Assembly of the cell division protein FtsZ into ladder-like structures in the aerial hyphae of Streptomyces coelicolor

In the filamentous bacterium Streptomyces coelicolor , the cell division protein FtsZ is required for the conversion of multinucleoidal aerial hyphae into chains of uninucleoidal spores, although it is not essential for viability. Using immunofluorescence microscopy, we have shown that FtsZ assembles into long, regularly spaced, ladder-like arrays in developing aerial hyphae, with an average spacing of about 1.3 μm. Within individual hyphae, ladder formation was relatively synchronous and extended for distances over 100 μm. These ladders were present only transiently, decreasing in intensity as chromosomes separated into distinct nucleoids and disappearing upon the completion of septum formation. Evidence from the overall intensity of immunofluorescence staining suggested that ladder formation was regulated in part at the level of the accumulation and degradation of FtsZ within individual aerial hyphae. Finally, FtsZ ladder formation was under developmental control in that long arrays of FtsZ rings could not be detected in certain so-called white mutants ( whiG , whiH and whiB ), which are blocked in spore formation. The assembly of FtsZ into ladders represents the earliest known molecular manifestation of the process of spore formation, and its discovery provides insight into the role of whi genes in the conversion of aerial hyphae into chains of spores. We have also described a novel use of a cell wall-staining technique to visualize apical tip growth in vegetatively growing hyphae.     

Programmed cell death in bacteria

Programmed death (PDC) of individual cells is a genetically controlled biological process related to the development of multicellular organisms. It proceeds in most cases as apoptosis characterized by DNA degradation and breakdown of dying cells to apoptotic bodies, and ending by their phagocytosis by macrophages or by the surrounding tissue. Unlike apoptosis, necrosis is a genetically unregulated sudden death of a group of cells caused by a severe damage of membranes and other cell components. In bacteria, programmed cell death is mostly related to population development. This holds mainly for sporulation of bacilli where the process is best understood at the morphological, physiological and genetic level. Sporulation of bacilli begins by an asymmetric division of the nongrowing cell into two parts—the mother and the forespore compartment, whose fate is different. Whereas the smaller compartment develops into the spore, the function of the larger is twofold. It participates in the spore development mainly by forming spore coast but it also synthesizes or activates the autolytic apparatus which lyzes the sporangium cell wall at the end of the process. Some phases of the development of myxobacteria and streptomycetes also have characteristic features of programmed death. Unlike sporulation of bacilli, the autolysis of a portion of population of myxobacteria or hyphae of streptomycetes proceeds in the middle of their developmental cycle. Extensive turnover of cell membranes in growing myxobacteria results in the formation of a fatty acid mixture—theautocide—which kills a smaller or greater portion of the myxobacterial population. The dead cells are digested by extracellular enzymes released by myxobacteria and the digest is used as nutrient for completion of the developmental cycle of the remaining living population. Similar events take place also during the formation of aerial mycelium in streptomycetes. Here the autolysis of a portion of vegetative (substrate) mycelium supplies amino acids for the formation of aerial mycelium. The recently discovered programmed death of plasmid-free descendants of a plasmid-bearing population of different bacteria is based on the loss of control of toxin activity by its antidote. Both substances are encoded by plasmid DNA and the loss of the plasmid results in an “enforced suicide” of the host cell because the effective concentration of the antidote decreases more rapidly than that of the toxin. The mechanisms of this suicide can vary. In addition to the above mentioned kinds of programmed death, other events of developmentally regulated death of prokaryotes probably exist. Some bacteria contain “death genes” in their chromosome which trigger cell death at the onset of the stationary phase. The physiological function of this kind of suicide is not known. However, most nonsporulating bacteria developed a strategy of surviving at the nongrowing stage by transforming the growing cell to a more resistant dormant (cryptobiological) form.     

