A High Diversity in Chitinolytic and Chitosanolytic Species and Enzymes and Their Oligomeric Products Exist in Soil with a History of Chitin and Chitosan Exposure

Morphological and structural characterization of chitin as a substrate for the screening, production, and molecular characterization of chitinase by Bacillus velezensis

The processing of shellfishery industrial wastes is gaining much interest in recent times due to the presence of valuable components. Chitin is one of the valuable components and is insoluble in most common solvents including water. In this study, a novel gram-positive bacterial strain capable of solubilizing chitin was screened from a prawn shell dumping yard. The chitinolytic activity of the isolated strain was observed through the zone of hydrolysis plate assay. The hyper-producing isolate was identified as Bacillus velezensis through the 16S rRNA sequencing technique. The structural and morphological characterization of raw and colloidal chitin preparation was carried out using FTIR, XRD, and SEM analysis. The residual protein and mineral content, degree of polymerization, and degree of acetylation were reported for both raw and colloidal chitin preparations. There was a linear increase in the chitinase activity with an increase in the colloidal chitin concentration. The maximum activity of chitinase was observed as 38.98 U/mL for the initial colloidal chitin concentration of 1.5%. Supplement of additional carbon sources, viz., glucose and maltose, did not improve the production of chitinase and resulted in a diauxic growth pattern. The maximum chitinase activity was observed to be 33.10 and 30.28 U/mL in the colloidal chitin-containing medium with and without glucose as a secondary carbon source, respectively. Interestingly, the addition of complex nitrogen sources has increased the production of chitinase. A 1.95- and 2.14-fold increase in the enzyme activity was observed with peptone and yeast extract, respectively. The chitinase was confirmed using SDS-PAGE, native PAGE, and zymograms. The optimum pH and temperature for chitinase enzyme activity were found to be 7.0 and 44 °C, respectively.

Multifarious functional traits of free-living rhizospheric fungi, with special reference to Aspergillus spp. isolated from North Indian soil, and their inoculation effect on plant growth

Purpose

Rhizospheric soil fungi are critical for plant and soil health. However, their multiple functional traits and impact on plant growth have not been systematically explored.

Methods

During this study, biochemical traits of 73 indigenous soil fungal isolates and 15 unidentified isolates related to plant growth promotion and production of extracellular enzymes were studied.

Results

Forty four (65.67%) of the total isolates produced indole acetic acid (IAA) followed by siderophore (52.23%), phosphate solubilization (37.31%), and antibiotic (11.93%). 91.04% of the studied isolates produced ammonia whereas 28.35% produced organic acid. Extracellular enzyme activities of lipase, amylase, chitinase, and cellulase were detected among 95.52%, 61.11%, 35.82%, and 41.79% isolates, respectively. Based on these activities, 73 fungal isolates were categorized into different biotypes. Quantitative analysis of IAA production and phosphate solubilization was carried out for Aspergillus, Penicillium, and Rhizopus isolates. Aspergillus isolates exhibited varying activities of IAA production and phosphate solubilization. Most of the Aspergillus isolates and some other fungi demonstrated multiple activities. Based on the multiple traits of selected fungal isolates, Aspergillus sp-07, Penicillium sp-03, and Rhizopus sp-02 were further evaluated in different combinations for their inoculation effect on the growth and yield of wheat under field conditions.

Conclusions

The results indicated that these isolates could be developed into bio-inoculants to enhance plant growth. The consortium of these three isolates was also found to be compatible and beneficial for plant growth.

Resolving the Mortierellaceae phylogeny through synthesis of multi-gene phylogenetics and phylogenomics

Early efforts to classify Mortierellaceae were based on macro- and micromorphology, but sequencing and phylogenetic studies with ribosomal DNA (rDNA) markers have demonstrated conflicting taxonomic groupings and polyphyletic genera. Although some taxonomic confusion in the family has been clarified, rDNA data alone is unable to resolve higher level phylogenetic relationships within Mortierellaceae. In this study, we applied two parallel approaches to resolve the Mortierellaceae phylogeny: low coverage genome (LCG) sequencing and high-throughput, multiplexed targeted amplicon sequencing to generate sequence data for multi-gene phylogenetics. We then combined our datasets to provide a well-supported genome-based phylogeny having broad sampling depth from the amplicon dataset. Resolving the Mortierellaceae phylogeny into monophyletic groups led to the definition of 14 genera, 7 of which are newly proposed. Low-coverage genome sequencing proved to be a relatively cost-effective means of generating a well-resolved phylogeny. The multi-gene phylogenetics approach enabled much greater sampling depth and breadth than the LCG approach, but was unable to resolve higher-level organization of groups. We present this work to resolve some of the taxonomic confusion and provide a genus-level framework to empower future studies on Mortierellaceae diversity, biology, and evolution.

