Paenibacillus strains with nitrogen fixation and multiple beneficial properties for promoting plant growth

Paenibacillus is a large genus of Gram-positive, facultative anaerobic, endospore-forming bacteria. The genus Paenibacillus currently comprises more than 150 named species, approximately 20 of which have nitrogen-fixation ability. The N₂-fixing Paenibacillus strains have potential uses as a bacterial fertilizer in agriculture. In this study, 179 bacterial strains were isolated by using nitrogen-free medium after heating at 85 °C for 10 min from 69 soil samples collected from different plant rhizospheres in different areas. Of the 179 bacterial strains, 25 Paenibacillus strains had nifH gene encoding Fe protein of nitrogenase and showed nitrogenase activities. Of the 25 N₂-fixing Paenibacillus strains, 22 strains produced indole-3-acetic acid (IAA). 21 strains out of the 25 N₂-fixing Paenibacillus strains inhibited at least one of the 6 plant pathogens Rhizoctonia cerealis, Fusarium graminearum, Gibberella zeae, Fusarium solani, Colletotrichum gossypii and Alternaria longipes. 18 strains inhibited 5 plant pathogens and Paenibacillus sp. SZ-13b could inhibit the growth of all of the 6 plant pathogens. According to the nitrogenase activities, antibacterial capacities and IAA production, we chose eight strains to inoculate wheat, cucumber and tomato. Our results showed that the 5 strains Paenibacillus sp. JS-4, Paenibacillus sp. SZ-10, Paenibacillus sp. SZ-14, Paenibacillus sp. BJ-4 and Paenibacillus sp. SZ-15 significantly promoted plant growth and enhanced the dry weight of plants. Hence, the five strains have the greater potential to be used as good candidates for biofertilizer to facilitate sustainable development of agriculture.