SapB and the chaplins: connections between morphogenetic proteins in Streptomyces coelicolor

The evolution of morphological development is congruent with the species phylogeny in the genus Streptomyces

As the canonical model organism to dissect bacterial morphological development, Streptomyces species has attracted much attention from the microbiological society. However, the evolution of development-related genes in Streptomyces remains elusive. Here, we evaluated the distribution of development-related genes, thus indicating that the majority of these genes were ubiquitous in Streptomyces genomes. Furthermore, the phylogenetic topologies of related strict orthologous genes were compared to the species tree of Streptomyces from both concatenation and single-gene tree analyses. Meanwhile, the reconciled gene tree and normalization based on the number of parsimony-informative sites were also employed to reduce the impact of phylogenetic conflicts, which was induced by uncertainty in single-gene tree inference based merely on the sequence and the bias in the amount of phylogenetic information caused by variable numbers of parsimony-informative sites. We found that the development-related genes had higher congruence to the species tree than other strict orthologous genes. Considering that the development-related genes could also be tracked back to the common ancestor of Streptomyces, these results suggest that morphological development follows the same pattern as species divergence.

Unexpected Methyllanthionine Stereochemistry in the Morphogenetic Lanthipeptide SapT

Lanthipeptides are polycyclic peptides characterized by the presence of lanthionine (Lan) and/or methyllanthionine (MeLan). They are members of the ribosomally synthesized and post-translationally modified peptides (RiPPs). The stereochemical configuration of (Me)Lan cross-links is important for the bioactivity of lanthipeptides. To date, MeLan residues in characterized lanthipeptides have either the 2S,3S or 2R,3R stereochemistry. Herein, we reconstituted in Escherichia coli the biosynthetic pathway toward SapT, a class I lanthipeptide that exhibits morphogenetic activity. Through the synthesis of standards, the heterologously produced peptide was shown to possess three MeLan residues with the 2S,3R stereochemistry (d-allo-l-MeLan), the first time such stereochemistry has been observed in a lanthipeptide. Bioinformatic analysis of the biosynthetic enzymes suggests this stereochemistry may also be present in other lanthipeptides. Analysis of another gene cluster in Streptomyces coelicolor that is widespread in actinobacteria confirmed another example of d-allo-l-MeLan and verified the bioinformatic prediction. We propose a mechanism for the origin of the unexpected stereochemistry and provide support using site-directed mutagenesis.

Reviewing a plethora of oxidative-type reactions catalyzed by whole cells of Streptomyces species

Selective oxidation reactions represent a challenging task for conventional organic chemistry. Whole-cell biocatalysis provides a very convenient, easy to apply method to carry out different selective oxidation reactions including chemo-, regio-, and enantio-selective reactions. Streptomyces species are important biocatalysts as they can catalyze these selective reactions very efficiently owing to the wide diversity of enzymes and enzymatic cascades in their cell niche. In this review, we present and analyze most of the examples reported to date of oxidative reactions catalyzed by Streptomyces species as whole-cell biocatalysts. We discuss 33 different Streptomyces species and strains and the role they play in different oxidative reactions over the past five decades. The oxidative reactions have been classified into seven categories that include: hydroxylation of steroids/non-steroids, asymmetric sulfoxidations, oxidation of aldehydes, multi-step oxidations, oxidative cleavage, and N-oxidations. The role played by Streptomyces species as recombinant hosts catalyzing bio-oxidations has also been highlighted.

Identification of the cognate response regulator of the orphan histidine kinase OhkA involved in both secondary metabolism and morphological differentiation in Streptomyces coelicolor

In the model actinomycete strain, Streptomyces coelicolor, an orphan histidine kinase (HK) named OhkA (encoded by SCO1596), which belongs to bacterial two-component regulatory systems (TCSs), has been identified as being involved in the regulation of both antibiotic biosynthesis and morphological development. However, its cognate response regulator (RR) remains unknown due to its isolated genetic location on the genome, which impedes the elucidation of the mechanism underlying OhkA-mediated regulation. Here, we identified the orphan RR OrrA (encoded by SCO3008) as the cognate RR of OhkA according to mutant phenotypic changes, transcriptomics analysis, and bacterial two-hybrid experiment. Considering that the partner RR of the orphan HK is also orphan, a library of mutants with in-frame individual deletion of these functionally unknown orphan RR-encoding genes were generated. Through phenotypic analysis, it was found that the ∆orrA mutant exhibited similar phenotypic changes as that of the ∆ohkA mutant, showing increased production of actinorhodin (ACT) and undecylprodigiosin (RED), and pink colony surface. Further transcriptomics analysis showed these two mutants exhibited highly similar transcriptomics profiles. Finally, the direct interaction between OhkA and OrrA was revealed by bacterial two-hybrid system. The identification of the partner RR of OhkA lays a good foundation for an in-depth elucidation of the molecular mechanism underlying OhkA-mediated regulation of development and antibiotic biosynthesis in Streptomyces. KEY POINTS: • OrrA was identified as the partner RR of the orphan histidine kinase OhkA. • The ∆orrA and ∆ohkA mutants showed similar phenotype and transcriptomic profiling. • Specific interaction of OrrA and OhkA was revealed by bacterial two-hybrid system.

Current Understanding on Adhesion and Biofilm Development in Actinobacteria

Biofilm formation and microbial adhesion are two related and complex phenomena. These phenomena are known to play an important role in microbial life and various functions with positive and negative aspects. Actinobacteria have wide distribution in aquatic and terrestrial ecosystems. This phylum is very large and diverse and contains two important genera Streptomyces and Mycobacteria. The genus Streptomyces is the most biotechnologically important, while the genus Mycobacteria contains the pathogenic species of Mycobacteriaceae. According to the literature, the majority of studies carried out on actinomycetes are focused on the detection of new molecules. Despite the well-known diversity and metabolic activities, less attention has been paid to this phylum. Research on adhesion and biofilm formation is not well developed. In the present review, an attempt has been made to review the literature available on the different aspects on biofilm formation and adhesion of Actinobacteria. We focus especially on the genus Streptomyces. Furthermore, a brief overview about the molecules and structures involved in the adhesion phenomenon in the most relevant genus is summarized. We mention the mechanisms of quorum sensing and quorum quenching because of their direct association with biofilm formation.

