Isolation of a thermotolerant bacterium producing medium-chain-length polyhydroxyalkanoate

Aims:  The aim of this study was to isolate a thermotolerant micro‐organism that produces polyhydroxyalkanoates (PHAs) composed of medium‐chain‐length (mcl) HA units from a biodiesel fuel (BDF) by‐product as a carbon source. Methods and Results:  We successfully isolated a thermotolerant micro‐organism, strain SG4502, capable to accumulate mcl‐PHA from a BDF by‐product as a carbon source at a cultivation temperature of 45°C. The strain could also produce mcl‐PHA from acetate, octanoate and dodecanoate as sole carbon sources at cultivation temperatures up to 55°C. Taxonomic studies and 16S rRNA gene sequence analysis revealed that strain SG4502 was phylogenetically affiliated with species of the genus Pseudomonas. This study is the first report of PHA synthesis by a thermotolerant Pseudomonas. Conclusions:  A novel thermotolerant bacterium capable to accumulate mcl‐PHA from a BDF by‐product was successfully isolated. Significance and Impact of the Study:  A major issue regarding industrial production of microbial PHAs is their much higher production cost compared with conventional petrochemical‐based plastic materials. Especially significant are the cost of a fermentative substrate and the running cost to maintain a temperature suitable for microbial growth. Thus, strain SG4502, isolated in this study, which assimilates BDF by‐product and produces PHA at high temperature, would be very useful for practical application in industry.     

A novel lipopeptide produced by a Pacific Ocean deep-sea bacterium, Rhodococcus sp. TW53

Aims: Our goal was to find a novel, biosurfactant‐producing bacterium from Pacific Ocean deep‐sea sediments. Methods and Results: An oil‐degrading biosurfactant‐producing bacterium TW53 was obtained from deep‐sea sediment, and was identified through 16S rDNA analysis as belonging to the genus Rhodococcus. It lowered the surface tension of its culture to 34·4 mN m^?1. Thin layer chromatography (TLC) showed that the crude biosurfactants of TW53 were composed of lipopeptides and free fatty acids (FA). The lipopeptides were purified with column chromatography and then hydrolysed with 6 mol l^?1 HCl. Gas chromatography‐mass spectrometry analysis showed that the hydrolyte in the hydrophobic fraction contained five kinds of FA with chain lengths of C₁₄–C₁₉, and C₁₆H₃₂O₂ was a major component making up 59·18% of the total. However, 3‐hydroxyl FA was not found, although it is usually found in lipopeptides. Silica gel TLC revealed that the hydrolyte in the hydrophilic fraction was composed of five kinds of amino acids; consistently, ESI‐Q‐TOF‐MS analysis confirmed the composition results and provided their sequence tentatively as Ala‐Ile‐Asp‐Met‐Pro. Furthermore, the yield and CMC (critical micelle concentrations) of purified lipopeptides were examined. The purified product reduced the surface tension of water to 30·7 mN m^?1 with a CMC value of 23·7 mg l^?1. These results suggest that Rhodococcus sp. TW53 produces a novel lipopeptide that we have named rhodofactin. Conclusion: The deep‐sea isolate Rhodococcus sp. TW53 was the first reported lipopeptide‐producing bacterium of this genus. The lipopeptides had novel chemical compositions. Significance and Impact of the Study: Rhodococcus sp. TW53 has potential in the exploration of new biosurfactants and could be used in bioremediation of marine oil pollution.     

