Flocculation properties of poly(γ-glutamic acid) produced by Bacillus subtilis

Efficacy of exopolysaccharide in dye-laden wastewater treatment: A comprehensive review

The discharge of dye-laden wastewater into the water streams causes severe water and soil pollution, which poses a global threat to aquatic ecosystems and humans. A diverse array of microorganisms such as bacteria, fungi, and algae produce exopolysaccharides (EPS) of different compositions and exhibit great bioflocculation potency to sustainably eradicate dyes from water bodies. Nanomodified chemical composites of EPS enable their recyclability during dye-laden wastewater treatment. Nevertheless, the selection of potent EPS-producing strains and physiological parameters of microbial growth and the remediation process could influence the removal efficiency of EPS. This review will intrinsically discuss the fundamental importance of EPS from diverse microbial origins and their nanomodified chemical composites, the mechanisms in EPS-mediated bioremediation of dyes, and the parametric influences on EPS-mediated dye removal through sorption/bioflocculation. This review will pave the way for designing and adopting futuristic green and sustainable EPS-based bioremediation strategies for dye-laden wastewater in situ and ex situ.

Effective Removal of Different Heavy Metals Ion (Cu, Pb, and Cd) from Aqueous Solutions by Various Molecular Weight and Salt Types of Poly-γ-Glutamic Acid

In light of industrial developments, water pollution by heavy metals as hazardous chemicals has garnered attention. Addressing the urgent need for efficient heavy metal removal from aqueous environments, this study delves into using poly-γ-glutamic acid (γ-PGA) for the bioflocculation of heavy metals. Utilizing γ-PGA variants from Bacillus subtilis with different molecular weights and salt forms (Na-bonded and Ca-bonded), the research evaluates their adsorption capacities for copper (Cu), lead (Pb), and cadmium (Cd) ions. It was found that Na-bonded γ-PGA with a high molecular weight showed the highest heavy metal adsorption (92.2-98.3%), particularly at a 0.5% concentration which exhibited the highest adsorption efficiency. Additionally, the study investigated the interaction of γ-PGA in mixed heavy metal environments, and it was discovered that Na-γ-PGA-HM at a 0.5% concentration showed a superior adsorption efficiency for Pb ions (85.4%), highlighting its selectivity as a potential effective biosorbent for wastewater treatment. This research not only enlightens the understanding of γ-PGA's role in heavy metal remediation but also underscores its potential as a biodegradable and non-toxic alternative for environmental cleanup. The findings pave the way for further exploration into the mechanisms and kinetics of γ-PGA's adsorption properties.

Sequential electron beam and bioflocculation for treatment of textile nanodyes

Nanodyes are a new class of hazardous materials that are used in textile coloring. Their small size, color, stability and high dispersion characteristics pose a huge threat if they are released in open water systems. The aim of the present study is to test electron beam irradiation, bioflocculation and their sequential use for nanodye removal. The nanodye was obtained from a factory and was characterized using UV-visible spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, dynamic light scattering, zeta potential and energy dispersive X-ray (EDX). The obtained results show that applying 7.5 kGy electron beam irradiation results in complete color removal in 10 min for 50 and 100 ppm nanodye, while at 200 and 400 ppm concentrations, the decolorization reaches 90% but leaving a residual brownish color. Adding 5 mg mL^-1 of Serratia marcescens N2 biosurfactant resulted in agglomeration of 80% dye removal for 400 ppm nanodye after 24 h. On the other hand, the use of sequential electron beam and bioflocculation led to an initial removal of 80% in 1 h. The residual dyes were tested for toxicity on normal dermal HFB4 cells. The toxicity result was 1.19% after electron beam treatment, while those for sequential treatment and bioflocculation were 6.28 and 6.9%, respectively. It can be concluded that electron beam technology provides fast and highly efficient nanodye removal, while biosurfactants offer a low-cost, eco-friendly approach with a chance for dye retrieval.

A Novel Bioflocculant Produced by Cobetia marina MCCC1113: Optimization of Fermentation Conditions by Response Surface Methodology and Evaluation of Flocculation Performance when Harvesting Microalgae

A preliminary study was carried out to optimize the culture medium conditions for producing a novel microbial flocculant from the marine bacterial species Cobetia marina. The optimal glucose, yeast extract, and glutamate contents were 30, 10, and 2 g/l, respectively, while the optimal initial pH of the culture medium was determined to be 8. Following response surface optimization, the maximum bioflocculant production level of 1.36 g/l was achieved, which was 43.40% higher than the original culture medium. Within 5 min, a 20.0% (v/v) dosage of the yielded bioflocculant applied to algal cultures resulted in the highest flocculating efficiency of 93.9% with Spirulina platensis. The bioflocculant from C. marina MCCC1113 may have promising application potential for highly productive microalgae collection, according to the findings of this study.

