Transparent Colloids of Detonation Nanodiamond: Physical, Chemical and Biological Properties.

Aqueous suspensions (colloids) containing detonation nano-diamond (DND) feature in most applications of DND and are an indispensable stage of its production; therefore, the interaction of DND with water is actively studied. However, insufficient attention has been paid to the unique physico-chemical and biological properties of transparent colloids with low DND content (≤0.1%), which are the subject of this review. Thus, such colloids possess giant dielectric permittivity which shows peculiar temperature dependence, as well as quasi-periodic fluctuations during slow evaporation or dilution. In these colloids, DND interacts with water and air to form cottonwool-like fibers comprising living micro-organisms (fungi and bacteria) and DND particles, with elevated nitrogen content due to fixation of atmospheric N2. Prolonged contact between these solutions and air lead to the formation of ammonium nitrate, sometimes forming macroscopic crystals. The latter was also formed during prolonged oxidation of fungi in aqueous DND colloids. The possible mechanism of N2 fixation is discussed, which can be attributable to the high reactivity of DND.

Effect of the earthworms Lumbricus terrestris and Aporrectodea caliginosa on bacterial diversity in soil.

Earthworms ingest large amounts of soil and have the potential to radically alter the biomass, activity, and structure of the soil microbial community. In this study, the diversity of eight bacterial groups from fresh soil, gut, and casts of the earthworms Lumbricus terrestris and Aporrectodea caliginosa were studied by single-strand conformation polymorphism (SSCP) analysis using both newly designed 16S rRNA gene-specific primer sets targeting Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, and Firmicutes and a conventional universal primer set for SSCP, with RNA and DNA as templates. In parallel, the study of the relative abundance of these taxonomic groups in the same samples was performed using fluorescence in situ hybridization. Bacteroidetes, Alphaproteobacteria, and Betaproteobacteria were predominant in communities from the soil and worm cast samples. Representatives of classes Flavobacteria and Sphingobacteria (Bacteroidetes) and Pseudomonas spp. (low-abundant Gammaproteobacteria) were detected in soil and worm cast samples with conventional and taxon-targeting SSCP and through the sequence analysis of 16S rRNA clone libraries. Physiologically active unclassified Sphingomonadaceae (Alphaproteobacteria) and Alcaligenes spp. (Betaproteobacteria) also maintained their diversities during transit through the earthworm intestine and were found on taxon-targeting SSCP profiles from the soil and worm cast samples. In conclusion, our results suggest that some specific bacterial taxonomic groups maintain their diversity and even increase their relative numbers during transit through the gastrointestinal tract of earthworms.

Nitrogen Fixation and Biological Behavior of Nanodiamond Colloidal Solutions.

Detonation-produced nanodiamond, both as a powder (with adsorbed water) and especially when suspended in an aqueous colloid, can support the growth (both aerobic and anaerobic) of bacteria and fungi. These were isolated and identified by microbiological methods, optical and electron microscopy, as species of Penicillium, Purpureocillium, Beaveria, Trichoderma and Aspergillus genera. The C : N molar ratio of the developing fibers (comprising fungal mycelia with attached bacteria and entrapped nanodiamond) decreased from 25 to 11 between the 1st and 10th week of incubation (cf. 40 in initial nanodiamond, 4.6 typical for bacteria and 8.3 for fungi), and from 4 to <1 after the 12th week, as the lysis of microorganisms releases carbon as CO2 and nitrogen as NH4+ or NO3- . The nitrogen content of the colloid increased by an order of magnitude and more, due to fixation of N2 by nanodiamond under ambient conditions.The process requires water but not necessarily oxygen present.