Conversion of Chitin to Defined Chitosan Oligomers: Current Status and Future Prospects

Chitin is an abundant polysaccharide primarily produced as an industrial waste stream during the processing of crustaceans. Despite the limited applications of chitin, there is interest from the medical, agrochemical, food and cosmetic industries because it can be converted into chitosan and partially acetylated chitosan oligomers (COS). These molecules have various useful properties, including antimicrobial and anti-inflammatory activities. The chemical production of COS is environmentally hazardous and it is difficult to control the degree of polymerization and acetylation. These issues can be addressed by using specific enzymes, particularly chitinases, chitosanases and chitin deacetylases, which yield better-defined chitosan and COS mixtures. In this review, we summarize recent chemical and enzymatic approaches for the production of chitosan and COS. We also discuss a design-of-experiments approach for process optimization that could help to enhance enzymatic processes in terms of product yield and product characteristics. This may allow the production of novel COS structures with unique functional properties to further expand the applications of these diverse bioactive molecules.

Chitin and chitin-related compounds in plant-fungal interactions

Chitin is the second abundant polysaccharide in the world after cellulose. It is a vital structural component of the fungal cell wall but not for plants. In plants, fungi are recognised through the perception of conserved microbe-associated molecular patterns (MAMPs) to induce MAMP-triggered immunity (MTI). Chitin polymers and their modified form, chitosan, induce host defence responses in both monocotyledons and dicotyledons. The plants' response to chitin, chitosan, and derived oligosaccharides depends on the acetylation degree of these compounds which indicates possible biocontrol regulation of plant immune system. There has also been a considerable amount of recent research aimed at elucidating the roles of chitin hydrolases in fungi and plants as chitinase production in plants is not considered solely as an antifungal resistance mechanism. We discuss the importance of chitin forms and chitinases in the plant-fungal interactions and their role in persistent and possible biocontrol. Abbreviations ET, ethylene; GAP, GTPase-activating protein; GEF, GDP/GTP exchange factor; JA, jasmonic acid; LysM, lysin motif; MAMP, microbe-associated molecular pattern; MTI, MAMP-triggered immunity; NBS, nucleotide-binding site; NBS-LRR, nucleotide-binding site leucine-rich repeats; PM, powdery mildew; PR, pathogenesis-related; RBOH, respiratory burst oxidase homolog; RLK, receptor-like kinase; RLP, receptor-like protein; SA, salicylic acid; TF, transcription factor.

Chitosanase purified from bacterial isolate Bacillus licheniformis of ruined vegetables displays broad spectrum biofilm inhibition

A number of bacterial species produces chitosanases which has variety of applications because of its high biodegradability, non-toxicity and antimicrobial assets. In the present study chitosanase is purified from new bacterial species Bacillus licheniformis from spoiled vegetable. This novel strain of Bacillus licheniformis isolated from spoilt cucumber and pepper samples has the ability to produce the chitosanase enzyme when grown on chitosan substrate. Study also examined its antibiofilm properties against diverse bacterial species with biofilm forming ability. The purified chitosanase inhibited the biofilm formation ability for all Gram-negative and Gram-positive biofilm-forming bacteria [biofilm producers] tested in this study in congo red agar and microtiter plate's methods. Highly antibiofilm activity of chitosanase was recorded against Pseudomonas aeruginosa followed by Klebsiella pneumoniae with reduction of biofilm formation upto 22 and 29%, respectively compared with [100] % of control. Biofilm formation has multiple role including ability to enhance resistance and self-protection from external stress. This chitosanase has promising benefit as antibiofilm agent against biofilm forming pathogenic bacteria and has promising application as alternative antibiofilm agents to combat the growing number of multidrug resistant pathogen-associated infections, especially in situation where biofilms are involved.