Production and purification of bioflocculants from newly isolated bacterial species: a comparative decolourization study of cationic and anionic textile dyes

Bioflocculant-producing bacteria were isolated from various water reservoirs and sediments of the water treatment plant. Four promising strains were identified by standard biochemical methods and 16s rRNA gene sequencing. Bioflocculants were produced in a batch bioreactor of 3 L under optimized conditions. Fourier transformed infrared spectroscopy and scanning electron microscopy (SEM) were used to confirm the chemical and morphological nature of bioflocculants. Anionic and cationic textile dyes congo red (CR) and rhodamine-B (RB) decolourization efficiency by ethanol precipitated bioflocculants were accessed under different values of pH, temperature, dose of flocculant and presence of monovalent, divalent and trivalent cations. Bioflocculants of all the four isolates were found to be highly efficient in decolourization of dye from an aqueous medium with the removal rate up to 99.56%. The removal rate of CR and RB from aqueous medium was largely influenced by the physiochemical condition of the solution viz. pH, temperature, concentration of ions and dose of flocculants. The microbial bioflocculants are biodegradable and highly stable as well as possess abroad range of pH, temperature and ions tolerance range. So, they may be economical and can be greener substitutes for the present harsh chemical-based wastewater effluent treatment methods.

Microalgal bio-flocculation: present scenario and prospects for commercialization

The need for sustainable production of renewable biofuel has been a global concern in the recent times. Overcoming the tailbacks of the first- and second-generation biofuels, third-generation biofuel using microalgae as feedstock has emerged as a plausible alternative. It has an added advantage of preventing any greenhouse gas (GHG) emissions with simultaneous carbon dioxide sequestration. Dewatering of microalgal culture is one of the many concerns regarding industrial-scale biofuel production. The small size of microalgae and dilute nature of its growth cultures creates huge operational cost during biomass separation, limiting economic feasibility of algae-based fuels. Considering the recovery efficiency, operation economics, technological feasibility and cost-effectiveness, bio-flocculation is a promising method of harvesting. Moreover, advantage of bio-flocculation over other conventional methods is that it does not incur the addition of any external chemical flocculants. This article reviews the current status of bio-flocculation technique for harvesting microalgae at industrial scale. The various microbial strains that can be prospective bioflocculants have been reviewed along with its application and advantages over chemical flocculants. Also, this article proposes that the primary focus of an appropriate harvesting technique should depend on the final utilization of the harvested biomass. This review article attempts to bring forth the beneficial aspects of microbial aided microalgal harvesting with a special attention on genetically modified self-flocculation microalgae.

Bioflocculants Produced by Bacterial Strains Isolated from Palm Oil Mill Effluent for Application in the Removal of Eriochrome Black T Dye from Water

Four strains of bioflocculant-producing bacteria were isolated from a palm oil mill effluent (POME). The four bacterial strains were identified as Pseudomonas alcaliphila (B1), Pseudomonas oleovorans (B2), Pseudomonas chengduensis (B3), and Bacillus nitratireducens (B4) by molecular identification. Among the four bacterial strains, Bacillus nitratireducens (B4) achieved the highest flocculating activity (49.15%) towards kaolin clay suspension after eight hours of cultivation time and was selected for further studies. The optimum conditions for Eriochrome Black T (EBT) flocculation regarding initial pH, type of cation, and B4 dosage were determined to be pH 2, Ca²⁺ cations, and a dosage of 250 mL/L of nutrient broth containing B4. Under these conditions, above 90% of EBT dye removal was attained. Fourier transform infrared spectroscopic (FT-IR) analysis of the bioflocculant revealed the presence of hydroxyl, alkyl, carboxyl, and amino groups. This bioflocculant was demonstrated to possess a good flocculating activity, being a promissory, low-cost, harmless, and environmentally friendly alternative for the treatment of effluents contaminated with dyes.

Engineering Expression Cassette of pgdS for Efficient Production of Poly-γ-Glutamic Acids With Specific Molecular Weights in Bacillus licheniformis

Poly-γ-glutamic acid (γ-PGA) is an emerging biopolymer with various applications and γ-PGAs with different molecular weights exhibit distinctive properties. However, studies on the controllable molecular weights of biopolymers are limited. The purpose of this study is to achieve production of γ-PGAs with a wide range of molecular weights through manipulating the expression of γ-PGA depolymerase (PgdS) in Bacillus licheniformis WX-02. Firstly, the expression and secretion of PgdS were regulated through engineering its expression elements (four promoters and eight signal peptides), which generated γ-PGAs with molecular weights ranging from 6.82 × 10⁴ to 1.78 × 10⁶ Da. Subsequently, through combination of promoters with signal peptides, the production of γ-PGAs with a specific molecular weight could be efficiently obtained. Interestingly, the γ-PGA yield increased with the reduced molecular weight in flask cultures (Pearson correlation coefficient of −0.968, P < 0.01). Finally, in batch fermentation, the highest yield of γ-PGA with a weight-average molecular weight of 7.80 × 10⁴ Da reached 39.13 g/L under glutamate-free medium. Collectively, we developed an efficient strategy for one-step production of γ-PGAs with specific molecular weights, which have potential application for industrial production of desirable γ-PGAs.

