The existence and diversity of myxobacteria in lake mud - a previously unexplored myxobacteria habitat

Macroevolutionary Dynamics in Micro-organisms: Generalists Give Rise to Specialists Across Biomes in the Ubiquitous Bacterial Phylum Myxococcota

Prokaryotes dominate the Tree of Life, but our understanding of the macroevolutionary processes generating this diversity is still limited. Habitat transitions are thought to be a key driver of prokaryote diversity. However, relatively little is known about how prokaryotes successfully transition and persist across environments, and how these processes might vary between biomes and lineages. Here, we investigate biome transitions and specialization in natural populations of a focal bacterial phylum, the Myxococcota, sampled across a range of replicated soils and freshwater and marine sediments in Cornwall (UK). By targeted deep sequencing of the protein-coding gene rpoB, we found >2,000 unique Myxococcota lineages, with the majority (77%) classified as biome specialists and with only <5% of lineages distributed across the salt barrier. Discrete character evolution models revealed that specialists in one biome rarely transitioned into specialists in another biome. Instead, evolved generalism mediated transitions between biome specialists. State-dependent diversification models found variation in speciation rates across the tree, but this variation was independent of biome association or specialization. Our findings were robust to phylogenetic uncertainty, different levels of species delineation, and different assumed amounts of unsampled diversity resulting in an incomplete phylogeny. Overall, our results are consistent with a "jack-of-all-trades" tradeoff where generalists suffer a cost in any individual environment, resulting in rapid evolution of niche specialists and shed light on how bacteria could transition between biomes.

Diversity of Myxobacteria Isolated from Indonesian Mangroves and Their Potential for New Antimicrobial Sources

Mangroves are unique intertidal ecosystems that provide ecological niches to different microbes, which play various roles in nutrient recycling and diverse environmental activities. The association between myxobacteria and mangroves are hitherto poorly understood. The aim of our study was to evaluate the myxobacterial community composition as well as isolate myxobacteria and to characterize the antimicrobial activity of myxobacteria isolates from Indonesian mangroves. Twenty-five cultivable myxobacteria were affiliated in six genera: Myxococcus, Corallococcus, Archangium, Chondromyces, Racemicystis and Nannocystis of the order Myxococcales based on partial 16S rRNA gene sequences. Thirteen crude extracts showed moderate activities against at least one of human pathogenic microorganisms. The crude extract of Racemicystis sp. strain 503MSO indicated a novel compound, which has not been reported in the database yet and the identification of this compound needs further study. The myxobacterial communities of three different sampling sites were analyzed using primers adapted for the myxobacteria group identification. The results showed that myxobacterial communities are more diverse than assumed. Therefore, our study has highlighted the importance of the mangrove habitat as promising harbor of myxobacteria as well as novel antimicrobial compounds with activity against pathogenic microorganisms.

Concepts and conjectures concerning predatory performance of myxobacteria

Myxobacteria are excellent model organisms for investigation of predator-prey interactions and predatory shaping of microbial communities. This review covers interdisciplinary topics related to myxobacterial predation and provides current concepts and challenges for determining predatory performance. Discussed topics include the role of specialized metabolites during predation, genetic determinants for predatory performance, challenges associated with methodological differences, discrepancies between sequenced and environmental myxobacteria, and factors that influence predation.

Genomes of Novel Myxococcota Reveal Severely Curtailed Machineries for Predation and Cellular Differentiation

