight were applied three times, along with normal chemical fertilizers, and all monitored parameters of rice growth and grain yield significantly improved in soil with a toxic Al3+ content of 10.8 meq 100 g−1. A mixed four cultures most effectively increased grain yield (86.8%) compared with no applied PNSB. Remediation of the pot soil was exhibited in decreased exchangeable Na in soil and proline content in leaves. The four PNSB could act as biofertilizers, PGP and bioremediators with potential to enhance rice yield in rice-shrimp systems for sustainable rice cultivation.

Use of potent acid resistant strains of Rhodopseudomonas spp. in Mn-contaminated acidic paddies to produce safer rice and improve soil fertility

Purple nonsulfur bacteria (PNSB) can potentially improve rice growth, grain yield and soil fertility in acid sulfate soils (ASS) by acting as biofertilizers and bioremediators. Six strains of acid resistant PNSB (Rhodopseudomonas palustris; TLS12, VNS19, VNS32, VNS62 and VNW95, and Rhodopseudomonas harwoodiae TLW42) were evaluated, as single cultures and a mixed culture of the six strains, for their effects on rice growth and soil fertility in ASS with high Mn concentrations sampled at three sites in the Mekong Delta, Vietnam. In pot experiments, all single PNSB strains in the liquid biofertilizer, especially strain VNS32, significantly improved most plant growth parameters, rice yield, and soil fertility. They increased NH4+ and available phosphorus (Pavail) but reduced Mn2+ compared with the controls in all three soils. In pot experiments, the solid PNSB biofertilizers significantly improved rice growth and grain yield, reduced accumulated Mn and increased soil fertility. The solid formula of six mixed strains was the most effective, followed by VNS32 singly, and lastly the carrier control with no added PNSB. In the field trials, the solid mixed PNSB biofertilizer combined with 75% NP fertilizer significantly enhanced rice growth, producing the same grain yields as 100% NP fertilizer at two of the sites, and a higher yield at one of the sites. In acidic paddy fields, acid resistant PNSB can act as biofertilizers and bioremediators to produce improvements in soil fertility and healthier rice crops.

Isolation and Selection of Purple Non-Sulfur Bacteria for Nutrient Rich Biomass Production from Wastes

Purple nonsulfur bacteria (PNSB) are anoxygenic photosynthetic bacteria, which are able to photoheterotrophically grow in the presence of excessive nutrients. Hence, PNSB can convert organic components, in waste waters into nutrient rich biomass. This suggests the feasibility of converting wastes into valuable products. In this research, method for isolation of PNSB was optimized, and subsequently used for the isolation of PNSB from domestic waste and pond water samples taken in Hanoi. In addition, the effects of carbon and nitrogen sources and types of waste on biomass and nutrients (protein and carotenes) were also investigated. Four PNSB strains were isolated and based on comparative 16S rDNA analysis and their morphological characteristics, they were identified as Rhodobacter (Rb.) capsulatus, Rhodobacter (Rb.) sphaeroides, Rhodobacter (Rb.) sediminis and Rhodopseudomonas (Rp.) palustris. In terms of the effects of carbon and nitrogen sources on their biomass and nutrient production, glucose or maltose and ammonium chloride or urea were found to be more enhancive than starch and peptone, respectively. Among the studied strains, Rb. capsulatus MD1 and Rb. sphaeroides MD3 showed significantly higher biomass production (up to 0.7 g/l) when growing with various carbon and nitrogen sources, in comparison with the other strains. Moreover, MD1 and MD3 also produced at least four-fold more carotenoid and up to two-fold more protein in tofu processing wastewater compared with the other wastewater. The results suggest potential applications of the PNSB strains for efficient conversions of organic compounds in wastes into biomass of high nutritional values.