Prodiginines Postpone the Onset of Sporulation in Streptomyces coelicolor

Bioactive natural products are typically secreted by the producer strain. Besides that, this allows the targeting of competitors, also filling a protective role, reducing the chance of self-killing. Surprisingly, DNA-degrading and membrane damaging prodiginines (PdGs) are only produced intracellularly, and are required for the onset of the second round of programmed cell death (PCD) in Streptomyces coelicolor. In this work, we investigated the influence of PdGs on the timing of the morphological differentiation of S. coelicolor. The deletion of the transcriptional activator gene redD that activates the red cluster for PdGs or nutrient-mediated reduction of PdG synthesis both resulted in the precocious appearance of mature spore chains. Transcriptional analysis revealed an accelerated expression of key developmental genes in the redD null mutant, including bldN for the developmental σ factor BldN which is essential for aerial mycelium formation. In contrast, PdG overproduction due to the enhanced copy number of redD resulted in a delay or block in sporulation. In addition, confocal fluorescence microscopy revealed that the earliest aerial hyphae do not produce PdGs. This suggests that filaments that eventually differentiate into spore chains and are hence required for survival of the colony, are excluded from the second round of PCD induced by PdGs. We propose that one of the roles of PdGs would be to delay the entrance of S. coelicolor into the dormancy state (sporulation) by inducing the leakage of the intracellular content of dying filaments thereby providing nutrients for the survivors.

Antibiotic Production and Antibiotic Resistance: The Two Sides of AbrB1/B2, a Two-Component System of Streptomyces coelicolor

Antibiotic resistance currently presents one of the biggest threats to humans. The development and implementation of strategies against the spread of superbugs is a priority for public health. In addition to raising social awareness, approaches such as the discovery of new antibiotic molecules and the elucidation of resistance mechanisms are common measures. Accordingly, the two-component system (TCS) of Streptomyces coelicolor AbrB1/B2, offer amenable ways to study both antibiotic production and resistance. Global transcriptomic comparisons between the wild-type strain S. coelicolor M145 and the mutant ΔabrB, using RNA-Seq, showed that the AbrB1/B2 TCS is implicated in the regulation of different biological processes associated with stress responses, primary and secondary metabolism, and development and differentiation. The ΔabrB mutant showed the up-regulation of antibiotic biosynthetic gene clusters and the down-regulation of the vancomycin resistance gene cluster, according to the phenotypic observations of increased antibiotic production of actinorhodin and undecylprodigiosin, and greater susceptibility to vancomycin. The role of AbrB1/B2 in vancomycin resistance has also been shown by an in silico analysis, which strongly indicates that AbrB1/B2 is a homolog of VraR/S from Staphylococcus aureus and LiaR/S from Enterococcus faecium/Enterococcus faecalis, both of which are implied in vancomycin resistance in these pathogenic organisms that present a serious threat to public health. The results obtained are interesting from a biotechnological perspective since, on one hand, this TCS is a negative regulator of antibiotic production and its high degree of conservation throughout Streptomyces spp. makes it a valuable tool for improving antibiotic production and the discovery of cryptic metabolites with antibiotic action. On the other hand, AbrB1/B2 contributes to vancomycin resistance and is a homolog of VraR/S and LiaR/S, important regulators in clinically relevant antibiotic-resistant bacteria. Therefore, the study of AbrB1/B2 could provide new insight into the mechanism of this type of resistance.

A novel XRE family regulator that controls antibiotic production and development in Streptomyces coelicolor

Although the genome of the Streptomyces model strain S. coelicolor was sequenced nearly two decades ago, the function of many annotated genes has not been verified, including that of gene sco1979, which was predicted to encode a transcriptional regulator of the xenobiotic response element (XRE) family. In this study, we showed that SCO1979 represses its own transcription and that deletion of sco1979 from S. coelicolor markedly enhanced production of three antibiotics, which are actinorhodin (ACT), undecylprodigiosin (RED), and calcium-dependent antibiotic (CDA), suggesting that SCO1979 represses their biosynthesis. We demonstrated that transcription of genes in the ACT, RED, and CDA pathways was generally increased in the mutant strain Δ1979 compared with levels in the wild-type strain M145. Additionally, purified recombinant SCO1979 interacted with DNA sequences upstream of sco1979 and actII-orf4, redZ, and cdaR, the pathway-specific regulators for the three pathways, implying that SCO1979 potentially regulates the ACT, RED, and CDA pathways via their specific regulators. In addition, disruption of sco1979 led to the notably delayed formation of aerial mycelium and spores, and consistent with this, transcription of genes associated with aerial hyphae and spore formation, such as chp and rdl, and ram, was reduced in Δ1979, implying the involvement of SCO1979 in cellular development control as well. In summary, our findings demonstrated that SCO1979 is a pleiotropic regulator with roles in both secondary metabolism and morphological development in S. coelicolor. KEY POINTS: • SCO1979 is a novel Streptomyces regulator of the XRE family. • SCO1979 regulates its own transcription. • SCO1979 regulates antibiotic production and cellular development.

Antarctic Streptomyces fildesensis So13.3 strain as a promising source for antimicrobials discovery

Antarctic have been suggested as an attractive source for antibiotics discovery and members of Streptomyces genus have historically been studied as natural producers of antimicrobial metabolites. Nonetheless, our knowledge on antibiotic-producing Streptomyces from Antarctic is very limited. In this study, the antimicrobial activity of organic extracts from Antarctic Streptomyces strains was evaluated by disk diffusion assays and minimum inhibitory concentration. The strain Streptomyces sp. So13.3 showed the greatest antibiotic activity (MIC = 15.6 μg/mL) against Gram-positive bacteria and growth reduction of Gram‒negative pathogens. The bioactive fraction in the crude extract was revealed by TLC‒bioautography at R_f = 0.78 with molecular weight between 148 and 624 m/z detected by LC-ESI-MS/MS. The strain So13.3 was taxonomically affiliated as Streptomyces fildesensis. Whole genome sequencing and analysis suggested a 9.47 Mb genome size with 42 predicted biosynthetic gene clusters (BGCs) and 56 putative clusters representing a 22% of total genome content. Interestingly, a large number of them (11 of 42 BGCs and 40 of 56 putative BGCs), did not show similarities with other known BGCs. Our results highlight the potential of the Antarctic Streptomyces strains as a promising source of novel antimicrobials, particularly the strain Streptomyces fildesensis So13.3, which first draft genome is reported in this work.