Cultured Myxococcota are predominantly aerobic soil inhabitants, characterized by their highly coordinated predation and cellular differentiation capacities. Little is currently known regarding yet-uncultured Myxococcota from anaerobic, nonsoil habitats. We analyzed genomes representing one novel order (o__JAFGXQ01) and one novel family (f__JAFGIB01) in the Myxococcota from an anoxic freshwater spring (Zodletone Spring) in Oklahoma, USA. Compared to their soil counterparts, anaerobic Myxococcota possess smaller genomes and a smaller number of genes encoding biosynthetic gene clusters (BGCs), peptidases, one- and two-component signal transduction systems, and transcriptional regulators. Detailed analysis of 13 distinct pathways/processes crucial to predation and cellular differentiation revealed severely curtailed machineries, with the notable absence of homologs for key transcription factors (e.g., FruA and MrpC), outer membrane exchange receptor (TraA), and the majority of sporulation-specific and A-motility-specific genes. Further, machine learning approaches based on a set of 634 genes informative of social lifestyle predicted a nonsocial behavior for Zodletone Myxococcota. Metabolically, Zodletone Myxococcota genomes lacked aerobic respiratory capacities but carried genes suggestive of fermentation, dissimilatory nitrite reduction, and dissimilatory sulfate-reduction (in f_JAFGIB01) for energy acquisition. We propose that predation and cellular differentiation represent a niche adaptation strategy that evolved circa 500 million years ago (Mya) in response to the rise of soil as a distinct habitat on Earth. IMPORTANCE The phylum Myxococcota is a phylogenetically coherent bacterial lineage that exhibits unique social traits. Cultured Myxococcota are predominantly aerobic soil-dwelling microorganisms that are capable of predation and fruiting body formation. However, multiple yet-uncultured lineages within the Myxococcota have been encountered in a wide range of nonsoil, predominantly anaerobic habitats, and the metabolic capabilities, physiological preferences, and capacity of social behavior of such lineages remain unclear. Here, we analyzed genomes recovered from a metagenomic analysis of an anoxic freshwater spring in Oklahoma, USA, that represent novel, yet-uncultured, orders and families in the Myxococcota. The genomes appear to lack the characteristic hallmarks for social behavior encountered in Myxococcota genomes and displayed a significantly smaller genome size and a smaller number of genes encoding biosynthetic gene clusters, peptidases, signal transduction systems, and transcriptional regulators. Such perceived lack of social capacity was confirmed through detailed comparative genomic analysis of 13 pathways associated with Myxococcota social behavior, as well as the implementation of machine learning approaches to predict social behavior based on genome composition. Metabolically, these novel Myxococcota are predicted to be strict anaerobes, utilizing fermentation, nitrate reduction, and dissimilarity sulfate reduction for energy acquisition. Our results highlight the broad patterns of metabolic diversity within the yet-uncultured Myxococcota and suggest that the evolution of predation and fruiting body formation in the Myxococcota has occurred in response to soil formation as a distinct habitat on Earth.

Myxobacteria as a Source of New Bioactive Compounds: A Perspective Study

Myxobacteria are unicellular, Gram-negative, soil-dwelling, gliding bacteria that belong to class δ-proteobacteria and order Myxococcales. They grow and proliferate by transverse fission under normal conditions, but form fruiting bodies which contain myxospores during unfavorable conditions. In view of the escalating problem of antibiotic resistance among disease-causing pathogens, it becomes mandatory to search for new antibiotics effective against such pathogens from natural sources. Among the different approaches, Myxobacteria, having a rich armor of secondary metabolites, preferably derivatives of polyketide synthases (PKSs) along with non-ribosomal peptide synthases (NRPSs) and their hybrids, are currently being explored as producers of new antibiotics. The Myxobacterial species are functionally characterized to assess their ability to produce antibacterial, antifungal, anticancer, antimalarial, immunosuppressive, cytotoxic and antioxidative bioactive compounds. In our study, we have found their compounds to be effective against a wide range of pathogens associated with the concurrence of different infectious diseases.

Global Geographic Diversity and Distribution of the Myxobacteria

Bacteria are globally distributed in various environments on earth, but a global view of the geographic diversity and distribution of a single taxon is lacking. The Earth Microbiome Project (EMP) has established a global collection of microbial communities, providing the possibility for such a survey. Myxococcales is a bacterial order with a potent ability to produce diverse natural products and have wide application potential in agriculture, biomedicine, and environmental protection. In this study, through a comparative analysis of the EMP data and public information, we determined that myxobacteria account for 2.34% of the total bacterial operational taxonomic units (OTUs), and are one of the most diverse bacterial groups on Earth. Myxococcales OTUs are globally distributed and prefer nonsaline soil and sediments, followed by saline environments, but rarely appear in host-associated environments. Myxobacteria are among the least-investigated bacterial groups. The presently cultured and genome-sequenced myxobacteria are most likely environmentally widespread and abundant taxa, and account for approximately 10% and 7% of the myxobacterial community (>97% similarity), respectively. This global panoramic view of the geographic distribution and diversity of myxobacteria, as well as their cultured and genome-sequenced information, will enable us to explore these important bioresources more reasonably and efficiently. The diversity and distribution of myxobacteria beyond the EMP data are further discussed.

