The phytochrome phy1 of Azospirillum brasilense Az39 is involved in bacteria response to red light under in vitro and in planta conditions

MOLINA, ROMINA; CONIGLIO ANAHÍ; NIEVAS SOFIA; TORRES DANIELA; MORA VERONICA; CASSAN, FABRICIO

Otro; Relar PGPR; 2021

A. brasilense Az39 is a non-photosynthetic bacterium extensively used as active principle of inoculants formulated for both seeds and foliar treatment. In this work, we analyzed the in vitro and in planta behavior of Az39 and the phytochrome (phy1) deficient mutant Az39Δphy1 exposed to red (RL), blue (BL) or day (DL) light. For in vitro assays, pure cultures of both bacteria with a title of 1.109cfu/ml were decimally diluted, spreaded on Luria Bertani or MMAB agar plates and individually exposed to RL, BL, DL or maintained in darkness (O) at 36 or 28 °C respectively. The in planta experiments were performed by foliar inoculation of soybean seedlings at V3 stage with 1.105 cfu/ml of each bacterium. After inoculation, seedlings were exposed to RL, BL, DL or O until the end of the experiment. Periodically, the number of viable cells recovered from light-exposed soybean leaves was obtained. Our results demonstrated that DL and BL were lethal for both Az39 and Az39Δphy1 when they grew in LB medium at 36 or 28°C. Furthermore, DL and BL were lethal for Az39 in both culture media at 28°C while the mutant was able to growth in similar experimental conditions. Contrary, Az39Δphy1 was unable to grow in MMAB medium exposed to LR at 28°C while Az39 did. Under in planta conditions, a higher bacterial sensitivity was observed to RL for Az39Δphy1 which was recovered from soybean leaves up to 24 h post-inoculation in comparison to Az39 recovered until 96 h post-inoculation. These results suggest that tolerance of Az39 to LR depends of the presence and functionality of the phytochrome coded by phy1. Additionally, both the nutritional composition of culture medium and incubation temperature were able to modify the bacterial tolerance to DL and BL.