Exiguobacterium: an overview of a versatile genus with potential in industry and agriculture.

The bacterial genus Exiguobacterium accommodates many versatile species isolated from diverse environments. Exiguobacterium was described as a genus approximately three decades ago, and now, 17 species, growing over a broad range of temperatures and pH, have been recognized. Various isolates from different niches have been explored for biotechnological and industrial purposes, including enzyme production, bioremediation and degradation of toxic substances released into the environment. Some isolates possess plant growth promoting capabilities, and they are currently being explored for increasing agricultural production. The genome sequences of various strains of this genus have shown the presence of many genes encoding products of importance to agriculture and the environment. In addition, many strains possess stress-responsive genes helping them to colonize and thrive in diverse ecological niches. This review provides a broad view of the versatile genus Exiguobacterium and its potential for applications in agriculture, the environment and industry, as well as the underlying genomic determinants that drive its diversity and adaptability to various extreme environments.

Efficient synthesis of hydroxystyrenes via biocatalytic decarboxylation/deacetylation of substituted cinnamic acids by newly isolated Pantoea agglomerans strains.

BACKGROUND: Decarboxylation of substituted cinnamic acids is a predominantly followed pathway for obtaining hydroxystyrenes-one of the most extensively explored bioactive compounds in the food and flavor industry (e.g. FEMA GRAS approved 4-vinylguaiacol). For this, mild and green strategies providing good yields with high product selectivity are needed. RESULTS: Two newly isolated bacterial strains, i.e. Pantoea agglomerans KJLPB4 and P. agglomerans KJPB2, are reported for mild and effective decarboxylation of substituted cinnamic acids into corresponding hydroxystyrenes. Key operational parameters for the process, such as incubation temperature, incubation time, substrate concentration and effect of co-solvent, were optimized using ferulic acid as a model substrate. With strain KJLPB4, 1.51 g L⁻¹ 4-vinyl guaiacol (98% yield) was selectively obtained from 2 g L⁻¹ ferulic acid at 28 °C after 48 h incubation. However, KJPB2 provided vanillic acid in 85% yield after 72 h following the oxidative decarboxylation pathway. In addition, KJLPB4 was effectively exploited for the deacetylation of acetylated α-phenylcinnamic acids, providing corresponding compounds in 65-95% yields. CONCLUSION: Two newly isolated microbial strains are reported for the mild and selective decarboxylation of substituted cinnamic acids into hydroxystyrenes. Preparative-scale synthesis of vinyl guaiacol and utilization of renewable feedstock (ferulic acid extracted from maize bran) have been demonstrated to enhance the practical utility of the process.

Cellulases from psychrophilic microorganisms: a review.

Cellulases are hydrolytic enzymes that catalyze total hydrolysis of cellulose into sugars. Cellulases are produced by various groups of microorganisms and animals; however, psychrophiles are the ideal candidates for the production of enzymes active at low temperature and stable under alkaline conditions, in the presence of oxidants and detergents, which are in large demand as laundry additives. The cellulases from psychrophiles also find application in environmental bioremediation, food industry and molecular biology. Research work on cellulase has been done over the last six decades, but there is no exclusive review available on the cellulases from psychrophiles. This review is an attempt to fill this gap by providing all the relevant information exclusively for cellulases from psychrophiles, with a focus on the present status of knowledge on their activity, molecular characteristics, gene cloning, statistical experimental designs, crystal structure, and strategies for the improvement of psychrophilic cellulases.

Cloning and expression of low temperature active endoglucanase EG5C from Paenibacillus sp. IHB B 3084.

The endoglucanase gene designated as EG5C encoding cold active endoglucanase produced by Paenibacillus sp. IHB B 3084 was cloned and expressed in Escherichia coli BL21(DE3). The gene consisting of 1719bp open reading frame encoded a protein of 573 amino acids with a predicted molecular weight of 63.5kDa. The presence of N-terminal catalytic domain of the glycosyl hydrolase family 5 (GH5) and C-terminal carbohydrate binding X2 domain suggested the modular nature of the enzyme. The native signal peptide of EG5C was capable of efficiently secreting the enzyme with near equal activities in the cytoplasmic and extracellular fractions. The recombinant enzyme purified 9.46 fold to homogeneity with 22.33% yield gave 7.758IU/mg specific activity. The enzyme was stable over the broad pH range of 4-12 with more than 50% residual activity. The optimal activity was at 40°C with 70% relative activity at 5°C. The low temperature activity despite the shorter linker region suggested a novel cold adaptation mechanism by the enzyme. The enzyme displayed higher activity on carboxymethylcellulose than avicel which is useful in maintaining the tensile strength of fiber. The efficient secretion and low temperature activity offer prospect for large-scale production and industrial application of the endoglucanase.

Isolation of a psychrotrophic Exiguobacterium sp. SKPB5 (MTCC 7803) and characterization of its alkaline protease.

Out of nine psychrotrophic bacterial strains isolated from cold environments of the Western Himalayas, SKPB5 was selected for protease purification and characterization because it had the largest zone of clearance on plate assay. On the basis of the phenotypic and biochemical characterization and 16S rRNA gene-sequencing studies, isolate was identified as Exiguobacterium sp. SKPB5. The protease was purified near to homogeneity with a purification fold of 7.1, and its molecular weight was determined to be 36 kDa. The enzyme exhibited maximum stability at 50 degrees C and an optimal pH of 8.0. Metal ions Mg2+, Ca2+, Zn2+, and Mn2+ enhanced the enzyme activity, whereas Cu2+ had no effect. Phenylmethanesulfonyl fluoride and ethylenediaminetetraacetic acid did not show any effect on the activity of the enzyme, whereas a 20% increase in activity was observed when it was incubated in presence of reducing agents such as beta-mercaptoethanol and dithiothreitol. This suggests that the protease isolated from psychrotrophic Exiguobacterium sp. SKPB5 belongs to the cysteine family. The results highlight the relevance of unexplored microbes from cold environments of Western Himalayas for the isolation of protease enzymes active at wide range of temperature and pH.

Isolation and identification of a novel strain of Pseudomonas chlororaphis capable of transforming isoeugenol to vanillin.

Vanillin is undoubtedly one of the most popular and widely used flavoring agents in the world. Taking into consideration the worldwide demand for natural vanillin and its limited supply, alternative routes for its production including biotransformation are being constantly explored. In this regard, a novel soil bacterium capable of converting isoeugenol to vanillin was isolated by conventional enrichment process from soils of Ocimum field. On the basis of morphological and physiochemical characteristics and 16S rRNA gene sequence analysis, the isolate was identified as Pseudomonas chlororaphis CDAE5 (EMBL # AM158279). Vanillin formation was analyzed by gas chromatography (GC), and its structure was confirmed by GC-mass spectrometry and nuclear magnetic resonance. After 24-h reaction, the vanillin concentration reached 1.2 g L(-1) from 10 g L(-1) isoeugenol in 20-mL reaction solution at 25 degrees C and 180 rpm. The strain showed potential to be a good candidate for biotechnological production of vanillin from isoeugenol. Further studies for standardization and optimization for higher yield of vanillin production needs to be investigated.