Increased Production of the Value-Added Biopolymers Poly(R-3-Hydroxyalkanoate) and Poly(γ-Glutamic Acid) From Hydrolyzed Paper Recycling Waste Fines

Reject fines, a waste stream of short lignocellulosic fibers produced from paper linerboard recycling, are a cellulose-rich paper mill byproduct that can be hydrolyzed enzymatically into fermentable sugars. In this study, the use of hydrolyzed reject fines as a carbon source for bacterial biosynthesis of poly(R-3-hydroxyalkanoate) (PHA) and poly(γ-glutamic acid) (PGA) was investigated. Recombinant Escherichia coli harboring PHA biosynthesis genes were cultivated with purified sugars or crude hydrolysate to produce both poly(R-3-hydroxybutyrate) (PHB) homopolymer and medium chain length-containing copolymer (PHB-co-MCL). Wild-type Bacillus licheniformis WX-02 were cultivated with crude hydrolysate to produce PGA. Both PHB and short chain-length-co-medium chain-length (SCL-co-MCL) PHA yields from crude hydrolysate were a 2-fold improvement over purified sugars, and the MCL monomer fraction was decreased slightly in copolymers produced from crude hydrolysate. PGA yield from crude hydrolysate was similarly increased 2-fold. The results suggest that sugars from hydrolyzed reject fines are a viable carbon source for PHA and PGA biosynthesis. The use of crude hydrolysate is not only possible but beneficial for biopolymer production, eliminating the need for costly separation and purification techniques. This study demonstrates the potential to divert a lignocellulosic waste stream into valuable biomaterials, mitigating the environmental impacts of solid waste disposal.

Study of fluvial water treatability using γ-polyglutamic acid based biopolymer coagulant

Successful treatment of surface water for public use requires the evaluation of raw water and coagulant efficacy. The purpose of water treatment is to remove impurities, allowing its quality to be classified to meet the needs of the population. The conditions of urban rivers that flow though the city of São Paulo, which were already undergoing major transformations, particularly due to intense urbanization, have deteriorated further due to the precariousness of basic sanitation and increasing environmental pollution.This study focused on an analysis of the efficiency of PGα21Ca, a water purification product, in the treatment of Pinheiros River water, based on coagulation-flocculation and sedimentation tests. The biopolymer PGα21Ca reduced in the order of 100% the total phosphorus. The best sedimentation velocity for the coagulant under study was 1 cm min-1. The PGα21Ca performed well in the removal of turbidity and apparent color, with residual turbidity ​​of 1.84 NTU, 96.95% removal of apparent color, and little change in the pH of the medium.

Application of Poly-γ-Glutamic Acid Flocculant to Flocculation–Sedimentation Treatment of Ultrafine Cement Suspension

We examined the effect of poly-γ-glutamic acid flocculant (PGAF) on the removal of ultrafine cement (UFC) particles stabilized by a poly-carboxylate co-polymer, which is a superplasticizer (SP). The flocculation–sedimentation treatment with PGAF successfully removed the SP-stabilized cement particles through the gravitational settling of the formed flocs. The removal efficiency reduced with the increase in the ionic strength, probably because of the shrunk form of poly-γ-glutamic acid (γ-PGA) at high ionic strengths. Increasing the mixing intensity during rapid mixing improved the removal efficiency. A series of flocculation–sedimentation experiments provided a diagram showing the relationship between ionic strengths and the addition amount of PGAF. Our results suggest that PGAF is a good candidate for the purification of cement suspension by flocculation–sedimentation, and a better removal performance can be obtained at lower ionic strengths with intense rapid mixing. From the diagram of the control charts presented in this study, we can determine the optimal addition amount of PGAF for achieving the target removal rate for cement suspension under any ionic strength.

A review on chemical mechanism of microalgae flocculation via polymers

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Mechanism involved in microalgal flocculation has been reviewed.

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Commercially, bioflocculation is suitable and cost-effective.

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Organic & inorganic flocculants and their features are covered.

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Ideal proportion amongst flocculants and biomass decides their efficiency.

Industrially, harvesting of the microalgal biomass is a techno-economic tailback, which essentially meant for the algal biomass industry. It is considered energy as well as cost-intensive in view of the fact that the dewatering process during harvesting. In this review chemical reactions involved in the flocculation of microalage biomass via various certain principal organic polymers are focused. Besides, it focuses on natural biopolymers as flocculants to harvest the cultivated microalgae. Commercially, bio-flocculation is suitable and cost-effective in the midst of a range of adopted harvesting techniques and the selection of an appropriate bioflocculant depends on its efficacy on the several microalgae strains like potential biomass fixation, ecological stride and non-perilous nature. The harvesting of toxin free microalgae biomass in large quantity by such flocculants can be considered to be one of the most cost-effective performances towards sustainable biomass recovery.