Molybdate reduction by Pseudomonas sp. strain DRY2

Aims: To isolate and characterize a potent molybdenum‐reducing bacterium. Methods and Results: A minimal salt medium supplemented with 10 mmol l^?1 molybdate, glucose (1·0%, w/v) as a carbon source and ammonium sulfate (0·3%, w/v) as a nitrogen source was used in the screening process. A molybdenum‐reducing bacterium was isolated and tentatively identified as Pseudomonas sp. strain DRY2 based on carbon utilization profiles using Biolog GN plates and partial 16S rDNA molecular phylogeny. Strain DRY2 produced 2·4, 3·2 and 6·2 times more molybdenum blue compared to Serratia marcescens strain DRY6, Enterobacter cloacae strain 48 and Eschericia coli K12, respectively. Molybdate reduction was optimum at 5 mmol l^?1 phosphate. The optimum molybdate concentration that supported molybdate reduction at 5 mmol l^?1 phosphate was between 15 and 25 mmol l^?1. Molybdate reduction was optimum at 40°C and at pH 6·0. Phosphate concentrations higher than 5 mmol l^?1 strongly inhibited molybdate reduction. Inhibitors of electron transport system such as antimycin A, rotenone, sodium azide and cyanide did not inhibit the molybdenum‐reducing enzyme activity. Chromium, copper, mercury and lead inhibited the molybdenum‐reducing activity. Conclusions: A novel molybdenum‐reducing bacterium with high molybdenum reduction capacity has been isolated. Significance and Impact of the Study: Molybdenum is an emerging global pollutant that is very toxic to ruminants. The characteristics of this bacterium suggest that it would be useful in the bioremediation of molybdenum pollutant.     

A polyhydroxyalkanoates bioprocess improvement case study based on four fed-batch feeding strategies

The modelling and optimization of a process for the production of the medium chain length polyhydroxyalkanoate (mcl-PHA) by the bacterium Pseudomonas putida KT2440 when fed a synthetic fatty acid mixture (SFAM) was investigated. Four novel feeding strategies were developed and tested using a constructed model and the optimum one implemented in further experiments. This strategy yielded a cell dry weight of 70.6 g l⁻¹ in 25 h containing 38% PHA using SFAM at 5 l scale. A phosphate starvation strategy was implemented to improve PHA content, and this yielded 94.1 g l⁻¹ in 25 h containing 56% PHA using SFAM at 5 l scale. The process was successfully operated at 20 l resulting in a cell dry weight of 91.2 g l⁻¹ containing 65% PHA at the end of a 25-h incubation.     

Zobellella denitrificans strain MW1, a newly isolated bacterium suitable for poly(3-hydroxybutyrate) production from glycerol

Aims: To search for new bacteria for efficient production of polyhydroxyalkanoates (PHAs) from glycerol. Methods and Results: Samples were taken from different environments in Germany and Egypt, and bacteria capable of growing in mineral salts medium with glycerol as sole carbon source were enriched. From a wastewater sediment sample in Egypt, a Gram‐negative bacterium (strain MW1) was isolated that exhibited good growth and that accumulated considerable amounts of polyhydroxybutyrate (PHB) from glycerol and also from other carbon sources. The 16S rRNA gene sequence of this isolate exhibited 98·5% and 96·2% similarity to Zobellella denitrificans strain ZD1 and to Zobellella taiwanensis strain ZT1 respectively. The isolate was therefore affiliated as strain MW1 of Z. denitrificans. Strain MW1 grows optimally on glycerol at 41°C and pH 7·3 and accumulated PHB up to 80·4% (w/w) of cell dry weight. PHB accumulation was growth‐associated. Although it was not an absolute requirement, 20 g l^?1 sodium chloride enhanced both growth (5 g cell dry weight per litre) and PHB content (87%, w/w). Zobellella denitrificans strain MW1 is also capable to accumulate the poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) copolymer if sodium propionate was used as cosubstrate in addition to glycerol. Conclusions: A new PHB‐accumulating strain was isolated and identified. This strain is able to utilize glycerol for growth and PHB accumulation to high content especially in the presence of NaCl that will enable the utilization of waste glycerol from biodiesel industry. Significance and Impact of the Study: This study is the first report on accumulation of PHA in a member of the new genus Zobellella. Furthermore, utilization of glycerol as the sole carbon source for fast growth and PHB biosynthesis, growth in the presence of NaCl and high PHB contents of the cells will make this newly isolated bacterium a potent candidate for industrial production of PHB from crude glycerol occurring as byproduct during biodiesel production.     