Developmental mutants ofStreptomyces coeruleorubidus,a producer of anthracyclines: Isolation and preliminary characterization

Abstbact The wild strainStreptomyces coeruleorubidus JA 10092 was found to segregate into two spontaneous morphological variants (spo-1 andbld-1) with a different ability to form aerial mycelium in media with glucose as the main carbon source. Six new types of developmental mutants were obtained from the bald variantbld-1 after treatment with mutagens (UV light, γ radiation, nitrous acid) and after natural selection Formation of the aerial mycelium was fully suppressed in thebld-2 type growing on media both with glucose and with starch. The other types were bald only on starch media, forming the aerial mycelium on media with glucose; typesspo-2, spo-3, spo-4 andspo-5 differed in size, shape and surface structure of spores, the typewhi formed asporogenous aerial hyphae.     

SsgA-like proteins determine the fate of peptidoglycan during sporulation of Streptomyces coelicolor

During developmental cell division in sporulation-committed aerial hyphae of streptomycetes, up to a hundred septa are simultaneously produced, in close harmony with synchromous chromosome condensation and segregation. Several unique protein families are involved in the control of this process in actinomycetes, including that of the SsgA-like proteins (SALPs). Mutants for each of the individual SALP genes were obtained, and high-resolution and fluorescence imaging revealed that each plays an important and highly specific role in the control of the sporulation process, and their function relates to the build-up and degradation of septal and spore-wall peptidoglycan. While SsgA and SsgB are essential for sporulation-specific cell division in Streptomyces coelicolor, SsgC-G are responsible for correct DNA segregation/condensation (SsgC), spore wall synthesis (SsgD), autolytic spore separation (SsgE, SsgF) or exact septum localization (SsgG). Our experiments paint a picture of a novel protein family that acts through timing and localization of the activity of penicillin-binding proteins and autolysins, thus controlling important steps during the initiation and the completion of sporulation in actinomycetes.     

A novel taxonomic marker that discriminates between morphologically complex actinomycetes

In the era when large whole genome bacterial datasets are generated routinely, rapid and accurate molecular systematics is becoming increasingly important. However, 16S ribosomal RNA sequencing does not always offer sufficient resolution to discriminate between closely related genera. The SsgA-like proteins are developmental regulatory proteins in sporulating actinomycetes, whereby SsgB actively recruits FtsZ during sporulation-specific cell division. Here, we present a novel method to classify actinomycetes, based on the extraordinary way the SsgA and SsgB proteins are conserved. The almost complete conservation of the SsgB amino acid (aa) sequence between members of the same genus and its high divergence between even closely related genera provides high-quality data for the classification of morphologically complex actinomycetes. Our analysis validates Kitasatospora as a sister genus to Streptomyces in the family Streptomycetaceae and suggests that Micromonospora, Salinispora and Verrucosispora may represent different clades of the same genus. It is also apparent that the aa sequence of SsgA is an accurate determinant for the ability of streptomycetes to produce submerged spores, dividing the phylogenetic tree of streptomycetes into liquid-culture sporulation and no liquid-culture sporulation branches. A new phylogenetic tree of industrially relevant actinomycetes is presented and compared with that based on 16S rRNA sequences.     

Effects of modification of membrane lipid composition on Bacillus subtilis sporulation and spore properties

