Characterization of Cellulose and Starch Degradation by Extracellular Enzymes in Frankia Strains

Annually, a considerable amount of agricultural waste is produced leading to serious environmental pollution if not managed effectively. A wide range of bio-decomposers, including fungi, bacteria, and actinomycetes may break down the complex agro-residues in an eco-friendly way through secreting many cellulolytic and amylolytic enzymes. The present study aimed at exploring the ability of Frankia to degrade cellulose and starch and identifying the cellulase and α-amylase genes in Frankia genomes for potential agricultural waste degradation. Frankia alni ACN14a and Frankia casuarinae CcI3 produced clear zones around growing hyphae on carboxymethyl cellulose (CMC) and starch substrates. The hydrolytic index (HI) ranged from 1 to 2.14 reflecting variation in their degradation efficacy. Quantification of CMCase (carboxymethyl cellulase) production in strain ACN14a presented the maximum activity (0.504 U/mL) under 1% CMC after 16 days whereas strain CcI3 produced a weak activity after 6 days from incubation. Besides, amylase activity in strain ACN14a reached the highest value (3.215 U/mL) after 4 days of growing with 1% starch, while strain CcI3 had the superior production (3.04 U/mL) after 12 days from 1% starch condition. Data mining and genome blasting led to the identification of multiple genes related to cellulose and starch degradation. Two endoglucanases (celA1, FRAAL4955 and celA2, FRAAL4956), two glycosyl hydrolase family 16 (FRAAL6120 and FRAAL2663), and one glycosyl hydrolase family 16 (Francci3_3843) were predicted in the two genomes. Likewise, the α-amylase genes (FRAAL5900) from Frankia alni ACN14a and (Francci3_3679) from strain CcI3 were identified. The gene expression of endo-1, 4-beta-glucanase (celA2, FRAAL4956) revealed the maximum increment in its mRNA abundance under 0.25% CMC exposure and showed a 3.3-fold increase. Frankia capability to degrade cellulose and starch represents a critical process in nutrient cycling and environment protection.