Production and Characterization of a Bioflocculant Produced by Bacillus salmalaya 139SI-7 and Its Applications in Wastewater Treatment

The production, optimization, and characterization of the bioflocculant QZ-7 synthesized by a novel Bacillus salmalaya strain 139SI isolated from a private farm soil in Selangor, Malaysia, are reported. The flocculating activity of bioflocculant QZ-7 present in the selected strain was found to be 83.3%. The optimal culture for flocculant production was achieved after cultivation at 35.5 °C for 72 h at pH 7 ± 0.2, with an inoculum size of 5% (v/v) and sucrose and yeast extract as carbon and nitrogen sources. The maximum flocculating activity was found to be 92.6%. Chemical analysis revealed that the pure bioflocculant consisted of 79.08% carbohydrates and 15.4% proteins. The average molecular weight of the bioflocculant was calculated to be 5.13 × 10⁵ Da. Infrared spectrometric analysis showed the presence of carboxyl (COO-), hydroxyl (-OH), and amino (-NH₂) groups, polysaccharides and proteins. The bioflocculant QZ-7 exhibited a wide pH stability range from 4 to 7, with a flocculation activity of 85% at pH 7 ± 0.2. In addition, QZ-7 was thermally stable and retained more than 80% of its flocculating activity after being heated at 80 °C for 30 min. SEM analysis revealed that QZ-7 exhibited a clear crystalline brick-shaped structure. After treating wastewater, the bioflocculant QZ-7 showed significant flocculation performance with a COD removal efficiency of 93%, whereas a BOD removal efficiency of 92.4% was observed in the B. salmalaya strain 139SI. These values indicate the promising applications of the bioflocculant QZ-7 in wastewater treatment.

Investigation of poly(γ-glutamic acid) production via online determination of viscosity and oxygen transfer rate in shake flasks

BACKGROUND

Poly(γ-glutamic acid) (γ-PGA) is a biopolymer with many useful properties making it applicable for instance in food and skin care industries, in wastewater treatment, in biodegradable plastics or in the pharmaceutical industry. γ-PGA is usually produced microbially by different Bacillus spp. The produced γ-PGA increases the viscosity of the fermentation broth. In case of shake flask fermentations, this results in an increase of the volumetric power input. The power input in shake flasks can be determined by measuring the torque of an orbitally rotating lab shaker. The online measurement of the volumetric power input enables to continuously monitor the formation or degradation of viscous products like γ-PGA. Combined with the online measurement of the oxygen transfer rate (OTR), the respiration activity of the organisms can be observed at the same time.

RESULTS

Two different Bacillus licheniformis strains and three medium compositions were investigated using online volumetric power input and OTR measurements as well as thorough offline analysis. The online volumetric power input measurement clearly depicted changes in γ-PGA formation due to different medium compositions as well as differences in the production behavior of the two investigated strains. A higher citric acid concentration and the addition of trace elements to the standard medium showed a positive influence on γ-PGA production. The online power input signal was used to derive an online viscosity signal which was validated with offline determined viscosity values. The online measurement of the OTR proved to be a valuable tool to follow the respiration activity of the cultivated strains and to determine its reproducibility under different cultivation conditions.

CONCLUSIONS

The combination of the volumetric power input and the OTR allows for an easy and reliable investigation of new strains, cultivation conditions and medium compositions for their potential in γ-PGA production. The power input signal and the derived online viscosity directly reflect changes in γ-PGA molecular weight and concentration, respectively, due to different cultivation conditions or production strains.

Draft Genome Sequence of Bacillus subtilis subsp. natto Strain CGMCC 2108, a High Producer of Poly-γ-Glutamic Acid

Here, we report the 4.1-Mb draft genome sequence of Bacillus subtilis subsp. natto strain CGMCC 2108, a high producer of poly-γ-glutamic acid (γ-PGA). This sequence will provide further help for the biosynthesis of γ-PGA and will greatly facilitate research efforts in metabolic engineering of B. subtilis subsp. natto strain CGMCC 2108.

Statistical optimization of harvesting Chlorella vulgaris using a novel bio-source, Strychnos potatorum

The present study was aimed at harvesting microalga, Chlorella vulgaris, by bioflocculation using seed powder of clearing nut, Strychnos potatorum. The research was essentially the prime step to yield a large biomass for utilising the cells in biodiesel production. Optimization of the parameters influencing bioflocculation was carried out statistically using RSM. The optimized conditions were 100 mg L^-1 bioflocculant concentration, 35 °C temperature, 150 rpm agitation speed and 30 min incubation time and resulted in a maximum efficiency of 99.68%. Through cell viability test, using Trypan blue stain, it was found that cells were completely intact when treated with bioflocculant, but destroyed when exposed to chemical flocculant, alum. The overall study represented that S. potatorum could potentially be a bioflocculant of microalgal cells and a promising substitute for expensive and hazardous chemical flocculants. Moreover, this bioflocculant demonstrated their utility to harvest microalgal cells by economically, effectively and in an ecofriendly way.