Visual and Microscopic Evaluation of Streptomyces Developmental Mutants

Streptomycetes are filamentous soil bacteria belonging to the phylum Actinobacteria that are found throughout the world and produce a wide array of antibiotics and other secondary metabolites. Streptomyces coelicolor is a well-characterized, non-pathogenic species that is amenable to a variety of analyses in the lab. The phenotyping methods described here use S. coelicolor as a model streptomycete; however, the methods are applicable to all members of this large genus as well as some closely related actinomycetes. Phenotyping is necessary to characterize new species of Streptomyces identified in the environment, and it is also a vital first step in characterizing newly isolated mutant strains of Streptomyces. Proficiency in phenotyping is important for the many new researchers who are entering the field of Streptomyces research, which includes the study of bacterial development, cell division, chromosome segregation, and second messenger signaling. The recent crowdsourcing of antibiotic discovery through the isolation of new soil microbes has resulted in an increased need for training in phenotyping for instructors new to the field of Streptomyces research and their college or high school students. This manuscript describes methods for bacterial strain propagation, storage, and characterization through visual and microscopic examination. After reading this article, new researchers (microbiology education laboratories and citizen scientists) should be able to manipulate Streptomyces strains and begin visual characterization experiments.

Genome-based classification of micromonosporae with a focus on their biotechnological and ecological potential

There is a need to clarify relationships within the actinobacterial genus Micromonospora, the type genus of the family Micromonosporaceae, given its biotechnological and ecological importance. Here, draft genomes of 40 Micromonospora type strains and two non-type strains are made available through the Genomic Encyclopedia of Bacteria and Archaea project and used to generate a phylogenomic tree which showed they could be assigned to well supported phyletic lines that were not evident in corresponding trees based on single and concatenated sequences of conserved genes. DNA G+C ratios derived from genome sequences showed that corresponding data from species descriptions were imprecise. Emended descriptions include precise base composition data and approximate genome sizes of the type strains. antiSMASH analyses of the draft genomes show that micromonosporae have a previously unrealised potential to synthesize novel specialized metabolites. Close to one thousand biosynthetic gene clusters were detected, including NRPS, PKS, terpenes and siderophores clusters that were discontinuously distributed thereby opening up the prospect of prioritising gifted strains for natural product discovery. The distribution of key stress related genes provide an insight into how micromonosporae adapt to key environmental variables. Genes associated with plant interactions highlight the potential use of micromonosporae in agriculture and biotechnology.

Deletion of MtrA Inhibits Cellular Development of Streptomyces coelicolor and Alters Expression of Developmental Regulatory Genes

The developmental life cycle of Streptomyces species includes aerial hyphae formation and spore maturation, two distinct developmental processes that are controlled, respectively, by two families of developmental regulatory genes, bld and whi. In this study, we show that the response regulator MtrA (SCO3013) is critical for normal development of aerial hyphae in S. coelicolor and related species. ΔmtrA, a deletion mutant of the response regulator gene mtrA, exhibited the bald phenotype typical of bld mutants defective in aerial mycelium formation, with formation either much delayed or absent depending on the culture medium. Transcriptional analysis indicated that MtrA activates multiple genes involved in formation of aerial mycelium, including chp, rdl, and ram genes, as well as developmental regulatory genes of the bld and whi families. However, the major regulatory gene bldD showed enhanced expression in ΔmtrA, suggesting it is repressed by MtrA. electrophoretic mobility shift assays indicated that MtrA binds upstream of several genes with altered expression in ΔmtrA, including bldD and whiI, and sequences similar to the consensus binding sequence for MtrA of another actinomycete, Mycobacterium tuberculosis, were found in the bound sites. A loosely conserved recognition sequence containing two short, direct repeats was identified for MtrA of S. coelicolor and was validated using mutational analysis. MtrA homologs are widely distributed among Streptomyces species, and as with S. coelicolor, deletion of the mtrA homologs sve_2757 from S. venezuelae and sli_3357 from S. lividans resulted in conditional bald morphology. Our study suggests a critical and conserved role for MtrA in Streptomyces development.

'Exploring' the regulation of Streptomyces growth and development

The Streptomyces life cycle encompasses three well-established developmental stages: vegetative hyphae, aerial hyphae and spores. Many regulators governing the transitions between these life cycle stages have been identified, and recent work is shedding light on their specific functions. A new discovery has shown Streptomyces can deviate from this classic life cycle through a process termed 'exploration', where cells rapidly traverse solid surfaces. Exploration does not require any of the traditional developmental regulators, and therefore provides an exciting new context in which to uncover novel developmental pathways. Here, we summarize our understanding of how Streptomyces exploration is controlled, and we speculate on how insight into classical regulation and stress response systems can inform future research into the regulation of exploratory growth.

The MtrAB two-component system controls antibiotic production in Streptomyces coelicolor A3(2)

MtrAB is a highly conserved two-component system implicated in the regulation of cell division in the Actinobacteria. It coordinates DNA replication with cell division in the unicellular Mycobacterium tuberculosis and links antibiotic production to sporulation in the filamentous Streptomyces venezuelae. Chloramphenicol biosynthesis is directly regulated by MtrA in S. venezuelae and deletion of mtrB constitutively activates MtrA and results in constitutive over-production of chloramphenicol. Here we report that in Streptomyces coelicolor, MtrA binds to sites upstream of developmental genes and the genes encoding ActII-1, ActII-4 and RedZ, which are cluster-situated regulators of the antibiotics actinorhodin (Act) and undecylprodigiosin (Red). Consistent with this, deletion of mtrB switches on the production of Act, Red and streptorubin B, a product of the Red pathway. Thus, we propose that MtrA is a key regulator that links antibiotic production to development and can be used to upregulate antibiotic production in distantly related streptomycetes.

The Role of Functional Amyloids in Multicellular Growth and Development of Gram-Positive Bacteria

Amyloid fibrils play pivotal roles in all domains of life. In bacteria, these fibrillar structures are often part of an extracellular matrix that surrounds the producing organism and thereby provides protection to harsh environmental conditions. Here, we discuss the role of amyloid fibrils in the two distant Gram-positive bacteria, Streptomyces coelicolor and Bacillus subtilis. We describe how amyloid fibrils contribute to a multitude of developmental processes in each of these systems, including multicellular growth and community development. Despite this variety of tasks, we know surprisingly little about how their assembly is organized to fulfill all these roles.

