Screening of Cellulolytic Bacteria from Various Ecosystems and Their Cellulases Production under Multi-Stress Conditions

Abstract

Cellulose represents the most abundant component of plant biomass on earth; it is degraded by cellulases, specific enzymes produced by microorganisms. However, cellulases of bacterial origin attract more interest due to their natural diversity and ability to inhabit a variety of niches, allowing the selection of cellulolytic strains resistant to environmental stresses. The screening of the cellulolytic activity of 398 bacteria isolated from various ecosystems in Algeria (cave, ruins, chott, thermal station, and rhizosphere of arid and semi-arid regions) was performed by the appearance of a hydrolysis zone on carboxymethylcellulose (CMC) medium. The cellulase activity on CMC (1%) broth allowed to select 26 strains among which 12 had the best activity (0.3 U/mL to 2.2 U/mL). Optimization of physicochemical parameters (salinity: 0–1 M NaCl; pH: 3, 4, 7, 9, and 11; temperature: 30, 45, and 50 °C; PEG8000: 0 and 30%) involved in growth and cellulose production showed that the majority of strains were mesophilic, neutrophilic, or alkali- tolerant and tolerant to 30% of PEG8000. The cellulase activity and stability under different stress allowed to retain five strains, which the most efficient. Based on the 16S-rRNA sequencing results, they belonged to the genus Bacillus. The physicochemical properties of cellulases (crude extract) showed a CMCase active over a wide range of pH (4 to 11), optimal at 50 °C and 60 °C. The inhibiting salinity effect on the activity was not detected and was negligible on the enzymatic stability. The residual CMCase activity remained between 40 and 70% in a temperature range between 40 and 70 °C, was stable over a wide range of saline concentrations (0–2000 mM), and was weakly affected at 30% of PEG8000. The crude enzyme extract was able to hydrolyze both soluble and insoluble cellulosic substrates. The evaluation of the hydrolysis capacity of lignocellulosic waste revealed the ability of tested strains to degrade wheat bran, barley bran, and corncob. In addition, the enzyme showed significant multi-stress resistance on solid and liquid media. By these characteristics, these cellulolytic bacteria could be attractive to be used in various industrial and biotechnology applications.

Diversity of Cellulolytic Microorganisms Associated with the Subterranean Termite Reticulitermes grassei

“…Florencio et al [ 49 ] suggest that the diameter of the hydrolysis zone is useful for selecting isolates that can efficiently degrade polysaccharides such as cellulose. In addition, there is a broad diversity of studies in the literature that conclude that determining the radial growth and EI parameters on CMC or even growth with this compound as the sole carbon source is enough to have a first approach about the cellulolytic activity of microorganisms [ 54 , 87 , 88 ]. However, further studies will be conducted in the future to evaluate specific biochemical tests such as some lignin- and xylan-degrading enzyme assays to determine the highest cellulase producers by quantitative methods [ 89 , 90 ].…”

The Effect of Encapsulating a Prebiotic-Based Biopolymer Delivery System for Enhanced Probiotic Survival

“…To detect cellulase activity, fecalase was placed in wells cut on agar with the substrate 1% carboxymethyl cellulose, which was then spilled with Congo red or Lugol solutions [ 60 ]. The presence of the enzyme was recorded by the appearance of hydrolysis zones, the diameter of which averaged 23–26 mm, which indicated significant cellulase activity (data not provided).…”

The Effect of Cultivation Conditions on Antifungal and Maize Seed Germination Activity of Bacillus-Based Biocontrol Agent

“…BioSol021 strain in the group of highly efficient cellulase producers, even in the commercial medium nutrient broth, with a hydrolysis zone diameter of over 40 mm. The cellulase activity evaluated between 26 strains belonging to the Bacillus genus and the index of enzymatic activity up to six [ 53 ] suggested the necessity of medium and cultivation condition optimization in order to maximize the extracellular cellulolytic activity of the Bacillus sp. BioSol021 strain.…”