Poly-γ-glutamic acid produced from Bacillus licheniformis CGMCC 2876 as a potential substitute for polyacrylamide in the sugarcane industry

As an environmentally friendly and industrially useful biopolymer, poly-γ-glutamic acid (γ-PGA) from Bacillus licheniformis CGMCC 2876 was characterized by the high-resolution mass spectrometry and (1)H NMR. A flocculating activity of 11,474.47 U mL(-1) obtained with γ-PGA, and the effects of carbon sources, ions, and chemical properties (D-/L-composition and molecular weight) on the production and flocculating activity of γ-PGA were discussed. Being a bioflocculant in the sugar refinery process, the color and turbidity of the sugarcane juice was IU 1,877.36 and IU 341.41 with 0.8 ppm of γ-PGA, respectively, which was as good as the most widely used chemically synthesized flocculant in the sugarcane industry--polyacrylamide with 1 ppm. The γ-PGA produced from B. licheniformis CGMCC 2876 could be a promising alternate of chemically synthesized flocculants in the sugarcane industry.

Exploration on bioflocculation of Nannochloropsis oculata using response surface methodology for biodiesel production

Harvesting of algal biomass in biodiesel production involves high energy input and cost incurred process. In order to overcome these problems, bioflocculation process was employed and the efficiency of this process was further improved by the addition of a cationic inducer. In this work marine Bacillus subtilis was used for bioflocculation of Nannochloropsis oculata and ZnCl2 as cationic inducer. This study worked under the principle of divalent cationic bridging (DCB) theory. Under temperature stress and high pH, the bacterium produced exopolysaccharide that bound with microalga Nannochloropsis oculata and flocculated them. A maximum efficiency of 95.43% was observed with the optimised RSM parameters-temperature 30.78°C, pH 10.8, flocculation time 6.7 h, bioflocculant size 0.38 mL, and cationic inducer concentration 0.035 mM. The present investigation focused on the cost effective harvesting of microalga on a larger scale for biodiesel production than using toxic, ecofriendly chemical flocculants.

Microbial production and chemical transformation of poly-γ-glutamate

Poly-γ-glutamate (PGA), a novel polyamide material with industrial applications, possesses a nylon-like backbone, is structurally similar to polyacrylic acid, is biodegradable and is safe for human consumption. PGA is frequently found in the mucilage of natto, a Japanese traditional fermented food. To date, three different types of PGA, namely a homo polymer of D-glutamate (D-PGA), a homo polymer of L-glutamate (L-PGA), and a random copolymer consisting of D- and L-glutamate (DL-PGA), are known. This review will detail the occurrence and physiology of PGA. The proposed reaction mechanism of PGA synthesis including its localization and the structure of the involved enzyme, PGA synthetase, are described. The occurrence of multiple carboxyl residues in PGA likely plays a role in its relative unsuitability for the development of bio-nylon plastics and thus, establishment of an efficient PGA-reforming strategy is of great importance. Aside from the potential applications of PGA proposed to date, a new technique for chemical transformation of PGA is also discussed. Finally, some techniques for PGA and its derivatives in advanced material technology are presented.

Production of ultra-high molecular weight poly-γ-glutamic acid with Bacillus licheniformis P-104 and characterization of its flocculation properties

A novel strain of Bacillus licheniformis P-104 was isolated from Chinese soybean paste to produce a bioflocculant. The bioflocculant was confirmed as ultra-high molecular weight poly-γ-glutamic acid (γ-PGA) using Fourier transform infrared spectrum, high-performance liquid chromatography, and gel permeation chromatography with multi-angle laser light scattering. The production technology and flocculation properties of γ-PGA were investigated. By fed-batch fermentation in a 7-L bioreactor, the maximum γ-PGA yield reached 41.6 g L(-1) with a productivity rate of 1.07 g L(-1) h(-1). The flocculating activity of γ-PGA for kaolin suspension was 33.5±1.6 1/OD under the optimized flocculation conditions (6 mM Ca(2+), 1.5 mg L(-1) γ-PGA, and pH 6.0). The optimized dosage of γ-PGA for flocculation was just about 30 % of that of reported γ-PGA produced by other strains. Moreover, the flocculation activity of γ-PGA produced by strain P-104 was much higher than commercial γ-PGA with the molecular weight ranging 200-500 kDa and 1,500-2,500 kDa. This study provided a promising strain and an efficient method for production of ultra-high molecular weight γ-PGA which could be used as a potential green bioflocculant.