The pH-dependent assembly of Chaplin E from Streptomyces coelicolor

Chaplin E, is one of five self-assembling peptides secreted by Streptomyces coelicolor that assist aerial growth by lowering the surface tension of water. Although the surface activity of a mixture of chaplin peptides has observed to depend on pH, it is unclear how the solvent environment (i.e. pH) influences the structure, assembly and subsequent functionality of these individual peptides. In this study, the conformation and fibril forming propensity of the Chaplin E peptide was assessed as a function of pH using a combination of experimental measurements and molecular dynamics simulations. At an acidic pH of 3.0, Chaplin E retained a random coil structure, whereas at the isoelectric point of 6.7 or a basic pH of 10.0, Chaplin E rapidly formed amyloid fibrils rich in β-sheet structure with high efficiency (>93%). Molecular dynamics simulations indicate the persistence of greater α-helical content at the N-terminus at high pH; this is likely partly due to the lack of electrostatic repulsion between residues His6 and Lys10. Since fibril formation was observed at high but not at low pH, we propose that the presence of an N-terminal α-helix in the monomeric form of Chaplin E is required for aggregation and conversion to β-amyloid fibrils. The pH sensitivity of Chaplin E peptide structure provides a route to control peptide assembly and may be important for the physiological function of this peptide, as a surface active agent in the transition from vegetative to aerial growth and could assist Streptomyces coelicolor in response to environmental fluctuations in pH.

The Diverse Structures and Functions of Surfactant Proteins

Surface tension at liquid–air interfaces is a major barrier that needs to be surmounted by a wide range of organisms; surfactant and interfacially active proteins have evolved for this purpose. Although these proteins are essential for a variety of biological processes, our understanding of how they elicit their function has been limited. However, with the recent determination of high-resolution 3D structures of several examples, we have gained insight into the distinct shapes and mechanisms that have evolved to confer interfacial activity. It is now a matter of harnessing this information, and these systems, for biotechnological purposes.

Interfacially active proteins fulfill a wide range of biological functions in organisms ranging from bacteria and fungi to mammals.

Their physicochemical properties make interfacially active proteins attractive for biotechnological applications; for example, as coatings on nanodevices or medical implants and as emulsifiers in food and personal-care products.

High-resolution 3D structures show that the mechanisms by which interfacially active proteins achieve their function are highly diverse.

Taxonomy, Physiology, and Natural Products of Actinobacteria

Actinobacteria are Gram-positive bacteria with high G+C DNA content that constitute one of the largest bacterial phyla, and they are ubiquitously distributed in both aquatic and terrestrial ecosystems. Many Actinobacteria have a mycelial lifestyle and undergo complex morphological differentiation. They also have an extensive secondary metabolism and produce about two-thirds of all naturally derived antibiotics in current clinical use, as well as many anticancer, anthelmintic, and antifungal compounds. Consequently, these bacteria are of major importance for biotechnology, medicine, and agriculture. Actinobacteria play diverse roles in their associations with various higher organisms, since their members have adopted different lifestyles, and the phylum includes pathogens (notably, species of Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, and Tropheryma), soil inhabitants (e.g., Micromonospora and Streptomyces species), plant commensals (e.g., Frankia spp.), and gastrointestinal commensals (Bifidobacterium spp.). Actinobacteria also play an important role as symbionts and as pathogens in plant-associated microbial communities. This review presents an update on the biology of this important bacterial phylum.

c-di-GMP signalling and the regulation of developmental transitions in streptomycetes

The complex life cycle of streptomycetes involves two distinct filamentous cell forms: the growing (or vegetative) hyphae and the reproductive (or aerial) hyphae, which differentiate into long chains of spores. Until recently, little was known about the signalling pathways that regulate the developmental transitions leading to sporulation. In this Review, we discuss important new insights into these pathways that have led to the emergence of a coherent regulatory network, focusing on the erection of aerial hyphae and the synchronous cell division event that produces dozens of unigenomic spores. In particular, we highlight the role of cyclic di-GMP (c-di-GMP) in controlling the initiation of development, and the role of the master regulator BldD in mediating c-di-GMP signalling.

Synthesis of the spore envelope in the developmental life cycle of Streptomyces coelicolor

Members of the family of Streptomycetaceae, the main producer of antibiotics and other secondary metabolites, are Gram-positive multi-cellular soil bacteria with a complex life cycle. By apical tip extension Streptomyces coelicolor forms a multiply branching vegetative mycelium penetrating the substrate. Upon nutrient limitation, a hydrophobic aerial mycelium is erected, which eventually develops into a regular chain of spores that are able to survive detrimental environmental conditions. Morphological differentiation involves a switch in the peptidoglycan synthesizing machinery. Whereas apical tip extension is directed by the so-called polarisome, sporulation septation and synthesis of the thickened spore wall involves a multi-protein complex, which resembles the elongasome of rod-shaped bacteria. The Streptomyces spore wall synthesizing complex (SSSC) does not only direct synthesis of the peptidoglycan layer but is also involved in the incorporation of anionic spore wall glycopolymers, which contribute to the resistance of spores. The SSSC also contains eukaryotic type serine/threonine kinases which might control its activity by protein-phosphorylation.

A genome-wide transcriptomic analysis reveals diverse roles of the two-component system DraR-K in the physiological and morphological differentiation of Streptomyces coelicolor

A novel two-component system (TCS) of DraR-K was previously identified as playing differential roles in the biosynthesis of antibiotics (blue-pigmented type II polyketide actinorhodin (ACT), red-pigmented tripyrrole undecylprodigiosin (RED), and yellow-pigmented type I polyketide (yCPK)) in Streptomyces coelicolor M145 under the conditions of minimal medium (MM) supplemented with a high concentration of different nitrogen sources (e.g., 75 mM glutamine). To assess whether DraR-K has more globalized roles, a genome-wide transcriptomic analysis of the parental strain M145 and a ΔdraR-K mutant under the condition of MM supplemented with 75 mM glutamine was performed using DNA microarray analysis combined with real-time reverse transcriptase PCR (RT-qPCR). The analyses showed that deletion of the draR-K genes led to the differential expression not only of the biosynthetic gene clusters of ACT, RED, and yCPK but also of other five secondary metabolite biosynthetic clusters. In addition, a number of primary metabolism-related genes in the ΔdraR-K mutant, such as ureA/B/C/D/G/F, the pstSCAB operon, and the chb gene, exhibited altered expression, which might enable the organism to balance the C/N/P ratio under the condition of a high concentration of glutamine. We also found that the expression of many developmental genes, including ramR, chpA/D/E, and the whiE gene cluster, was affected by the draR-K deletion. Furthermore, the direct role of DraR-K on the transcription of several genes, including chb and pepA/pepA2, was validated using electrophoretic mobility shift assays (EMSAs). In summary, our transcriptomic analyses revealed that DraR-K plays global regulatory roles in the physiological and morphological differentiation of S. coelicolor.

