Nanomaterials for the control of bacterial blight disease in pomegranate: quo vadis?

Bacterial blight, caused by Xanthomonas axonopodis pv. punicae, Xap is a serious threat to commercially successful pomegranate (Punica granatum L) crop. Owing to the non-availability of disease-resistant varieties of pomegranate, integrated disease management involving change of season, adequate nutrition, and preventive sprays of bactericides is used to control Xap. We undertook a systematic study to assess the efficacy of metal-based nanomaterials (Cu, CuO, ZnO, CaO, MgO) for the control of Xap. The antimicrobial effectiveness was in the order Cu > ZnO > MgO > CuO with MIC (minimum inhibitory concentration) 2.5, 20, 190, 200, and 1600 μg/ml. A time-to-kill curve indicated that Cu nanoparticles (CuNPs) killed Xap cells within 30 min at 2.5 μg/ml. Under controlled conditions (polyhouse), foliar application of CuNPs (400 μg/ml) resulted in ~ 90 and ~ 15% disease reduction in 6-month-old infected plants at early (disease severity 10%) and established (disease severity 40%) stages of infection, respectively. In a subsequent field study on severely infected 7-year-old plants, applications of nanoparticles reduced the disease incidence by ~ 20% as compared to untreated control. Microscopic observations revealed that CuNPs reduced the bacterial colonization of the leaf surface. Anti-Xap activity of foliar applied CuNPs was on par with conventionally used copper oxychloride (3000 μg/ml) albeit at 8-fold reduced copper concentration. Thus, early disease detection and application of effective dosage of copper nanoparticles can indeed help the farmer in achieving rapid infection control. Further studies on use of combinations of nanoparticles for management of bacterial blight are warranted.

Transcriptome analysis of silver nanoparticles treated Staphylococcus aureus reveals potential targets for biofilm inhibition

The biofilms of Staphylococcus aureus on the implanted materials and chronic wounds are life-threatening and are a substantial financial burden on the healthcare system. Silver nanoparticles (SNP), known for their multi-level physiological effects in planktonic cells could be a promising agent in the treatment of biofilm-related infections also. To gain insight into the effects of SNP on various physiological processes in biofilms we studied the transcriptome of Staphylococcus aureus ATCC 29213. To distinguish between 'nanoparticles-specific' and 'ion-specific' effect of silver, we performed a comparative analysis of the functional genes in response to Ag⁺. As compared to untreated biofilms, 21% (i.e. 629 genes) and 28.5% (i. e. 830 genes) of the total functional coding genes were differentially regulated upon exposure to SNP and Ag⁺. Genes encoding capsular polysaccharides, intercellular adhesion, virulence were downregulated in SNP and Ag⁺ treated biofilms. Genes involved in carbohydrate, protein metabolism including DNA and RNA synthesis, oxidative stress etc. were differentially expressed. Further, activation of efflux pumps and multidrug export proteins was observed, which clearly indicates the presence of metal stress resistance determinants in S. aureus. Silver blocked the integration of mobile genetic elements in S. aureus genome. Our study points out quorum sensing and virulence determinants as possible targets for inhibition of biofilms possibly with/without existing antibiotics. However, further studies on these aspects are warranted. Scanning electron microscopy (SEM) and confocal microscopy revealed changes in biofilm morphology, architecture and thickness in presence of silver nanoparticles and ionic silver, substantiating the transcriptome data.

Applications of bacterial cellulose and its composites in biomedicine

Bacterial cellulose produced by few but specific microbial genera is an extremely pure natural exopolysaccharide. Besides providing adhesive properties and a competitive advantage to the cellulose over-producer, bacterial cellulose confers UV protection, ensures maintenance of an aerobic environment, retains moisture, protects against heavy metal stress, etc. This unique nanostructured matrix is being widely explored for various medical and nonmedical applications. It can be produced in various shapes and forms because of which it finds varied uses in biomedicine. The attributes of bacterial cellulose such as biocompatibility, haemocompatibility, mechanical strength, microporosity and biodegradability with its unique surface chemistry make it ideally suited for a plethora of biomedical applications. This review highlights these qualities of bacterial cellulose in detail with emphasis on reports that prove its utility in biomedicine. It also gives an in-depth account of various biomedical applications ranging from implants and scaffolds for tissue engineering, carriers for drug delivery, wound-dressing materials, etc. that are reported until date. Besides, perspectives on limitations of commercialisation of bacterial cellulose have been presented. This review is also an update on the variety of low-cost substrates used for production of bacterial cellulose and its nonmedical applications and includes patents and commercial products based on bacterial cellulose.

