凡纳滨对虾不同养殖密度高位池水体细菌群落动态

Dynamics of the bacterial community in rearing water from an intensive pond containing different stocking densities of Litopenaeus vannamei

通过对养殖水体环境基因组DNA中细菌16S rRNA基因V4–V5区的高通量测序和生物信息学分析,研究了两种养殖密度的凡纳滨对虾(Litopenaeus vannamei)高位池水体中细菌群落在养殖过程中的动态。结果显示,养殖过程中各菌群相对丰度变化明显,细菌多样性随时间逐渐提高,优势菌群为变形菌门(Proteobacteria)、蓝藻门(Cyanobacteria)、拟杆菌门(Bacteroidetes)、放线菌门(Actinobacteria)和浮霉菌门(Planctomycetes)。随着养殖时间增长,蓝藻丰度所占比例逐渐减少,而变形菌、拟杆菌和浮霉菌丰度逐渐增大,同时养殖前期高密度池浮霉菌丰度显著高于低密度池(P<0.01),而其他菌群无显著差异。结果表明,养殖期前50 d不同养殖密度水体细菌群落差异较大,而后30 d内细菌群落的时间异质性大于空间异质性,这意味着高位池水体菌相被划分为两类,到养殖后期菌相快速转变,养殖密度所带来的影响被减弱。

Pacific white shrimp,Litopenaeus vannamei, is the most popular shrimp species cultured worldwide. Previous studies have indicated that high stocking densities negatively affect growth and survival rates, production, water quality, and immune parameters but promote disease outbreaks. Bacteria play a key role in organic con-tamination. However, little is known about the stress of stocking density on the rearing pond microbial community. Accordingly, the purpose of this investigation was to reveal the effect of shrimp stocking density on microbial community structure in intensive ponds as part of a recirculating aquaculture system. Water samples were col-lected from a high-density pond （200 ind/m^2） and a low-density pond （133 ind/m^2） every 15 days during the rear-ing period and filtered through 0.22-μm polycarbonate filters to collect bacterial cells. Environmental genomic DNA was extracted from the membrane filters. The microbial communities were profiled by high-throughput se-quencing of the V4–V5 hypervariable region of 16S rRNA gene using the MiSeq Illumina sequencing platform. The results showed that 1264 operational taxonomic units （OTUs） were obtained via high-throughput sequencing and bioinformatics analyses. The mean number of bacterial OTUs was higher in the high-density pond （549.4） than that in the low-density pond （431.8）. Clear differences in relative abundance among bacterial phyla were de-tected in different samples. Five phylogenetic subgroups were the most dominant in the entire bacterial community, including Proteobacteria, Cyanobacteria, Bacteroidetes, Actinobacteria, and Planctomycetes, accounting for 〉98% of all OTUs. The mean Shannon–Wiener diversity index for the high-density pond （4.36） was higher than that for the low-density pond （3.51）, and bacterial diversity increased gradually over timein both rearing ponds. This result suggests that new dominant bacterial populations appeared fromthe high nutrient input during the later rearing period, leading to higher bacterial diversity at a higher nutrient level. The relative abundance of Planctomycetes was significantly higher in the high-density pond （P〈0.01） during the initial rearing period than that in the low-density pond, which may have contributed to degradation of more residual feed in the high-density pond. The multidimensional scaling plot and cluster analysis demonstrated that all samples grouped into three clusters, indi-cating clear differences in the bacterial community structure between the high- and low-density ponds during the initial 50 days of rearing. However, the bacterial communities in the two ponds were more similarduringthe late stage compared with the marked differences during the initial stage, suggesting an initial stage （days 0–50） and a late stage （days 50–80）, based on bacterial community structure. The effect of different stocking densities on the bacterial community decreased during the late stage.