Harvesting of microalgae by flocculation with poly (γ-glutamic acid)

In an effort to search for an efficient and environmentally friendly harvesting method, a commercially available microbial flocculant poly (γ-glutamic acid) (γ-PGA) was used to harvest oleaginous microalgae. Conditions for flocculation of marine Chlorella vulgaris and freshwater Chlorella protothecoides were optimized by response surface methodology (RSM) and determined to be 22.03 mg L(-1) γ-PGA, 0.57 g L(-1) biomass, and 11.56 g L(-1) salinity, and 19.82 mg L(-1) γ-PGA and 0.60 g L(-1) biomass, respectively. Application of the two optimized flocculation methods to Nannochloropsis oculata LICME 002, Phaeodactylum tricornutum, C. vulgaris LICME 001, and Botryococcus braunii LICME 003 gave no less than 90% flocculation efficiency and a concentration factor greater than 20. Micrographs of the harvested microalgal cells showed no damage to cell integrity, and hence no lipid loss during the process. The results show that flocculation with γ-PGA is feasible for harvesting microalgae for biodiesel production.

Removal of Cr(III), Ni(II) and Cu(II) by poly(γ-glutamic acid) from Bacillus subtilis NX-2

Poly(gamma-glutamic acid) (gamma-PGA) derived from Bacillus subtilis NX-2 was investigated as a sorbent for heavy metal ions in batch adsorption experiments. The results showed that the heavy metal adsorption capacity of gamma-PGA enhanced with the increase of pH, in the following order: Cr(III) > Cu(II) > Ni(II), within the pH range 3-5. The Langmuir sorption model effectively described the metal sorption of y-PGA through the experiments of isotherm sorption, and it was deduced that the affinity of gamma-PGA for metals was following the sequence: Cr(III) > Cu(II) > Ni(II). Gamma-PGA was also used to trap trace amounts of heavy metals from the electroplating wastewater, which were difficult to be entirely removed by the traditional hydroxide precipitation method. The results showed that Cr(III) and Ni(II) in the electroplating effluent decreased from 3.07 and 9.46 mg/l to 0.15 and 1.01 mg/l, respectively, and the treated solutions reached the effluent standard. Therefore, gamma-PGA is satisfactory as a well biosorbent for the removal of heavy metals. The adsorption mechanism of gamma-PGA binding heavy metals was also studied using HyperChem simulation and FT-IR.

Studies on bioflocculant production by Arthrobacter sp. Raats, a freshwater bacteria isolated from Tyume River, South Africa

A bioflocculant-producing bacteria was isolated from Tyume River in the Eastern Cape Province, South Africa and identified by 16S rRNA gene nucleotide sequence to have 91% similarity to Arthrobacter sp. 5J12A, and the nucleotide sequence was deposited in GenBank as Arthrobacter sp. Raats (accession number HQ875723). The bacteria produced an extracellular bioflocculant when grown aerobically in a production medium containing glucose as sole carbon source and had an initial pH of 7.0. Influences of carbon, nitrogen and metal ions sources, as well as initial pH on flocculating activity were investigated. The bacteria optimally produced the bioflocullant when lactose and urea were used as sole sources of carbon and nitrogen respectively with flocculating activities of 75.4% and 83.4% respectively. Also, the bacteria produced the bioflocculant optimally when initial pH of the medium was 7.0 (flocculating activity 84%), and when Mg(2+) was used as cation (flocculating activity 77%). Composition analyses indicated the bioflocculant to be principally a glycoprotein made up of about 56% protein and 25% total carbohydrate.

Halomonas sp. OKOH--a marine bacterium isolated from the bottom sediment of Algoa Bay--produces a polysaccharide bioflocculant: partial characterization and biochemical analysis of its properties

A bioflocculant-producing bacterium isolated from seawater was identified based on 16S rRNA gene nucleotide sequence to have 99% similarity to that of Halomonas sp. Au160H and the nucleotide sequence was deposited as Halomonas sp. OKOH (Genbank accession number is HQ875722). Influences of carbon source, nitrogen source, salt ions and pH on flocculating activity were investigated. The bioflocculant was optimally produced when glucose (87% flocculating activity) and urea (88% flocculating activity) were used as sources of carbon and nitrogen, respectively. Also, initial pH of 7.0 and Ca²⁺ supported optimal production of the bioflocculant with flocculating activities of 87% respectively. Chemical analyses revealed the bioflocculant to be a polysaccharide.

Flocculating performances of exopolysaccharides produced by a halophilic bacterial strain cultivated on agro-industrial waste

This study reports the first systematic investigation of the flocculation dynamics of exopolysaccharides (EPSs) produced by a halophilic bacterial strain grown on pretreated molasses as fermentation substrate. The potential use of these EPSs as an easily biodegradable, natural alternative for synthetic polyelectrolytes which are widely used and contain toxic and carcinogenic monomers was investigated. Flocculating activities of the EPS samples in synthetic water, synthetic sea water and natural sea water media which were used as model raw waters were monitored via the Photometric Dispersion Analyser (PDA 2000) instrument and removals were determined by measuring residual turbidities. One of the six EPS specimens, which formed the largest flocs thus performed highest turbidity removal, exhibited flocculation performance and particle removal efficiency comparable with commercial cationic, nonionic and anionic synthetic polyelectrolytes.