Hydrothermal synthesis and characterization of carbon nanospheres: a mechanistic insight

SEM and PL for CNS synthesized for 4 h by hydrothermal reaction of glucose.

Radio frequency induced hyperthermia mediated by dextran stabilized LSMO nanoparticles: in vitro evaluation of heat shock protein response

Dextran stabilized La(0.7)Sr(0.3)MnO(3) (Dex-LSMO) is an alternative cancer hyperthermia agent holding considerable promise. Here, we have carried out a comparative study on radio frequency (~264 kHz) induced Dex-LSMO mediated heating and extraneous heating (mimicking generalized hyperthermia) in terms of changes in the morphology, proliferation pattern and induction of heat shock proteins in a human melanoma cell line (A375). Our results clearly show that the cellular effects seen with extraneous heating (60 min at 43 °C) could be reproduced by just six minutes of radio frequency induced Dex-LSMO mediated heating. More importantly, the observed enhanced levels of HSP 70 and 90 (molecular markers of heat shock that trigger favorable immunological reactions) seen with Dex-LSMO mediated heating were comparable to extraneous heating. These results suggest the possible utility of Dex-LSMO as a cancer hyperthermia agent.

Flocculation of dimorphic yeast Benjaminiella poitrasii is altered by modulation of NAD-glutamate dehydrogenase

A strategy to control flocculation is investigated using dimorphic yeast, Benjaminiella poitrasii as a model. Parent form of this yeast (Y) exhibited faster flocculation (11.1 min) than the monomorphic yeast form mutant Y-5 (12.6 min). Atomic force microscopy revealed higher surface roughness of Y (439.34 rms) than Y-5 (52 rms). Also, the former had a zeta potential of -65.97+/-3.45 as against -50.21+/-2.49 for the latter. Flocculation of both Y and Y-5 could be altered by supplementing either substrates or inhibitor of NAD-glutamate dehydrogenase (NAD-GDH) in the growth media. The rate of flocculation was promoted by alpha-ketoglutarate or isophthalic acid and decelerated by glutamate with a statistically significant inverse correlation to corresponding NAD-GDH levels. These interesting findings open up new possibilities of using NAD-GDH modulating agents to control flocculation in fermentations for easier downstream processing.

Hydrazine based facile synthesis and ordered assembly of metal nanoparticles (Au, Ag) on a bacterial surface layer protein template

An efficient and facile procedure is developed for concurrent in situ synthesis and ordered assembly of metal nanoparticles on a periodic two dimensional protein array. The S-layer protein of Bacillus subtilis exhibiting uniform pore size is used as template. Synthesis of gold and silver nanoparticles anchoring on the pores of S-layer is achieved by chemical reduction of respective metal salt laden protein template. Transmission electron microscopy reveals formation of well ordered and separated gold and silver nanoparticles with an average diameter of 6 +/- 1 nm and 4 +/- 1 nm, respectively. The periodic arrangement of nanoparticles is dictated by the native structure of S-layer protein array as the nanoparticle locations are found to be correlated to the nanosized pores of the crystalline S-layer array.

Biodegradation of γ-hexachlorocyclohexane (Lindane) by a non-white rot fungus conidiobolus 03-1-56 isolated from litter

Biodegradation of chlorinated pesticide γ-hexachlorocyclohexane (lindane) by a nonwhite rot fungus Conidiobolus 03-1-56 is reported for the first time. Conidiobolus 03-1-56, a phycomyceteous fungus isolated from litter, completely degraded lindane on the 5th day of incubation in the culture medium, and GC-ECD studies confirmed that lindane removal did not occur via adsorption on the fungal biomass. Degradation studies using different medium compositions showed that nitrogen/carbon limiting conditions (stress conditions) and presence of veratryl alcohol, induced the secretion of extracellular oxidative enzymes, which enhanced the rate of lindance biodegradation. Under optimum nutrient-limiting conditions, GC-ECD and GC-MS analysis showed complete absence of any degradation metabolite, indicating that lindane was completely mineralized. Assays for tannic acid utilization and lignin peroxidase showed similar enzymatic profiles between Conidiobolus 03-1-56 and standard white rot fungi Pleurotus ostreatus 1200 and Trametes versicolor 1086. Although Conidiobolus 03-1-56 showed a reduced enzyme activity compared to white rot fungi, preliminary evidence indicates that enzymes responsible for lignin degradation by white rots play a key role in lindane degradation by Conidiobolus 03-1-56.

