Diversity of endophytic bacterial communities in Pinus flexilis foliage

Background/Question/Methods

Endophytic bacteria within healthy forest tree tissue can influence tree development, growth, adaptation, and response to environmental perturbations. Thus, when exploring tree stress adaptation, endophytic bacteria need to be considered in addition to the plant itself. A better understanding of endophytic bacteria may help elucidate their function and potential role in the development of sustainable forests in a changing climate. To date, most endophytic bacterial diversity studies have utilized culture-dependent methods, yet many bacteria are difficult or impossible to cultivate. Therefore, the use of culture-independent methods, such as 454-pyrosequencing of the 16s rRNA gene, will improve our knowledge of endophytic bacterial diversity. In this study, we used 454 pyrosequencing with primers targeting bacterial 16S rRNA genes to explore the diversity of endophytic bacteria associated with six Pinus flexilis individuals at two sites in Niwot Ridge, CO.

Results/Conclusions

The endophytic community from 6 individuals of P. flexilis sampled at two sites were all dominated by Alphaproteobacteria (50-70%), with little variation in bacterial richness and OTU abundance among and within individuals. The dominant genera were an unclassified Acetobacteraceae, Gluconacetobacter sp., and Acetobacter sp., together making up 45-60% of total bacteria in the sample. These genera have been identified as nitrogen fixers in other plants. The presence of endophytic nitrogen fixers was confirmed with PCR amplification of the nitrogenase reductase gene, nifH in each sample. This suggests that P. flexis endophytic communities are dominated by a core community of nitrogen-fixing endophytes. Thus, although commonly attributed to soil bacteria, nitrogen-fixation in forests could also be carried out by endophytes.