Aims: To determine effects of inner membrane lipid composition on Bacillus subtilis sporulation and spore properties. Methods and Results: The absence of genes encoding lipid biosynthetic enzymes had no effect on B. subtilis sporulation, although the expected lipids were absent from spores’ inner membrane. The rate of spore germination with nutrients was decreased c. 50% with mutants that lacked the major cardiolipin (CL) synthase and another enzyme for synthesis of a major phospholipid. Spores lacking the minor CL synthase or an enzyme essential for glycolipid synthesis exhibited 50–150% increases in rates of dodecylamine germination, while spores lacking enzymes for phosphatidylethanolamine (PE), phosphatidylserine (PS) and lysylphosphatidylglycerol (l‐PG) synthesis exhibited a 30–50% decrease. Spore sensitivity to H₂O₂ and tert‐butylhydroperoxide was increased 30–60% in the absence of the major CL synthase, but these spores’ sensitivity to NaOCl or Oxone^? was unaffected. Spores of lipid synthesis mutants were less resistant to wet heat, with spores lacking enzymes for PE, PS or l‐PG synthesis exhibiting a two to threefold decrease and spores of other strains exhibiting a four to 10‐fold decrease. The decrease in spore wet heat resistance correlated with an increase in core water content. Conclusions: Changing the lipid composition of the B. subtilis inner membrane did not affect sporulation, although modest effects on spore germination and wet heat and oxidizing agent sensitivity were observed, especially when multiple lipids were absent. The increases in rates of dodecylamine germination were likely due to increased ability of this compound to interact with the spore’s inner membrane in the absence of some CL and glycolipids. The effects on spore wet heat sensitivity are likely indirect, because they were correlated with changes in core water content. Significance and Impact of the Study: The results of this study provide insight into roles of inner membrane lipids in spore properties.     

Sporulation and regeneration efficiency of phosphobacteria (<Emphasis Type="Italic">Bacillus megaterium</Emphasis> var <Emphasis Type="Italic">phosphaticum</Emphasis>)

Sporulation in Bacillus megaterium var phosphaticum (PB — 1) was induced using modified nutrient media. This modified medium induced sporulation within 36 h. After spore induction the spores were kept under refrigerated (5°C) and room temperature (32°C) for five months and survival of spores was studied at 15 days intervals by plating them in nutrient agar medium. It was observed that there was not much variation in the storage temperature (5°C & 32°C). The spore cells of Bacillus megaterium var phosphaticum (PB — 1) were observed up to five months of storage under refrigerated (5°C) and room temperature (32°C). Regeneration of spore cells into vegetative cells was studied in tap water, rice gruel, nutrient broth, sterile lignite and sterile water at different concentrations of spore inoculum. The multiplication of sporulated Bacillus megaterium var phosphaticum culture was fast and reached its maximum (29.5 × 10⁸ cfu ml⁻¹) in nutrient broth containing 5 per cent inoculum level.     

Improved yields of daunomycinone glycosides in developmental mutants ofStreptomyces coeruleorubidus

When improvingStreptomyces coeruleorubidus JA 10092, a producer of antibiotics of the daunomycinone complex, the most active variants were found among isolates of morphological typesbld-1 (with a suppressed production of the aerial mycelium on organic media containing glucose) andwhi (with an asporogenic aerial mycelium on glucose media and with the bald phenotype on media containing starch). Submerged cultures of thewhi mutants produced increased quantities of daunomycinone glycosides in the antibiotic complex, the amount of free anthracyclinones being simultaneously decreased. Thewhi strains differed from the wild type also in higher demands for aeration, concentration of glucose and in an increased production capacity in starch media. The overall antibiotic activity increased more than 40 times after a six-step selection (application of UV light, γ-radiation, nitrous acid and natural spreads) combined with an altered fermentation technology.     

Properties of Bacillus anthracis spores prepared under various environmental conditions

Bacillus anthracis makes highly stable, heat-resistant spores which remain viable for decades. Effect of various stress conditions on sporulation in B. anthracis was studied in nutrient-deprived and sporulation medium adjusted to various pH and temperatures. The results revealed that sporulation efficiency was dependent on conditions prevailing during sporulation. Sporulation occurred earlier in culture sporulating at alkaline pH or in PBS than control. Spores formed in PBS were highly sensitive towards spore denaturants whereas, those formed at 45°C were highly resistant. The decimal reduction time (D-10 time) of the spores formed at 45°C by wet heat, 2 M HCl, 2 M NaOH and 2 M H₂O₂ was higher than the respective D-10 time for the spores formed in PBS. The dipicolinic acid (DPA) content and germination efficiency was highest in spores formed at 45°C. Since DPA is related to spore sensitivity towards heat and chemicals, the increased DPA content of spores prepared at 45°C may be responsible for increased resistance to wet heat and other denaturants. The size of spores formed at 45°C was smallest amongst all. The study reveals that temperature, pH and nutrient availability during sporulation affect properties of B. anthracis spores.     

