CO-INOCULATION WITH MICROALGAE IMPROVES PLANT GROWTH PROMOTING BACTERIA PERFORMANCE UNDER DESSICATION

SANCHEZ RIZZA LARA; MARONICHE GM; CURATTI, L.; CREUS, CECILIA M.; PAGNUSSAT LA

Congreso; SAMIGE 2023; 2023

Plant growth-promoting bacteria (PGPBs) are frequently used to improve extensive andintensive crop performance. Azospirillum. argentinense, strain Az39, and Pseudomonasputida, strain LSR1 have been proven to be plant growth promoters, however, PGPBinoculated onto seeds must survive dry spells until appropriate conditions emerge tocolonize roots. For this reason, inoculants often require adjuvants to improve their viability.Microalgae, such as Scenedesmus obliquus C1S, are ubiquitous microorganisms thatproduce exopolysaccharides (EPS) that provide protection as well as a wet and nutritiousenvironment for adjacent bacteria of the phychosphere. The aim of this study was to analyzewhether these properties of the microalga can contribute to stress tolerance of modelPBPBs co-inoculated onto seeds.To evaluate whether co-inoculation with microalgae protects and improves the viabilityof PGPBs, the resistance of different PGPBs/microalgae consortia under saline stress anddesiccation in vitro was studied. Suspensions of Az39, LSR1, Az39/LSR1, Az39/C1S,LSR1/C1S, Az39/LSR1/C1S were spotted onto Nfb-NO3 in 10 μl droplets on media with orwithout 150 mM NaCl for 48 hours. Resulting macrocolonies were mechanically removedfrom the agar and each organism was individually counted. Under control conditions, Az39population increases in co-culture with LSR1. The deleterious effect of salinity on Az39populations in single cultures was reversed in Az39/LSR1 and also in Az39/LSR1/C1Smacrocolonies. Whereas, LSR1 outperformed in Az39/LSR1/C1S consortia with andwithout salt.The survival of PGPBs/microalgae consortia was additionally evaluated after drying onnylon filters (0,22 mm) for 0, 1, 3, and 7 days. Then, filters were carefully placed onto NfbNO3 medium, and after 48 hours of growth at 30°C, each organism population was counted.In the control treatment, Az39 viable bacteria were 10 times higher in Az39/C1S andAz39/C1S/LSR1 consortia than in single or Az39/LSR1 macrocolonies. After 1, 3 and 7 daysof drying, Az39 count was reduced to 104 CFU/mL. However, when co-cultured withmicroalgae, viable bacteria achieve 100-1000 higher counts, particularly in the tripleconsortia (107 CFU/mL), reaching similar levels to those reported without drought. LSR1survival, on the other hand, remained consistent among treatments. The results reveal thatunder drought and saline stress, both bacteria and microalgae benefit from theirinterspecific interaction in vitro. These results suggest that microalgae act as protectivevehicles to improve PGPBs survival upon post-inoculation stress and constitute promisingbiotechnological perspectives for inoculant formulation improvement