Halomonas profundus sp. nov., a new PHA-producing bacterium isolated from a deep-sea hydrothermal vent shrimp

Aims:  The objective of the present work was to describe a new deep-sea, aerobic, mesophilic and heterotrophic bacterium, referenced as strain AT1214, able to produce polyhydroxyalkanoates (PHAs) under laboratory conditions. This bacterium was isolated from a shrimp collected nearby a hydrothermal vent located on the Mid-Atlantic Ridge. Methods and Results:  This micro-organism, on the basis of the phenotypical features and genotypic investigations, can be clearly assigned to the Halomonas genus and the name of Halomonas profundus is proposed. Optimal growth occurred between 32 and 37°C at a pH between 8 and 9 and at ionic strength between 20 and 30 g l⁻¹ of sea salts. The G + C content of DNA was 58·6%. This bacterium produced PHAs of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from different carbon sources. Conclusions:  The bacterium H. profundus produces PHA of 3HB and 3HV monomers from different carbon sources. Significance and Impact of the Study:  PHAs share physical and material properties that suggest them for application in various areas, and are considered as an alternative to nonbiodegradable plastics produced from fossil oils. In this study, we describe a new bacteria isolated from a deep-sea hydrothermal vent with the capability to produce polyesters of biotechnological interest.     

Isolation of biosurfactant producers, optimization and properties of biosurfactant produced by Acinetobacter sp. from petroleum-contaminated soil

Aims: To screen and identify biosurfactant producers from petroleum‐contaminated soil; to use response surface methodology (RSM) for medium optimization to enhance biosurfactant production; and to study the properties of the newly obtained biosurfactant towards pH, temperature and salinity. Methods and Results: We successfully isolated three biosurfactant producers from petroleum‐contaminated soil and identified them through 16S rRNA sequence analysis, which exhibit the highest similarities to Acinetobacter beijerinckii (100%), Kocuria marina (99%) and Kineococcus marinus (99%), respectively. A quadratic response model was constructed through RSM designs, leading to a 57·5% increase of the growth‐associated biosurfactant production by Acinetobacter sp. YC‐X 2 with an optimized medium: beef extract 3·12 g l^?1; peptone 20·87 g l^?1; NaCl 1·04 g l^?1; and n‐hexadecane 1·86 g l^?1. Biosurfactant produced by Acinetobacter sp. YC‐X 2 retained its properties during exposure to a wide range of pH values (5–11), high temperatures (up to 121°C) and high salinities [up to 18% (w/v) Na⁺ and Ca²⁺], which was more sensitive to Ca²⁺ than Na⁺. Conclusions: Two novel biosurfactant producers were isolated from petroleum‐contaminated soil. Biosurfactant from Acinetobacter sp. YC‐X 2 has good properties to a wide range of pH, high temperature and high salinity, and its production was optimized successfully through RSM. Significance and Impact of the Study: The fact, an increasing demand of high‐quality surfactants and the lack of cost‐competitive bioprocesses of biosurfactants for commercial utilization, motivates researchers to develop cost‐effective strategies for biosurfactant production through isolating new biosurfactant producers with special surface‐active properties and optimizing their cultural conditions. Two novel biosurfactant producers in this study will widen our knowledge about this kind of micro‐organism. This work is the first application of RSM designs for cultural optimization of biosurfactant produced by Acinetobacter genus and the first report that biosurfactant may be more sensitive to Ca²⁺ than Na⁺.     

Optimization of physico‐chemical and nutritional parameters for a novel pullulan‐producing fungus,Eurotium chevalieri