Developmental biology of Streptomyces from the perspective of 100 actinobacterial genome sequences

To illuminate the evolution and mechanisms of actinobacterial complexity, we evaluate the distribution and origins of known Streptomyces developmental genes and the developmental significance of actinobacteria-specific genes. As an aid, we developed the Actinoblast database of reciprocal blastp best hits between the Streptomyces coelicolor genome and more than 100 other actinobacterial genomes (http://streptomyces.org.uk/actinoblast/). We suggest that the emergence of morphological complexity was underpinned by special features of early actinobacteria, such as polar growth and the coupled participation of regulatory Wbl proteins and the redox-protecting thiol mycothiol in transducing a transient nitric oxide signal generated during physiologically stressful growth transitions. It seems that some cell growth and division proteins of early actinobacteria have acquired greater importance for sporulation of complex actinobacteria than for mycelial growth, in which septa are infrequent and not associated with complete cell separation. The acquisition of extracellular proteins with structural roles, a highly regulated extracellular protease cascade, and additional regulatory genes allowed early actinobacterial stationary phase processes to be redeployed in the emergence of aerial hyphae from mycelial mats and in the formation of spore chains. These extracellular proteins may have contributed to speciation. Simpler members of morphologically diverse clades have lost some developmental genes.

Pivotal roles for Streptomyces cell surface polymers in morphological differentiation, attachment and mycelial architecture

Cells that are part of a multicellular structure are typically embedded in an extracellular matrix, which is produced by the community members. These matrices, the composition of which is highly diverse between different species, are typically composed of large amounts of extracellular polymeric substances, including polysaccharides, proteins, and nucleic acids. The functions of all these matrices are diverse: they provide protection, mechanical stability, mediate adhesion to surfaces, regulate motility, and form a cohesive network in which cells are transiently immobilized. In this review we discuss the role of matrix components produced by streptomycetes during growth, development and attachment. Compared to other bacteria it appears that streptomycetes can form morphologically and functionally distinct matrices using a core set of building blocks.

Functional analysis of the gene SCO1782 encoding Streptomyces hemolysin (S-hemolysin) in Streptomyces coelicolor M145

In the process of evaluating the growth of Streptomyces coelicolor on rich media such as blood agar, we found that S. coelicolor a non-pathogenic, well-known antibiotic producer had the ability to grow and produce a prominent hemolytic zone. By comparing the growth with an agarase gene mutant of S. coelicolor, a similar prominent hemolytic zone was found to develop due to the organism's hemolytic activity. After the confirmation of hemolytic activity from S. coelicolor, the genome was searched for hemolysin-coding genes; consequently, SCO1782, SCO2534, and SCO3882 were identified, whose products were annotated as a putative, membrane, and hypothetical proteins, respectively. Functional characterization of all the recombinant proteins expressed in Escherichia coli BL21(DE3) revealed that only SCO1782 exhibited hemolytic activity. This S. coelicolor protein, designated as S-hemolysin, showed sequence similarity toward hemolysins from Brachyspira hyodysenteriae (35%) and Mycobacterium tuberculosis (62%). Recombinant hemolysin exhibited activity against sheep blood erythrocytes and cytolytic activity against human fibroblast cells. Deletion of SCO1782 resulted in complete loss of hemolysin activity in S. coelicolor.

The pleiotropic effect of WD-40 domain containing proteins on cellular differentiation and production of secondary metabolites in Streptomyces coelicolor

The genome of Streptomyces coelicolor encodes six potential WD-40 genes. Two of them, the wdpB (SCO5953) and the wdpC (SCO4422) genes, were studied to determine their function. Deletion of the wdpB gene resulted in a considerable decrease of aerial hyphae formation, leading to a conditionally bald phenotype, and reduced undecylprodigiosin production. In addition, the aerial hyphae of the ΔwdpB mutant strain were unusually branched and showed the signs of irregular septation and precocious lysis. Disruption of wdpC resulted in the reduction of undecylprodigiosin and delayed actinorhodin production. The ΔwdpC mutant strain showed precocious lysis of hyphae and delayed sporulation without typical curling of aerial hyphae in the early sporulation stage. The whole-genome transcriptome analysis revealed that deletion of wdpB affects the expression of genes involved in aerial hyphae differentiation, sporulation and secondary metabolites production. Deletion of wdpC caused downregulation of several gene clusters encoding secondary metabolites. Both the wdp genes seem to possess transcriptional autoregulatory function. Overexpression and genetic complementation studies confirmed the observed phenotype of both mutants. The results obtained suggest that both genes studied have a pleiotropic effect on physiological and morphological differentiation.

Genomic and transcriptomic insights into the thermo-regulated biosynthesis of validamycin in Streptomyces hygroscopicus 5008

Background

Streptomyces hygroscopicus 5008 has been used for the production of the antifungal validamycin/jinggangmycin for more than 40 years. A high yield of validamycin is achieved by culturing the strain at 37°C, rather than at 30°C for normal growth and sporulation. The mechanism(s) of its thermo-regulated biosynthesis was largely unknown.

Results

The 10,383,684-bp genome of strain 5008 was completely sequenced and composed of a linear chromosome, a 164.57-kb linear plasmid, and a 73.28-kb circular plasmid. Compared with other Streptomyces genomes, the chromosome of strain 5008 has a smaller core region and shorter terminal inverted repeats, encodes more α/β hydrolases, major facilitator superfamily transporters, and Mg²⁺/Mn²⁺-dependent regulatory phosphatases. Transcriptomic analysis revealed that the expression of 7.5% of coding sequences was increased at 37°C, including biosynthetic genes for validamycin and other three secondary metabolites. At 37°C, a glutamate dehydrogenase was transcriptionally up-regulated, and further proved its involvement in validamycin production by gene replacement. Moreover, efficient synthesis and utilization of intracellular glutamate were noticed in strain 5008 at 37°C, revealing glutamate as the nitrogen source for validamycin biosynthesis. Furthermore, a SARP-family regulatory gene with enhanced transcription at 37°C was identified and confirmed to be positively involved in the thermo-regulation of validamycin production by gene inactivation and transcriptional analysis.

Conclusions

Strain 5008 seemed to have evolved with specific genomic components to facilitate the thermo-regulated validamycin biosynthesis. The data obtained here will facilitate future studies for validamycin yield improvement and industrial bioprocess optimization.

