Abstract
Duckweed farming can be a sustainable practice for biofuel production, animal feed supplement, and wastewater treatment, although large scale production remains a challenge. Plant growth promoting bacteria (PGPB) have been shown to improve plant health by producing phytohormones such as auxin. While some of the mechanisms for plant growth promotion have been characterized in soil epiphytes, more work is necessary to understand how plants may select for bacterial endophytes that have the ability to provide an exogenous source of phytohormones such as auxin. We have isolated and characterized forty-seven potentially endophytic bacteria from surface-sterilized duckweed tissues and screened these bacterial strains for production of indole related compounds using the Salkowski colorimetric assay. Indole-3-acetic acid (IAA), indole-3-lactic acid (ILA), and indole produced by various bacterial isolates were verified by mass spectrometry. Using the Salkowski reagent, we found that 79% of the isolated bacterial strains from our collection may be capable of producing indole related compounds to various extents during in vitro growth. Of these bacteria that are producing indole related compounds, 19% are additionally producing indole. There is an apparent correlation between the type of indole related compound produced by a particular bacteria and the duckweed genus from which the bacterial strain is derived. These results suggest the possible association between different duckweed genera and endophytes that are producing distinct types of secondary metabolites. Understanding the role of indole related compounds during interaction between endophytes and the plant host may be useful to help design synthetic bacterial communities that could target specific or multiple species of duckweed in the future to sustainably enhance plant growth.
Highlights
Duckweeds are aquatic plant species that preferentially reproduce via asexual propagation and are found all over the world
Duckweed tissues that were selected from the RDSC or collected from various locations in New Jersey, USA are of the genera Wolffia, Lemna, Spirodela, and Landoltia (Supplementary Table 1)
62% belong to the Proteobacteria phylum, 23% belong to the Firmicutes phylum, 11% belong to the Actinobacteria phylum, and 4% belong to the Bacteroidetes phylum (Supplementary Table 1)
Summary
Duckweeds are aquatic plant species that preferentially reproduce via asexual propagation and are found all over the world. Their fast growth rate and ability to remove excess nitrogen and phosphate pollutants makes them attractive for use in wastewater treatment (Korner and Vermaat, 1998). Duckweed biomass can be harvested for biofuel production or as animal feed additives, Indole Related Compounds From Duckweed Endophytes since strains with high levels of starch or protein can be identified (Cheng and Stomp, 2009). In nature, duckweed grows rapidly in stagnant ponds during the summer months. Man-made duckweed ponds often are susceptible to algae growth and must be harvested frequently to maintain optimal biomass production
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