Aims: To isolate the novel nonmelanin pullulan‐producing fungi from soil and to optimize the physico‐chemical and nutritional parameters for pullulan production. Methods and Results: A selective enrichment method was followed for the isolation, along with development of a suitable medium for pullulan production, using shake flask experiments. Pullulan content was confirmed using pure pullulan and pullulanase hydrolysate. Eurotium chevalieri was able to produce maximum pullulan (38 ± 1·0 g l^?1) at 35°C, pH 5·5, 2·5% sucrose, 0·3% ammonium sulfate and 0·2% yeast extract in a shake flash culture medium with an agitation rate of 30 rev min^?1 for 65 h. Conclusions: The novel pullulan‐producing fungus was identified as E. chevalieri (MTCC no. 9614), which was able to produce nonmelanin pullulan at from poorer carbon and nitrogen sources than Aureobasidium pullulans and may therefore be useful for the commercial production of pullulan. Significance and Impact of the Study: Eurotium chevalieri could produce pullulan in similar amounts to A. pullulans. Therefore, in future, this fungus could also be used for commercial pullulan production, because it is neither polymorphic nor melanin producing, hence its handling during pullulan fermentation will be easier and more economical.     

The influence of light on copper‐limited growth of an oceanic diatom,Thalassiosira oceanica (Coscinodiscophyceae)

Thalassiosira oceanica (CCMP 1005) was grown over a range of copper concentrations at saturating and subsaturating irradiance to test the hypothesis that Cu and light were interacting essential resources. Growth was a hyperbolic function of irradiance in Cu‐replete medium (263 fmol Cu′ · L^?1) with maximum rates achieved at 200 μmol photons · m^?2 · s^?1. Lowering the Cu concentration at this irradiance to 30.8 fmol Cu′ · L^?1 decreased cellular Cu quota by 7‐fold and reduced growth rate by 50%. Copper‐deficient cells had significantly slower (P < 0.0001) rates of maximum, relative photosynthetic electron transport (rETR_max) than Cu‐sufficient cells, consistent with the role of Cu in photosynthesis in this diatom. In low‐Cu medium (30.8 fmol Cu′ · L^?1), growth rate was best described as a positive, linear function of irradiance and reached the maximum value measured in Cu‐replete cells when irradiance increased to 400 μmol photons · m^?2 · s^?1. Thus, at high light, low‐Cu concentration was no longer limiting to growth: Cu concentration and light interacted strongly to affect growth rate of T. oceanica (P < 0.0001). Relative ETR_max and Cu quota of cells grown at low Cu also increased at 400 μmol photons · m^?2 · s^?1 to levels measured in Cu‐replete cells. Steady‐state uptake rates of Cu‐deficient and sufficient cells were light‐dependent, suggesting that faster growth of T. oceanica under high light and low Cu was a result of light‐stimulated Cu uptake.     

Production of polyhydroxyalkanoates from whey by Thermus thermophilus HB8

The thermophilic bacterium Thermus thermophilus HB8 is able to utilize lactose from whey-based media for the biosynthesis of polyhydroxyalkanoates (PHAs) under nitrogen limitation. T. thermophilus can utilize both, glucose and galactose, the products of lactose hydrolysis. When T. thermophilus HB8 was grown in culture media containing 24% (v/v) whey, PHA was accumulated up to 35% (w/w) of its biomass after 24 h of cultivation. The effect of initial phosphate concentration on the PHA production was also investigated. Using an initial phosphate concentration of 50 mM the PHA accumulation was enhanced. Analysis of the produced PHA from T. thermophilous HB8 grown in whey-based media revealed a novel heteropolymer consisting of the short chain length 3-hydroxyvalerate (3HV; 38 mol%) and the medium chain length, 3-hydroxyheptanoate (3HHp; 9.89 mol%), 3-hydroxynanoate (3HN; 16.59 mol%) and 3-hydroxyundecanoate (3HU; 35.42 mol%). Despite the low molecular weight of the produced PHA by T. thermophilus, whey could be an excellent substrate for the production of heteropolymers with unique properties.     