The potential use of purple nonsulfur bacteria to simultaneously treat chicken slaughterhouse wastewater and obtain valuable plant growth promoting effluent and their biomass for agricultural application

Abstract Treatment of wastewater with purple nonsulfur bacteria (PNSB) simultaneously produces the biomass of plant growth promoting bacteria (PGPB) and the effluent containing plant growth promoting substances (PGPS). Among 46 PNSB strains isolated from chicken slaughterhouse wastewater (CSW) treatment unit, only four strains grew well in non-sterile effluent of the anaerobic digester (CSW-Di), under both microaerobic light and aerobic dark conditions. However, only strains WS308 and WS502 were selected as inoculants for subsequent experiments since they released high levels of 5-aminolevulinic acid (ALA) into the digester effluent medium under both incubating conditions. Based on 16S rRNA genes analysis, the strains WS308 and WS502 were identified as Rhodopseudomonas faecalis and Rhodopseudomonas palustris, respectively. The central composite design (CCD) experiments were conducted by using a mixed culture of the two strains (1:1) treating the non-sterile CSW-Di (soluble chemical oxygen demand, sCOD 736 mg/L) under 72-hr microaerobic light condition. The optimal conditions on the multivariate regression were found at the inoculum size (X1) of 3.63% (roughly 106 cells/mL), initial pH (X2) of 6.9 and light intensity (X3) of 3731 lux. At this condition, sCOD removal was predicted at 85.3%, while the verification test result favorably achieved 88.1% removal. ALA concentration in CSW-Di of the verification set was found at 0.13 mg/L. All trace elements detected in CSW-Di effluent were much lower than recommended maximum concentrations for irrigation water. Treating wastewater with potent PNSB strains could produce effluent containing PGPS, such as ALA, and also the biomass as PGPB for organic agricultural applications.

Mechanisms of acid-resistant Rhodopseudomonas palustris strains to ameliorate acidic stress and promote plant growth

Abstract The low level of nutrients in acid sulfate soils (ASS) presents a serious obstacle to plant growth. This study aimed to investigate the mechanisms that acid-resistant purple nonsulfur bacteria (PNSB) use to resist acidic stress; Rhodopseudomonas palustris strains TLS06, VNW02, VNW64 and VNS89 released plant growth promoting substances (PGPS) including the plant nutrients NH4+ and PO43−. All tested PNSB strains produced siderophores to solubilize PO43− from Al–P and Fe–P, either as individual or combined P sources. Siderophores were produced under both aerobic dark and microaerobic light incubating conditions. A strong positive relationship was indicated between released siderophores and released P with correlation indices (r) of 0.6362–0.6567 and 0.7415 to 0.8656 in light and dark conditions, respectively. In addition, the release of PGPS by PNSB coincided with an increase in pH from an initial 4.5 to 6.5–7.90. A positive high correlation between released PGPS and pH existed: for NH4+, siderophores, indole-3-acetic acid (IAA) and 5-aminolevulinic acid (ALA), respective r values were 0.8155–0.9980, 0.7576–0.8294, 0.8869–0.9980 and 0.5185–0.9919. It can be concluded that the mechanisms by which PNSB release PGPS and plant nutrients significantly increased pH. By overcoming acidic stress in this way, PNSB show great potential for use as plant growth promoters in paddy fields on ASS.

The potential of mercury resistant purple nonsulfur bacteria as effective biosorbents to remove mercury from contaminated areas

Abstract This study aimed to investigate the possibility to remove mercury (Hg) using the live or dead biomass of Hg resistant purple nonsulfur bacteria (PNSB) for their potential application to clean up shrimp ponds and during cultivation. The efficiency of Hg2+ removal by three PNSB strains; Rhodovulum sulfidophilum SRW1–5, and Afifella marina strains SSS2-1 and SSW15-1, grown with 2 different growth conditions (microaerobic light and aerobic dark conditions) were tested (2 mg/L HgCl2, 4.5 mg dry cell weight/mL, 30 min). It was found that the efficiency to remove Hg2+ by the dead cells of all strains was significantly higher than for live cells; and the most effective strain was SSS2-1. The highest Hg2+ removal under the optimum conditions using a 4 mg/L initial HgCl2 concentration by live and dead cells grown with both incubation conditions were approximately 87% and 95%, respectively. Under both incubation conditions, Hg2+ biosoption by strain SSS2-1 fitted the Freundlich model for live cells and the Langmuir model for dead cells. The kinetics of Hg2+ biosorption by both cell types of strain SSS2-1 suggests the process as a pseudo-second order kinetic model. This study demonstrates that biomass of the strain SSS2-1 has great potential for its biosorption to remove Hg2+ from contaminated areas like shrimp ponds.

