Lentibacillus saliphilus. sp. nov., a moderately halophilic bacterium isolated from a saltern in Korea.

A novel moderately halophilic bacterial strain, designated YIM 93176T, was isolated from a saltern in Korea and subjected to a polyphasic taxonomic study. This isolate YIM 93176T was observed to grow in the presence of 0-22% (w/v) NaCl and at pH 6.0-10.0 and 10-45 °C; optimum growth was observed with 5-10% (w/v) NaCl and at pH 7.0-9.0 and 28-37 °C. Based on 16S rRNA gene sequences analysis, the nearest relatives were Lentibacillus alimentarius M2024T (96.5% similarity), followed by Virgibacillus carmonensis LMG 20964T (96.0%) and the other type strains of the family Bacillaceae, but phylogenetic analysis indicated that strain YIM 93176T belonged to the cluster comprising type species of the genus Lentibacillus. Genome sequencing of strain YIM 93176T revealed a genome size of 3.2 Mb and a DNA G + C content of 40.5 mol%. The major fatty acids were anteiso-C15:0 (40.7%) and iso-C15:0 (26.4%), while the predominant respiratory quinone was menaquinone 7. The polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. These genotypic and chemotaxonomic characteristics supported affiliation of strain YIM 93176T to the genus Lentibacillus. In addition, phenotypic characteristics could distinguish strain YIM 93176T from its closely related species in genus Lentibacillus. Based on the cumulative evidences from the polyphasic taxonomic study, strain YIM 93176T represents a novel species of the genus Lentibacillus, for which name Lentibacillus saliphilus sp. nov. (type strain YIM 93176T = CCTCC AB 208139T = DSM 21375T) is proposed.

An extended bacterial reductive pyrimidine degradation pathway that enables nitrogen release from ß-alanine.

The reductive pyrimidine catabolic pathway is the most widespread pathway for pyrimidine degradation in bacteria, enabling assimilation of nitrogen for growth. This pathway, which has been studied in several bacteria including Escherichia coli B, releases only one utilizable nitrogen atom from each molecule of uracil, whereas the other nitrogen atom remains trapped in the end product ß-alanine. Here, we report the biochemical characterization of a ß-alanine:2-oxoglutarate aminotransferase (PydD) and an NAD(P)H-dependent malonic semialdehyde reductase (PydE) from a pyrimidine degradation gene cluster in the bacterium Lysinibacillus massiliensis Together, these two enzymes converted ß-alanine into 3-hydroxypropionate (3-HP) and generated glutamate, thereby making the second nitrogen from the pyrimidine ring available for assimilation. Using bioinformatics analyses, we found that PydDE homologs are associated with reductive pyrimidine pathway genes in many Gram-positive bacteria in the classes Bacilli and Clostridia. We demonstrate that Bacillus smithii grows in a defined medium with uracil or uridine as its sole nitrogen source and detected the accumulation of 3-HP as a waste product. Our findings extend the reductive pyrimidine catabolic pathway and expand the diversity of enzymes involved in bacterial pyrimidine degradation.

Efficacy of alkyltrimethylammonium bromide for decontaminating salt-cured hides from the red heat causing moderately halophilic bacteria.