Isolation and characterization of a novel organic solvent-tolerant Anoxybacillus sp. PGDY12, a thermophilic Gram-positive bacterium

Aims: To isolate and characterize new bacteria capable of tolerating high concentrations of organic solvents at high temperature. Methods and Results: A solvent‐tolerant, thermophilic bacterium was isolated from hot spring samples at 55°C. The strain PGDY12 was characterized as a Gram‐positive bacterium. It was able to tolerate 100% solvents, such as toluene, benzene and p‐xylene on plate overlay and high concentrations of these solvents in liquid cultures. A comparison of growth showed that 0·2% (v/v) benzene and 0·15% (v/v) p‐xylene were capable of enhancing the final cell yields. Transmission electron micrographs showed the incrassation of electron‐transparent intracellular material and the distorted cytoplasm in case of the cells grown in toluene. A phylogenetic analysis based on 16S rRNA sequence data indicated that the strain PGDY12 was member of the genus Anoxybacillus. Conclusions: The thermophilic, Gram‐positive Anoxybacillus sp. PGDY12 exhibited a unique and remarkable ability to tolerate solvents at 55°C. Significance and Impact of the Study: The solvent tolerance properties are less known in thermophilic bacteria. The Anoxybacillus sp. PGDY12 is the first strictly thermophilic bacterium able to tolerate a broad range of solvents. This strain is a promising candidate for use as a high temperature biocatalyst in the biotechnological applications.     

Spirulina enhances the viability of Lactobacillus rhamnosus E/N after freeze-drying in a protective medium of sucrose and lactulose

Aims: Response surface methodology (RSM) was used to optimize a protective medium for enhancing the viability of Lactobacillus rhamnosus E/N cells during lyophilization. Methods and Results: Spirulina, sucrose and lactulose were selected, on the basis of a Plackett‐Burman factorial design, as important protectants having the following protective effects on cell viability: 102·025, 36·885 and ?34·42, respectively. A full‐factorial central composite design was applied to determine optimal levels of three used agents. Conclusion: The optimal protective medium composition was determined to be: Spirulina 1·304% (w/v), lactulose 5·48% (w/v), and sucrose 13·04% (w/v) (Polish Patent P‐393189). The predictive value of cell viability in this medium was 89·619%, and experimental viability obtained during freeze‐drying was 87·5%. Significance and Impact of the Study: In this study, Spirulina was used for the first time as the protective agent in freeze‐drying medium, significantly increasing lactobacilli viability and giving synbiotic character of the final product.     

Description of Triplophysa luochengensis sp. nov. (Teleostei: Nemacheilidae) from a karst cave in Guangxi,China

A new cave‐dwelling fish Triplophysa luochengensis is described based on specimens collected from a karst cave in Guangxi Zhuang Autonomous Region, China, that is interconnected to the Hongshui River drainage. The species can be distinguished from its congeners by a combination of characters: eyes degenerated, anal fin with six branched rays, caudal fin with 16–17 branched rays, pectoral‐fin length 72·4–95·8% of the distance between pectoral‐fin origin and pelvic‐fin origin, lateral head length 26·2–28·2% of standard length (L_S), eye diameter 7·5–8·6 of L_S, body covered by sparse scales, lateral line complete and 7–8 pre‐operculo‐mandibular pores. Dark pigments irregularly present on dorsum of head, dorsum and flank.     

Balitora eddsi,a new species of hillstream loach (Ostariophysi: Balitoridae) from Nepal

A new species of hillstream loach Balitora eddsi is described from the Karnali River drainage in south‐western Nepal. The new species is distinguished from all its congeners by possessing the following combination of characters: six to seven unbranched pectoral‐fin rays, pelvic‐fin length 12–14% standard length (L_S), dorsal surface without circular or irregular shaped dark blotches, snout pointed, median lobe between anterior rostral barbels pointed posteriorly, dorsal‐fin origin posterior to pelvic‐fin origin, lateral line scales 66–67, caudal peduncle length 22–23·2% L_S, caudal peduncle depth 4·1–4·2 times its length.     