Taguchi approach significantly increases bioremediation process efficiency: a case study with Hg (II) removal by Pseudomonas aeruginosa

AIM

Optimization of process parameters for mercury removal by an Hg (II)-reducing Pseudomonas aeruginosa strain.

METHODS AND RESULTS

A strain of Ps. aeruginosa was found to reduce 10 mg l(-1) Hg (II) to Hg0 with 70% efficiency in 24 h. To optimize process performance, a statistical tool--Taguchi design of experiments (DOE)--was used to carry out 18 well-defined experiments (L18 Orthogonal array) with eight variable parameters (viz. agitation, temperature, pH, carbon source, medium volume: flask volume ratio and concentrations of Hg (II), ammonium sulfate and yeast extract). When data obtained were analyzed using specialized software for Taguchi design, Qualitek-4 (Nutek Inc., MI, USA), Hg (II) reduction efficiency was predicted to be 95% in 24 h under the optimized process parameters (also suggested by the software). In the validation experiment, Hg (II) removal of 99.29% in 24 h was indeed obtained.

CONCLUSIONS

Using Taguchi DOE, Hg (II) reduction (and hence its removal) using Ps. aeruginosa could be improved by 29.3%.

SIGNIFICANCE AND IMPACT OF THE STUDY

Taguchi approach could be employed as an efficient and time-saving strategy for parameter optimization in bioremediation processes.

Arsenic (III) oxidizing Microbacterium lacticum and its use in the treatment of arsenic contaminated groundwater

AIMS

To develop a microbially-assisted process for the removal of arsenic from contaminated groundwater.

METHODS AND RESULTS

A culture of Microbacterium lacticum oxidizing up to 50 mmol l(-1) arsenic (III) was isolated from municipal sewage by an enrichment culture technique. Using culture immobilized on brick pieces and packed in a glass column, complete oxidation of As (III) from groundwater could be quickly achieved at neutral pH and ambient temperature with methanol as substrate. The oxidized As species were removed from groundwater using three different methods: zero valent iron, activated charcoal and ferric chloride.

CONCLUSIONS

The oxidation of groundwater As (III) by a M. lacticum-immobilized column, followed by its removal using activated carbon, could be an efficient method for the treatment of As (III)-contaminated groundwater.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study will be useful in developing a combined microbiological-chemical process for treating arsenic-contaminated groundwater.

Microbial synthesis of semiconductor CdS nanoparticles, their characterization, and their use in the fabrication of an ideal diode

Cadmium sulfide nanoparticles were synthesized intracellularly by a Schizosaccharomyces pombe strain when challenged with 1 mM cadmium in solution. The nanoparticles, a known semiconducting material, exhibited an absorbance maximum at 305 nm. X-ray scattering data showed that the nanoparticles had a Wurtzite (Cd(16)S(20))-type hexagonal lattice structure and most of the nanoparicles were in the size range of 1-1.5 nm. The nanoparticles were used in the fabrication of a heterojunction with poly (p-phenylenevinylene). The diode exhibited approximately 75 mA/cm(2) current at 10 V when forward biased and the breakdown occurred at approximately 15 V in the reverse biased mode. These characteristics are considered ideal for a diode.

Comparative studies on metal biosorption by two strains of Cladosporium cladosporioides

Two strains of a fungus, Cladosporium cladosporioides 1 and C. cladosporioides 2 showed different metal biosorption properties. Strain 1 showed preferential sorption of gold and silver, while strain 2 could bind metals such as copper and cadmium in addition to gold and silver. Strain 1 had a cell-wall hexosamine content of 0.1%. X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red spectroscopy (FTIR) analyses indicated that nitrogen was not involved in metal biosorption by the strain. In strain 2 the cell-wall hexosamine content was 150 times that of strain 1. These results indicated that hexosamine was responsible for non-specific metal binding while cell-wall polymers other than hexosamines had a role in conferring selectivity in precious-metal binding.

Biodetoxification of silver-cyanide from electroplating industry wastewater

A bacterial consortium capable of utilizing metal-cyanides as a source of nitrogen was used to develop a microbiological process for the detoxification of silver-cyanide from electroplating wastewater. When the treatment was carried out in a 27-l rotating biological contactor (R3C) in continuous mode, the system could achieve > 99.5% removal of 0.1 mmol l(-1) silver-cyanide (approximately 5 mg l(-1) cyanide and 10 mg l(-1) silver) in 10 h with sugarcane molasses (0.1 ml l(-1)) as carbon source. The silver ions set free during biodegradation were efficiently adsorbed by the bacterial biomass. The RBC-treated effluent was found to be safe for discharge into the environment, as confirmed by chemical analysis and fish bioassay studies.