cmdABCDEF, a cluster of genes encoding membrane proteins for differentiation and antibiotic production in Streptomyces coelicolor A3(2)

Background  

Streptomyces coelicolor is the most studied Streptomyces species and an excellent model for studying differentiation and antibiotic production. To date, many genes have been identified to be required for its differentiation (e.g. bld genes for aerial growth and whi genes for sporulation) and antibiotics production (including actII-orf4, redD, cdaR as pathway-specific regulatory genes and afsR, absA1/A2 as pleiotropic regulatory genes).     

Fate and role of peroxisomes during the life cycle of the yeast Saccharomyces cerevisiae: inheritance of peroxisomes during meiosis

 Sporulation in the yeast Saccharomyces cerevisiae is a meiotic developmental process that occurs in MAT a/MATα heterozygotes in response to nutrient deprivation. Here, the fate and role of peroxisomes during sporulation and germination has been examined by a combination of immunoelectron microscopy and the use of pex mutants defective in peroxisomal functions. Using a green fluorescent protein probe targeted to peroxisomes we show that peroxisomes are inherited through meiosis and that they do not increase in number either during sporulation or spore germination. In addition, there is no requirement for peroxisome degradation prior to spore packaging. Unlike the situation in filamentous fungi, peroxisomes do not proliferate during the yeast life cycle. Functional peroxisomes are dispensable for efficient meiotic development on acetate medium since homozygous Δpex6 diploids sporulated well and produced mature spores that were resistant to diethyl ether. Like haploids, diploid cells can proliferate their peroxisomes in response to oleate as sole carbon source in liquid medium, but under these conditions they do not sporulate. On solid oleate medium, homozygous pex5,Δpex6, and pex7 cells were unable to sporulate efficiently, whereas the wild type was. The results presented here are discussed in terms of the transmission of organelles to progeny cells. Accepted: 19 December 1997     

Sporulation of Streptomyces griseus in submerged culture.

A wild-type strain of Streptomyces griseus forms spores both on solid media (aerial spores) and in liquid culture (submerged spores). Both spore types are highly resistant to sonication, but only aerial spores are resistant to lysozyme digestion. Electron micrographs suggest that lysozyme sensitivity may result from the thinner walls of the submerged spores. Studies of the life cycle indicate that neither streptomycin excretion nor extracellular protease activity is required for sporulation: the analysis of mutants, however, suggests that antibiotic production may be correlated with the ability to sporulate. A method was devised to induce the rapid sporulation of S. griseus in a submerged culture. This method, which depends on nutrient deprivation, was used to determine that either ammonia or phosphate starvation can trigger sporulation and that the enzyme glutamine synthetase may be useful as a sporulation marker after phosphate deprivation.     

The Bacillus subtilis germinant receptor GerA triggers premature germination in response to morphological defects during sporulation

During sporulation in Bacillus subtilis, germinant receptors assemble in the inner membrane of the developing spore. In response to specific nutrients, these receptors trigger germination and outgrowth. In a transposon‐sequencing screen, we serendipitously discovered that loss of function mutations in the gerA receptor partially suppress the phenotypes of > 25 sporulation mutants. Most of these mutants have modest defects in the assembly of the spore protective layers that are exacerbated in the presence of a functional GerA receptor. Several lines of evidence indicate that these mutants inappropriately trigger the activation of GerA during sporulation resulting in premature germination. These findings led us to discover that up to 8% of wild‐type sporulating cells trigger premature germination during differentiation in a GerA‐dependent manner. This phenomenon was observed in domesticated and undomesticated wild‐type strains sporulating in liquid and on solid media. Our data indicate that the GerA receptor is poised on a knife's edge during spore development. We propose that this sensitized state ensures a rapid response to nutrient availability and also elicits premature germination of spores with improperly assembled protective layers resulting in the elimination of even mildly defective individuals from the population.