Seagrass meadows are one of the most important marine ecosystems. Alkanes are the common hydrocarbon contaminants that can affect seagrass growth. In this study, a large spatial-scale investigation has been carried out on the alkane-degrading bacterial community structure in the rhizosphere and non-rhizosphere sediments of two seagrass species (Thalassia hemprichii and Halophila ovalis). AlkB gene was employed as a biomarker gene to study the alkane-degrading bacterial community structure. The results showed that the alpha diversity of the alkane-degrading bacterial community in T. hemprichii non-rhizosphere sediments was higher than that of its rhizosphere sediments. However, the alpha diversity of the alkane-degrading bacterial community in H. ovalis rhizosphere sediments was higher than that of its non-rhizosphere sediments in the open sea, but the result was contrast in the coast area. In addition, the alpha diversity of alkane-degrading bacterial communities in the coast area was higher than that of far away from the coast in the T. hemprichii rhizosphere and non-rhizosphere sediments. The phylogenetic analysis result revealed that the alkB sequences from the seagrass ecosystem were mainly affiliated with the class Alphaproteobacteria, and had the two novel lineages. Genus Agrobacterium was the most predominant alkane-degrading bacteria. These results contributed to disclose the geographical distribution pattern of alkane-degrading bacteria in the seagrass ecosystem of the South China Sea.

海草草甸是最重要的海洋生态系统之一。烷烃是影响海草生长的常见碳氢化合物污染物。在这项研究中，对两种海草（Thalassia hemprichii和Halophila Ovalis）的根际和非根际沉积物中的烷烃降解细菌群落结构进行了大规模的空间尺度调查。AlkB基因被用作生物标志物基因来研究烷烃降解细菌群落结构。结果表明，T. hemprichii非根际沉积物中烷烃降解细菌群落的α多样性高于其根际沉积物中的α多样性。然而，烷烃降解细菌群落的α多样性H.ovalis根际沉积物在公海高于其非根际沉积物，但结果在沿海地区相反。此外，在T. hemprichii根际和非根际沉积物中，沿海地区烷烃降解细菌群落的α多样性高于远离海岸的地区。系统发育分析结果表明，来自海草生态系统的alkB序列主要隶属于Alphaproteobacteria，并具有两个新的谱系。属农杆菌是最主要的烷烃降解细菌。这些结果有助于揭示南海海草生态系统中烷烃降解细菌的地理分布格局。