Nitrogen-fixing bacteria and Oxalis – evidence for a vertically inherited bacterial symbiosis
Date
2019-10-23
Journal Title
Journal ISSN
Volume Title
Publisher
BMC (part of Springer Nature)
Abstract
Background: Plant-endophyte symbioses often revolve around nitrogen metabolism, and involve varying degrees
of intimacy. Although evidence for vertical inheritance of nitrogen-fixing endophytic bacteria is increasing, it is
confined mostly to crop plants, and to date no such system has been reported for geophytes.
Methods: Bacterial endophytes associated with Oxalis, the most species-rich geophytic genus form the Cape Flora
in southern Africa was studied. Culturable endophytes were isolated from surface-sterilized vegetative and
reproductive plant organs for six host species at three locations. Colonies of microbes on various artificial media
were morphotyped, enumerated and identified using sequence data. Filter exclusion experiments were conducted
to determine if endophytes were vertically transmitted to seeds, determine if mucilage plays a role to actively
attract microbes from the soil and to assess microbial richness isolated from the mucilage of Oxalis seedlings.
Fluorescent microscopy was implemented in order to visualize endophytic bacteria in cryo-sectioned seeds.
Results: Evidence for a novel, vertically transmitted symbiosis was reported. Communities of nitrogen-fixing and plant
growth-promoting Bacillus endophytes were found to associate with selected Oxalis hosts from nitrogen-deficient
environments of the Cape. Bacillus endophytes were ubiquitous and diverse across species and plant bodies, and were
prominent in seeds. Three common nitrogen-fixing Bacillus have known oxalotrophic properties and appear to be
housed inside specialised cavities (containing oxalates) within the plant body and seeds.
Conclusions: The discovery of vertical transmission and potential benefits to both host and endophyte suggest a
particularly tight mutualism in the Oxalis-endophyte system. This discovery suggests unexpected ways in which
geophytes might avoid nitrogen deficiency, and suggest that such symbioses are more common than previously
expected.
Description
CITATION: Jooste, M., et al. 2019. Nitrogen-fixing bacteria and Oxalis – evidence for a vertically inherited bacterial symbiosis. BMC Plant Biology, 19:441, doi:10.1186/s12870-019-2049-7.
The original publication is available at https://bmcplantbiol.biomedcentral.com
Publication of this article was funded by the Stellenbosch University Open Access Fund.
The original publication is available at https://bmcplantbiol.biomedcentral.com
Publication of this article was funded by the Stellenbosch University Open Access Fund.
Keywords
Nitrogen -- Fixation, Plant-endophyte symbioses, Geophytes, Plant-microbial interactions, Endophytic bacteria
Citation
Jooste, M., et al. 2019. Nitrogen-fixing bacteria and Oxalis – evidence for a vertically inherited bacterial symbiosis. BMC Plant Biology, 19:441, doi:10.1186/s12870-019-2049-7