Plant growth-promoting bacteria (PGPB) enhance plant growth, as well as protect plants from several biotic and abiotic stresses through a variety of mechanisms. Therefore, the exploitation of PGPB in agriculture is feasible as it offers sustainable and eco-friendly approaches to maintaining soil health while increasing crop productivity. The vital key of PGPB application in agriculture is its effectiveness in colonizing plant roots and the phyllosphere, and in developing a protective umbrella through the formation of microcolonies and biofilms. Biofilms offer several benefits to PGPB, such as enhancing resistance to adverse environmental conditions, protecting against pathogens, improving the acquisition of nutrients released in the plant environment, and facilitating beneficial bacteria–plant interactions. Therefore, bacterial biofilms can successfully compete with other microorganisms found on plant surfaces. In addition, plant-associated PGPB biofilms are capable of protecting colonization sites, cycling nutrients, enhancing pathogen defenses, and increasing tolerance to abiotic stresses, thereby increasing agricultural productivity and crop yields. This review highlights the role of biofilms in bacterial colonization of plant surfaces and the strategies used by biofilm-forming PGPB. Moreover, the factors influencing PGPB biofilm formation at plant root and shoot interfaces are critically discussed. This will pave the role of PGPB biofilms in developing bacterial formulations and addressing the challenges related to their efficacy and competence in agriculture for sustainability.

The agro-industrial sector in Indonesia produces significant amounts of nutrient-rich waste and wastewater, which pose environmental risks but also present opportunities for valorization within a circular bioeconomy. Microalgae provide a promising solution for transforming these wastewaters into valuable products such as biomass for bioenergy, biofertilizers, or pigments, all while helping to remediate pollutants. This review synthesizes current knowledge on the use of major Indonesian agro-industrial effluents, specifically palm oil mill effluent (POME), byproducts from cassava and sugarcane, and soybean residues, as substrates for microalgal biomass production and cultivation. Furthermore, various cultivation strategies are summarized, including autotrophic, heterotrophic, and mixotrophic methods, as well as the use of open ponds, photobioreactors, and hybrid systems. These cultivation processes influence biomass yield, metabolite production, and nutrient removal. Reported studies indicate high removal efficiencies for organic loads, nitrogen, and phosphorus, along with considerable production of lipids, proteins, pigments, and biofuels. Yet, effluent pretreatment, concerns about heavy metal and pathogen contamination, high downstream processing costs, and biosafety issues remains as challenges. Nonetheless, the application of microalgal cultivation into Indonesia’s agro-industrial wastes treatment can provide the dual benefits of waste mitigation and resource recovery, helping to advance climate goals and promote rural development.