Symbiotic hemolymph bacteria reduce hexavalent chromium to protect the host from chromium toxicity in Procambarus clarkii.

Hexavalent chromium (Cr(VI)) is a cytotoxic heavy metal pollutant that adversely affects all life forms. Interestingly, the crustacean Procambarus clarkii exhibits a relatively high tolerance to heavy metals. The underlying mechanisms remain unclear. In this study, we investigated the role of symbiotic bacteria in P. clarkii in alleviating Cr(VI)-induced damage and explored their potential mechanisms of action. Through transcriptomic analysis, we observed that Cr(VI) activated P. clarkii's antimicrobial immune responses and altered the bacterial composition in the hemolymph. After antibiotic treatment to reduce bacterial populations, Cr(VI)-induced intestinal and liver damage worsened, and crayfish exhibited lower levels of GSH/CAT/SOD activity. The Exiguobacterium, the symbiotic bacteria in the hemolymph of P. clarkii, were proved to be primary contributor to Cr(VI) tolerance. Further investigation suggested that it resists Cr(VI) through the activation of the ABC transporter system and the reduction of Cr(VI) via the reductase gene nfsA. To validate the role of Exiguobacterium in Cr(VI) tolerance, crayfish treated with antibiotics then supplemented with Exiguobacterium H6 and recombinant E. coli (with the nfsA gene), reduced Cr(VI)-induced ovarian damage. Overall, this study revealed that the symbiotic bacteria Exiguobacterium can absorb and reduce hexavalent chromium, mitigating Cr(VI)-induced damage in P. clarkii. These findings provide new insights into hexavalent chromium tolerance mechanisms in crustaceans.

Salinity of animal manure and potential risk of secondary soil salinization through successive manure application.

To enhance animal productivity and maximize economic returns, mineral salts are routinely added to animal feed worldwide. Salinity and ionic composition of animal manure from intensive poultry and livestock farms in Guangdong province were investigated. Field experiments were conducted for six successive crops of Brassica Parachinensis to evaluate the possibility of secondary soil salinization by successive application of chicken manure (CM) and pigeon manure (PM) to a garden soil. The concentration of total soluble salts (TSS), which were mainly composed of sulfate and chloride of potassium and sodium, averaged 49.0, 20.6 and 60.3 g.kg(- 1) in chicken, pig and pigeon manure, respectively. After three crops, successive application of CM and PM increased soil concentrations of TSS, Na(+), K(+), Mg(2+), SO(4)(2-), and Cl(-) with application rate, resulting in a rise in soil salinity from low to medium levels and a slight reduction in soil pH. After heavy rains during the last three crops, soil TSS was reduced considerably and pH showed a slight increase. Concentrations of Cl(-) and Mg(2+) increased and Ca(2+) decreased at the end of the experiment, all leading to changes in the ionic composition of soil salinity. Manure with higher ion concentrations appeared to play a more important role in affecting ionic composition of soil salinity. The results further suggest that even in a region with abundant rainfall like Guangzhou, there is still potential risk for secondary soil salinization when high rates of CM and PM are applied.

[Conservation efficiency of local chicken breeds in different farms as revealed by microsatellite markers].

Twenty-eight microsatellite markers were used to analyze the conservation efficiency of two local chicken breeds (Dagu Chicken and Beijing Fatty Chicken) in different farms. Genotypes were detected in 125 samples. The genetic variations among and within the populations were calculated by the number of alleles, gene frequency, genetic heterozygosity (H), PIC, F-statistics, Nei's genetic distance and UPGMA. High polymorphism was found in the four populations, and H and PIC values of each population were more than 0. 5. All loci detected in the study showed polymorphism and the number of alleles ranged from 2 to 22 in total population. Most of these loci were at Hardy-Weinberg equilibrium except two loci (LE110194, MCW0032). The four conservation farms for the two breeds were shown to have retained substantial biodiversity, indicating that the conservation programs are efficient. However, differences between the farms of the same breeds were observed.

[Analysis of genetic relationship of egg-type chickens using microsatellite markers].

Twenty microsatellite markers were used to analyse the genetic relationship among four package lines (A, B, C, D) of egg-type chickens introduced in 2001 an 2002. The genetic heterozygosity, polymorphism information content (PIC), effective allele number, and genetic distance among lines were calculated and dendrogram was constructed to evaluate the genetic variability within line and genetic relations among lines. In total, 65 alleles in 20 microsatellite markers were detected. Average allele number for microsatellite markers is 3.250, and average effective allele number for those markers is 2.395. The PIC of microsatellite markers averaged at 0.454, ranging from 0.102 to 0.729. The heterozygosity of microsatellite markers ranged from 0.108 to 0.765. The heterozygosity of A2001 (0.390) was lowest, and that of D2001 (0.452) highest. The genetic distances among A and B lines were 0.005-0.016, while those among C and D lines were 0.094-0.119. Genetic resemble coefficients among A and B lines were above 0.984, while those among C and D lines around 0.900. The results proved, on the molecular level, that A and B are identical or two lines but very closed in genetic background while C and D are two different lines.

[Genetic diversity in Tibetan chicken].

Morphological traits and living habit of Tibetan chicken, which is an aboriginal chicken breed on plateau with its own characteristic populational genetic features, are in great common with the Red Jungle Fowl, the assumed ancestry of domestic chicken. To fully exploit this chicken resource, Multiplex PCR with semi-automated polyacrilamide gel electrophoresis (PAGE) using fluorescently labeled microsatellite primers was used to detect the polymorphism at 20 microsatellite loci. At the same time, we randomly test the individual morphology and performance. It showed that numbers of polymorphic alleles were 4 approximately 10, with mean value 7.25 per locus. Polymorphism Information Content (C(PI)) and Heterozygosity (H) had mean values 0.67 and 0.74, respectively. Macrochromosomes had relatively higher polymorphism than microchromosomes(P > 0.05). In all, high polymorphisms at microsatellite loci related to the uneven production performance and morphological discrepancy of population genetic characteristics in Tibetan chicken.

[Comparison of denatured and non-denatured PAGE-silver-staining detection of PCR product of microsatellites].

The genomic DNAs from six chicken breeds in China were amplified using two microsatellite primers. The PCR products were detected by non-denatured and denatured PAGE gels respectively, and the gels were dyed by silver. There were distinct differences between the two kinds of gel. In non-denatured gels. There were many nonspecific bands while clear purposed bands were showed in denatured gels.