Construction and characterization of a phage-plasmid hybrid (phagemid), pCAK1, containing the replicative form of viruslike particle CAK1 isolated from Clostridium acetobutylicum NCIB 6444

The Clostridium-infecting filamentous phage CAK1 genome analysis allows to define a new potential clade of Tubulavirales

What we know about Tubulavirales, i.e. filamentous phages, essentially comes from Gram-negative-infecting Inoviridae. However, metagenomics recently suggests filamentous phages are much more widespread and diverse. Here, we report the complete sequence and functional annotation of CAK1, a 6.6 kb filamentous phage that was shown to chronically infect Clostridium beijerinckii 30 years ago and only represents the second filamentous phage cultivated on a Gram-positive bacterium. CAK1 has a typical filamentous phage modular genome with no homologs in databases and we were interested to compare it with a pig gut filamentous phage metagenomics dataset that we previously assembled and for which many filamentous phages were predicted to infect Clostridium species by bioinformatics means. CAK1 is distantly related to nine of these sequences, two of which have been predicted as Clostridium-associated. In itself, this small cluster of CAK1-connected sequences sheds light on the diversity of filamentous phages that putatively infect Clostridium species, and probably many other Gram-positive genera.

Ribozyme-Mediated Downregulation Uncovers DNA Integrity Scanning Protein A (DisA) as a Solventogenesis Determinant in Clostridium beijerinckii

Carbon catabolite repression (CCR) limits microbial utilization of lignocellulose-derived pentoses. To relieve CCR in Clostridium beijerinckii NCIMB 8052, we sought to downregulate catabolite control protein A (CcpA) using the M1GS ribozyme technology. A CcpA-specific ribozyme was constructed by tethering the catalytic subunit of Escherichia coli RNase P (M1 RNA) to a guide sequence (GS) targeting CcpA mRNA (M1GS^CcpA). As negative controls, the ribozyme M1GS^CcpA–Sc (constructed with a scrambled GS^CcpA) or the empty plasmid pMTL500E were used. With a ∼3-fold knockdown of CcpA mRNA in C. beijerinckii expressing M1GS^CcpA (C. beijerinckii_M1GS^CcpA) relative to both controls, a modest enhancement in mixed-sugar utilization and solvent production was achieved. Unexpectedly, C. beijerinckii_M1GS^CcpA–Sc produced 50% more solvent than C. beijerinckii_pMTL500E grown on glucose + arabinose. Sequence complementarity (albeit suboptimal) suggested that M1GS^CcpA–Sc could target the mRNA encoding DNA integrity scanning protein A (DisA), an expectation that was confirmed by a 53-fold knockdown in DisA mRNA levels. Therefore, M1GS^CcpA–Sc was renamed M1GS^DisA. Compared to C. beijerinckii_M1GS^CcpA and _pMTL500E, C. beijerinckii_M1GS^DisA exhibited a 7-fold decrease in the intracellular c-di-AMP level after 24 h of growth and a near-complete loss of viability upon exposure to DNA-damaging antibiotics. Alterations in c-di-AMP-mediated signaling and cell cycling likely culminate in a sporulation delay and the solvent production gains observed in C. beijerinckii_M1GS^DisA. Successful knockdown of the CcpA and DisA mRNAs demonstrate the feasibility of using M1GS technology as a metabolic engineering tool for increasing butanol production in C. beijerinckii.

Microbial cellulose utilization: fundamentals and biotechnology

Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

Microbial cellulose utilization: fundamentals and biotechnology

Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

Detection, cloning, and sequence analysis of an indigenous plasmid from cellulolytic clostridial strain MCF1

Nucleotide sequence analysis of a 2451-bp plasmid (pMCF1) from a cellulolytic Clostridium revealed that the protein specified by the largest open reading frame (ORF1) was homologous to RepB of Clostridium butyricum plasmid pCB101. The data suggest that pMCF1 belongs to the pC194 family of rolling-circle replicating plasmids and the ORF1 protein functions as its replication protein.

Heterologous expression of endo-beta-1,4-D-glucanase from Clostridium cellulovorans in Clostridium acetobutylicum ATCC 824 following transformation of the engB gene

Heterologous expression of the Clostridium cellulovorans engB gene by Clostridium acetobutylicum BKW-1 was detected as zones of hydrolysis on carboxymethyl cellulose (CMC) Trypticase glucose yeast plates stained with Congo red. The extracellular cellulase preparation from C. acetobutylicum BKW-1 has a specific activity towards CMC which is more than fourfold that present in C. acetobutylicum ATCC 824. Western blot (immunoblot) analysis using the C. cellulovorans anti-EngB primary antibody demonstrated that an additional 44-kDa protein band was present in the supernatant derived from C. acetobutylicum BKW-1 but was not present in ATCC 824 or ATCC 824(pMTL500E).