Cyclic Di-GMP phosphodiesterases RmdA and RmdB are involved in regulating colony morphology and development in Streptomyces coelicolor

Cyclic dimeric GMP (c-di-GMP) regulates numerous processes in Gram-negative bacteria, yet little is known about its role in Gram-positive bacteria. Here we characterize two c-di-GMP phosphodiesterases from the filamentous high-GC Gram-positive actinobacterium Streptomyces coelicolor, involved in controlling colony morphology and development. A transposon mutation in one of the two phosphodiesterase genes, SCO0928, hereby designated rmdA (regulator of morphology and development A), resulted in decreased levels of spore-specific gray pigment and a delay in spore formation. The RmdA protein contains GGDEF-EAL domains arranged in tandem and possesses c-di-GMP phosphodiesterase activity, as is evident from in vitro enzymatic assays using the purified protein. RmdA contains a PAS9 domain and is a hemoprotein. Inactivation of another GGDEF-EAL-encoding gene, SCO5495, designated rmdB, resulted in a phenotype identical to that of the rmdA mutant. Purified soluble fragment of RmdB devoid of transmembrane domains also possesses c-di-GMP phosphodiesterase activity. The rmdA rmdB double mutant has a bald phenotype and is impaired in aerial mycelium formation. This suggests that RmdA and RmdB functions are additive and at least partially overlapping. The rmdA and rmdB mutations likely result in increased local pools of intracellular c-di-GMP, because intracellular c-di-GMP levels in the single mutants did not differ significantly from those of the wild type, whereas in the double rmdA rmdB mutant, c-di-GMP levels were 3-fold higher than those in the wild type. This study highlights the importance of c-di-GMP-dependent signaling in actinomycete colony morphology and development and identifies two c-di-GMP phosphodiesterases controlling these processes.

Expression of the chaplin and rodlin hydrophobic sheath proteins in Streptomyces venezuelae is controlled by σ(BldN) and a cognate anti-sigma factor, RsbN

The chaplin and rodlin proteins together constitute the major components of the hydrophobic sheath that coats the aerial hyphae and spores in Streptomyces, and mutants lacking the chaplins are unable to erect aerial hyphae and differentiate on minimal media. We have gained insight into the developmental regulation of the chaplin (chp) and rodlin (rdl) genes by exploiting a new model species, Streptomyces venezuelae, which sporulates in liquid culture. Using microarrays, the chaplin and rodlin genes were found to be highly induced during submerged sporulation in a bldN-dependent manner. Using σ(BldN) ChIP-chip, we show that this dependence arises because the chaplin and rodlin genes are direct biochemical targets of σ(BldN) . sven3186 (here named rsbN for regulator of sigma BldN), the gene lying immediately downstream of bldN, was also identified as a target of σ(BldN) . Disruption of rsbN causes precocious sporulation and biochemical experiments demonstrate that RsbN functions as a σ(BldN) -specific anti-sigma factor.

Multi-tier regulation of the streptomycete morphogenetic peptide SapB

Streptomyces coelicolor is a morphologically complex bacterium requiring the secretion of surface-active proteins to progress through its life cycle. SapB represents an important class of these biosurfactants, as illustrated by its ability to restore aerial hyphae formation when applied exogenously to developmental mutants. However, such aerial hyphae fail to sporulate, exemplifying the need to co-ordinate the timing of SapB production with other developmental events. SapB has an unusual lantibiotic structure. Its structural gene, ramS, is only 38 nucleotides downstream of the gene encoding its putative modification enzyme, RamC. Transient, co-ordinated expression of the operon was thought to be controlled by the response regulator RamR. However, we show that ramS is transcribed throughout the cell cycle with a dual expression profile dissimilar to the tightly controlled ramC expression. Surprisingly, post-translational modification relies on prior membrane localization of the precursor peptide, RamS, as demonstrated by the absence of RamS modification in S. coelicolor hyphae treated with the Bacillus subtilis lipoprotein surfactin. Our results demonstrate that interspecies interaction can also be mediated by interference of post-translational events. Further, temporal and spatial regulation of irreversible post-translational modification of a surface-active morphogenetic peptide suggests a new model for the control of key developmental events.

SapB and the rodlins are required for development of Streptomyces coelicolor in high osmolarity media

Streptomyces coelicolor produces spore-forming aerial hyphae after a period of vegetative growth. These aerial structures are decorated with a hydrophobic coating of rodlets consisting of chaplins and rodlins. Here, we show that rodlins and the surface-active peptide SapB are essential for development during growth in a medium with high osmolarity. To this end, both vegetative and aerial hyphae secrete SapB, whereas rodlins are only secreted by the spore-forming aerial hyphae.

Aerial development in Streptomyces coelicolor requires sortase activity

Streptomyces coelicolor is a multicellular bacterium whose life cycle encompasses three differentiated states: vegetative hyphae, aerial hyphae and spores. Among the factors required for aerial development are the 'chaplins', a family of eight secreted proteins that coat the surface of aerial hyphae. Three chaplins (the 'long' chaplins, ChpA, B and C) possess an LAXTG-containing C-terminal sorting signal and are predicted sortase substrates. The five remaining 'short' chaplins are presumed to be associated with the cell surface through interactions with the long chaplins. We show here that two sortase enzymes, SrtE1 and SrtE2, cleave LAXTG-containing peptides at two distinct positions in vitro, and are required for cell wall anchoring of ChpC in vivo. srtE1/E2 double mutants are delayed in aerial hyphae formation, do not sporulate and fail to display all short chaplins on their aerial surfaces. Surprisingly, these mutant characteristics were not shared by a long chaplin mutant, which exhibited only modest delays in aerial development, leading us to revise the current model of chaplin-mediated aerial development. The sortase mutant phenotype, instead, appears to stem from an inability to transcribe aerial hyphae-specific genes, whose products have diverse functions. This suggests that sortase activity triggers an important, and previously unknown, developmental checkpoint.

Signals and regulators that govern Streptomyces development

Streptomyces coelicolor is the genetically best characterized species of a populous genus belonging to the gram-positive Actinobacteria. Streptomycetes are filamentous soil organisms, well known for the production of a plethora of biologically active secondary metabolic compounds. The Streptomyces developmental life cycle is uniquely complex and involves coordinated multicellular development with both physiological and morphological differentiation of several cell types, culminating in the production of secondary metabolites and dispersal of mature spores. This review presents a current appreciation of the signaling mechanisms used to orchestrate the decision to undergo morphological differentiation, and the regulators and regulatory networks that direct the intriguing development of multigenomic hyphae first to form specialized aerial hyphae and then to convert them into chains of dormant spores. This current view of S. coelicolor development is destined for rapid evolution as data from '-omics' studies shed light on gene regulatory networks, new genetic screens identify hitherto unknown players, and the resolution of our insights into the underlying cell biological processes steadily improve.