Comparative performance of pearl millet- and sorghum- based diets vs. wheat- and rice-based diets for trace metal bioavailability

Pearl millet and sorghum offer a cheap source of energy compared to wheat and rice and are widely consumed by rural communities in many parts of the world. Due to the low consumption of vegetables and animal foods, millets also are the major suppliers of micronutrients especially for low-income groups. It is of prime importance to study how millets perform in terms of bioavailable contents of trace metals. Investigations were carried out using weanling mice which offer a model for the initial testing of bioavailability of trace metals before human trials. Four isocaloric diets differing only in the type of cereal, i.e. pearl millet, sorghum, wheat and rice, were prepared representing habitual dietary patterns observed by National Nutrition Monitoring Bureau (NNMB) of India. Mice were allocated randomly to 4 groups of 8 mice each, and housed individually in metal free metabolic cages. A fifth group of 8 mice fed a balanced synthetic diet served as control. All the groups were fed ad libitum. The absorption of zinc and iron averaged for 3 periods of 5 days each was significantly higher for the wheat and pearl millet group than for the other 2 experimental groups (p < 0.05), as were also the levels of liver zinc and iron. The weight gain was also highest (6.9 +/- 1.2 g) in the pearl millet group as compared to sorghum (1.58 +/- 0.59 g), wheat (1.66 +/- 1.27 g) and rice (-0.72 +/- 0.62 g) groups. The levels of liver copper were comparable in all the 5 groups. These results further confirm our earlier in vitro results indicating the superiority of pearl millet but not sorghum in bioavailability of zinc and iron.

Biosorption of lead, cadmium, and zinc by Citrobacter strain MCM B-181: characterization studies

The biosorption process for removal of lead, cadmium, and zinc by Citrobacter strain MCM B-181, a laboratory isolate, was characterized. Effects of environmental factors and growth conditions on metal uptake capacity were studied. Pretreatment of biomass with chemical agents increased cadmium sorption efficiency; however, there was no significant enhancement in lead and zinc sorption capacity. Metal sorption by Citrobacter strain MCM B-181 was found to be influenced by the pH of the solution, initial metal concentration, biomass concentration, and type of growth medium. The metal sorption process was not affected by the age of the culture or change in temperature. Equilibrium metal sorption was found to fit the Langmuir adsorption model. Kinetic studies showed that metal uptake by Citrobacter strain MCM B-181 was a fast process, requiring <20 min to achieve >90% adsorption efficiency. The presence of cations reduced lead, zinc, and cadmium sorption to the extent of 11. 8%, 84.3%, and 33.4%, respectively. When biomass was exposed to multimetal solutions, metals were adsorbed in the order Co2+ < Ni2+ < Cd2+ < Cu2+ < Zn2+ < Pb2+. Among various anions tested, only phosphate and citrate were found to hamper metal sorption capacity of cells. Biosorbent beads prepared by immobilizing the Citrobacter biomass in polysulfone matrix exhibited high metal loading capacities. A new mathematical model used for batch kinetic studies was found to be highly useful in prediction of experimentally obtained metal concentration profiles as a function of time. Metal desorption studies indicated that Citrobacter beads could, in principle, be regenerated and reused in adsorption-desorption cycles. In an expanded scale trial, biosorbent beads were found to be useful in removal/recovery of metals such as lead from industrial wastewaters.

Effect of riboflavin supplementation on zinc and iron absorption and growth performance in mice

Diets prevalent in vegetarian populations using rice and other whole grains as staples with little consumption of yellow vegetables are low in riboflavin. These diets have poor bioavailability of iron and zinc because metals are present as inorganic salts with low solubility. Riboflavin has the capacity to form complexes, and supplementation of riboflavin may result in increased absorption of zinc and iron, thus increasing the cellular transport. Therefore, riboflavin may have direct as well as indirect effects on growth. Using this as the conceptual basis, experiments were conducted on pregnant and lactating mice. Two groups, each of 12 mice (9 females and 3 males), were observed on a low-riboflavin rice-based diet (adequate in all other nutrients), one with and one without supplementation of 10 mg riboflavin/kg diet. There was significant improvement in the growth parameters like percent conception, mean weight gain in pregnancy, mean weight of pups at the age of 21 d, and percentage hemoglobin due to riboflavin supplementation (p < 0.05). Percent zinc absorption, for the low-riboflavin diet, the supplemented diet, and the synthetic control diet were 16.4+/-5.7, 33.7+/-8.9, and 44.6+/-4.0, respectively, indicating the beneficial effect of riboflavin supplementation on iron and zinc utilization.

