Bacterial diversity in saline-alkali ponds rearing common carp (Cyprinus carpio) as revealed by 16S rRNA gene sequences

Nitrogen Removal of Water and Sediment in Grass Carp Aquaculture Ponds by Mixed Nitrifying and Denitrifying Bacteria and Its Effects on Bacterial Community

Nitrification and denitrification are important for nitrogen (N) cycling in fish ponds culture, but the effects of nitrifying and denitrifying bacteria concentrations on pond water and sediments remain largely unknown. Here, we used 0, 0.15, 0.30, 0.60 mg/L different concentrations of mixed nitrifying and denitrifying bacteria to repair the pond substrate through an enclosure experiment lasting 15 days. The results showed that the purification effect of nitrifying and denitrifying bacteria was most obvious on pond nitrogen from day 4 to day 7. The optimal relative concentration was 0.60 mg/L for nitrifying and denitrifying bacteria; NH4+-N (ammonia nitrogen) decreased by 75.83%, NO2−-N (nitrite) by 93.09%, NO3−-N (nitrate) by 38.02%, and TN (total nitrogen) by 45.16% in this concentration group on pond water. In one cycle, C/N (carbon/nitrogen) ratio of both water body and bottom sediment significantly increased, but C/N ratio of water body increased more significantly than that of sediment. Water C/N ratio increased by 76.00%, and sediment C/N ratio increased by 51.96% in the 0.60 mg/L concentration group. Amplicon sequencing of pond sediment showed that the change in nitrifying and denitrifying bacterium diversity was consistent with that in water quality index. Dominant nitrifying bacteria had a relatively high percentage, with significant differences in dominant bacterium percentage across different bacterial addition groups, while dominant denitrifying bacterium percentage was not high without significant differences among different groups. The dominant species of nitrifying bacteria were, respectively, Nitrosomonas, Nitrosovibrio, Nitrosospira, and Aeromonas, and the dominant species of denitrifying bacteria were Thauera, Azoarcus, Magnetospirillum, Azospira, and Idiomarina. The correlation analyses showed an aerobic nitrification and facultative anaerobic denitrification in pond sediments. Research shows that the addition of exogenous nitrifying and denitrifying bacteria can effectively reduce the nitrogen load of pond water and sediment. At the concentration of 0.6 mg/L, the nitrogen load of pond water and sediment decreased most obviously, which had the best effect on pond purification.

Investigation of bacterial diversity and pathogen abundances in gibel carp (Carassius auratus gibelio) ponds during a cyprinid herpesvirus 2 outbreak

Cyprinid herpesvirus 2 (CyHV-2) infection is detrimental to gibel carp health and may result in severe economic loss in freshwater aquaculture. However, information regarding the interaction of this pathogen with the aquatic environment is scarce. In this study, quantitative polymerase chain reaction (qPCR) and high-throughput sequencing were used to determine the abundances of pathogens and bacterial community compositions in two aquaculture ponds in Jiangsu Province, China. The results indicate that the concentrations of six selected pathogens were higher in the water than in the sediment and that these concentrations peaked during disease outbreak. In total, 8,326 and 18,244 operational taxonomic units were identified from water and sediment samples, respectively. The dominant phyla were Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, and Chlorobi in water samples and Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi, and Bacteroidetes in sediment samples. Bacterial communities were similar at the phylum level in different ponds, although significant differences were observed at the genus level. In addition, bacterial diversity was associated with environmental factors (temperature, chemical oxygen demand, NO2- -N, NO3- -N, and NH4+ -N) in the pond where the outbreak occurred. Additionally, CyHV-2 abundance was positively correlated with dissolved oxygen levels and Aeromonas spp. abundance in pond water (p < .01). This study provides comprehensive insight into the mechanisms of interaction between potential pathogens and the freshwater environment of aquaculture ponds during CyHV-2 disease outbreaks. Furthermore, the results from this study can contribute to improvement of the aquatic environment and establishment of disease prevention and control measures.

Bacterial community in the rumen of Tibetan sheep and Gansu alpine fine-wool sheep grazing on the Qinghai-Tibetan Plateau, China

The rumen microbiome plays a vital role in ruminant nutrition and health, and its community is affected by environmental factors. However, little is known about the rumen bacterial community of ruminants living in the special ecological environment of the Qinghai-Tibetan Plateau (QTP) of China. The objectives of this study were to investigate the rumen bacterial community of the typical plateau sheep (Tibetan sheep, TS, and Gansu alpine fine-wool sheep, GS) grazing on the QTP, using 16S rRNA gene sequence analysis, and to evaluate the relationship between the rumen bacterial community and the QTP environment. A total of 116 sequences (201 clones) were examined and divided into 53 operational taxonomic units (OTUs) in the TS library and 46 OTUs in the GS library. Phylogenetic analysis showed that the sequences that belonged to the Firmicutes were the most predominant bacteria in both TS and GS libraries, representing 79.4% and 62.8% of the total clones, respectively. The remaining sequences belonged to Bacteroidetes, Proteobacteria, Actinobacteria, or were unclassified bacteria. Sequence analysis revealed that the TS and GS rumens harbored many novel sequences associated with uncultured bacteria that accounted for 63.6% and 46.8% of the total clones, respectively. Comparison of the composition and diversity of the TS and GS rumen bacteria revealed few overlapping known bacteria between the two breeds, and a higher diversity in TS. The rumen bacteria of the plateau sheep showed higher percentages of bacteria that belonged to Firmicutes and novel species compared with the low-elevation sheep. The unique bacterial community in the plateau sheep rumens is perhaps one of the major reasons that they can adapt to the harsh plateau environment. These results can help identify the rumen bacterial community of the ruminants in the QTP, and provide bacteria resources and basic data to improve ruminant productivity.