Prevalence and characterization of Clostridium perfringens isolated from different chicken farms in China.

Clostridium perfringens (C. perfringens) is a common pathogenic microorganism present in nature, which can cause animal and human diseases, such as necrotizing enteritis (NE) in poultry. Little is known about the current prevalence status of C. perfringens from poultry farms of different types and regions in China. From December 2018 to August 2019, we investigated the prevalence, genotype distribution and drug resistance of C. perfringens from Guangdong, Pingyin, Tai'an and Weifang. A total of 622 samples were collected and processed for C. perfringens isolation, among which 239 (38.42%) samples were determined to be positive for C. perfringens. A total of 312 isolates of C. perfringens were recovered (1-5 strains were isolated for each positive sample), and 98.72% of the isolates were identified as type A, while the others were type F. Antimicrobial susceptibility testing revealed that 47.71% of the isolates were resistant to at least five classes of commonly used antibiotics. Multilocus sequence typing (MLST) showed that 74 representative isolates were divided into 63 sequence types (STs), and the Simpson's diversity index (Ds) of the STs for the five farms was 0.9799. 37.84% of the isolates were classified into seven clonal complexes (CC1-CC7), and the isolates from the same farm were more concentrated in the minimum spanning tree. In addition, some cloaca isolates and feed isolates were distributed in the same ST or CC; this result indicates that the C. perfringens in chicken can come from the environment (feed etc.).

The spatio-temporal features of chicken mitochondrial ND2 gene heteroplasmy and the effects of nutrition factors on this gene.

Mitochondrial heterogeneity is the presence of two or more types of mitochondrial (mt)DNA in the same individual/tissue/cell. It is closely related to animal health and disease. ND2 is a protein-coding gene in mtDNA, which participates in mitochondrial respiratory chain and oxidative phosphorylation. In previous studies, we observed that the mt.A5703T and mt.T5727G sites in the ND2 gene were the heteroplasmic variation sites. We used pyrophosphate sequencing technology to examine chicken mt.A5703T and mt.T5727G heteroplasmic sites in the ND2 gene, in different tissues and at different development stages in chickens. We also investigated whether nutritional factors could affect the mt.A5703T and mt.T5727G heteroplasmy. Our results showed that chicken mt.A5703T and mt.T5727G heteroplasmy had clear spatio-temporal specificities, which varied between tissues/development stages. The mtDNA heterogeneity was relatively stable upon nutrition intervention, 30% dietary energy restriction (from 18 to 48 days old) and different types of dietary fats (at 5% concentration, from 1 to 42 days old) did not change the breast muscle heteroplasmy of broilers at the mt.A5703T and mt.T5727G sites. In addition, multiple potential heteroplasmic sites were detected by clone sequencing in the ND2 region, which potentially reflected abundant heteroplasmy in the chicken mitochondrial genome. These results provide an important reference for further research on heteroplasmy in chicken mitochondria.

The Sterility of Allotriploid Fish and Fertility of Female Autotriploid Fish.

Based on the formation of an autotetraploid fish line (4nAUT, 4n = 200; F2-F11) derived from the distant hybridization of female Carassius auratus red var. (RCC, 2n = 100) × male Megalobrama amblycephala (BSB, 2n = 48), we produced autotriploid hybrids (3nAUT) by crossing females of RCC with males of 4nAUT and allotriploid hybrids (3nALT) by crossing females of Cyprinus carpio (CC, 2n = 100) with males of 4nAUT. The aim of this study was to comparatively investigate the reproductive characteristics of 3nALT and 3nAUT. We investigated morphological traits, chromosomal numbers, DNA content and gonadal development in 3nAUT and 3nALT. The results indicated both 3nAUT and 3nALT possessed 150 chromosomes and were triploid hybrids. The females and males of 3nALT and males of 3nAUT had abnormal gonadal development and could not generate mature eggs or sperm, but the females of 3nAUT had normal gonadal development and generated mature eggs at 2 years old. The females of 3nAUT generated different sizes of eggs, which fertilized with haploid sperm from RCC and formed viable diploid, triploid, and tetraploid offspring. The formation of these two kinds of triploid hybrids provides an ideal model for studying the reproductive traits of triploid hybrids, which is of great value in animal genetics and reproductive biology.

Nucleolar Dominance in a Tetraploidy Hybrid Lineage Derived From Carassius auratus red var. () × Megalobrama amblycephala ().

Nucleolar dominance is related to the expression of 45S rRNA genes inherited from one progenitor due to the silencing of the other progenitor's rRNA genes. To investigate nucleolar dominance associated with tetraploidization, we analyzed the changes regarding the genetic traits and expression of 45S rRNA genes in tetraploidy hybrid lineage including F1 allotetraploids (4n = 148) and F2 autotetraploids (4n = 200) derived from the distant hybridization of Carassius auratus red var. (2n = 100) () ×Megalobrama amblycephala (2n = 48) (). Results showed that nucleolar dominance from the females was established in F1 hybrids and it was inherited in F2 hybrids, suggesting that tetraploidization can lead to rapid establishment of nucleolar dominance in the hybrid origin's tetraploid lineage. These results extend the knowledge of nucleolar dominance in polyploidy hybrid animals, which are of significance for the evolution of hybrids in vertebrates.

The Formation of the Goldfish-Like Fish Derived From Hybridization of Female Koi Carp × Male Blunt Snout Bream.

Goldfish (Carassius auratus var., GF; 2n = 100) is the most popular ornamental fish in the world. It is assumed that GF evolved from red crucian carp (C. auratus red var., RCC; 2n = 100). However, this hypothesis lacks direct evidence. Furthermore, our knowledge of the role of hybridization in the formation of new species is sparse. In this study, goldfish-like fish with twin tails (GF-L; 2n = 100) was produced by self-mating red crucian carp-like fish (RCC-L; 2n = 100) derived from the distant crossing of koi carp (Cyprinus carpio haematopterus, KOC; 2n = 100; ♀) with blunt snout bream (Megalobrama amblycephala, BSB; 2n = 48; ♂). The phenotypes and genotypes of GF-L and RCC-L were very similar to those of GF and RCC, respectively. Microsatellite DNA and 5S rDNA analyses revealed that GF-L and RCC-L were closely related to GF and RCC, respectively. The presence of a twin tail of GF-L was related to a base mutation in chordinA from G in RCC-L to T in GF-L, indicating that the lineage of RCC-L and GF-L can be used to study gene variation and function. The sequences of 5S rDNA in GF-L and RCC-L were mapped to the genomes of CC and BSB, which revealed that the average similarities of both GF-L and RCC-L to CC were obviously higher than those to BSB, supporting that the genomes of both RCC-L and GF-L were mainly inherited from KOC. GF-L and RCC-L were homodiploids that were mainly derived from the genome of KOC with some DNA fragments from BSB. The reproductive traits of GF-L and RCC-L were quite different from those of their parents, but were the same as those of GF and RCC. RCC-L easily diversified into GF-L, suggesting that RCC and GF evolved within the same period in their evolutionary pathway. This study provided direct evidence of the KOC-RCC-GF evolutionary pathway that was triggered by distant hybridization, which had important significance in evolutionary biology and genetic breeding.