Microbial Communities of Spinach at Various Stages of Plant Growth from Seed to Maturity

Little is known about how the leaf bacterial community is affected by the seed microbiota at different stages of plant development. The bacterial populations of spinach seed and leaves after germination were compared using DGGE, to assess bacterial community richness, and realtime PCR to compare the abundance of select phyla (total bacteria, Actinobacteria, Bacteroidetes, Firmicutes, -Proteobacteria and Proteobacteria). To determine the effect of environment, the plants were grown in the field and growth chambers. Vertical transmission of bacterial community members was evident; the developmental stage of the plant affected the richness and abundance of select bacterial phyla. The bacterial richness of plants grown in the two environments was not affected. However, overall numbers of bacteria increased in field grown samples in comparison to those produced in growth chambers during development. A statistically significant interaction was seen between growth stage and environment with each of the selected phyla. Populations on cotyledons were smaller than mature leaves, but were not significantly different than the 3-4 leaf stage plants. The culturable populations of bacteria on seeds (~5 log CFU/g) were significantly smaller than determined using real time PCR (~7 log copies). Of these bacteria cultured from spinach seeds, isolates belonging to the genera Pantoea were found to inhibit growth of E. coli O157:H7 in vitro. This study highlights the importance of vertical transmission on the bacterial community of plants and suggests the importance of