Conventionally, animal hide and skin necessitates 95% saturated brine solution (SBS) for its preservation. This salt is primarily derived from different sources including solar-saltern, evaporation ponds, etc., which are laden with different types of halophilic micro-organisms. Previous studies confirmed that the presence of moderately halophilic bacteria caused red heat on cured hide, which adversely affects the leather quality and causes substantial economic losses for leather industries. Thus, this investigation was carried out to examine the effects of different concentrations of alkyltrimethylammonium bromide (ATMB) on selected halophilic-bacteria attributed to the deterioration of hide quality. In nutrient broth solution (NBS), ATMB at 250 and 500 ppm reduced individual halo-bacteria, that is, Halomonas halodenitrificans, Halomonas eurihalina, Alkalibacillus haloalkaliphilus and Salimicrobium album, by averages of 0·64 and 1·90, 1·5 and 2·61, 0·90 and 2·27, 1·65 and 3·36 log CFU per ml respectively in 5 min. ATMB treatment in SBS at 500 ppm for 18 h resulted in a reduction of H. halodenitrificans, H. eurihalina, A. haloalkaliphilus and S. album by averages of 1·9, 1·25, 0·96 and 1·34 log CFU per ml respectively, when compared with the controls. Likewise, 5000 ppm ATMB reduced the cocktail population nearly to zero from that cultivated in SBS for 18 h. SIGNIFICANCE AND IMPACT OF THE STUDY: In this investigation, the inhibition of different halophilic bacteria that causes red heat in salt-preserved hides is described for the first time. The antimicrobial susceptibility test executed via solution procedures for selected halophilic bacterial strains (i.e. resistant to the salt environment) revealed significant efficacy of alkyltrimethylammonium bromide (ATMB). The current study suggests that, chemical compound like ATMB could be utilized to prevent red heat-related damage on salt-cured hides caused by halophilic bacteria, which is a persisting concern of the leather industry.

Time-Course Transcriptome of Parageobacillus thermoglucosidasius DSM 6285 Grown in the Presence of Carbon Monoxide and Air.

Parageobacillus thermoglucosidasius is a metabolically versatile, facultatively anaerobic thermophile belonging to the family Bacillaceae. Previous studies have shown that this bacterium harbours co-localised genes coding for a carbon monoxide (CO) dehydrogenase (CODH) and Ni-Fe hydrogenase (Phc) complex and oxidises CO and produces hydrogen (H2) gas via the water-gas shift (WGS) reaction. To elucidate the genetic events culminating in the WGS reaction, P. thermoglucosidasius DSM 6285 was cultivated under an initial gas atmosphere of 50% CO and 50% air and total RNA was extracted at ~8 (aerobic phase), 20 (anaerobic phase), 27 and 44 (early and late hydrogenogenic phases) hours post inoculation. The rRNA-depleted fraction was sequenced using Illumina NextSeq, v2.5, 1x75bp chemistry. Differential expression revealed that at 8 vs 20, 20 vs 27 and 27 vs 44 hours post inoculation, 2190, 2118 and 231 transcripts were differentially (FDR < 0.05) expressed. Cluster analysis revealed 26 distinct gene expression trajectories across the four time points. Of these, two similar clusters, showing overexpression at 20 relative to 8 hours and depletion at 27 and 44 hours, harboured the CODH and Phc transcripts, suggesting possible regulation by O2. The transition between aerobic respiration and anaerobic growth was marked by initial metabolic deterioration, as reflected by up-regulation of transcripts linked to sporulation and down-regulation of transcripts linked to flagellar assembly and metabolism. However, the transcriptome and growth profiles revealed the reversal of this trend during the hydrogenogenic phase.

Two selenium tolerant Lysinibacillus sp. strains are capable of reducing selenite to elemental Se efficiently under aerobic conditions.

Microbes play important roles in the transport and transformation of selenium (Se) in the environment, thereby influencing plant resistance to Se and Se accumulation in plant. The objectives are to characterize the bacteria with high Se tolerance and reduction capacity and explore the significance of microbial origins on their Se tolerance, reduction rate and efficiency. Two bacterial strains were isolated from a naturally occurred Se-rich soil at tea orchard in southern Anhui Province, China. The reduction kinetics of selenite was investigated and the reducing product was characterized using scanning electron microscopy and transmission electron microscopy-energy dispersive spectroscopy. The bacteria were identified as Lysinibacillus xylanilyticus and Lysinibacillus macrolides, respectively, using morphological, physiological and molecular methods. The results showed that the minimal inhibitory concentrations (MICs) of selenite for L. xylanilyticus and L. macrolides were 120 and 220 mmol/L, respectively, while MICs of selenate for L. xylanilyticus and L. macrolides were 800 and 700 mmol/L, respectively. Both strains aerobically reduced selenite with an initial concentration of 1.0 mmol/L to elemental Se nanoparticles (SeNPs) completely within 36 hr. Biogenic SeNPs were observed both inside and outside the cells suggesting either an intra- or extracellular reduction process. Our study implied that the microbes from Se-rich environments were more tolerant to Se and generally quicker and more efficient than those from Se-free habitats in the reduction of Se oxyanions. The bacterial strains with high Se reduction capacity and the biological synthesized SeNPs would have potential applications in agriculture, food, environment and medicine.

