Understanding microbial divisions of labor

Divisions of labor are ubiquitous in nature and can be found at nearly every level of biological organization, from the individuals of a shared society to the cells of a single multicellular organism. Many different types of microbes have also evolved a division of labor among its colony members. Here we review several examples of microbial divisions of labor, including cases from both multicellular and unicellular microbes. We first discuss evolutionary arguments, derived from kin selection, that allow divisions of labor to be maintained in the face of non-cooperative cheater cells. Next we examine the widespread natural variation within species in their expression of divisions of labor and compare this to the idea of optimal caste ratios in social insects. We highlight gaps in our understanding of microbial caste ratios and argue for a shift in emphasis from understanding the maintenance of divisions of labor, generally, to instead focusing on its specific ecological benefits for microbial genotypes and colonies. Thus, in addition to the canonical divisions of labor between, e.g., reproductive and vegetative tasks, we may also anticipate divisions of labor to evolve to reduce the costly production of secondary metabolites or secreted enzymes, ideas we consider in the context of streptomycetes. The study of microbial divisions of labor offers opportunities for new experimental and molecular insights across both well-studied and novel model systems

Understanding Microbial Divisions of Labor

Divisions of labor are ubiquitous in nature and can be found at nearly every level of biological organization, from the individuals of a shared society to the cells of a single multicellular organism. Many different types of microbes have also evolved a division of labor among its colony members. Here we review several examples of microbial divisions of labor, including cases from both multicellular and unicellular microbes. We first discuss evolutionary arguments, derived from kin selection, that allow divisions of labor to be maintained in the face of non-cooperative cheater cells. Next we examine the widespread natural variation within species in their expression of divisions of labor and compare this to the idea of optimal caste ratios in social insects. We highlight gaps in our understanding of microbial caste ratios and argue for a shift in emphasis from understanding the maintenance of divisions of labor, generally, to instead focusing on its specific ecological benefits for microbial genotypes and colonies. Thus, in addition to the canonical divisions of labor between, e.g., reproductive and vegetative tasks, we may also anticipate divisions of labor to evolve to reduce the costly production of secondary metabolites or secreted enzymes, ideas we consider in the context of streptomycetes. The study of microbial divisions of labor offers opportunities for new experimental and molecular insights across both well-studied and novel model systems

Genome rearrangements and megaplasmid loss in the filamentous bacterium Kitasatospora viridifaciens are associated with protoplast formation and regeneration

Filamentous Actinobacteria are multicellular bacteria with linear replicons. Kitasatospora viridifaciens DSM 40239 contains a linear 7.8 Mb chromosome and an autonomously replicating plasmid KVP1 of 1.7 Mb. Here we show that lysozyme-induced protoplast formation of the multinucleated mycelium of K. viridifaciens drives morphological diversity. Characterisation and sequencing of an individual revertant colony that had lost the ability to differentiate revealed that the strain had not only lost most of KVP1 but also carried deletions in the right arm of the chromosome. Strikingly, the deletion sites were preceded by insertion sequence elements, suggesting that the rearrangements may have been caused by replicative transposition and homologous recombination between both replicons. These data indicate that protoplast formation is a stressful process that can lead to profound genetic changes

Mutational meltdown of putative microbial altruists in Streptomyces coelicolor colonies

In colonies of the filamentous multicellular bacterium Streptomyces coelicolor, a subpopulation of cells arises that hyperproduces metabolically costly antibiotics, resulting in a division of labor that increases colony fitness. Because these cells contain large genomic deletions that cause massive reductions to individual fitness, their behavior is similar to altruistic worker castes in social insects or somatic cells in multicellular organisms. To understand these mutant cells’ reproductive and genomic fate after their emergence, we use experimental evolution by serially transferring populations via spore-to-spore transfer for 25 cycles, reflective of the natural mode of bottlenecked transmission for these spore-forming bacteria. We show that in contrast to wild-type cells, putatively altruistic mutant cells continue to decline in fitness during transfer while they lose more fragments from their chromosome ends. In addition, the base-substitution rate in mutants increases roughly 10-fold, possibly due to mutations in genes for DNA replication and repair. Ecological damage, caused by reduced sporulation, coupled with DNA damage due to point mutations and deletions, leads to an inevitable and irreversible type of mutational meltdown in these cells. Taken together, these results suggest the cells arising in the S. coelicolor division of labor are analogous to altruistic reproductively sterile castes of social insects