IMPORTANCE The diversity and distribution of bacteria are crucial for our understanding of their ecological importance and application potential. Myxobacteria are fascinating prokaryotes with multicellular behaviors and a potent capacity for producing secondary metabolites, and have a wide range of potential applications. The ecological importance of myxobacteria in major ecosystems is becoming established, but the global geographic diversity and distribution remain unclear. From a global survey we revealed that Myxococcales OTUs are globally distributed and prefer nonsaline soil and sediments, followed by saline environments, but rarely appear in host-associated environments. The global panoramic view of the geographic distribution and diversity of myxobacteria, as well as their cultured and genome-sequenced information, will enable us to explore these important bioresources more reasonably and efficiently.

Culture-dependent and -independent methods revealed an abundant myxobacterial community shaped by other bacteria and pH in Dinghushan acidic soils

Myxobacteria are one of the most promising secondary metabolites producers. However, they are difficult to isolate and cultivate. To obtain more myxobacteria and know the effects of environmental factors on myxobacterial community, we characterized myxobacterial communities in Dinghushan acidic forest soils of pH 3.6-4.5 with culture-dependent and -independent techniques, and analyzed environmental factors shaping myxobacterial communities. A total of 21 myxobacteria were isolated using standard cultivation methods, including eleven isolates of Corallococcus, nine isolates of Myxococcus and one isolate of Archangium, and contained three potential novel species. In addition, a total of 67 unknown myxobacterial operational taxonomic units (OTUs) were obtained using high-throughput sequencing method. The abundance of Myxococcales account for 0.9-2.2% of bacterial communities, and Sorangium is the most abundant genus (60.1%) in Myxococcales. Correlation analysis demonstrated that bacterial diversity and soil pH are the key factors shaping myxobacterial community. These results revealed an abundant myxobacterial community which is shaped by other bacteria and pH in Dinghushan acidic forest soils.

Meta-16S rRNA Gene Phylogenetic Reconstruction Reveals the Astonishing Diversity of Cosmopolitan Myxobacteria

Numerous ecological studies on myxobacteria have been conducted, but their true diversity remains largely unknown. To bridge this gap, we implemented a comprehensive survey of diversity and distribution of myxobacteria by using 4997 publicly available 16S rRNA gene sequences (≥1200 bp) collected from several hundred sites across multiple countries and regions. In this study, the meta-16S rRNA gene phylogenetic reconstruction clearly revealed that these sequences could be classified into 998 species, 445 genera, 58 families, and 20 suborders, the great majority of which belonged to new taxa. Most cultured myxobacteria were strongly inclined to locate on the shallow branches of the phylogenetic tree; on the contrary, the majority of uncultured myxobacteria located on the deep branches. The geographical analysis of sequences based on their environmental categories clearly demonstrated that myxobacteria show a nearly cosmopolitan distribution, despite the presence of some habitat-specific taxa, especially at the genus and species levels. Among the abundant suborders, Suborder_4, Suborder_15, and Suborder_17 were more widely distributed in marine environments, while the remaining suborders preferred to reside in terrestrial ecosystems. In conclusion, this study profiles a clear framework of diversity and distribution of cosmopolitan myxobacteria and sheds light on the isolation of uncultured myxobacteria.

Microbiomes of the Enteropneust, Saccoglossus bromophenolosus, and Associated Marine Intertidal Sediments of Cod Cove, Maine

