Analysis of the Impact of low Oxygen Tensions on the Physiology of Agriculturally Important Pseudomonas species.

AGRANATTI, CAROLA; MARTINIANO M RICARDI; PAULA M. TRIBELLI

Chapadmadal

Congreso; XVIII Congreso Argentino de Microbiología General SAMIGE 2023; 2023

SAMIGE

The soil and the different parts of the plants harbor a vastdiversity of microbes. ThePseudomonas genus includes several plant growth promoterbacteria (PGPB). PGPB canexert their beneficial effects on plant growth through theproduction of secondarymetabolites such as siderophores and plant hormone analogs,or increasing nutrientavailability. Oxigen is a key factor that affects bacterialphysiology, and variations on itsavailability cause changes in a large number of cellularfunctions. In the environment,oxygen gradients can be found in the different parts of theplant, as well as in the soil.Pseudomonas' physiology responds diversely to O2availability, with complex alternativemetabolisms. In this work we analyze the effect of lowoxygen conditions in different PGPBcharacteristics of P. extremaustralis in vitro and in vivo.We determine pyoverdineproduction in microaerobic and aerobic cultures in King Bmedium, determining thefluorescence emission at 485 nm. At microaerobic conditionswe showed a higherpyoverdine production compared with aerobiosis for P.extremaustralis (Pex M:36.24fluorescence arbitrary units/OD600nm, FAI vs Pex A: 4.02fluorescence arbitraryunits/OD600 nm, FAI). The well-known PGPB P. protegens Pf-5showed a similar trend.Phosphate solubilization was determined using NBRIP platesinoculated with bacterialcultures incubated under aerobic or microaerobic conditionsand showed no differencesunder the tested conditions.The indolic acetic acid (IAA)was determined by the Salkowskymethod in the supernatant of aerobic and microaerobiccultures of P. extremaustralis andP. protegens Pf-5. Under low oxygen conditions the IAAproduced was higher for Pextremaustralis compared to those obtained under aerobicconditions while no differenceswere found in P. protegenes Pf-5 between aerobic andmicroaerobic conditions.Additionally, Arabidopsis thaliana?s radicles, belonging to24 hours germinated seeds, wereinoculated with aerobic or microaerobic cultures of P.extremaustralis and P. protegens Pf-5. After 2 days, root length, lateral roots and root hairswere measured for 3 consecutivedays and analyzed with ImageJ. A large number of root hairswas observed in plantsinoculated with P extremaustralis that resulted higher thanthe control without bacteria.Inoculation with P. protegens Pf-5 resulted perjudicial forthis plant species causingchlorosis and killing most of the seedlings. Presence of P.extremaustralis modified the rootarchitecture by shortening the main root (6 days postgermination Pex A:9.32 mm, PexM:9.25 mm vs Control:18.28 mm) and increasing the number oflateral roots. Additionally wealso observed a tendency for a higher number of root hairscomparing plants inoculatedwith aerobic vs microaerobic cultures.Our results showed that the PGPB characteristics wereinfluenced by the oxygenavailability, further experiments should be done tounderstand the metabolic featuresinvolved in this physiological response