Antibiotic production in Streptomyces is organized by a division of labor through terminal genomic differentiation

One of the hallmark behaviors of social groups is division of labor, where different group members become specialized to carry out complementary tasks. By dividing labor, cooperative groups increase efficiency, thereby raising group fitness even if these behaviors reduce individual fitness. We find that antibiotic production in colonies of Streptomyces coelicolor is coordinated by a division of labor. We show that S. coelicolor colonies are genetically heterogeneous because of amplifications and deletions to the chromosome. Cells with chromosomal changes produce diversified secondary metabolites and secrete more antibiotics; however, these changes reduced individual fitness, providing evidence for a trade-off between antibiotic production and fitness. Last, we show that colonies containing mixtures of mutants and their parents produce significantly more antibiotics, while colony-wide spore production remains unchanged. By generating specialized mutants that hyper-produce antibiotics, streptomycetes reduce the fitness costs of secreted secondary metabolites while maximizing the yield and diversity of these products

Stress-induced formation of cell wall-deficient cells in filamentous actinomycetes

The cell wall is a shape-defining structure that envelopes almost all bacteria and protects them from environmental stresses. Bacteria can be forced to grow without a cell wall under certain conditions that interfere with cell wall synthesis, but the relevance of these wall-less cells (known as L-forms) is unclear. Here, we show that several species of filamentous actinomycetes have a natural ability to generate wall-deficient cells in response to hyperosmotic stress, which we call S-cells. This wall-deficient state is transient, as S-cells are able to switch to the normal mycelial mode of growth. However, prolonged exposure of S-cells to hyperosmotic stress yields variants that are able to proliferate indefinitely without their cell wall, similarly to L-forms. We propose that formation of wall-deficient cells in actinomycetes may serve as an adaptation to osmotic stress

Exhumation History of the Greater Khingan Mountains (NE China) Since the Late Mesozoic: Implications for the Tectonic Regime Change of Northeast Asia

The Greater Khingan Mountains (GKMs) are a prominent orogenic zone in Northeast Asia that offers significant insights into the evolution of the Mongol-Okhotsk Ocean and the Pacific Ocean during the Phanerozoic. A comprehensive study integrating a low-temperature thermochronology analysis pertaining to the Greater Khingan area and its associated basins has been conducted. Apatite fission-track (AFT) tests conducted on detrital samples from the GKMs in Northeast China have yielded central ages ranging from 260 to 62 Ma. Two-dimensional thermal history inversion modeling and three-dimensional numerical simulations were used to investigate the GKMs' thermal history, revealing at least two distinct tectonic cooling and exhumation events: one occurring between 147 and 70 Ma and another around 35 Ma. The fission-track age groups of the GKMs, Hailar-Erlian Basin, and Mohe Basin bear some resemblance (>105 Ma), but the results from the Songliao Basin are unique. This implies that the Songliao Basin and the GKMs were likely under the influence of different tectonic domains during this period, while AFT age peaks between 105 and 45 Ma, indicating the basin-mountain systems were likely influenced by a unified Paleo-Pacific plate process, which prevailed from about 105 Ma. The 147–70 Ma cooling event can be attributed to the combined effects of the compression orogeny, resulting from the closure of the Mongol-Okhotsk Ocean during the Early Cretaceous and the extension orogeny triggered by the subduction of the Paleo-Pacific Ocean during the early Late Cretaceous. Since approximately 35 Ma, the increase in Pacific plate subduction speed may have established a post-arc extensional tectonic environment in the GKMs that has persisted until now