Enteropneusts are widely distributed marine invertebrates that accumulate high concentrations of halogenated aromatics. Some of these compounds affect benthic biogeochemistery (e.g., denitrification and ammonia oxidation), but little is known about interactions between enteropneusts and their associated microbial communities. Even less is known about enteropneust host-microbe relationships in the digestive tract. More generally, microbial community composition and diversity in intertidal sediments have received little attention. In this study, high throughput sequence analyses of 16S rRNA genes extracted from microbial communities associated with sediment-free whole individuals of Saccoglossus bromophenolosus and freshly excreted S. bromophenolosus gut sediments revealed a potential Spirochaete symbiont that was abundant, present in gut sediment, but absent in other sediments. Relative to surface sediments, gut communities also revealed evidence for selective losses of some groups and blooms of others, especially Colwellia, Photobacterium, Pseudoalteromonas, and Vibrio. After deposition, gut sediment communities rapidly resembled those of surface sediments. Although hierarchical cluster analysis and Linear Discriminant Analysis Effect Size (LEfSe) differentiated among burrow walls of S. bromophenolosus and a polychaete, Alitta virens, as well as between surface and sub-surface sediments, most operational taxonomic units (OTUs) were shared, with differences largely occurring in relative abundances. This suggests that sediment mixing through bioturbation might act to homogenize community composition, while species-specific impacts by infauna might alter local population abundances. Although Cod Cove is a relatively isolated intertidal system, microbial community members included groups with cosmopolitan distributions and roles in sulfur cycling, e.g., Gammaproteobacteria BD7 and Sva0071, as well as novel OTUs representing a large number of phyla.

Diversity of Myxobacteria-We Only See the Tip of the Iceberg

The discovery of new antibiotics is mandatory with regard to the increasing number of resistant pathogens. One approach is the search for new antibiotic producers in nature. Among actinomycetes, Bacillus species, and fungi, myxobacteria have been a rich source for bioactive secondary metabolites for decades. To date, about 600 substances could be described, many of them with antibacterial, antifungal, or cytostatic activity. But, recent cultivation-independent studies on marine, terrestrial, or uncommon habitats unequivocally demonstrate that the number of uncultured myxobacteria is much higher than would be expected from the number of cultivated strains. Although several highly promising myxobacterial taxa have been identified recently, this so-called Great Plate Count Anomaly must be overcome to get broader access to new secondary metabolite producers. In the last years it turned out that especially new species, genera, and families of myxobacteria are promising sources for new bioactive metabolites. Therefore, the cultivation of the hitherto uncultivable ones is our biggest challenge.

Myxobacteria in high moor and fen: An astonishing diversity in a neglected extreme habitat

Increasing antibiotic resistances of numerous pathogens mean that myxobacteria, well known producers of new antibiotics, are becoming more and more interesting. More than 100 secondary metabolites, most of them with bioactivity, were described from the order Myxococcales. Especially new myxobacterial genera and species turned out to be reliable sources for novel antibiotics and can be isolated from uncommon neglected habitats like, for example, acidic soils. Almost nothing is known about the diversity of myxobacteria in moors, except some information from cultivation studies of the 1970s. Therefore, we evaluated the myxobacterial community composition of acidic high moor and fen both with cultivation‐independent 16S rRNA clone bank analysis and with cultivation. Phylogenetic analyses of clone sequences revealed a great potential of undescribed myxobacteria in high moor and fen, whereby all sequences represent unknown taxa and were detected exclusively by cultivation‐independent analyses. However, many clones were assigned to sequences from other cultivation‐independent studies of eubacterial diversity in acidic habitats. Cultivation revealed different strains exclusively from the genus Corallococcus. Our study shows that the neglected habitat moor is a promising source and of high interest with regard to the cultivation of prospective new bioactive secondary metabolite producing myxobacteria.

Error-prone DnaE2 Balances the Genome Mutation Rates in Myxococcus xanthus DK1622

dnaE is an alpha subunit of the tripartite protein complex of DNA polymerase III that is responsible for the replication of bacterial genome. The dnaE gene is often duplicated in many bacteria, and the duplicated dnaE gene was reported dispensable for cell survivals and error-prone in DNA replication in a mystery. In this study, we found that all sequenced myxobacterial genomes possessed two dnaE genes. The duplicate dnaE genes were both highly conserved but evolved divergently, suggesting their importance in myxobacteria. Using Myxococcus xanthus DK1622 as a model, we confirmed that dnaE1 (MXAN_5844) was essential for cell survival, while dnaE2 (MXAN_3982) was dispensable and encoded an error-prone enzyme for replication. The deletion of dnaE2 had small effects on cellular growth and social motility, but significantly decreased the development and sporulation abilities, which could be recovered by the complementation of dnaE2. The expression of dnaE1 was always greatly higher than that of dnaE2 in either the growth or developmental stage. However, overexpression of dnaE2 could not make dnaE1 deletable, probably due to their protein structural and functional divergences. The dnaE2 overexpression not only improved the growth, development and sporulation abilities, but also raised the genome mutation rate of M. xanthus. We argued that the low-expressed error-prone DnaE2 played as a balancer for the genome mutation rates, ensuring low mutation rates for cell adaptation in new environments but avoiding damages from high mutation rates to cells.