Sortase enzymes in Gram-positive bacteria

In Gram-positive bacteria proteins are displayed on the cell surface using sortase enzymes. These cysteine transpeptidases join proteins bearing an appropriate sorting signal to strategically positioned amino groups on the cell surface. Working alone, or in concert with other enzymes, sortases either attach proteins to the cross-bridge peptide of the cell wall or they link proteins together to form pili. Because surface proteins play a fundamental role in microbial physiology and are frequently virulence factors, sortase enzymes have been intensely studied since their discovery a little more than a decade ago. Based on their primary sequences and functions sortases can be partitioned into distinct families called class A to F enzymes. Most bacteria elaborate their surfaces using more than one type of sortase that function non-redundantly by recognizing unique sorting signals within their protein substrates. Here we review what is known about the functions of these enzymes and the molecular basis of catalysis. Particular emphasis is placed on 'pilin' specific class C sortases that construct structurally complex pili. Exciting new data have revealed that these enzymes are amazingly promiscuous in the substrates that they can employ and that there is a startling degree of diversity in their mechanism of action. We also review recent data that suggest that sortases are targeted to specific sites on the cell surface where they work with other sortases and accessory factors to properly function.

Dual amyloid domains promote differential functioning of the chaplin proteins during Streptomyces aerial morphogenesis

The chaplin proteins are functional amyloids found in the filamentous Streptomyces bacteria. These secreted proteins are required for the aerial development of Streptomyces coelicolor, and contribute to an intricate rodlet ultrastructure that decorates the surfaces of aerial hyphae and spores. S. coelicolor encodes eight chaplin proteins. Previous studies have revealed that only three of these proteins (ChpC, ChpE, and ChpH) are necessary for promoting aerial development, and of these three, ChpH is the primary developmental determinant. Here, we show that the model chaplin, ChpH, contains two amyloidogenic domains: one in the N terminus and one in the C terminus of the mature protein. These domains have different polymerization properties as determined using fluorescence spectroscopy, secondary structure analyses, and electron microscopy. We coupled these in vitro assays with in vivo genetic studies to probe the connection between ChpH amyloidogenesis and its biological function. Using mutational analyses, we demonstrated that both N- and C-terminal amyloid domains of ChpH were required for promoting aerial hypha formation, while the N-terminal domain was dispensable for assembly of the rodlet ultrastructure. These results suggest that there is a functional differentiation of the dual amyloid domains in the chaplin proteins.

An orphan histidine kinase, OhkA, regulates both secondary metabolism and morphological differentiation in Streptomyces coelicolor

We report here the physiological and genetic characterization of an orphan histidine kinase (HK) (OhkA, SCO1596) in Streptomyces coelicolor and its homolog (OhkAsav, SAV_6741) in Streptomyces avermitilis. The physiological analysis showed that the ohkA mutant of S. coelicolor exhibits impaired aerial mycelium formation and sporulation and overproduction of multiple antibiotics on mannitol-soy flour (MS) medium, especially actinorhodin (ACT) and calcium-dependent antibiotic (CDA), and disruption of ohkAsav in S. avermitilis also led to the similar phenotypes of impaired morphological differentiation and significantly increased oligomycin A production. DNA microarray analysis combined with real-time reverse transcription-PCR (RT-PCR) and RNA dot blot assay in the S. coelicolor ohkA deletion mutant confirmed the physiological results by showing the upregulation of genes involved in the biosynthesis of ACT, CDA, undecylprodigiosin (RED), a yellow type I polyketide (CPK, SCO6273-6289), and a sesquiterpene antibiotic, albaflavenone (SCO5222-5223). The results also suggested that the increased production of ACT and RED in the mutant could be partly ascribed to the enhanced precursor malonyl coenzyme A (malonyl-CoA) supply through increased transcription of genes encoding acetyl-CoA carboxylase (ACCase). Interestingly, DNA microarray analysis also showed that deletion of ohkA greatly downregulated the transcription of chpABCDEFGH genes essential for aerial mycelium formation by S. coelicolor on MS medium but significantly increased transcription of ramS/C/R, which is responsible for SapB formation and regulation and is normally absent on MS medium. Moreover, many other genes involved in development, such as bldM/N, whiG/H/I, ssgA/B/E/G/R, and whiE, were also significantly downregulated upon ohkA deletion. The results clearly demonstrated that OhkA is an important global regulator for both morphological differentiation and secondary metabolism in S. coelicolor and S. avermitilis.

The actinobacteria-specific gene wblA controls major developmental transitions in Streptomyces coelicolor A3(2)

The Streptomyces coelicolor A3(2) sporulation gene whiB is the paradigm of a family of genes (wbl, whiB-like) that are confined to actinobacteria. The chromosome of S. coelicolor contains 11 wbl genes, among which five are conserved in many actinobacteria: whiB itself; whiD, a sporulation gene; wblC, which is required for multi-drug resistance; and wblA and wblE, whose roles had previously been little studied. We succeeded in disrupting wblA and the six non-conserved genes, but could not disrupt wblE. Although mutations in the six non-conserved wbl genes (including some multiple wbl mutants) produced no readily detectable phenotype, mutations in wblA had novel and complex effects. The aerial mycelium of wblA mutants was coloured red, because of the ectopic presence of pigmented antibiotics (actinorhodin and undecylprodigiosin) normally confined to lower parts of wild-type colonies, and consisted almost entirely of non-sporulating, thin, straight filaments, often bundled together in a fibrillar matrix. Rare spore chains were also formed, which exhibited wild-type properties but were genetically still wblA mutants. A wblA mutant achieved higher biomass than the wild-type. Microarray analysis indicated major transcriptional changes in a wblA mutant: using a relatively stringent cut-off, 183 genes were overexpressed, including genes for assimilative primary metabolism and actinorhodin biosynthesis, and 103 were underexpressed, including genes associated with stages of aerial hyphal growth. We suggest that WblA is important in both the slow-down of biomass accumulation and the change from aerial hyphal initial cells to the subapical stem and apical compartments that precede sporulation; and that the mutant aerial mycelium consists of recapitulated defective aerial hyphal initial cells.

