Characterization of two novel plasmids from Geobacillus sp. 610 and 1121 strains

New Platform for Screening Genetic Libraries at Elevated Temperatures: Biological and Genomic Information and Genetic Tools of Geobacillus thermodenitrificans K1041

Geobacillus thermodenitrificans K1041 is an unusual thermophile that is highly transformable via electroporation, making it a promising host for screening genetic libraries at elevated temperatures. In this study, we determined its biological properties, draft genome sequence, and effective vectors and also optimized the electroporation procedures in an effort to enhance its utilization. The organism exhibited swarming motility but not detectable endospore formation, and growth was rapid at 60°C under neutral and relatively low-salt conditions. Although the cells showed negligible acceptance of shuttle plasmids from general strains of Escherichia coli, methylation-controlled plasmids from dam mutant strains were efficiently accepted, suggesting circumvention of a restriction-modification system in G. thermodenitrificans K1041. We optimized the electroporation procedure to achieve efficiencies of 10³ to 10⁵ CFU/μg for five types of plasmids, which exhibited the different copy numbers and segregational stabilities in G. thermodenitrificans K1041. Some sets of plasmids were compatible. Moreover, we observed substantial plasmid-directed production of heterologous proteins in the intracellular or extracellular environments. Our successful construction of a library of promoter mutants using K1041 cells as hosts and subsequent screening at elevated temperatures to identify improved promoters revealed that G. thermodenitrificans K1041 was practical as a library host. The draft genomic sequence of the organism contained 3,384 coding genes, including resA and mcrB genes, which are involved in restriction-modification systems. Further examination revealed that in-frame deletions of resA increased transformation efficiencies, but mcrB deletion had no effect. The ΔresA mutant exhibited transformation efficiencies of >10⁵ CFU/μg for some plasmids. IMPORTANCE Geobacillus thermodenitrificans K1041 has yet to be fully characterized. Although it is transformable via electroporation, it rarely accepts Escherichia coli-derived plasmids. This study clarified the biological and genomic properties of G. thermodenitrificans K1041. Additionally, we developed an electroporation procedure resulting in efficient acceptance of E. coli-derived plasmids. This procedure produced transformants using small amounts of plasmids immediately after the ligation reaction. Thus, G. thermodenitrificans K1041 was identified as a host for screening promoter mutants at elevated temperatures. Furthermore, because this strain efficiently produced heterologous proteins, it could serve as a host for screening thermostable proteins encoded in random mutant libraries or metagenomes. We also generated a ΔresA mutant that exhibited transformation efficiencies of >10⁵ CFU/μg, which were highest in cases of electroporation-based transformation of Geobacillus spp. with E. coli-derived plasmids. Our findings provide a new platform for screening diverse genetic libraries at elevated temperatures.

Draft Genome Sequence of Parageobacillus thermoglucosidasius Strain TG4, a Hydrogenogenic Carboxydotrophic Bacterium Isolated from a Marine Sediment

Parageobacillus thermoglucosidasius possesses biotechnological potential for fuel generation. Here, we report the draft genome sequence of P. thermoglucosidasius strain TG4, which was first isolated from a marine sediment.

Parageobacillus thermoglucosidasius possesses biotechnological potential for fuel generation. Here, we report the draft genome sequence of P. thermoglucosidasius strain TG4, which was first isolated from a marine sediment. The genome sequence provides insight into the plasmid diversity and carbon monoxide-dependent hydrogen production capacity of P. thermoglucosidasius.

The Geobacillus Plasmid Set: A Modular Toolkit for Thermophile Engineering

Geobacillus thermoglucosidasius is a Gram-positive thermophile of industrial interest that exhibits rapid growth and can utilize a variety of plant-derived feedstocks. It is an attractive chassis organism for high temperature biotechnology and synthetic biology applications but is currently limited by a lack of available genetic tools. Here we describe a set of modular shuttle vectors, including a promoter library and reporter proteins. The compact plasmids are composed of interchangeable modules for molecular cloning in Escherichia coli and stable propagation in G. thermoglucosidasius and other Geobacillus species. Modules include two origins of replication, two selectable markers and three reporter proteins for characterization of gene expression. For fine-tuning heterologous expression from these plasmids, we include a characterized promoter library and test ribosome binding site design. Together, these gene expression tools and a standardized plasmid set can facilitate modularity and part exchange to make Geobacillus a thermophile chassis for synthetic biology.

The genus Geobacillus and their biotechnological potential

The genus Geobacillus comprises a group of Gram-positive thermophilic bacteria, including obligate aerobes, denitrifiers, and facultative anaerobes that can grow over a range of 45-75°C. Originally classified as group five Bacillus spp., strains of Bacillus stearothermophilus came to prominence as contaminants of canned food and soon became the organism of choice for comparative studies of metabolism and enzymology between mesophiles and thermophiles. More recently, their catabolic versatility, particularly in the degradation of hemicellulose and starch, and rapid growth rates have raised their profile as organisms with potential for second-generation (lignocellulosic) biorefineries for biofuel or chemical production. The continued development of genetic tools to facilitate both fundamental investigation and metabolic engineering is now helping to realize this potential, for both metabolite production and optimized catabolism. In addition, this catabolic versatility provides a range of useful thermostable enzymes for industrial application. A number of genome-sequencing projects have been completed or are underway allowing comparative studies. These reveal a significant amount of genome rearrangement within the genus, the presence of large genomic islands encompassing all the hemicellulose utilization genes and a genomic island incorporating a set of long chain alkane monooxygenase genes. With G+C contents of 45-55%, thermostability appears to derive in part from the ability to synthesize protamine and spermine, which can condense DNA and raise its Tm.