Novel bioflocculant produced by salt-tolerant, alkaliphilic strain Oceanobacillus polygoni HG6 and its application in tannery wastewater treatment.

The optimized production of MBF-HG6, which is a novel salt-tolerant alkaliphilic bioflocculant produced by Oceanobacillus polygoni with its application in tannery wastewater treatment was investigated in this study. It was found the optimal carbon source, nitrogen source, cation, and initial pH of the medium for bioflocculant production were starch, urea, Fe2+, and pH 9.0, respectively. The best stability in the temperature range was from 0 to 80°C and the purified MBF-HG6 contained polysaccharides of 81.53% and proteins of 9.98%. The carboxyl, hydroxyl, and amino groups were determined in bioflocculants, while the optimized bioflocculating activity was observed as 90.25% for the dosages of 6.96mL MBF-HG6, 4.77mL CaCl2 (1%, m/v), and 19.24g/L NaCl using response surface methodology. In addition, SS and turbidity removal rates of the tannery wastewater (4g/L MBF-HG6) could, respectively, reach 46.49% and 91.08%, indicating that the great potential was emerged in enhancement of tannery wastewater treatment by MBF-HG6.

Biofilm characteristics and evaluation of the sanitation procedures of thermophilic Aeribacillus pallidus E334 biofilms.

The ability of Aeribacillus pallidus E334 to produce pellicle and form a biofilm was studied. Optimal biofilm formation occurred at 60 °C, pH 7.5 and 1.5% NaCl. Extra polymeric substances (EPS) were composed of proteins and eDNA (21.4 kb). E334 formed biofilm on many surfaces, but mostly preferred polypropylene and glass. Using CLSM analysis, the network-like structure of the EPS was observed. The A. pallidus biofilm had a novel eDNA content. DNaseI susceptibility (86.8% removal) of eDNA revealed its importance in mature biofilms, but the purified eDNA was resistant to DNaseI, probably due to its extended folding outside the matrix. Among 15 cleaning agents, biofilms could be removed with alkaline protease and sodium dodecyl sulphate (SDS). The removal of cells from polypropylene and biomass on glass was achieved with combined SDS/alkaline protease treatment. Strong A. pallidus biofilms could cause risks for industrial processes and abiotic surfaces must be taken into consideration in terms of sanitation procedures.

Viable bacterial population and persistence of foodborne pathogens on the pear carpoplane.

BACKGROUND: Knowledge on the culturable bacteria and foodborne pathogen presence on pears is important for understanding the impact of postharvest practices on food safety assurance. Pear fruit bacteria were investigated from the point of harvest, following chlorine drenching and after controlled atmosphere (CA) storage to assess the impact on natural bacterial populations and potential foodborne pathogens. RESULTS: Salmonella spp. and Listeria monocytogenes were detected on freshly harvested fruit in season one. During season one, chemical drenching and CA storage did not have a significant effect on the bacterial load of orchard pears, except for two farms where the populations were lower 'after CA storage'. During season two, bacterial populations of orchard pears from three of the four farms increased significantly following drenching; however, the bacterial load decreased 'after CA storage'. Bacteria isolated following enumeration included Enterobacteriaceae, Microbacteriaceae, Pseudomonadaceae and Bacillaceae, with richness decreasing 'after drench' and 'after CA storage'. CONCLUSION: Salmonella spp. and L. monocytogenes were not detected after postharvest practices. Postharvest practices resulted in decreased bacterial species richness. Understanding how postharvest practices have an impact on the viable bacterial populations of pear fruit will contribute to the development of crop-specific management systems for food safety assurance. © 2016 Society of Chemical Industry.

Solid-phase synthesis and in vitro biological activity of a Thr4→Ser4 analog of daptomycin.

