Bacterial Production of Indole Related Compounds Reveals Their Role in Association Between Duckweeds and Endophytes

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.

Skimming the surface: duckweed as a model system in ecology and evolution

“…Obtaining axenic cultures from wild‐collected duckweed is straightforward (Bowker et al., ), and we have ourselves exploited this property to ensure constant environmental conditions in common garden experiments (Barks et al., ). Axenic culture is also useful in the study of plant microbiomes, a topic currently of intense interest (e.g., Gilbert et al., ). Finally, under axenic conditions, duckweed cultures can be maintained at low temperature for up to a year without requiring human intervention, which allows for simple long‐term maintenance of stock cultures.…”

Cryptococcus neoformanssecretes small molecules that inhibit IL-1β inflammasome-dependent secretion

“…Three candidates met our criteria of being small, polar, and heat and protease resistant molecules (Fig 5): DL-3-Phenyllactic acid (PLA); DL-p-Hydroxyphenyllactic acid (HPLA) and DL-Indole-3-lactic acid (ILA) (S4 Fig). All three are aromatic metabolites derived from amino acid metabolism and are produced by several species of prokaryotes and eukaryotes [61,62]. Testing these three metabolites individually revealed that ILA was the most inhibitory to the inflammasome (Fig 6A), while not affecting TNF-α secretion (Fig 6B).…”

“…ILA is an aromatic metabolite derived from the tryptophan pathway. It is produced by a wide variety of organisms and microorganisms, ranging from soil bacteria to humans [61,62]. ILA production in fungi is mostly reported in endophytic and phytopathogenic species, being described as important for plant tissue colonization [79].…”

Wolffia globosa–Mankai Plant-Based Protein Contains Bioactive Vitamin B12 and Is Well Absorbed in Humans

“…On the other hand, since vitamin B 12 is not measurably present in plant-based foods, individuals adhering to a vegan diet without vitamin B 12 supplementation are at risk of developing vitamin B 12 deficiency with potentially serious and sometimes irreversible consequences [ 3 , 11 ]. Indeed, various types of edible algae have been reported to contain vitamin B 12 [ 4 , 12 ]. However, recent data indicate that pseudo B 12 forms, such as OH-pseudoB 12 , Ado-pseudoB 12 , Me-pseudoB 12 , and CN-pseudoB 12 , which are considered inactive in humans, and might compete with B 12 , are the predominant corrinoids present in the algae [ 4 , 12 ].…”

“…Indeed, various types of edible algae have been reported to contain vitamin B 12 [ 4 , 12 ]. However, recent data indicate that pseudo B 12 forms, such as OH-pseudoB 12 , Ado-pseudoB 12 , Me-pseudoB 12 , and CN-pseudoB 12 , which are considered inactive in humans, and might compete with B 12 , are the predominant corrinoids present in the algae [ 4 , 12 ].…”