Administration of purple nonsulfur bacteria as single cell protein by mixing with shrimp feed to enhance growth, immune response and survival in white shrimp (Litopenaeus vannamei) cultivation

Single cell protein (SCP) is an alternative way to increase nutrients for animal consumption; and purple nonsulfur bacteria (PNSB) should be considered as SCP due to their rich sources of protein, vitamins and photopigments. Hence, the aim of this study was to investigate the potential of promising PNSB to be used as SCP by mixing with commercial shrimp feed for white shrimp cultivation starting from postlarval until early juvenile stages for 60 days. PNSB strains, Rhodobacter sphaeroides SS15 and Afifella marina STW181 were selected, based on high amounts of biologically complete protein and photopigments, to use as SCP at a ratio of 1:1; and their lyophilized cells at 1, 3 and 5% (w/w) were mixed well with commercial shrimp feed to obtain modified shrimp feed recipes; Diet 1, Diet 2 and Diet 3, respectively. Levels of NH4+, NO2−, NO3− and COD in rearing water from Diet 2 and 3 sets were significantly higher than control set. However, Diet 1 set showed the lowest levels of these water parameters among modified diet sets as no significant difference levels of NO3− and COD between Diet 1 and control sets. Shrimp growth performance on the basis of relative gain rate and other growth parameters found that Diet 1 set was much better than sets of Diet 2, Diet 3 and control with the lowest found in the control set. In addition, the maximum shrimp survival was observed in Diet 1 set (85%) although no significant difference among them as 80% in control set. No significant difference was found among control and all modified shrimp diets for total hemocyte count in shrimp; however, significant increases of superoxide dismutase activity found in sets of Diet 1, while phenoloxidase activity found in Diet 2 and Diet 3. The results of hepatopancreas (HP) histopathology analysis also showed a good condition of HP as healthy shrimp. PNSB biomass as SCP at optimal level has the potential to be an effective source of a novel protein in shrimp feed to enhance shrimp growth and also to increase shrimp survival as more nutritious with no effect on water quality.

Single-stage photofermentative biohydrogen production from sugar beet molasses by different purple non-sulfur bacteria.

Biohydrogen production via fermentative routes offers considerable advantages in waste recycling and sustainable energy production. This can be realized by single-stage dark or photofermentative processes, or by a two-stage integrated process; the latter offering the higher production yields due to complete conversion of sugar substrates into H2 and CO2. However, problems arising from the integration of these two processes limit its scale-up and implementation. Hence, high efficiency one-step fermentative biohydrogen production processes from sugar-rich wastes are preferable. In this study, different strains of purple non-sulfur bacteria were investigated for their biohydrogen production capacity on pure sucrose and sugar beet molasses, and the feasibility of single-stage photofermentative biohydrogen production was evaluated. A single-stage photofermentation process was carried out using four different strains of purple non-sulfur bacteria (Rhodobacter capsulatus DSM 1710, R. capsulatus YO3, Rhodobacter sphaeroides O.U.001, and Rhodopseudomonas palustris DSM 127) on different initial sucrose concentrations. The highest hydrogen yield obtained was 10.5mol H2/mol of sucrose and the maximum hydrogen productivity was 0.78mmol/Lh by Rp. palustris on 5mM sucrose. A hydrogen yield of 19mol H2/mol sucrose, which represents 79% of theoretical yield, and a maximum hydrogen productivity of 0.55mmol/L h were obtained by Rp. palustris from sugar beet molasses. The yield was comparable to those values obtained in two-stage processes. The present study demonstrates that single-stage photofermentation using purple non-sulfur bacteria on sucrose-based wastes is promising.

Isolation and selection of purple non-sulfur bacteria for phosphate removal in rearing water from shrimp cultivation