Daptomycin is a Ca(+2)-dependent cyclic lipodepsipeptide antibiotic used clinically to treat serious infections caused by Gram-positive bacteria. The recent appearance of daptomycin-resistant strains, daptomycin's lack of activity in the presence of lung surfactant, and its incompletely understood mechanism of action underscores the need for establishing detailed structure-activity relationships. Here we report a solid-phase synthesis of a daptomycin analog in which Thr4, 3-MeGlu12 and Kyn13 in daptomycin were replaced with Ser, Glu and Trp residues, respectively (Dap-S4-E12-W13). The Thr4 to Ser4 substitution was detrimental to activity, as Dap-S4-E12-W13 was at least 20-fold less active at physiological Ca(+2) concentration than Dap-E12-W13. Much of its activity could be recovered at high (100 mM) Ca(+2) concentration, suggesting that the residue at position 4 affects Ca(+2) binding and, consequently, biological activity.

Mercuric reductase activity of multiple heavy metal-resistant Lysinibacillus sphaericus G1.

A culture was isolated from an industrial mercuric salt-contaminated soil, which could tolerate Cd, Co, Zn, Cr, and Hg up to 190, 525, 350, 935, and 370 µM, respectively. The isolate was identified as Lysinibacillus sphaericus by 16S rRNA gene sequencing. It bioaccumulated Cd, Co, and Zn, and reductively detoxified Cr and Hg. Chromate reductase and mercuric reductase (MerA) activities in the cell extract were 2.4 and 0.13 units mg(-1) protein, respectively. The study also describes designing of broad-specificity primers based on firmicute merA genes. These primers were successfully used to amplify a 440 bp merA fragment from the current isolate. Based on the partial sequence, complete merA ORF of 1641 bp was amplified. It showed 99% similarity to a putative merA gene from distantly related Streptococcus agalactiae, but only 72% identity with the well-characterized merA from a more closely related Bacillus cereus RC607. The gene sequence possessed all the features required for the functioning of MerA enzyme, and its function was confirmed by recombinant expression in E. coli. To the best of our knowledge, this is the first report of full length merA gene from L. sphaericus.

Oceanobacillus picturae alleviates cadmium stress and promotes growth in soybean seedlings.

Cadmium (Cd) is a heavy metal that significantly impacts human health and the environment. Microorganisms play a crucial role in reducing heavy metal stress in plants; however, the mechanisms by which microorganisms enhance plant tolerance to Cd stress and the interplay between plants and microorganisms under such stress remain unclear. In this study, Oceanobacillus picturae (O. picturae) was isolated for interaction with soybean seedlings under Cd stress. Results indicated that Cd treatment alone markedly inhibited soybean seedling growth. Conversely, inoculation with O. picturae significantly improved growth indices such as plant height, root length, and fresh weight, while also promoting recovery in soil physiological indicators and pH. Metabolomic and transcriptomic analyses identified 157 genes related to aspartic acid, cysteine, and flavonoid biosynthesis pathways. Sixty-three microbial species were significantly associated with metabolites in these pathways, including pathogenic, adversity-resistant, and bioconductive bacteria. This research experimentally demonstrates, for the first time, the growth-promoting effect of the O. picturae strain on soybean seedlings under non-stress conditions. It also highlights its role in enhancing root growth and reducing Cd accumulation in the roots under Cd stress. Additionally, through the utilization of untargeted metabolomics, metagenomics, and transcriptomics for a multi-omics analysis, we investigated the impact of O. picturae on the soil microbiome and its correlation with differential gene expression in plants. This innovative approach unveils the molecular mechanisms underlying O. picturae's promotion of root growth and adaptation to Cd stress.

Low-temperature decontamination with hydrogen peroxide or chlorine dioxide for space applications.

