# Selection and In Vitro Assessment of Plant Growth-Promoting Bacteria from Black Soldier Fly (Hermetia illucens) Frass

## TL;DR

This study identifies plant growth-promoting bacteria in Black Soldier Fly frass and shows their potential for use as biofertilizers.

## Contribution

The study isolates and characterizes thermotolerant plant growth-promoting bacteria from BSF frass for biofertilizer development.

## Key findings

- Six bacterial isolates from BSF frass showed plant growth-promoting traits in vitro and in vivo.
- Some isolates survived heat treatment (70 °C, 1 h), indicating thermotolerance.
- The bacteria influenced seed germination, root elongation, and root hair development in Arabidopsis thaliana.

## Abstract

Frass, the principal byproduct of Black Soldier Fly (BSF)
farming,
is increasingly valued as a sustainable organic fertilizer, partly
due to its potential to harbor plant growth-promoting microorganisms
(PGPM). This study investigated the presence and activity of PGPM
in frass obtained from 10 rearing substrates and evaluated the effect
of mandatory heat treatment (70 °C, 1 h). Using a rhizosphere-mimicking
agar medium, 149 bacterial isolates were recovered and screened for
PGPM-specific traits. Six promising isolates, belonging to Serratia, Peribacillus, Acinetobacter, Pseudocitrobacter, Bacillus, and Enterobacter, were further tested in vivo on Arabidopsis thaliana. They displayed variable effects
on seed germination, root elongation, and root hair development linked
to their phytohormone profiles. Several strains were recovered from
both untreated and heat-treated frass, highlighting their thermotolerance.
These findings demonstrate that BSF frass harbors PGPM with strong
potential for biofertilizer development.