F96

Nocardiopsis species: Incidence, ecological roles and adaptations

Members of the genus Nocardiopsis are ecologically versatile and biotechnologically important. They produce a variety of bioactive compounds such as antimicrobial agents, anticancer substances, tumor inducers, toxins and immunomodulators. They also secrete novel extracellular enzymes such as amylases, chitinases, cellulases, β-glucanases, inulinases, xylanases and proteases. Nocardiopsis species are aerobic, Gram-positive, non-acid-fast, catalase-positive actinomycetes with nocardioform substrate mycelia and their aerial mycelia bear long chains of spores. Their DNA possesses high contents of guanine and cytosine. There is a marked variation in properties of the isolates obtained from different ecological niches and their products. An important feature of several species is their halophilic or halotolerant nature. They are associated with a variety of marine and terrestrial biological forms wherein they produce antibiotics and toxins that help their hosts in evading pathogens and predators. Two Nocardiopsis species, namely, N. dassonvillei and N. synnemataformans (among the thirty nine reported ones) are opportunistic human pathogens and cause mycetoma, suppurative infections and abscesses. Nocardiopsis species are present in some plants (as endophytes or surface microflora) and their rhizospheres. Here, they are reported to produce enzymes such as α-amylases and antifungal agents that are effective in warding-off plant pathogens. They are prevalent as free-living entities in terrestrial locales, indoor locations, marine ecosystems and hypersaline habitats on account of their salt-, alkali- and desiccation-resistant behavior. In such natural locations, Nocardiopsis species mainly help in recycling organic compounds. Survival under these diverse conditions is mediated by the production of extracellular enzymes, antibiotics, surfactants, and the accumulation of compatible solutes. The accommodative genomic features of Nocardiopsis species support their existence under the diverse conditions where they prevail.

Nocardiopsis species as potential sources of diverse and novel extracellular enzymes

Members of the genus Nocardiopsis are generally encountered in locations that are inherently extreme. They are present in frozen soils, desert sand, compost, saline or hypersaline habitats (marine systems, salterns and soils) and alkaline places (slag dumps, lake soils and sediments). In order to survive under these severe conditions, they produce novel and diverse enzymes that allow them to utilize the available nutrients and to thrive. The members of this genus are multifaceted and release an assortment of extracellular hydrolytic enzymes. They produce enzymes that are cold-adapted (α-amylases), thermotolerant (α-amylases and xylanases), thermoalkalotolerant (cellulases, β-1,3-glucanases), alkali-tolerant thermostable (inulinases), acid-stable (keratinase) and alkalophilic (serine proteases). Some of the enzymes derived from Nocardiopsis species act on insoluble polymers such as glucans (pachyman and curdlan), keratin (feathers and prion proteins) and polyhydroxyalkanoates. Extreme tolerance exhibited by proteases has been attributed to the presence of some amino acids (Asn and Pro) in loop structures, relocation of multiple salt bridges to outer regions of the protein or the presence of a distinct polyproline II helix. The range of novel enzymes is projected to increase in the forthcoming years, as new isolates are being continually reported, and the development of processes involving such enzymes is envisaged in the future.

Recombinant production and characterization of full-length and truncated β-1,3-glucanase PglA from Paenibacillus sp. S09

Background

β-1,3-Glucanases catalyze the hydrolysis of glucan polymers containing β-1,3-linkages. These enzymes are of great biotechnological, agricultural and industrial interest. The applications of β-1,3-glucanases is well established in fungal disease biocontrol, yeast extract production and wine extract clarification. Thus, the identification and characterization of novel β-1,3-glucanases with high catalytic efficiency and stability is of particular interest.

Results

A β-1,3-glucanase gene designated PglA was cloned from a newly isolated strain Paenibacillus sp. S09. The gene PglA contained a 2631-bp open reading frame encoding a polypeptide of 876 amino acids which shows 76% identity with the β-1,3-glucanase (BglH) from Bacillus circulans IAM1165. The encoded protein PglA is composed of a signal peptide, an N-terminal leader region, a glycoside hydrolase family 16 (GH16) catalytic domain and a C-terminal immunoglobulin like (Ig-like) domain. The Escherichia coli expression system of PglA and five truncated derivatives containing one or two modules was constructed to investigate the role of catalytic and non-catalytic modules. The pH for optimal activity of the enzymes was slightly affected (pH 5.5-6.5) by the presence of different modules. However, the temperature for optimal activity was strongly influenced by the C-terminal domain and ranged from 50 to 60°C. Deletion of C-terminal domain resulted in obviously enhancing enzymatic thermostability. Specific activity assay indicated that PglA specifically hydrolyzes β-1,3-glucan. Insoluble β-1,3-glucan binding and hydrolysis were boosted by the presence of N-and C-terminal domains. Kinetic analysis showed that the presence of N-and C-terminus enhances the substrate affinity and catalytic efficiency of the catalytic domain toward laminarin. Carbohydrate-binding assay directly confirmed the binding capabilities of the N-and C-terminal domains.

Conclusions

This study provides new insight into the impacts of non-catalytic modules on enzymatic properties of β-1,3-glucanase. Activity comparison of full-length PglA and truncated forms revealed the negative effect of C-terminal region on thermal stability of the enzyme. Both the N-and C-terminal domains exerted strong binding activity toward insoluble β-1,3-glucan, and could be classified into CBM families.