Chitinase production by a newly isolated thermotolerant Paenibacillus sp. BISR-047

Isolation, screening, and identification of chitinase-producing bacterial strains from riverbank soils at Ambo, Western Ethiopia

Chitinases are hydrolytic enzymes that dissolve the glycosidic linkages in chitin. Chitin is a cell wall component of fungi and fund in exoskeleten of worms and arthropods. Chitinase has been applied in agriculture, as a biopesticide for the control of plant fungal infections, in medicine, and in waste management. This research aimed to isolate, screen, and identification of chitinase-producing bacteria from riverbank soils. Twenty nine chitinolytic bacteria were isolated from the river bank soil samples, from which 9 of them had strong chitinolytic properties. Chitinase production was determined by zones of hydrolysis produced after 96 h of incubation at 37 °C. The different bacterial isolates were characterized morphologically, microscopically, and biochemically and finally eight strain were identified at species level by Matrix Assisted Laser Desorption Ionization - Time of Flight Mass Spectrometry (MALDI-TOF MS). From the eight, bacterial isolates investigated in this study Stenotrophomonas maltophilia showed the highest chitinase enzyme activity (625 μg/mL) followed by Pseudomonas putida with the enzyme activity of (553 μg/mL) and the least enzyme activity was recorded for Lilliottia amnigena (80 μg/mL). An incubation temperature of 45 °C, neutral pH and an incubation period of 96 h are found to be the optimum condition for the chitinase enzyme production from Stenotrophomonas maltophilia. The results of this study indicated the possibility of the production of chitinase from the chitinolytic bacterial isolates, which was highly useful for a variety of applications, including biocontrol of harmful insects and pathogenic fungi as well as in the biochemical, pharmaceutical, and medical sectors.

Characterization of chitinolytic bacteria newly isolated from the termite Microcerotermes sp. and their biocontrol potential against plant pathogenic fungi

Chitinolytic bacteria were isolated from guts and shells of the termite Microcerotermes sp. Among the nineteen morphologically different chitinolytic isolates, three isolates with highest extracellular chitinase production ratio (≥2.26) were selected. Based on molecular identification of 16S rRNA gene sequences and biochemical characterizations using API test kits and MALDI-TOF MS, these isolates were closely related to Bacillus thuringiensis (Mc_E02) and Paenibacillus species (Mc_E07 and Mc_G06). Isolate Mc_E02 exhibited the highest chitinase-specific activity (2.45 U/mg protein) at 96 h of cultivation, and the enzyme activity was optimized at pH 7.0 and 45 °C. The isolate showed highest and broad-spectrum inhibitory effect against three phytopathogenic fungi (Curvularia lunata, Colletotrichum capsici, and Fusarium oxysporum). Its 36-kDa chitinase exhibited the biomass reduction and mycelium inhibition against all fungi, with highest effects to Curvularia lunata. This research provides novel information about termite chitinolytic bacteria and their effective chitinase, with potential use as biocontrol tool.

Enhanced chitinase production by Chitinolyticbacter meiyuanensis SYBC-H1 using staged pH control

The pH of a microbiological culture is important for both cell growth and chitinase accumulation, but the optimal pH is not normally the same for both. The objective of this study was to investigate the effect of pH on chitinase production by Chitinolyticbacter meiyuanensis strain SYBC-H1 (ATCC BAA-2140) in a mineral medium. The results of batch culture at different pH values showed that the optimum pH for cell growth and chitinase production varied with time, although KOH produced the best results for cell growth and chitinase production, NaOH was chosen because of cost considerations. We designed a three-stage pH control strategy using NaOH as the neutralizing agent. Maximum cell growth (1.07 g dry cell weight/l) and maximum chitinase activity (13.6 U/ml) were observed after culture at 26°C for 72 h in a mineral medium. These values were greater by 129% and 162%, respectively, and the length of time to attain maximum chitinase activity was decreased by 12 h, compared with results from an earlier study (Hao et al., 2011b).

An acidic, thermostable exochitinase with β-N-acetylglucosaminidase activity from Paenibacillus barengoltzii converting chitin to N-acetyl glucosamine

BACKGROUND

N-acetyl-β-D-glucosamine (GlcNAc) is widely used as a valuable pharmacological agent and a functional food additive. The traditional chemical process for GlcNAc production has some problems such as high production cost, low yield, and acidic pollution. Hence, to identify a novel chitinase that is suitable for bioconversion of chitin to GlcNAc is of great value.

RESULTS

A novel chitinase gene (PbChi74) from Paenibacillus barengoltzii was cloned and heterologously expressed in Escherichia coli as an intracellular soluble protein. The gene has an open reading frame (ORF) of 2,163 bp encoding 720 amino acids. The recombinant chitinase (PbChi74) was purified to apparent homogeneity with a purification fold of 2.2 and a recovery yield of 57.9%. The molecular mass of the purified enzyme was estimated to be 74.6 kDa and 74.3 kDa by SDS-PAGE and gel filtration, respectively. PbChi74 displayed an acidic pH optimum of 4.5 and a temperature optimum of 65°C. The enzyme showed high activity toward colloidal chitin, glycol chitin, N-acetyl chitooligosaccharides, and p-nitrophenyl N-acetyl β-glucosaminide. PbChi74 hydrolyzed colloidal chitin to yield N-acetyl chitobiose [(GlcNAc)2] at the initial stage, which was further converted to its monomer N-acetyl glucosamine (GlcNAc), suggesting that it is an exochitinase with β-N-acetylglucosaminidase activity. The purified PbChi74 coupled with RmNAG (β-N-acetylglucosaminidase from Rhizomucor miehei) was used to convert colloidal chitin to GlcNAc, and GlcNAc was the sole end product at a concentration of 27.8 mg mL(-1) with a conversion yield of 92.6%. These results suggest that PbChi74 may have great potential in chitin conversion.

CONCLUSIONS

The excellent thermostability and hydrolytic properties may give the exochitinase great potential in GlcNAc production from chitin. This is the first report on an exochitinase with N-acetyl-β-D-glucosaminidase activity from Paenibacillus species.