Comparison of Campylobacter jejuni isolates from human, food, veterinary and environmental sources in Iceland using PFGE, MLST and fla-SVR sequencing

Aims: To evaluate the probiotic properties of strains isolated from smoked salmon and previously identified as bacteriocin producers. Methods and Results: Strains Lactobacillus curvatus ET06, ET30 and ET31, Lactobacillus fermentum ET35, Lactobacillus delbrueckii ET32, Pediococcus acidilactici ET34 and Enterococcus faecium ET05, ET12 and ET88 survived conditions simulating the gastrointestinal tract (GIT) and produced bacteriocins active against several strains of Listeria monocytogenes, but presented very low activity against other lactic acid bacteria (LAB). Cell‐free supernatants containing bacteriocins, added to 3‐h‐old cultures of L. monocytogenes 603, suppressed growth over 12 h. Auto‐aggregation was strain‐specific, and values ranged from 7·2% for ET35 to 12·1% for ET05. Various degrees of co‐aggregation with L. monocytogenes 603, Lactobacillus sakei ATCC 15521 and Enterococcus faecalis ATCC 19443 were observed. Adherence of the bacteriocinogenic strains to Caco‐2 cells was within the range reported for Lactobacillus rhamnosus GG, a well‐known probiotic. The highest levels of hydrophobicity were recorded for Lact. curvatus (61·9–64·6%), Lact. fermentum (78·9%), Lact. delbrueckii (43·7%) and Ped. acidilactici (51·3%), which are higher than the one recorded for Lact. rhamnosus GG (53·3%). These strains were highly sensitive to several antibiotics and affected by several drugs from different generic groups in a strain‐dependent manner. Conclusions: Smoked salmon is a rich source of probiotic LAB. All strains survived conditions simulating the GIT and produced bacteriocins active against various pathogens. Adherence to Caco‐2 cells was within the range reported for Lact. rhamnosus GG, a well‐known probiotic. In addition, the high hydrophobicity readings recorded define the strains as good probiotics. Significance and Impact of the Study: Smoked salmon contains a number of different probiotic LAB and could be marketed as having a potential beneficial effect.     

A biosurfactant from Burkholderia cenocepacia BSP3 and its enhancement of pesticide solubilization

Aims: To isolate a biosurfactant (BS)‐producing bacterium, to characterize the BS properties and to evaluate its ability to enhance pesticide solubilization for further application in environmental remediation. Methods and Results: Five BS‐producing bacteria were isolated from fuel oil‐contaminated soil. Among them, Burkholderia cenocepacia BSP3 exhibited the highest emulsification index and was chosen for further study. Glucose‐containing medium supplemented with nitrate or sunflower seed oil provided suitable conditions for growth and BS production. The BS was identified as a glucolipid, having a critical micelle concentration (CMC) of 316 mg l^?1. It could lower the surface tension of deionized water to 25 ± 0·2 mN m^?1 and exhibited good emulsion stability. Finally, the application of the BS to facilitate pesticide solubilization demonstrated that this BS at the concentration below and above its CMC could enhance the apparent water solubility of three pesticides, i.e. methyl parathion, ethyl parathion and trifluralin. Conclusions: Burkholderia cenocepacia BSP3 is a BS‐producing bacterium isolated from oil‐contaminated soil. The BS was identified as a glucolipid having a molecular mass of 550·4 g mol^?1. An apparent yield of the BS was 6·5 ± 0·7 g l^?1. This glucolipid‐type BS noticeably enhanced pesticide solubilization suggesting its role in environmental remediation. Significance and Impact of the Study: A glucolipid type BS normally found in marine micro‐organisms was isolated from a soil‐bacterium. Due to its surface active properties and good performance in enhancement of pesticide solubilization, it could be used as a solubilizing agent for environmental remediation and synergistic treatment with bioremediation of pesticide‐contaminated soil.     

