Consortia of Cellulose-degrading Bacteria for Rice Straw Composing

Objective Bacteria with high efficiency cellulase for degrading rice straws were collected to improve the farm waste utilization under varied conditions.

Method Soil samples were collected from 11 habitats to preliminarily screen for candidate microbes using carboxymethyl cellulose sodium agar plates and Congo red staining. Based on the activities of cellulose-degrading enzymes, such as carboxymethyl cellulase (CMCase), filter paper enzyme (FPA), β-glucosidase (β-Gase), and exoglucanase (C₁), as well as the filter paper-disintegration, superior strains were identified using Gram staining and 16S rDNA gene sequence analysis. Composite consortia of the selected microorganisms were formed by evaluations based on the results obtained from antagonism experiments and cellulase activity assays. Single variable and response surface experiments were conducted to optimize the conditions of producing the target enzymes. Cellulose-degrading efficiency on rice straws of the selected microbes were compared.

Result (1) Forty-four strains were selected from the initially screening. Four superior performing microbes, i.e., JBN1, CY4-2, YF9, and H17, were tested to show CMCase activities of 30.58 U·mL⁻¹, 29.40 U·mL⁻¹, 26.81 U·mL⁻¹, and 12.30 U·mL⁻¹, respectively. (2) A Gram-negative bacterium, H17, was identified as a newly discovered species of Mangrovibacter plantisponsor, while JBN1, CY4-2, and YF9 were Gram-positive Bacillus subtilis, B. stercori, and B. velezensis, respectively. (3) Composite JC (JBN1 + CY4-2) and JYCH (CY4-2 + JBN1 + YF9 + H17) consortia delivered higher enzyme producing activities than the others. (4) The JC consortium yielded an average CMCase activity of 53.80 U·mL⁻¹ under the optimal conditions at 34°C and initial pH6.0 for 28h, and JYCH of 48.18 U·mL⁻¹ at 41°C and pH5.5 for 26h. (5) The rice straw degradation rates by JC and JYCH were 45.47% and 37.63%, respectively. Both were significantly higher than those of the consortia composed of only one individual strain.

Conclusion Composite JC consortium displayed higher enzyme producing capability and rice straw degrading activity, whereas JYCH was more tolerant to high temperature and acidic conditions than the others. These composite consortia of cellulose-degrading bacteria appeared to be applicable for composing the waste material under varied conditions.