One of the key environmental concerns about shrimp cultivation is the discharge of rearing water with high levels of nutrients, especially phosphate into waterways, resulting in eutrophication. To solve this problem, biological treatment is well-recognized and the use of purple non-sulfur bacteria (PNSB) is one of alternative attractive choices because of their high removal efficiency in wastewater treatment with various metabolic growth conditions. Therefore, this study aimed to isolate and screen PNSB from shrimp ponds with their ability for reducing phosphate in water from shrimp cultivation. A total of 83 PNSB strains were isolated from water and sediment samples collected from various 15 shrimp ponds located in Phang-nga and Songkhla provinces. For primary screening, there were 42 strains (51%) that grew well (OD660> 1.0) in glutamate-acetate broth supplemented with 1.5% (w/v) NaCl, under conditions of microaerobic-light and aerobic-dark. However, in secondary screening only two strains (W12 and W48) could grow in sterile rearing water collected from shrimp pond. They were selected for tertiary screening to investigate their ability to remove phosphate in sterile rearing water under both incubating conditions. Both PNSB strains produced no significant differences for phosphate removal efficiency (> 50%) with exception under microaerobic-light conditions as strain W12 roughly reduced 46% phosphate. Of these, 2 strains had the possibility to be used as inoculants for removal of phosphate from rearing water in shrimp ponds

Bioenergetics of lactate vs. acetate outside TCA enhanced the hydrogen evolution levels in two newly isolated strains of the photosynthetic bacterium Rhodopseudomonas.

Two local hydrogen-evolving strains of purple nonsulfur bacteria have been isolated, characterized, and identified as Rhodopseudomonas sp. TUT (strains Rh1 and Rh2). Lactate followed by succinate and malate supported the highest amounts of H2 production, growth (O.D.660nm, proteins and bacteriochlorphyll contents), nitrogenase activity, and uptake hydrogenase; the least of which was acetate. Alginate-immobilized cells evolved higher hydrogen amounts than free cell counterparts. Rh1 was more productive than Rh2 at all circumstances. Lactate-dependent hydrogen evolution was more than twice that of acetate, due to ATP productivity (2/-1, respectively), which is limiting to the nitrogenase activity. The preference of lactate over other acids indicates the feasibility of using these two strains in hydrogen production from dairy wastewater.

Synthesis of High-Molecular-Weight Polyhydroxyalkanoates by Marine Photosynthetic Purple Bacteria.

Polyhydroxyalkanoate (PHA) is a biopolyester/bioplastic that is produced by a variety of microorganisms to store carbon and increase reducing redox potential. Photosynthetic bacteria convert carbon dioxide into organic compounds using light energy and are known to accumulate PHA. We analyzed PHAs synthesized by 3 purple sulfur bacteria and 9 purple non-sulfur bacteria strains. These 12 purple bacteria were cultured in nitrogen-limited medium containing acetate and/or sodium bicarbonate as carbon sources. PHA production in the purple sulfur bacteria was induced by nitrogen-limited conditions. Purple non-sulfur bacteria accumulated PHA even under normal growth conditions, and PHA production in 3 strains was enhanced by nitrogen-limited conditions. Gel permeation chromatography analysis revealed that 5 photosynthetic purple bacteria synthesized high-molecular-weight PHAs, which are useful for industrial applications. Quantitative reverse transcription polymerase chain reaction analysis revealed that mRNA levels of phaC and PhaZ genes were low under nitrogen-limited conditions, resulting in production of high-molecular-weight PHAs. We conclude that all 12 tested strains are able to synthesize PHA to some degree, and we identify 5 photosynthetic purple bacteria that accumulate high-molecular-weight PHA molecules. Furthermore, the photosynthetic purple bacteria synthesized PHA when they were cultured in seawater supplemented with acetate. The photosynthetic purple bacteria strains characterized in this study should be useful as host microorganisms for large-scale PHA production utilizing abundant marine resources and carbon dioxide.

Arsenic contamination in areas surrounding mines and selection of potential As-resistant purple nonsulfur bacteria for use in bioremediation based on their detoxification mechanisms

The objectives of this study were to investigate arsenic (As) contamination in areas surrounding mines in Thailand and to isolate As-resistant purple nonsulfur bacteria (PNSB) for their potential application in microbial As bioremediation. Total As in water and soil samples collected from two As-contaminated sites in Thailand exceeded the standard guidelines. Four strains of As-resistant PNSB were selected from 348 isolates based on their As detoxification mechanisms, including biofilm formation, As redox transformations, glutathione (GSH) production, and production of methylcobalamin (vitamin B12) and S-adenosylmethionine (SAM) for As biomethylation. GSH production in these strains followed the order AB3 > L28 > C1. Strains AB3, C31, and L28 accumulated higher levels of intracellular vitamin B12 than strain C1. However, only strain C1 produced SAM and showed As biovolatilization activity. When strain C1 was incubated under microaerobic light conditions, it produced arsenobetaine [(AsB(V)] in medium with As(III) and monomethylarsonic acid [MMA(V)] in medium with As(V), which were found in the culture supernatants. Volatile methylated As compounds, such as dimethylarsenic acid [DMA(V)] and MMA(V)], were also detected in strain C1 during 30 days of incubation with As(III) and As(V). Strains AB3, C1, and L28 were identified as Rhodopseudomonas palustris and strain C31 as Rubrivivax benzoatilyticus. The resistance of these strains to As [As(III) and As(V)] based on minimum inhibition concentration values under aerobic dark and microaerobic light conditions, respectively, was in the order of C1 > AB3 > C31 > L28. The overall results demonstrate that all four selected strains of PNSB have a great potential for future application in the remediation of As-contaminated areas although R. palustris C1 was the most effective candidate.