Using Ruditapes philippinarum conglutination mud to produce bioflocculant and its applications in wastewater treatment

A novel bioflocculant-producing bacterium, ZHT4-13, was isolated from Ruditapes philippinarum conglutination mud. By biomicroscope morphological observation, 16S rDNA sequence identification and physiological and biochemical characteristics, strain ZHT4-13 was identified as Rothia sp. The bioflocculant MBF4-13 produced by strain ZHT4-13 had a flocculating efficiency of 86.22% for 5 g L(-1) Kaolin clay suspension when the initial pH was 9 and the temperature was 20 degrees C. It had flocculating effect in a wide range, pH 1-13 and temperature 4-100 degrees C. Analysis of MBF4-13 by UV-Vis spectrophotometer, Fourier-transform infrared spectrophotometer (FT-IR) and (1)H nuclear magnetic resonance (NMR) indicated that the main component of MBF4-13 is polysaccharide. The culture conditions to produce strain ZHT4-13 were optimized with orthogonal design of experiments. MBF4-13 had high efficiency in decolorizing dye solutions, had some abilities to remove heavy metal ions (Cr(2)O(7)(2-), Ni(2+)) and improve performance of activated sludge.

Characteristics of extracellular polymeric substances (EPS) fractions from excess sludges and their effects on bioflocculability

Extracellular polymeric substances (EPS) of biological origin are ubiquitous in excess sludges and can be applied as an underlying bioflocculant, owing to their high content of macromolecules and cations. However, low flocculating activity limits the feasibility of their practical applications. This study provides a novel EPS fractionation approach to improve their flocculability by extracting an active EPS fraction and removing the others with low flocculability. The results showed that for two excess sludges (called sludge A and sludge B), the tightly bound EPS (TB-EPS) fraction possessed a high flocculating rate to kaolin suspension compared with the other EPS fractions [i.e., supernatant, slime, and loosely bound EPS (LB-EPS) fraction] (>54.1+/-1.4% vs <7.8+/-1.6%). High bioflocculability of TB-EPS fraction could be attributable to high contents of macromolecules (330-1200 kDa) and trivalent cations (Fe(3+) and Al(3+)). Further investigation reveals that the TB-EPS fraction caused aggregation of particles by bridging and sweep flocculation.

Microbial Biosynthesis of Polyglutamic Acid Biopolymer and Applications in the Biopharmaceutical, Biomedical and Food Industries

This review article provides an updated critical literature review on the production and applications of Polyglutamic Acid (PGA). alpha-PGA is synthesized chemically, whereas gamma-PGA can be produced by a number of microbial species, most prominently various Bacilli. Great insight into the microbial formation of gamma-PGA has been gained thanks to the development of molecular biological techniques. Moreover, there is a great variety of applications for both isoforms of PGA, many of which have not been discovered until recently. These applications include: wastewater treatment, food products, drug delivery, medical adhesives, vaccines, PGA nanoparticles for on-site drug release in cancer chemotherapy, and tissue engineering.

Characterization of a bioflocculant from a newly isolated Vagococcus sp. W31

Screening of microorganisms producing flocculating substances was carried out. A strain secreting a large amount of bioflocculant was isolated from wastewater samples collected from the Little Moon River in Beijing. Based on the morphological properties and 16S rDNA sequence analysis, the isolate (designated W31) was classified as Vagococcus sp. A bioflocculant (named MBFW31) produced by W31 was extracted from the culture broth by ethanol precipitation and purified by gel chromatography. MBFW31 was heat-stable and had strong flocculating activity in a wide range of pH with relatively low dosage requirement. MBFW31 was identified as a polysaccharide with molecular weight over 2 x 10(6). It contained neutral sugar and uronic acid as its major and minor components, respectively. Infrared spectra showed the presence of hydroxyl, carboxyl and methoxyl group in its molecules. The present results suggested that MBFW31 had potential application in wastewater treatment.

