Conjugative reporter system for the use in Bacillus licheniformis and closely related Bacilli

Establishment of the CRISPR-Cpf1 gene editing system in Bacillus licheniformis and multiplexed gene knockout

Bacillus licheniformis is a significant industrial microorganism. Traditional gene editing techniques relying on homologous recombination often exhibit low efficiency due to their reliance on resistance genes. Additionally, the established CRISPR gene editing technology, utilizing Cas9 endonuclease, faces challenges in achieving simultaneous knockout of multiple genes. To address this limitation, the CRISPR-Cpf1 system has been developed, enabling multiplexed gene editing across various microorganisms. Key to the efficient gene editing capability of this system is the rigorous screening of highly effective expression elements to achieve conditional expression of protein Cpf1. In this study, we employed mCherry as a reporter gene and harnessed P mal for regulating the expression of Cpf1 to establish the CRISPR-Cpf1 gene editing system in Bacillus licheniformis. Our system achieved a 100 % knockout efficiency for the single gene vpr and up to 80 % for simultaneous knockout of the double genes epr and mpr. Furthermore, the culture of a series of protease-deficient strains revealed that the protease encoded by aprE contributed significantly to extracellular enzyme activity (approximately 80 %), whereas proteases encoded by vpr, epr, and mpr genes contributed to a smaller proportion of extracellular enzyme activity. These findings provide support for effective molecular modification and metabolic regulation in industrial organisms.

Living in a Puddle of Mud: Isolation and Characterization of Two Novel Caulobacteraceae Strains Brevundimonas pondensis sp. nov. and Brevundimonas goettingensis sp. nov

Brevundimonas is a genus of freshwater bacteria belonging to the family Caulobacteraceae. The present study describes two novel species of the genus Brevundimonas (LVF1T and LVF2T). Both were genomically, morphologically, and physiologically characterized. Average nucleotide identity analysis revealed both are unique among known Brevundimonas strains. In silico and additional ProphageSeq analyses resulted in two prophages in the LVF1T genome and a remnant prophage in the LVF2T genome. Bacterial LVF1T cells form an elliptical morphotype, in average 1 µm in length and 0.46 µm in width, with a single flagellum. LVF2T revealed motile cells approximately 1.6 µm in length and 0.6 µm in width with a single flagellum, and sessile cell types 1.3 µm in length and 0.6 µm in width. Both are Gram-negative, aerobic, have optimal growth at 30 °C (up to 0.5 to 1% NaCl). Both are resistant towards erythromycin, meropenem, streptomycin, tetracycline and vancomycin. Anaerobic growth was observed after 14 days for LVF1T only. For LVF1T the name Brevundimonas pondensis sp. nov. and for LVF2T the name Brevundimonas goettingensis sp. nov. are proposed. Type strains are LVF1T (=DSM 112304T = CCUG 74982T = LMG 32096T) and LVF2T (=DSM 112305T = CCUG 74983T = LMG 32097T).

Transmating: conjugative transfer of a new broad host range expression vector to various Bacillus species using a single protocol

BACKGROUND

The genus Bacillus includes a great variety of species with potential applications in biotechnology. While species such as B. subtilis or B. licheniformis are well-known and used to provide various products at industrial scale, other Bacillus species are less characterized and are not yet used in commercial processes. One reason for this is the fact that genetic manipulation of new isolates is usually complicated with conventional techniques which have to be adapted to each new strain. Even in well-established strains, the available transformation protocols often suffer from low efficiencies.

RESULTS

In this paper, we provide a new broad host range E. coli/Bacillus shuttle vector, named pBACOV (Bacillus conjugation vector), that can be efficiently transferred to various Bacillus species using a single protocol. A variant of pBACOV carrying the sfGFP gene was successfully transferred to eight different species from the genus Bacillus and to one Paenibacillus species using triparental conjugation ("transmating"). This was achieved using a single protocol and worked for nine out of eleven tested acceptor species. The transmating procedure was used to test expression of the heterologous reporter gene sfGFP under control of the P_aprE-promoter from B. subtilis in several Bacillus species in parallel. Expression of sfGFP was found in eight out of nine transmates. For several of the tested species, this is the first report of a method for genetic modification and heterologous gene expression. The expression level, analyzed by measuring the relative sfGFP-fluorescence normalized to the cell density of the cultures, was highest in B. mojavensis.

CONCLUSIONS

The new shuttle vector pBACOV can be transferred to many different Bacillus and Paenibacillus species using a simple and efficient transmating protocol. It is a versatile tool facilitating the application of recombinant DNA technology in new as well as established strains, or selection of an ideal host for heterologous gene expression from a multitude of strains. This paves the way for the genetic modification and biotechnological exploitation of the broad diversity of species of Bacillus and related genera as well as different strains from these species.

Genetic Tools and Techniques for Recombinant Expression in Thermophilic Bacillaceae

Although Escherichia coli and Bacillus subtilis are the most prominent bacterial hosts for recombinant protein production by far, additional species are being explored as alternatives for production of difficult-to-express proteins. In particular, for thermostable proteins, there is a need for hosts able to properly synthesize, fold, and excrete these in high yields, and thermophilic Bacillaceae represent one potentially interesting group of microorganisms for such purposes. A number of thermophilic Bacillaceae including B.methanolicus, B.coagulans, B.smithii, B.licheniformis, Geobacillus thermoglucosidasius, G. kaustophilus, and G. stearothermophilus are investigated concerning physiology, genomics, genetic tools, and technologies, altogether paving the way for their utilization as hosts for recombinant production of thermostable and other difficult-to-express proteins. Moreover, recent successful deployments of CRISPR/Cas9 in several of these species have accelerated the progress in their metabolic engineering, which should increase their attractiveness for future industrial-scale production of proteins. This review describes the biology of thermophilic Bacillaceae and in particular focuses on genetic tools and methods enabling use of these organisms as hosts for recombinant protein production.

Small RNA mediated repression of subtilisin production in Bacillus licheniformis

The species Bacillus licheniformis includes important strains that are used in industrial production processes. Currently the physiological model used to adapt these processes is based on the closely related model organism B. subtilis. In this study we found that both organisms reveal significant differences in the regulation of subtilisin, their main natural protease and a product of industrial fermentation processes. We identified and characterized a novel antisense sRNA AprAs, which represents an RNA based repressor of apr, the gene encoding for the industrial relevant subtilisin protease. Reduction of the AprAs level leads to an enhanced proteolytic activity and an increase of Apr protein expression in the mutant strain. A vector based complementation of the AprAs deficient mutant confirmed this effect and demonstrated the necessity of cis transcription for full efficiency. A comparative analysis of the corresponding genome loci from B. licheniformis and B. subtilis revealed the absence of an aprAs promoter in B. subtilis and indicates that AprAs is a B. licheniformis species specific phenomenon. The discovery of AprAs is of great biotechnological interest since subtilisin Carlsberg is one of the main products of industrial fermentation by B. licheniformis.