First exploration of Nitrobacter diversity in soils by a PCR cloning-sequencing approach targeting functional gene nxrA

Nitrite oxidoreductase (NXR) is the key enzyme responsible for the oxidation of NO(2)(-) to NO(3)(-) in nitrite-oxidizing bacteria. For the first time a molecular approach for targeting the nxrA gene was developed, encoding the catalytic subunit of the NXR, to study diversity of Nitrobacter-like organisms based on the phylogeny of nxrA gene sequences in soils. NxrA sequences of the Nitrobacter strains analysed (Nitrobacter hamburgensis, Nitrobacter vulgaris, Nitrobacter winogradskyi, Nitrobacter alkalicus) by PCR, cloning and sequencing revealed the occurrence of multiple copies of nxrA genes in these strains. The copy number and similarity varied among strains. The diversity of Nitrobacter-like nxrA sequences was explored in three soils (a French permanent pasture soil, a French fallow soil, and an African savannah soil) using a cloning and sequencing approach. Most nxrA sequences found in these soils (84%) differed from nxrA sequences obtained from Nitrobacter strains. Moreover, the phylogenetic distribution and richness of nxrA-like sequences was extremely variable depending on soil type. This nxrA tool extends the panel of functional genes available for studying bacteria involved in the nitrogen cycle.     

Sternal gland structures in males of bean flower thrips,Megalurothrips sjostedti,and Poinsettia thrips,Echinothrips americanus,in comparison with those of western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae)

Sternal pores are important features for identification of male thrips, especially within the subfamily Thripinae. They vary in shape, size and distribution even between species of one genus. Their functional role is speculated to be that of sex- and/or aggregation pheromone production. Yet, sexual aggregations are not reported in Echinothrips americanus, known to have sternal pores, while we observed aggregations in Megalurothrips sjostedti, previously reported to lack them.We examined the sternal glands and pores of the thripine species E. americanus and M. sjostedti males, in comparison with those of Frankliniella occidentalis using light microscopy, as well as scanning and transmission electron microscopy. Pore plates of F. occidentalis were ellipsoid and medial on sternites III–VII, while in E. americanus they were distributed as multiple micro pore plates on sternites III–VIII. In M. sjostedti they appeared as an extremely small pore in front of the posterior margin of each of sternites IV–VII. Pore plate and pore plate area were distributed similarly on sternites III–VII in F. occidentalis. However, in E. americanus the total pore plate area increased significantly from sternites III to VIII. Ultrastructure of cells associated with sternal glands showed typical characteristics of gland cells that differ in size, shape and number. The function of sternal glands is further discussed on the basis of morphological comparisons with other thrips species.     

Bioavailability of Glucosyl Hesperidin in Rats

Glucosyl hesperidin (G-hesperidin) is a water-soluble derivative of hesperidin. We compared the absorption and metabolism of G-hesperidin with those of hesperidin in rats. After oral administration of G-hesperidin or hesperidin to rats, hesperetin was detected in sera hydrolyzed with β-glucuronidase, but it was not detectable in unhydrolyzed sera. Serum hesperetin was found more rapidly in rats administered G-hesperidin than in those administered hesperidin. The area under the concentration-time curve for hesperetin in the sera of rats administered G-hesperidin was approximately 3.7-fold greater than that of rats administered hesperidin. In the urine of both administration groups, hesperetin and its glucuronide were found. Urinary excretion of metabolites was higher in rats administered G-hesperidin than in those administered hesperidin. These results indicate that G-hesperidin presents the same metabolic profile as hesperidin. Moreover, it was concluded that G-hesperidin is absorbed more rapidly and efficiently than hesperidin, because of its high water solubility.     