Comparison of myxobacterial diversity and evaluation of isolation success in two niches: Kiritimati Island and German compost

Myxobacteria harbor an enormous potential for new bioactive secondary metabolites and therefore the isolation of in particular new groups is of great interest. The diversity of myxobacteria present in two ecological habitats, namely sand from Kiritimati Island and German compost, was evaluated by both cultivation‐based and cultivation‐independent methods. Phylogenetic analyses of the strains in comparison with 16S rRNA gene sequences from cultured and uncultured material in GenBank revealed a great potential of undescribed myxobacteria in both sampling sites. Several OTUs (operational taxonomic units) represent unknown taxa and were detected by clone bank analyses, but not by cultivation. Clone bank analyses indicated that the myxobacterial community is predominantly indigenous. The 16S rDNA libraries from the two samples were generated from total community DNA with myxobacterial specific forward and universal reverse primer sets. The clones were partially sequenced. Cultivation was successful for exclusively bacteriolytic, but not for cellulolytic myxobacteria and revealed 42 strains from the genera Corallococcus, Myxococcus, and Polyangium. The genera of Myxococcaceae family were represented by both approaches. But, even in this well studied family, as well as in the suborders Sorangiineae and Nannocystineae, a considerable number of clones were assigned to, if any, uncultivated organisms. Our study shows an overrepresentation of the genera Myxococcus spp. and Corallococcus spp. with standard cultivation methods. However, high deficits are demonstrated in the cultivation success of the myxobacterial diversity detected by exclusively cultivation‐independent approaches. Especially, clades which are exclusively represented by clones are of high interest with regard to the cultivation of new bioactive secondary metabolite producers.

How Myxobacteria Cooperate

Prokaryotes often reside in groups where a high degree of relatedness has allowed the evolution of cooperative behaviors. However, very few bacteria or archaea have made the successful transition from unicellular to obligate multicellular life. A notable exception is the myxobacteria, in which cells cooperate to perform group functions highlighted by fruiting body development, an obligate multicellular function. Like all multicellular organisms, myxobacteria face challenges in how to organize and maintain multicellularity. These challenges include maintaining population homeostasis, carrying out tissue repair and regulating the behavior of non-cooperators. Here, we describe the major cooperative behaviors that myxobacteria use: motility, predation and development. In addition, this review emphasizes recent discoveries in the social behavior of outer membrane exchange, wherein kin share outer membrane contents. Finally, we review evidence that outer membrane exchange may be involved in regulating population homeostasis, thus serving as a social tool for myxobacteria to make the cyclic transitions from unicellular to multicellular states.

Extraordinary expansion of a Sorangium cellulosum genome from an alkaline milieu

Complex environmental conditions can significantly affect bacterial genome size by unknown mechanisms. The So0157-2 strain of Sorangium cellulosum is an alkaline-adaptive epothilone producer that grows across a wide pH range. Here, we show that the genome of this strain is 14,782,125 base pairs, 1.75-megabases larger than the largest bacterial genome from S. cellulosum reported previously. The total 11,599 coding sequences (CDSs) include massive duplications and horizontally transferred genes, regulated by lots of protein kinases, sigma factors and related transcriptional regulation co-factors, providing the So0157-2 strain abundant resources and flexibility for ecological adaptation. The comparative transcriptomics approach, which detected 90.7% of the total CDSs, not only demonstrates complex expression patterns under varying environmental conditions but also suggests an alkaline-improved pathway of the insertion and duplication, which has been genetically testified, in this strain. These results provide insights into and a paradigm for how environmental conditions can affect bacterial genome expansion.