The currently used microbial decontamination method for spacecraft and components uses dry-heat microbial reduction at temperatures of >110°C for extended periods to prevent the contamination of extraplanetary destinations. This process is effective and reproducible, but it is also long and costly and precludes the use of heat-labile materials. The need for an alternative to dry-heat microbial reduction has been identified by space agencies. Investigations assessing the biological efficacy of two gaseous decontamination technologies, vapor hydrogen peroxide (Steris) and chlorine dioxide (ClorDiSys), were undertaken in a 20-m(3) exposure chamber. Five spore-forming Bacillus spp. were exposed on stainless steel coupons to vaporized hydrogen peroxide and chlorine dioxide gas. Exposure for 20 min to vapor hydrogen peroxide resulted in 6- and 5-log reductions in the recovery of Bacillus atrophaeus and Geobacillus stearothermophilus, respectively. However, in comparison, chlorine dioxide required an exposure period of 60 min to reduce both B. atrophaeus and G. stearothermophilus by 5 logs. Of the three other Bacillus spp. tested, Bacillus thuringiensis proved the most resistant to hydrogen peroxide and chlorine dioxide with D values of 175.4 s and 6.6 h, respectively. Both low-temperature decontamination technologies proved effective at reducing the Bacillus spp. tested within the exposure ranges by over 5 logs, with the exception of B. thuringiensis, which was more resistant to both technologies. These results indicate that a review of the indicator organism choice and loading could provide a more appropriate and realistic challenge for the sterilization procedures used in the space industry.

An on-demand metalloprotease from psychro-tolerant Exiguobacterium undae Su-1, the activity and stability of which are controlled by the Ca2+ concentration.

We reported an on-demand type of metalloprotease from Exiguobacterium undae Su-1. Although this species of bacterium is known to inhabit the permafrost, there are no reports on either strong proteases or peptidases. We found that Su-1 protease is superior to commercially available proteases in proteolytic activity in a lower to normal range of temperature (10-50 °C) as well as in rapid inactivation heat-dependently on the Ca2+ concentration. These characteristics meet well with the demands from food processing and manufacturing. Biochemical investigations of the purified enzyme and protein structural analysis after gene cloning confirmed that Su-1 protease conserved high identity in its primary sequence with thermophilic proteases of the M4 family. On the other hand, its flexibility was enhanced when one Ca2+ binding site was lost and by replacement for proline and isoleucine residues.

Biosorption of Pb (II) and Zn (II) from aqueous solution by Oceanobacillus profundus isolated from an abandoned mine.

The present study investigated biosorption of Pb (II) and Zn (II) using a heavy metal tolerant bacterium Oceanobacillus profundus KBZ 3-2 isolated from a contaminated site. The effects of process parameters such as effect on bacterial growth, pH and initial lead ion concentration were studied. The results showed that the maximum removal percentage for Pb (II) was 97% at an initial concentration of 50 mg/L whereas maximum removal percentage for Zn (II) was at 54% at an initial concentration of 2 mg/L obtained at pH 6 and 30 °C. The isolated bacteria were found to sequester both Pb (II) and Zn (II) in the extracellular polymeric substance (EPS). The EPS facilitates ion exchange and metal chelation-complexation by virtue of the existence of ionizable functional groups such as carboxyl, sulfate, and phosphate present in the protein and polysaccharides. Therefore, the use of indigenous bacteria in the remediation of contaminated water is an eco-friendly way of solving anthropogenic contamination.

Biofilm-Forming Ability and Effect of Sanitation Agents on Biofilm-Control of Thermophile Geobacillus sp. D413 and Geobacillus toebii E134.

Geobacillus sp. D413 and Geobacillus toebii E134 are aerobic, non-pathogenic, endospore-forming, obligately thermophilic bacilli. Gram-positive thermophilic bacilli can produce heat-resistant spores. The bacteria are indicator organisms for assessing the manufacturing process's hygiene and are capable of forming biofilms on surfaces used in industrial sectors. The present study aimed to determine the biofilm-forming properties of Geobacillus isolates and how to eliminate this formation with sanitation agents. According to the results, extracellular DNA (eDNA) was interestingly not affected by the DNase I, RNase A, and proteinase K. However, the genomic DNA (gDNA) was degraded by only DNase I. It seemed that the eDNA had resistance to DNase I when purified. It is considered that the enzymes could not reach the target eDNA. Moreover, the eDNA resistance may result from the conserved folded structure of eDNA after purification. Another assumption is that the eDNA might be protected by other extracellular polymeric substances (EPS) and/or extracellular membrane vesicles (EVs) structures. On the contrary, DNase I reduced unpurified eDNA (mature biofilms). Biofilm formation on surfaces used in industrial areas was investigated in this work: the D413 and E134 isolates adhered to all surfaces. Various sanitation agents could control biofilms of Geobacillus isolates. The best results were provided by nisin for D413 (80%) and α-amylase for E134 (98%). This paper suggests that sanitation agents could be a solution to control biofilm structures of thermophilic bacilli.

