Overuse and arbitrary discarding of antibiotics have expanded antibiotic resistance reservoirs, from gut, waste water and activated sludge, to soil, freshwater and even the ocean. Based on the structured Antibiotic Resistance Genes Database and next generation sequencing, metagenomic analysis was used for the first time to detect and quantify antibiotic resistance genes (ARGs) in paddy soils from South China. A total of 16 types of ARGs were identified, corresponding to 110 ARG subtypes. The abundances and distribution pattern of ARGs in paddy soil were distinctively different from those in activated sludge and pristine deep ocean sediment, but close to those of sediment from human-impacted estuaries. Multidrug resistance genes were the most dominant type (38-47.5%) in all samples, and the ARGs detected encompassed the three major resistance mechanisms, among which extrusion by efflux pumps was predominant. Redundancy analysis (RDA) showed that pH was significantly correlated with the distribution of ARG subtypes (P < 0.05). Our results provided a broad spectrum profile of ARGs in paddy soil, indicating that ARGs are widespread in paddy soils of South China.

Digested residues from biogas plants are often used as biofertilizers for agricultural crops cultivation. The antibiotic resistance genes (ARGs) in digested residues pose a high risk to public health due to their potential spread to the disease-causing microorganisms and thus reduce the susceptibility of disease-causing microorganisms to antibiotics in medical treatment. A high-throughput sequencing (HTS)-based metagenomic approach was used in the present study to investigate the variations of ARGs in full-scale biogas reactors and the correlations of ARGs with microbial communities and metal resistance genes (MRGs). The total abundance of ARGs in all the samples varied from 7 × 10 to 1.08 × 10 copy of ARG/copy of 16S-rRNA gene, and the samples obtained from thermophilic biogas reactors had a lower total abundance of ARGs, indicating the superiority of thermophilic anaerobic digestion for ARGs removal. ARGs in all the samples were composed of 175 ARG subtypes; however, only 7 ARG subtypes were shared by all the samples. Principal component analysis and canonical correspondence analysis clustered the samples into three groups (samples from manure-based mesophilic reactors, manure-based thermophilic reactors, and sludge-based mesophilic reactors), and substrate, temperature, and hydraulic retention time (HRT) as well as volatile fatty acids (VFAs) were identified as crucial environmental variables affecting the ARGs compositions. Procrustes analysis revealed microbial community composition was the determinant of ARGs composition in biogas reactors, and there was also a significant correlation between ARGs composition and MRGs composition. Network analysis further revealed the co-occurrence of ARGs with specific microorganisms and MRGs.

Let ([0, 1), T) be the dynamical system of continued fractions. Let {zn}n⩾1 be a sequence of real numbers in [0, 1] and ψ: ℕ × [0, 1) → ℝ+ be a positive function. A point x∈[0, 1) is said to be ψ‐approximable by {zn}n ⩾ 1 if |Tnx − zn| < ψ(n, x) holds for infinitely many n ∈ ℕ. In this paper, the Hausdorff dimension of the set of ψ‐approximable points is studied. The dimensions are completely determined when ψ(n, x) = ψ(n) independent on x and when ψ(n,x)=e−(f(x)+⋯+f(Tn−1x)) with f a positive continuous function. For the proof of these results, a relationship between a ball in [0, 1) and the cylinders defined by the partial quotients in continued fractions is investigated. It is shown that a ball can be sufficiently packed by cylinders of the same order and of comparable length, which gives us explicit continued fraction representations in locating the points in a ball in [0, 1).