Azotobacter vinelandiisiderophore can provide nitrogen to support the culture of the green algaeNeochloris oleoabundansandScenedesmussp. BA032

Abstract

Microalgae are viewed as a potential future agricultural and biofuel feedstock and also provide an ideal biological means of carbon sequestration based on rapid growth rates and high biomass yields. Any potential improvement using high-yield microalgae to fix carbon will require additional fertilizer inputs to provide the necessary nitrogen required for protein and nucleotide biosynthesis. The free-living diazotroph Azotobacter vinelandii can fix nitrogen under aerobic conditions in the presence of reduced carbon sources such as sucrose or glycerol and is also known to produce a variety of siderophores to scavenge different metals from the environment. In this study, we identified two strains of green algae, Neochloris oleoabundans and Scenedesmus sp. BA032, that are able to utilize the A. vinelandii siderophore azotobactin as a source of nitrogen to support growth. When grown in a co-culture, S. sp. BA032 and N. oleoabundans obtained the nitrogen required for growth through the association with A. vinelandii. These results, indicating a commensalistic relationship, provide a proof of concept for developing a mutualistic or symbiotic relationship between these two species using siderophores as a nitrogen shuttle and might further indicate an additional fate of siderophores in the environment.

Gene Deletions Resulting in Increased Nitrogen Release by Azotobacter vinelandii: Application of a Novel Nitrogen Biosensor

“…This broad screening potential could have further benefits in identifying additional potential "nitrogen shuttle" compounds that might have further utility for providing nitrogen in coculture. A. vinelandii also produces additional nitrogen shuttle compounds such as siderophores that are suitable for supporting the growth of algae in coculture (11), as well as additional extracellular proteins (49). In these studies, the levels of nitrogen released to the culture medium by the amtB disruption were very low (i.e., a low micromolar range) and might be missed by less sensitive assays.…”

“…Cultures of Chlorella sorokiniana UTEX 1602 were obtained from the UTEX culture collection of algae (Austin, TX) and have been maintained for several years by subculturing on solid media (11). Algae strains were cultured in a freshwater medium as described previously (26).…”

“…Various laboratories have been investigating the potential of Azotobacter species to provide nitrogen to specific crops for many years, with various degrees of success (5)(6)(7)(8)(9)(10)(11). Although many nitrogen-fixing bacteria produce nitrogen in environments requiring very low oxygen, Azotobacter vinelandii has evolved the capability of fixing nitrogen as a free-living aerobe, despite the fact that nitrogenase is inherently sensitive to oxygen.…”

The Siderophore Metabolome of Azotobacter vinelandii

“…Several studies have shown that the siderophores of A. vinelandii can also bind metals other than Fe to enable uptake of additional metals required in nitrogenases (Mo, V) (4,8) or to sequester toxic heavy metals (e.g., W, Zn) (9-11). The siderophores secreted by A. vinelandii have also been found to support the growth of some freshwater algae in coculture by providing a significant source of nitrogen to these organisms (12).…”

Siderophore production in Azotobacter vinelandii in response to Fe‐, Mo‐ and V‐limitation

“…Large allocations of fixed nitrogen to siderophore production may have implications for the transfer of nitrogen from diazotrophs into ecosystems, as the fate of siderophore nitrogen is probably very different from that of the biomass. Siderophores might be more readily taken up by other microbes or plants as a source of nitrogen (Villa et al ., ) or stolen and traded with other microbes (Granger and Price, ; Traxler et al ., ). While it is unknown how these types of interactions play out in the environment, the large siderophore nitrogen investments seen in this study suggest the outcome may impact nitrogen cycling.…”