The combined antibacterial and anticancer properties of nano Ce-containing Mg-phosphate ceramic.

AIM: This paper was mainly aimed at synthesis of Ce-containing nano-Mg-phosphate ceramic as a multifunctional material. MATERIALS AND METHODS: Two ceramics based on Mg3(PO4)2 and Ce0.2Mg2.8(PO4)2 formulas (MP and MP-C, respectively) were synthesized. The synthesized powders were characterized by XRD, TEM, Zeta potential, and FTIR. Also, their dissolution behavior was tested in Tris-HCl buffer solution. Moreover, the antimicrobial efficacy was evaluated against gram-positive bacteria (Bacillus sphaericus MTCC 511 &Staphylococcus aureus MTCC 87) and gram-negative bacteria (Enterobacter aerogenes MTCC 111 &Pseudomonas aeruginosa MTCC 1034) using dick diffusion assay and microdilution method. Furthermore, the cell viability test was performed for the ceramics on Vero cells (African green monkey kidney cells), and their antitumor activity was determined by PC3 cell line (prostatic cancer). Also, the cellular uptake was determined by the flow cytometry. KEY FINDINGS: The results showed that the substitution of Mg by Ce decreased the particle size from 40 to 90 nm for MP sample to 2-10 nm for MP-C sample and increased the degradation rate. Both samples showed excellent antimicrobial activities. Moreover, MP demonstrated more cell viability than MP-C on Vero cells at high concentrations, whereas, MP-C showed more antitumor activity on PC3 cells than MP sample. Moreover, MP-C showed a higher cell uptake than MP due to its smaller size and more negative charge. SIGNIFICANCE: Mg-phosphate ceramic can be used in this study successfully as a delivery system for cerium ions and showed a high antitumor activity, which makes it highly recommended as safe and effective cancer treatment materials.

Robust experimental design for optimizing the microbial inhibitor test for penicillin detection in milk.

AIMS: To use experimental design techniques and a multiple logistic regression model to optimize a microbiological inhibition test with dichotomous response for the detection of Penicillin G in milk. METHODS AND RESULTS: A 2(3) x 2(2) robust experimental design with two replications was used. The effects of three control factors (V: culture medium volume, S: spore concentration of Geobacillus stearothermophilus, I: indicator concentration), two noise factors (Dt: diffusion time, Ip: incubation period) and their interactions were studied. The V, S, Dt, Ip factors and V x S, V x Ip, S x Ip interactions showed significant effects. CONCLUSIONS: The use of 100 microl culture medium volume, 2 x 10(5) spores ml(-1), 60 min diffusion time and 3 h incubation period is recommended. In these elaboration conditions, the penicillin detection limit was of 3.9 microg l(-1), similar to the maximum residue limit (MRL). Of the two noise factors studied, the incubation period can be controlled by means of the culture medium volume and spore concentration. SIGNIFICANCE AND IMPACT OF THE STUDY: We were able to optimize bioassays of dichotomous response using an experimental design and logistic regression model for the detection of residues at the level of MRL, aiding in the avoidance of health problems in the consumer.

Antibiotic resistance and heavy metal tolerance in cultured bacteria from hot springs as indicators of environmental intrinsic resistance and tolerance levels.

