Alginate and fucoidan changes the bacterial community in different directions and the alginate or fucoidan degrading bacteria isolated from paddy soil promotes the plant growth.

Seaweed and its extracts have been developed as fertilizers because they possess plant-growth-promoting and antibacterial compounds. For use as fertilizers, the major carbohydrates in seaweed, including fucoidan and alginate, need to be efficiently digested in the soil. We isolated fucoidan/alginate degrading bacteria from paddy soil and verified its use as a biofertilizer. Results show that Stenotrophomonas pavanii has a high alginate degrading activity, and also stimulating melon, pepper, and tomato growth. The growth stimulation effect of the bacteria was enhanced by alginate treatment. Bacillus sp. was isolated as a fucoidan degrading bacterium and this bacterium was also able to stimulate melon growth. Using 16S ribosomal DNA analysis, fucoidan/alginate resistant or susceptible bacteria were successively selected. Bacteria with increased population due to fucoidan and alginate had specificity to each carbohydrate, whereas those with decreased population showed susceptibility to both carbohydrates. This report demonstrates some bacteria for their use as biofertilizers with seaweed and demonstrated that a high throughput method is efficient in identifying bacteria with specific properties.