A purple non-sulfur bacterium producing polyhydroxybutyrate and the conserved region of pha synthase gene

This study aimed to screen purple non-sulfur bacteria capable of accumulating granules or polyhydroxybutyrate (PHB) inside the cells, identify the potent strain, assay the enzyme or PHA synthase, and compare the PHB synthase gene with that of related strains. A total of 58 strains of purple non-sulfur bacteria were isolated from 108 samples of chicken feces in the chicken-egg farm of the Department of Animal Science, Faculty of Natural Resources at Prince of Songkla University, Hat Yai, Thailand. After cultivating the bacteria in glutamate malate (GM) medium without added glutamic acid under light (3,000 Lux) at 35 o C for 5 days, the intracellular biopolymer granules of the bacteria were observed by using a Confocal Laser Scanning Microscope (CLSM) with excitation and emission wavelength of 530 and 605 nm, respectively. Gas chromatography (GC) was carried out for quantitative analysis of PHB. There were five strains, CH12, CH52, CH72, CH90 and CH92, showed biopolymer granules under CLSM, and accumulated PHB 5, 1.7, 1.5, 1.4 and 1.8% (w w -1 ) of the cell dry weight (CDW), respectively. The 16S rDNA sequence analysis of CH12 strain showed a high homology of 100% correlation to that of Rhodopseudomonas palustris strain NCIB8288. Regarding the taxonomic characteristics and 16S rDNA sequence analysis, CH12 strain was identified as Rps. palustris NCIB8288. The PHA synthase activity of the crude extract from CH12 strain was 25 units/mL. The conserved regions could be aligned and selected among 5 strains of Rhodopseudomonas palustris (strains BisA53, TIE-1, CGA009, HaA2 and BisB18). The purified PCR product was obtained for further studies.

Selection of salt tolerant purple nonsulfur bacteria producing 5-aminolevulinic acid (ALA) and reducing methane emissions from microbial rice straw degradation

Saline soil is one major problem that causes low productivity on rice, while paddy fields are also one source of methane (CH4) emissions that can have a considerable impact on global warming. By using purple nonsulfur bacteria (PNSB) it is possible to overcome both these serious problems because PNSB produce 5-aminolevulinic acid (ALA), a compound that reduces salt stress for plants, and they are also good competitors for methanogens in the paddy fields. Therefore, the objective of this study was to select salt resistant PNSB with an ability to release ALA and reduce CH4 emissions. The PNSB isolates used were obtained from saline paddy fields in southern Thailand and the best were selected on the basis of their good growth under conditions of aerobic dark and anaerobic light while being salt tolerant, released ALA and reduced CH4 emissions under microaerobic light conditions. Among the 272 PNSB isolates, TN114 was the best ALA producer while PP803 was the best to reduce CH4 emissions. Both selected PNSB strains grew well in glutamate acetate (GA) broth containing NaCl up to 6.00% but 0.25% NaCl was their optimal concentration for growth. Under salt stress with 0.25% NaCl, the strain TN114 released 25.63μM ALA in GA broth. In scaled-up experiments, when it was mixed with native soil flora in rice straw broth the strain TN114 released 13.44μM ALA and the strain PP803 reduced CH4 emissions by 88.41%. These two strains were identified as Rhodopseudomonas palustris according to both traditional and 16S rRNA identifications. Overall the results demonstrated that they had a good potential as plant growth stimulating bacteria under salt stress, due to the release of ALA and also reduce CH4 emissions.