An ultrastructural study of iron and manganese deposition associated with extracellular polymers of pedomicrobium-like budding bacteria

Morphological characteristics of two Pedomicrobium-like budding bacteria are described. A structured surface layer was regularly observed on strain 868. Ruthenium red- and Alcian blue-staining polymers were found on both strains.When either strain was grown in the presence of iron or manganese, the corresponding oxides accumulated on their surfaces. In thin sections iron oxides appeared as fine threads, arrays of particles or dense coatings, depending on the source of iron. Manganese oxides appeared as branching filaments or convoluted ribbons. Both metal oxides stained with ruthenium red. Extraction of the oxides followed by ruthenium red staining revealed that polyanionic polymers previously deposited on the cells were associated with the metals.Treatment of cultures with glutaraldehyde, HgCl₂, or heat, inhibited manganese but not iron deposition, suggesting that iron oxides accumulated by passive, non-biological processes. Manganese oxides apparently accumulated under control of a biological manganese-oxidizing factor. Incomplete inhibition of manganese deposition observed in cell suspensions suggested that, if the oxidizing factor was an enzyme, it was unusually stable.Based on these results, possible mechanisms of iron and manganese deposition in association with extracellular polymers are suggested.     

Change in microbial communities in acetate- and glucose-fed microbial fuel cells in the presence of light

Power densities produced by microbial fuel cells (MFCs) in natural systems are changed by exposure to light through the enrichment of photosynthetic microorganisms. When MFCs with brush anodes were exposed to light (4000 lx), power densities increased by 8–10% for glucose-fed reactors, and 34% for acetate-fed reactors. Denaturing gradient gel electrophoresis (DGGE) profiles based on the 16S rRNA gene showed that exposure to high light levels changed the microbial communities on the anodes. Based on 16S rRNA gene clone libraries of light-exposed systems the anode communities using glucose were also significantly different than those fed acetate. Dominant bacteria that are known exoelectrogens were identified in the anode biofilm, including a purple nonsulfur (PNS) photosynthetic bacterium, Rhodopseudomonas palustris, and a dissimilatory iron-reducing bacterium, Geobacter sulfurreducens. Pure culture tests confirmed that PNS photosynthetic bacteria increased power production when exposed to high light intensities (4000 lx). These results demonstrate that power production and community composition are affected by light conditions as well as electron donors in single-chamber air-cathode MFCs.     

Insights into discharge argon-mediated biofilm inactivation

Formation of bacterial biofilms at solid–liquid interfaces creates numerous problems in biomedical sciences. Conventional sterilization and decontamination methods are not suitable for new and more sophisticated biomaterials. In this paper, the efficiency and effectiveness of gas discharges in the inactivation and removal of biofilms on biomaterials were studied. It was found that although discharge oxygen, nitrogen and argon all demonstrated excellent antibacterial and antibiofilm activity, gases with distinct chemical/physical properties underwent different mechanisms of action. Discharge oxygen- and nitrogen-mediated decontamination was associated with strong etching effects, which can cause live bacteria to relocate thus spreading contamination. On the contrary, although discharge argon at low powers maintained excellent antibacterial ability, it had negligible etching effects. Based on these results, an effective decontamination approach using discharge argon was established in which bacteria and biofilms were killed in situ and then removed from the contaminated biomaterials. This novel procedure is applicable for a wide range of biomaterials and biomedical devices in an in vivo and clinical setting.     

Enhancement in the viability and biosensing activity of freeze-dried recombinant bioluminescent bacteria

The genetically-engineeredEscherichia coli strain, DPD2540, which contains afabA::luxCDABE fusion gene, gives a bioluminescent output when membrane fatty acid synthesis is needed. For more practical application of this strain in the field as biosensor, freeze-drying was adopted. A 12% sucrose solution with Luria-Bertani (LB) broth, as determined by the viability after freeze-drying, was found to be the most effective composition for lyophilization solution among various compositions tested. Rapid freezing with liquid nitrogen also gave the best viability after freeze-drying as compared to samples frozen at −70°C and −20°C. The biosensing activities of the cells showed a greater sensitivity when the cells from the exponential phase were freeze-dried. Finally, the optimum temperature for use of the freeze-dried cells in the biosensor field was determined.