Abstract
The quest for novel biologically active metabolites such as enzymes is motivating researchers towards searching for unique microorganisms from diversified and unexplored habitats. Endophytes are a possible sources of unique bioactive metabolites due to their symbiotic relationship with the host plants. Among the biologically active metabolites producing microorganisms, Actinobacteria is gaining more recognition as one of the most important producers of extracellular enzymes and other secondary metabolites. In the present study, Actinobacteria was isolated from the roots and rhizopheric soil of Guiera senegalensis plant obtained from the north-western semi-arid climate of Nigeria. A total of five Actinobacteria were isolated on modified-starch casein agar and identified by morphological characteristics. The isolates were evaluated on substrate-specific liquid media for their ability to produce extracellular enzymes: amylase, cellulase, pectinase, protease, lipase, and keratinase. All the isolates were able to produce the target enzymes at different levels, with isolate EAc-2 exhibiting highest levels of amylase (373.44 U/mL), cellulase (274.63 U/mL) and pectinase (357.72 U/mL). To our knowledge, this is the first report on the isolation of endophytic and rhizospheric Actinobacteria obtained from the north-western semi-arid climate of Nigeria and the first overview of the extracellular enzymes they produce. This study contributes to knowledge on the industrial and biotechnological potentials of Actinobacteria associated with Guiera senegalensis plant. In conclusion, our results suggested that north-western semi-arid climates of Nigeria are promising sources of novel Actinobacteria with unique diversified characteristics and potentials in the production of novel bioactive metabolites such as extracellular enzymes.

Key words: Actinobacteria, Extracellular enzymes, Endophytes, Guiera senegalensis, Rhizospheric soil.