Associations of vitamin D-related single nucleotide polymorphisms with post-stroke depression among ischemic stroke population

ObjectiveTo investigate the relationship between single nucleotide polymorphisms (SNPs) related to vitamin D (VitD) metabolism and post-stroke depression (PSD) in patients with ischemic stroke.MethodsA total of 210 patients with ischemic stroke were enrolled at the Department of Neurology in Xiangya Hospital, Central South University, from July 2019 to August 2021. SNPs in the VitD metabolic pathway (VDR, CYP2R1, CYP24A1, and CYP27B1) were genotyped using the SNPscan™ multiplex SNP typing kit. Demographic and clinical data were collected using a standardized questionnaire. Multiple genetic models including dominant, recessive, and over-dominant models were utilized to analyze the associations between SNPs and PSD.ResultsIn the dominant, recessive, and over-dominant models, no significant association was observed between the selected SNPs in the CYP24A1 and CYP2R1 genes and PSD. However, univariate and multivariate logistic regression analysis revealed that the CYP27B1 rs10877012 G/G genotype was associated with a decreased risk of PSD (OR: 0.41, 95% CI: 0.18–0.92, p = 0.030 and OR: 0.42, 95% CI: 0.18–0.98, p = 0.040, respectively). Furthermore, haplotype association analysis indicated that rs11568820-rs1544410-rs2228570-rs7975232-rs731236 CCGAA haplotype in the VDR gene was associated with a reduced risk of PSD (OR: 0.14, 95% CI: 0.03–0.65, p = 0.010), whereas no significant association was observed between haplotypes in the CYP2R1 and CYP24A1 genes and PSD.ConclusionOur findings suggest that the polymorphisms of VitD metabolic pathway genes VDR and CYP27B1 may be associated with PSD in patients with ischemic stroke

Minimum Short Circuit Ratio Requirement for MMC-HVDC Systems Based on Small-Signal Stability Analysis

This paper determines the minimum short circuit ratio (SCR) requirement for a modular multilevel converter based high-voltage direct current (MMC-HVDC) transmission systems. Firstly, a simplified model of MMC is introduced; the MMC is represented by its AC and DC side equivalent circuit. Next, by linearizing the MMC subsystem and the DC network subsystem, the deduction of the small-signal models of MMC subsystem, the small-signal model of the DC network and MMC-HVDC are carried out successively. Thirdly, the procedure for determining the minimum SCR requirement of MMC-HVDC is described. Finally, case studies are performed on a two-terminal MMC-HVDC system under four typical control schemes. The results show that the restraint factors for the rectifier MMC is predominantly the voltage safety limit constraint, and the restraint factors for the inverter MMC are mainly the phase locked loop (PLL) or the outer reactive power controller. It is suggested that the minimum SCR requirement for the sending and the receiving systems should be 2.0 and 1.5 in the planning stage

Frequency selection method for urban low frequency multi‐terminal interconnected systems

Abstract Large‐scale urban power grid (LUPG) is normally under the operating mode by voltage layer and zone partition. One of the most important directions for the development of urban is to enhance the controllability by flexible low‐frequency interconnection technology. In this study, a frequency selection method for urban low‐frequency multi‐terminal interconnected systems (ULFMIS) is proposed. Firstly, the required support power under different conditions, the index number of sending partition (SP) and receiving partition (RP) are determined. Secondly, by calculating the current distribution along the line under different support powers, the upper limit of the transmission frequency (ULTF) of each line is obtained. Finally, the smallest transmission frequency among the ULTFs of different tie lines is selected as the ULTF of the ULFMIS. The proposed method is validated in a typical four‐terminal ULFMIS. The results demonstrate that the suggested method is suitable for calculating the ULTF taking account of the influence of the number of parallel lines on economic cost and provide guidance for future practical ULFMIS projects