Micro Nano Bubble (MNB) technology for its oxygenating properties. It has attracted a lot of attention in many fields including surface water remediation, medicine, food science and agriculture.
Several studies have shown that MNB technology can improve the microbial community composition of water bodies and thus restore them; however, relatively few studies have applied nanobubble technology to aquaculture production. And there is less research literature on the effects of MNB technology on shrimp pond water and sediment microbiota, and environmental factors.
The 16S rRNA gene is used as a criterion for microbial classification and identification, as it is present in most microorganisms and shows variation. High-throughput sequencing, also known as next-generation sequencing (NGS), describes technology that sequences DNA and RNA in a rapid and cost-effective manner. The technology is highly scalable, allowing the sequencing of an organism's entire genome at once. This information is important for developing ecological strategies to prevent the increase of pathogenic bacteria in the shrimp culture environment.
In this paper, we used 16S rRNA high-throughput sequencing to study the effects of nano-aerators on the water column, sediment and shrimp gut microbial community of South American white shrimp ( Litopenaeus vannamei ) culture ponds.
I. Research setup
1. The experiment was conducted for 14 weeks at a fisheries company Ltd. Two adjacent South American white shrimp ponds served as the control and experimental pond groups, each with an area of 500 m2 (depth 0.8 m). Nanobubble aerators with a power of 1 kW were installed in the experimental group and ordinary turbine aerators with a power of 1 kW were installed in the control group. Forty shrimp fry per square meter were placed in each pond and fed with local commercial feed.
2. Samples of pond soil and water and shrimp gut tissue were collected and various tests and analyses were performed during the study.
II. Results and Discussion
To our knowledge, this study is the first to describe the effects of nano-aerators on the water column of a South American white shrimp pond, as well as on the structure of the sediment microbial community. Our results show that the application of nano-aerators changed the structure of the water column and sediment microbial community compared to that of conventional aerators.
1. The results of the diversity analysis showed that there were significant differences in the composition of microbial communities in the water column and sediments. The indicators showed that the nano-aerators in the experimental group increased the diversity, richness and homogeneity of the microbial communities in the water column. The generated data showed that the overall abundance and diversity of the gut flora did not differ significantly between the two groups of samples.
However, we found a very peculiar distribution of the species composition of the intestinal flora. In the species composition analysis, we observed that the abundance of each dominant genus was significantly higher in the treatment group than in the control group. Our data showed an increase in the activity of beneficial bacteria (e.g., Erysipelas, Tremella, and E. faecalis) in the intestine due to the nano-aerator.
2. The effect of nano-aerators on sediment microbial communities may be affected by time. Under short-term aeration conditions, the microbial diversity in the nano aerator group was higher than that in the control group; however, as the aeration time increased, the microbial diversity in the control sediment exceeded that in the treatment group. Beneficial bacteria belonged to the genera Microbacterium and Immobacterium, as well as beneficial single-celled green algae. All of them increased in the water column due to nano-aerator-mediated oxygenation.
3、Nano aerator can use a variety of gas media, such as: hydrogen, nitrogen and ozone. However, existing studies have shown that nano aerators are often used in combination with ozone to kill pathogenic bacteria in cultured water. Other researchers have shown for the first time that ozone nanobubble treatment is efficient in disinfecting pathogenic bacteria in freshwater and also effectively reduces the potential pathogen air as a gas medium that causes red leg disease in South American white shrimp under freshwater culture conditions when using nano-aerators. Therefore, we hypothesize that nano aerators can also kill some pathogenic bacteria in the water column and substrate when using an air medium.
4. In our experiments, the nano aerator effectively inhibited the activity of bacteria in the water (e.g., Bacillus, Spirochetes and other anaerobic bacteria), as reported by other researchers who demonstrated that the bubbles reduced biomass through hydrophobicity or water repulsion, thereby inhibiting bacterial growth. This demonstrates that nano aerators can also inhibit anaerobic bacteria when air is used as the gas medium. We believe that this is an important finding for the future practical production and selection of aeration equipment.
5. Although this study revealed some important findings, there are some limitations, and the results of high-throughput sequencing may also be affected by various factors, such as: individual sampling methods and experimental methods. Due to the small sample size, these influencing factors cannot be excluded. However, the results still contribute to the understanding of the structure of the microbial ecosystem associated with the species and provide a theoretical basis for practical production. Therefore, testing nano-aerators under different tillage patterns is of great importance for future research.
We believe that our findings improve the understanding of microbial community structure in aquaculture pond water and sediments using nano-aerators. These results may help to improve the aquaculture environment to enhance the quality and health of crustaceans in aquaculture environments.
III. Perspectives of the study
Our results show changes in the pond water, sediment and gut microbial communities of South American white shrimp. The data showed that the diversity of the microbial community in the water gradually decreased with increasing experimental time, but the biodiversity of the treatment group was always higher than that of the control group due to the effect of nano-oxygenation. This may be due to the better oxygenation effect of nano-oxygenator, which helps to degrade some pollutants in the water when the nano-bubbles break, purify the water and provide a more suitable environment for various microorganisms in the water.
In addition, the nano-oxygenator also influenced to some extent the species composition of the microbial community in the water column, substrate and shrimp gut of the culture pond, increasing the proportion of some probiotic microorganisms. Our study and a follow-up study based on our results suggest that nanoaerators help to improve the culture conditions of South American white shrimp. However, different conditions - e.g., water temperature and salinity, or culture density - may affect the results, so we recommend further experiments to accurately determine these environmental factors.