Production of a bioflocculant by Aspergillus parasiticus and its application in dye removal

Aspergillus parasiticus was found to produce a bioflocculant with high flocculating activity for Kaolin suspension and water-soluble dyes. Results showed that the carbon and nitrogen sources favorable for the production of the bioflocculant were corn starch and peptone, and an optimal condition of 28 degrees C, initial pH 5-6 and shaking speed of 150 rpm. The highest flocculating efficiency achieved for Kaolin suspension was 98.1%, after 72 h cultivation. The bioflocculant was mainly composed of sugar (76.3%) and protein (21.6%), and an average molecular weight of 3.2x10(5) Da. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectra showed that amino, amide and hydroxyl groups were present in the bioflocculant molecules. The bioflocculant was effective in flocculating some soluble anionic dyes in aqueous solution, in particular Reactive Blue 4 and Acid Yellow 25 with a decolorization efficiency of 92.4 and 92.9%, respectively. The decolorization efficiency was dependent on the flocculant dosage and solution pH. XPS result shows that the amine groups in the bioflocculant were protonated at pH 5, and thus the positive bioflocculant was attracted to the negatively charged dye molecules. The amino and amide groups in the bioflocculant molecule are believed to play an important role in flocculation from the viewpoint of electrostatic interaction.

Flocculating activity of cross-linked poly-γ-glutamic acid against bentonite and Escherichia coli suspension pretreated with FeCl3 and its interaction with Fe3+

Cross-linked poly-gamma-glutamic acid (C-L gamma-PGA) at 5 microg/ml flocculated bentonite suspension pretreated with polyaluminum chloride (PAC) at 2 microg/ml Al3+-PAC to a transparency of approximately 30% after 30 min and more than 90% after 4 h, while Al3+ concentration in the upper phase of the suspension decreased with incubation time. When pretreated with FeCl3 at 16 microg/ml Fe3+-FeCl3, similar results were obtained. In the case of Escherichia coli suspension, the combination of C-L gamma-PGA and FeCl3 demonstrated a more marked flocculating activity with a satisfactory transparency occurring after 30 min of treatment, accompanied by a decrease in residual Fe3+ concentration. In the above two suspensions pretreated with FeCl3, small visible floats appeared in the early stage of incubation. These floats were found to be due to the direct interaction between FeCl3 and C-L gamma-PGA, indicating the formation of a water-insoluble complex. After allowing the suspension to stand for a long time, elemental analysis and inductively coupled plasma spectroscopy of the precipitates produced suggested that not only the complex was formed due to the interaction between Fe3+ in FeCl3 and COO- in the C-L gamma-PGA molecule, but also Fe2O3 and Fe(OH)3 might be entrapped in this complex. This could be applied to scavenge metal ions including Fe3+ from polluted water.

Extracellular biopolymeric flocculants. Recent trends and biotechnological importance

Many microorganisms secrete extracellular biopolymeric flocculants (EBFs) in the culture broth. This work reviews the development of EBF research and applications. Aspects discussed include a comparison of the chemical and biological flocculating agents, isolation of EBF-producing microorganisms, culture conditions, mechanisms of flocculation, the chemical structure of EBFs, and the role of physicochemical factors in the flocculating activity.

Flocculation of river silt using chitosan

Flocculation of silt in river water using chitosan was studied in the pH range 4-9, and suspended solid concentrations in the range 20-80 mg/L. Chitosan effectively reduces turbidity due to silt by flocculation and settling. Flocculation efficiency is very sensitive to pH, and reaches a maximum at pH 7. The optimal chitosan concentration required to effect flocculation is 0.5 mg/L and is independent of silt concentration within the range examined. Restabilisation of the suspension is observed at higher concentrations of chitosan, and the amount required for restabilisation increases with increasing concentration of suspended solids. Flocculation is faster at higher concentrations of silt and the flocs are large and fibrous.

The production of poly-(gamma-glutamic acid) from microorganisms and its various applications

This review article deals with the chemistry and biosynthesis of poly-(gamma-glutamic acid) (gamma-PGA) produced by various strains of Bacillus. Potential applications of gamma-PGA as thickener, cryoprotectant, humectant, drug carrier, biological adhesive, flocculant, or heavy metal absorbent, etc. with biodegradability in the fields of food, cosmetics, medicine and water treatments are also reviewed.

Production of a biopolymer flocculant from Bacillus licheniformis and its flocculation properties

Bacillus licheniformis CCRC 12826 produced extracellularly an excellent biopolymer flocculant in a large amount when it was grown aerobically in a culture medium containing citric acid, glutamic acid and glycerol as carbon sources. The biopolymer flocculant was an extremely viscous material with a molecular weight over 2 x 10(6) by gel permeation chromatography. It could be easily purified from the culture medium by ethanol precipitation. It was shown to be a homopolymer of glutamic acid by amino acid analysis and thin layer chromatography and presumed to be poly-glutamic acid (PGA). This bioflocculant efficiently flocculated various organic and inorganic suspensions. It flocculated a suspended kaolin suspension without cations, although its flocculating activity was synergistically stimulated by the addition of bivalent or trivalent cations Ca2+, Fe3+ and Al3+. However, the synergistic effects of metal cations were most effective at neutral pH ranges. The comparison of the flocculating activity between the present biopolymer and a commercial lower molecular weight product showed that the biopolymer of the present study had much higher activity. The high productivity and versatile applications of PGA make its development as a new biodegradable, harmless, biopolymer flocculant economical and advantageous.