Actinobacteria from Rhizosphere

Abstract Actinobacteria is a phylum of gram-positive bacteria, and members of bacteria belonging to this phylum are classified into six classes, namely Acidimicrobiia, Actinobacteria, Coriobacteriia, Nitriliruptoria, Rubrobacteria, and Thermoleophilia. Among the six different classes, members of the actinobacteria class are the most dominant and contain one of the largest genera, Streptomyces, with 961 distinct species. Members of phylum actinobacteria are ubiquitous in nature and have been isolated from various extreme environments (high temperatures, pH, salinities, pressure, and drought) and are associated with plants growing in different habitats. The rhizospheric actinobacteria are the most dominant in nature and they are of great economic importance to humans due to their huge contributions to soil systems. Based on a comprehensive literature analysis members of phylum actinobacteria have been reported from different genera such as Acidimicrobium, Actinomyces, Arthrobacter, Bifidobacterium, Cellulomonas, Clavibacter, Corynebacterium, Frankia, Microbacterium, Micrococcus, Mycobacterium, Nocardia, Propionibacterium, Pseudonocardia, Rhodococcus, Sanguibacter, and Streptomyces. Actinobacteria can be utilized as bioinoculants for sustainable agriculture as they can enhance plant growth and yield both by directly promoting plant growth by the fixation of atmospheric nitrogen, the solubilization of minerals such as phosphorus, potassium, and zinc, the production of siderophores and plant growth hormones such cytokinin, auxin, and gibberellins, and by indirect plant growth promotion via production of antagonistic substances by inducing resistance against plant pathogens. The actinobacteria has been proved to have immense importance in biotechnological applications in various industrial and agricultural processes that are discussed in this chapter.