Enhanced production of SCL-LCL-PHA co-polymer by sludge-isolated Pseudomonas aeruginosa MTCC 7925

Aim: To boost short‐chain‐length‐long‐chain‐length polyhydroxyalkanoate (SCL‐LCL‐PHA) co‐polymer yield in Pseudomonas aeruginosa MTCC 7925 by manipulating culture conditions. Methods and Results: Stationary phase culture of P. aeruginosa MTCC 7925 was subjected to various doses of different carbons and, N and P deficiencies. Enhanced co‐polymer yield was recorded under ethanol‐ and glucose‐supplemented cultures. Interaction of ethanol with N‐deficiency boosted co‐polymer accumulation maximally. Conclusions: The sludge‐isolated P. aeruginosa MTCC 7925 demonstrated good capability to synthesize SCL‐LCL‐PHA co‐polymer from unrelated carbon sources. Supplementation of ethanol under N‐deficiency boosted the co‐polymer yield up to 69% of dry cell weight, which is significantly higher when compared with other SCL‐MCL‐PHA co‐polymer accumulating bacterial species. Significance and Importance of the Study: This is the first report on P. aeruginosa MTCC 7925, which is capable of accumulating LCL 3‐hydroxyhexadecanoate and 3‐hydroxyoctadecanoate units with SCL 3‐hydroxybutyrate and 3‐hydroxyvalerate as constituents of PHAs. This opens up new possibilities for various industrial applications owing to the superior properties of this new co‐polymer.     

NITROGEN FIXATION,HYDROGEN CYCLING,AND ELECTRON TRANSPORT KINETICS IN TRICHODESMIUM ERYTHRAEUM (CYANOBACTERIA) STRAIN IMS1011

This study describes the relationships between dinitrogen (N₂) fixation, dihydrogen (H₂) production, and electron transport associated with photosynthesis and respiration in the marine cyanobacterium Trichodesmium erythraeum Ehrenb. strain IMS101. The ratio of H₂ produced:N₂ fixed (H₂:N₂) was controlled by the light intensity and by the light spectral composition and was affected by the growth irradiance level. For Trichodesmium cells grown at 50 μmol photons · m^?2 · s^?1, the rate of N₂ fixation, as measured by acetylene reduction, saturated at light intensities of 200 μmol photons · m^?2 · s^?1. In contrast, net H₂ production continued to increase with light levels up to 1,000 μmol photons · m^?2 · s^?1. The H₂:N₂ ratios increased monotonically with irradiance, and the variable fluorescence measured using a fast repetition rate fluorometer (FRRF) revealed that this increase was accompanied by a progressive reduction of the plastoquinone (PQ) pool. Additions of 2,5‐dibromo‐3‐methyl‐6‐isopropyl‐p‐benzoquinone (DBMIB), an inhibitor of electron transport from PQ pool to PSI, diminished both N₂ fixation and net H₂ production, while the H₂:N₂ ratio increased with increasing level of PQ pool reduction. In the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), nitrogenase activity declined but could be prolonged by increasing the light intensity and by removing the oxygen supply. These results on the coupling of N₂ fixation and H₂ cycling in Trichodesmium indicate how light intensity and light spectral quality of the open ocean can influence the H₂:N₂ ratio and modulate net H₂ production.     

Characterization and emulsifying property of a novel bioemulsifier by Aeribacillus pallidus YM-1

Aims: Biosurfactants and bioemulsifiers commonly have the advantages of biodegradability, low toxicity, selectivity and biocompatibility over chemically synthesized surfactants. The goal of the study is to present a novel bioemulsifier with great application potential. Methods and Results: Aeribacillus pallidus YM‐1, isolated from crude oil contaminated soil, was found to produce a novel high molecular bioemulsifier with an emulsification index of 60 ± 1% without remarkable surface tension reduction (45·7 ± 0·1 mN m^?1). The number‐average molecular weight was determined as 526 369 Da by gel permeation chromatography analysis. Bioemulsifier was subjected to FT‐IR and a complex of carbohydrates (41·1%), lipids (47·6%) and proteins (11·3%) was determined. Conclusions: The bioemulsifier of A. pallidus YM‐1 was isolated from the glucose‐based culture medium and characterized with the help of chemical analytical techniques. The bioemulsifier exhibited a promising emulsifying property for biotechnology application potential in bioremediation and microbial enhanced oil recovery. Significance and Impact of the Study: This is the first report of the bioemulsifier production by A. pallidus. The potential emulsifying activity of the bioemulsifier in the present study may be explored in various biotechnological and industrial applications.