Antibiotic resistance (AR) in the environment is a growing and global concern for public health, and intrinsic AR from pristine sites untouched by pharmaceutical antibiotics is not commonly studied. Forty aerobic bacteria were isolated from water and sediment samples of hot springs in South Africa. Resistance against ten antibiotics (carbenicillin, gentamicin, kanamycin, streptomycin, tetracycline, chloramphenicol, ceftriaxone, co-trimoxazole, nalidixic acid and norfloxacin) was tested using a standard disk diffusion assay. Resistance to one or two antibiotics were equally found in 37.5%, while the remaining 22% showed complete sensitivity. Intermediate resistance was found for ceftriaxone (52.5%), nalidixic acid (37.5%) and carbenicillin (22.5%), while low levels of resistance were observed for streptomycin (5%) and kanamycin (2.5%), and total sensitivity towards the other antibiotics. Twenty-nine isolates were also tested against eight different heavy-metal salts (Al, Cr, Cu, Fe, Hg, Mn, Ni and Pb) at 10 and 40 mM. All isolates were tolerant and able to grow on ≥2 heavy-metal salts at both concentrations. No association was observed between AR and heavy metal tolerance (HMT). Based on the relatively low AR levels, hot spring sites are pristine environments reflecting baseline levels for comparison to other potentially contaminated groundwater sites.

Volatilization and precipitation of tellurium by aerobic, tellurite-resistant marine microbes.

Microbial resistance to tellurite, an oxyanion of tellurium, is widespread in the biosphere, but the geochemical significance of this trait is poorly understood. As some tellurite resistance markers appear to mediate the formation of volatile tellurides, the potential contribution of tellurite-resistant microbial strains to trace element volatilization in salt marsh sediments was evaluated. Microbial strains were isolated aerobically on the basis of tellurite resistance and subsequently examined for their capacity to volatilize tellurium in pure cultures. The tellurite-resistant strains recovered were either yeasts related to marine isolates of Rhodotorula spp. or gram-positive bacteria related to marine strains within the family Bacillaceae based on rRNA gene sequence comparisons. Most strains produced volatile tellurides, primarily dimethyltelluride, though there was a wide range of the types and amounts of species produced. For example, the Rhodotorula spp. produced the greatest quantities and highest diversity of volatile tellurium compounds. All strains also produced methylated sulfur compounds, primarily dimethyldisulfide. Intracellular tellurium precipitates were a major product of tellurite metabolism in all strains tested, with nearly complete recovery of the tellurite initially provided to cultures as a precipitate. Different strains appeared to produce different shapes and sizes of tellurium containing nanostructures. These studies suggest that aerobic marine yeast and Bacillus spp. may play a greater role in trace element biogeochemistry than has been previously assumed, though additional work is needed to further define and quantify their specific contributions.

Organically modified clay supported chitosan/hydroxyapatite-zinc oxide nanocomposites with enhanced mechanical and biological properties for the application in bone tissue engineering.

The objective of this study is to design biomimetic organically modified montmorillonite clay (OMMT) supported chitosan/hydroxyapatite-zinc oxide (CTS/HAP-ZnO) nanocomposites (ZnCMH I-III) with improved mechanical and biological properties compared to previously reported CTS/OMMT/HAP composite. Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to analyze the composition and surface morphology of the prepared nanocomposites. Strong antibacterial properties against both Gram-positive and Gram-negative bacterial strains were established for ZnCMH I-III. pH and blood compatibility study revealed that ZnCMH I-III should be nontoxic to the human body. Cytocompatibility of these nanocomposites with human osteoblastic MG-63 cells was also established. Experimental findings suggest that addition of 5wt% of OMMT into CTS/HAP-ZnO (ZnCMH I) gives the best mechanical strength and water absorption capacity. Addition of 0.1wt% of ZnO nanoparticles into CTS-OMMT-HAP significantly enhanced the tensile strengths of ZnCMH I-III compared to previously reported CTS-OMMT-HAP composite. In absence of OMMT, control sample (ZnCH) also showed reduced tensile strength, antibacterial effect and cytocompatibility with osteoblastic cell compared to ZnCMH I. Considering all of the above-mentioned studies, it can be proposed that ZnCMH I nanocomposite has a great potential to be applied in bone tissue engineering.