Effect of nicotinic acid on zinc and iron metabolism

Nicotinic acid has functional groups capable of forming complexes with trace metals. The present study examines the effect of nicotinic acid supplementation on absorption and utilization of zinc and iron. In vitro zinc uptake by human erythrocytes was studied using blood samples of 10 healthy subjects. It was found that 8 mumoles nicotinic acid or NADP increased 65Zn uptake by 38.9% and 43.1% in fasting, and by 70.9% and 28.1% in postprandial conditions. In animal experiments, nicotinic acid supplementation to finger millet based diet resulted in significant enhancement of percent zinc absorption, liver zinc and growth of weanling mice (P < 0.05). When mice were fed with nicotinic acid-deficient, -adequate and -excess synthetic diets for four weeks it was observed that, in comparison with the nicotinic acid-deficient diet, percent zinc absorption, intestinal zinc, percent haeomoglobin and liver iron increased significantly under nicotinic acid-adequate and -excess conditions. The results obtained suggested that nicotinic acid, in addition to its known effect on growth and metabolism, may be playing an important role in enhancing zinc and iron utilization.

Biosorption of lead and zinc from solutions using Streptoverticillium cinnamoneum waste biomass

Mycelial wastes of microbial origin from fermentation industries have been recognized as potential biosorbents for decontamination of waste waters containing heavy metals. Dried, nonliving, granulated biomass of Streptoverticillium cinnamoneum was used for the recovery of lead and zinc from solutions. It was found that pretreatment of the biomass with boiling water for 15 min increased the biosorption of lead and zinc by 52 and 41%, respectively. The optimum pH range for lead uptake was 3.5-4.5 while for zinc it was 5.0-6.0. The lead and zinc adsorption data when applied to Freundlich and Langmuir isotherm equations showed good correlation (r2 = 0.97) and hence equal conformity to both models. The Scatchard plots indicated clearly that more than one type of binding sites were involved in the adsorption of lead and zinc by the biomass. The maximum loading capacity of S. cinnamoneum biomass was found to be 57.7 mg/g for lead and 21.3 mg/g for zinc with boiling water pretreatment. The loaded metals could be desorbed effectively with dilute hydrochloric acid, nitric acid and 0.1 M EDTA. Treatment with 0.1 M sodium carbonate permitted reuse of the desorbed biomass although the metal loading capacity in the subsequent cycles decreased by 14-37%. The metal biosorbent granules prepared are a value-added product that has the potential for removal/recovery of lead and zinc from dilute solutions on a commercial scale.

Assessment of pearl millet vs rice based diets for bioavailability of four trace metals

Cereals including millets are consumed in India as a staple with wide variety of pulses and vegetables in varying proportions. Trace mineral contents of pearl millet are two to ten times higher than that of rice. Comparative performance of pearl millet based (PM) diets as against rice based (RB) diets in terms of trace mineral bioavailability was studied, based on the prevailing dietary patterns in India. In vitro percent dialysability of zinc, iron, copper and manganese under simulated gastrointestinal conditions was considered as indicator of metal bioavailability. Dialysable zinc and iron were estimated using 65 Zn and 59 Fe as tracers, while dialysable copper and manganese were measured by Atomic absorption spectrophotometer for 20 food items and 15 RB and 17 PM diets prepared from these items. Results indicated that percent dialysability of zinc and copper was higher for RB diets than PM diets, while that of iron and manganese were comparable. Total dialysable iron, copper and manganese in PM diet was 2 to 4 times higher than RB diet.

Bacterial catalytic processes for transformation of metals

Microorganisms actively participate in the transformation of metals and metalloids by various processes including adsorption, absorption, alkylation, oxidation and reduction reactions. Bacteria of the genera Thiobacillus and Sulfolobus have a chemolithotrophic mode of metabolism and catalyze various metal transformations. These bacteria are primarily involved in oxidation-reduction reactions of metals. Metal sulfides can be either directly oxidized by the microbes or oxidized by ferric iron, an end-product of microbial metabolism. These processes result in solubilization of iron, copper, molybdenum, uranium, and many other metals as well. Bacteria capable of these reactions are found, and they function in a variety of environments. Conditions which favor their growth are acidic pH (1.5 to 3.5) and temperatures which can be as high as 75 degrees C for Sulfolobus. The microbes have potential for mobilization of pollutants, or toxic elements, during resource extraction processes. In the absence of oxygen, iron, molybdenum and chromium may be reduced by microbes.