海带夏季育苗系统褐藻酸降解菌数量组成分析

Quantity and composition of alginic acid decomposing bacterial community in summer seedling system of kelp Saccharina japonica

为研究褐藻酸降解菌对海带Saccharina japonica夏季育苗的影响及其与病害间的关系,全程跟踪监测育苗池水与苗帘上的可培养好氧异养细菌(heterotrophic aerobic bacteria,H)和褐藻酸降解菌(alginic acid decomposing bacteria,A)的数量变化,并对褐藻酸降解菌菌群组成进行初步分析。结果表明:孢子采苗使苗帘上好氧异养细菌量和褐藻酸降解菌量比附苗前明显增加,其中褐藻酸降解菌菌群的高活性+中活性菌的A/H值是附苗前的2.05倍;育苗池水与苗帘好氧异养细菌量在育苗期间相对稳定,分别为10~3~10~4cfu/m L和10~6~10~7cfu/g;苗帘A/H值在育苗前期呈下降趋势,在第21~28天出现峰值(36.98%~38.82%),高活性菌的比例增加1倍以上,这些变化与幼苗发生变形烂病较重的时间段一致;而育苗池水A/H峰值滞后,出现在第28天(53.33%),育苗池水与苗帘在育苗中后期A/H值均较高(分别为27.63%~43.67%和31.38%~40.56%),褐藻酸降解菌菌群组成在育苗前期以低活性菌为主,中后期高、中活性菌增长为优势菌,这可能是后期出现幼苗柄部病烂或脱苗的重要影响因素;16S r DNA测序比对结果表明,部分高活性褐藻酸降解菌与交替单胞菌属和假交替单胞菌属同源性高,但其降解能力与感染性存在菌株间差异。研究表明,褐藻酸降解菌数量、群落组成变化应是育苗生产过程中的重要生物监测指标。

The community composition, quantity and temporal variations in culturable heterotrophic aerobic bacteria（H ） and alginic acid decomposing bacteria （A ） were surveyed in seawater and palm curtains used in summer seedling of kelp Saccharina japonica to discuss the relationship between diseases during summer seedling and the bacteria. The results showed that the heterotrophic aerobic bacteria and alginic acid decomposing bacteria were in-creased an order of magnitude on the palm curtains attached by kelp spores compared to the palm curtain without kelp spores, and the A/H ratio of high and middle hydrolysis activity of bacteria was increased by 2. 05 times on the palm curtains attached by kelp spores. No significant changes in umber of heterotrophic aerobic bacteria in the seedling seawater and palm curtains were observed, fluctuating 10^3-10^4 cfu/mL and 10^6-10^7 cfu/g , respectively during summer seedling. A/H ratio of the palm curtain was shown to be a downward trend in the early seedling, a peak （36.98%-38. 82%） during 21-28 days, the proportion of bacteria with high hydrolysis activity being in-creased by more than one time. These changes were consistent with the occurrence of malformation disease in term of time, showing a close link between the proliferation of alginic acid decomposing bacteria and the disease of young spore. But A/H ratio of seedling seawater lagged, a peak in the 28 day （53. 33%）. A / H proportion in seedling seawater and palm curtains had high values （27. 6 3 % -43.6 7 % and 31.38% -40. 5 6 % , respectively） in the mid-dle and late seedling period. Low hydrolysis activity bacteria was dominant in the early, whereas high and middle hydrolysis activity bacteria ascended to the predominant bacteria in the middle and late seedling periods, which is involved in stipe rot or sporeling detachment disease. The 16S rDNA gene sequence alignment showed that alginic acid decomposing bacteria with high activity and infectivity had high homology with Alteromonas and Pseudoaltero- monas, and that there were differences in hydrolysis activity and infectivity among strains. Therefore, the variations in quantity and community composition of alginic acid decomposing bacteria would be the important biological indi-cators for kelp seedling.