Genome sequence of Kitasatospora setae NBRC 14216T: an evolutionary snapshot of the family Streptomycetaceae

Kitasatospora setae NBRC 14216^T (=KM-6054^T) is known to produce setamycin (bafilomycin B1) possessing antitrichomonal activity. The genus Kitasatospora is morphologically similar to the genus Streptomyces, although they are distinguishable from each other on the basis of cell wall composition and the 16S rDNA sequence. We have determined the complete genome sequence of K. setae NBRC 14216^T as the first Streptomycetaceae genome other than Streptomyces. The genome is a single linear chromosome of 8 783 278 bp with terminal inverted repeats of 127 148 bp, predicted to encode 7569 protein-coding genes, 9 rRNA operons, 1 tmRNA and 74 tRNA genes. Although these features resemble those of Streptomyces, genome-wide comparison of orthologous genes between K. setae and Streptomyces revealed smaller extent of synteny. Multilocus phylogenetic analysis based on amino acid sequences unequivocally placed K. setae outside the Streptomyces genus. Although many of the genes related to morphological differentiation identified in Streptomyces were highly conserved in K. setae, there were some differences such as the apparent absence of the AmfS (SapB) class of surfactant protein and differences in the copy number and variation of paralogous components involved in cell wall synthesis.

Myxococcus xanthus induces actinorhodin overproduction and aerial mycelium formation by Streptomyces coelicolor

Interaction of the predatory myxobacterium Myxococcus xanthus with the non‐motile, antibiotic producer Streptomyces coelicolor was examined using a variety of experimental approaches. Myxococcus xanthus cells prey on S. coelicolor, forming streams of ordered cells that lyse the S. coelicolor hyphae in the contact area between the two colonies. The interaction increases actinorhodin production by S. coelicolor up to 20‐fold and triggers aerial mycelium production. Other bacteria are also able to induce these processes in S. coelicolor though to a lesser extent. These studies offer new clues about the expression of genes that remain silent or are expressed at low level in axenic cultures and open the possibility of overproducing compounds of biotechnological interest by using potent inducers synthesized by other bacteria.

Regulation of a novel gene cluster involved in secondary metabolite production in Streptomyces coelicolor

Antibiotic biosynthesis in the streptomycetes is a complex and highly regulated process. Here, we provide evidence for the contribution of a novel genetic locus to antibiotic production in Streptomyces coelicolor. The overexpression of a gene cluster comprising four protein-encoding genes (abeABCD) and an antisense RNA-encoding gene (α-abeA) stimulated the production of the blue-pigmented metabolite actinorhodin on solid medium. Actinorhodin production also was enhanced by the overexpression of an adjacent gene (abeR) encoding a predicted Streptomyces antibiotic regulatory protein (SARP), while the deletion of this gene impaired actinorhodin production. We found the abe genes to be differentially regulated and controlled at multiple levels. Upstream of abeA was a promoter that directed the transcription of abeABCD at a low but constitutive level. The expression of abeBCD was, however, significantly upregulated at a time that coincided with the initiation of aerial development and the onset of secondary metabolism; this expression was activated by the binding of AbeR to four heptameric repeats upstream of a promoter within abeA. Expressed divergently to the abeBCD promoter was α-abeA, whose expression mirrored that of abeBCD but did not require activation by AbeR. Instead, α-abeA transcript levels were subject to negative control by the double-strand-specific RNase, RNase III.

Involvement of SigT and RstA in the differentiation of Streptomyces coelicolor

SigT is an ECF sigma factor in Streptomyces coelicolor. sigT and its putative anti-sigma factor gene rstA are located in one putative operon, and SigT could physically interact with RstA. Deletion of sigT or rstA caused accelerated morphological development and enhanced production of antibiotics, concomitant with over-expression of chpE, chpH, actII-orf4 and redD. Furthermore, SigT was undetectable after loss of rstA. These data suggested that SigT has a negative role on differentiation and that RstA negatively regulates the SigT activity through a putative antagonistic mechanism and at the post-transcriptional level.

Reciprocal regulation between SigK and differentiation programs in Streptomyces coelicolor

Here we reported that deletion of SigK (SCO6520), a sigma factor in Streptomyces coelicolor, caused an earlier switch from vegetative mycelia to aerial mycelia and higher expression of chpE and chpH than that in the wild type. Loss of SigK also resulted in accelerated and enhanced production of antibiotics, actinorhodin, and undecylprodigiosin and increased expression of actII-orf4 and redD. These results suggested that SigK had a negative role in morphological transition and secondary metabolism. Furthermore, the sigK promoter (sigKp) activity gradually increased and sigK expression was partially dependent on SigK, but this dependence decreased during the developmental course of substrate mycelia. Meanwhile, two potentially nonspecific cleavages occurred between SigK and green fluorescent protein, and the SigK fusion proteins expressed under the constitutive promoter ermEp* sharply decreased and disappeared when aerial mycelia emerged. If expressed under sigKp, 3FLAG-SigK showed similar dynamic patterns but did not decrease as sharply as SigK expressed under ermEp*. These data suggested that the climbing expression of sigK might reduce the prompt degradation of SigK during vegetative hypha development for the proper timing of morphogenesis and that SigK vanished to remove the block for the emergence of aerial mycelia. Thus, we proposed that SigK had inhibitory roles on developmental events and that these inhibitory effects may be released by SigK degradation.

Attachment of Streptomyces coelicolor is mediated by amyloidal fimbriae that are anchored to the cell surface via cellulose

The chaplin proteins ChpA-H enable the filamentous bacterium Streptomyces coelicolor to form reproductive aerial structures by assembling into surface-active amyloid-like fibrils. We here demonstrate that chaplins also mediate attachment of S. coelicolor to surfaces. Attachment coincides with the formation of fimbriae, which are connected to the cell surface via spike-shaped protrusions. Mass spectrometry, electron microscopy and Congo red treatment showed that these fimbriae are composed of bundled amyloid fibrils of chaplins. Attachment and fimbriae formation were abolished in a strain in which the chaplin genes chpA-H were inactivated. Instead, very thin fibrils emerged from the spike-shaped protrusions in this mutant. These fibrils were susceptible to cellulase treatment. This enzymatic treatment also released wild-type fimbriae from the cell surface, thereby abolishing attachment. The reduced attachment of a strain in which the gene of a predicted cellulose synthase was inactivated also indicates a role of cellulose in surface attachment. We propose that the mechanism of attachment via cellulose-anchored amyloidal fimbriae is widespread in bacteria and may function in initiation of infection and in formation of biofilms.