# Classical Optimization of Cellulase and Xylanase Production by a Marine _Streptomyces_ Species
## 1 Introduction  
Hydrolytic enzymes can be sourced from animals, plants, and microbes. However, microbial enzyme is favored for its higher scalability and malleability to industrial process conditions [1]. Hydrolytic enzymes include the cellulases and xylanas, which have gained increasing demand in several applications such as detergents production, processing in pulp and paper industry, as well as textiles, food, and feed industries [2]. In addition, lignocellulosices can serve as inexpensive resources for fermentable sugars and chemicals through the hydrolytic activity of these enzymes [3]. Cellulases and xylanas are inducible enzymes, usually synthesized by microbes when cultured on polysaccharide substrates, with lignocellulosic biomass as a foreseeable low-cost and readily available substrate for enzyme production [2,4]. The polysaccharide components of lignocellulose (LC) are cellulose and hemicellulose. Cellulose is a linearly arranged polysaccharide of glucose, with a repeating unit of cellobiose (disaccharide), connected through \(\beta\)-1.4-glycosidic bonds. Cellulose properties are influenced by the degree of polymerization and crystallinity. Intra- or intermolecular hydrogen bonds within the units form microfibrils which aggregate into high-order crystalline regions, or low-order amorphous regions, the former making cellulose a hydrolysis-resistant molecule [5]. Cellulase enzymes comprise endoglucanase (EC 3.2.1.4), exoglucanase (EC 3.2.1.91), and \(\beta\)-glucosidase (EC 3.2.1.21), which synergize in their activity for complete hydrolysis of cellulose. Hemicellulose polymers are classified according to the sugar residues of their backbone having xylan asthe major polymer. They comprise hexoses, including galactose and mannose; the pentoses, which are xylose and arabinose; and sugar acids (D-glucuronic acid) as monomeric units [6]. Xylanas are the enzyme complexes responsible for hydrolysis of xylan, and they include endo-\(\beta\)-1,4-xylanases (EC 3.2.1.8) and \(\beta\)-xylosidases (EC 3.2.1.37), in addition to side-chain-hydrolyzing enzymes [6]. These plant cell wall hydrolases can be secreted within the intracellular region, having the activities within the cytoplasm, periplasm, and the cell membrane of the microbe; or secreted as extracellular enzyme which is released into the culture filtrate [7]. A major setback in the resourceful use of lignocellulosic biomass is a lack of efficient and cost-effective enzyme technology [8]. The high demand and cost of available commercial enzymes needed for efficient bioconversion of lignocellulosic makes the process economically nonviable [5]. Consequently, bioprospecting and manipulation of microbes for higher productivity and enhancement of existing commercial enzymes is of continuous interest [9; 10]. Among other approaches, enzyme productivity can be increased by optimizing the production processes [8]. Optimization of cultural conditions is carried out so as to keep a balance in media composition, and favorable conditions for enhanced product formation [11]. Several investigations on varying cultivation conditions for optimal cellulase and xylanase production by different fungal and bacterial strains have been done; for instance, fungal genera including _Trichoderma_, _Penicillium_, and _Aspergillus_[12; 13]; and the bacterial genera such as _Bacillus_, _Cellulomonas_, _Clostridium_, _Thermonospora_ and _Arthobacter_[14]. However, reports on marine bacterial isolates are an emerging area of interest [15]. The marine environments contain complex polysaccharides (CP) derived from sources including terrestrial and aquatic plants, algae, fungi, bacteria, and crustaceans; hence, it is a rich resource for microorganisms equipped with the enzymes battery for CP degradation [16; 17]. Moreover, actinomycetes are microbial group not fully exploited for hydrolytic enzyme production despite their record of expansive metabolite production [18; 19].