A soil microorganism identified as Bacillum megaterium was found to produce several antibiotics substances after growth for 20 h at 37 degrees C in a mineral culture medium. Analysis both by electron spray ionization (ESI) and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) identified these substances as lipopeptides. Predominant peaks at m/z 1,041 and m/z 1,065 revealed ions which are compatible with surfactins and lichenysins, respectively. Two other ions m/z 1,057 and m/z 1,464 were further studied by collision-induced dissociation (CID) unveiling an iturin A at the first and fengycins A and B at the second m/z peaks. The CID spectrum of the m/z 1,464 ion also suggests the existence of fengycins A and B variants in which Ile was changed to Val in the position 10 of the peptide moiety. Raw mixtures of all these compounds were also assayed for antibiotic features. The data enlighten the unusual diversity of the lipopeptide mixture produced by a sole Bacillus species.

Late in the fourth larval instar, several regions of the Rhynchosciara amercana salivary gland chromosomes undergo "DNA puffing. " We have constructed a library ofcloned cDNAs synthesized from poly(A)+RNA isolated from salivary glands'during the period ofdevelopment when the DNA puffs are active. From this library we have studied clones representative of three genes active during this period but not active at earlier developmental periods of the gland. One of these genes is not amplified during the developmental process and encodes a 0.6-kilobase RNA molecule. The other two genes are located within the DNA-puffsites C3 and C8and.encode 1.25-kilobase and 1.95-kldobase RNA molecules, respectively. We estimate -from the quantitation -of transfer hybridization experiments that each of these genes undergoes 16-fold amplification during DNA puffing.Gene amplification in somatic cells was first detected by morphological criteria in the larval salivary glands offlies ofthe family Sciaridae. Several regions of the Rhynchosciara americana polytene chromosomes were found to show a type ofpuffing in which, after puff regression, there was more DNA in the bands involved compared with neighboring bands as indicated by Feulgen staining (1). This was later confirmed. both by spectrophotometric measurements (2) and by autoradiographical studies on the incorporation of [3H]thymidine (3). Subsequently, similar observations-were made on the salivary chromosomes of larvae from the genus Sciara (4-6).The DNA puffs, which appear in late fourth instar in-Rhynchosciara salivary glands, are involved in the production of messenger RNAs (7,8). These encode several peptides of the communal cocoon, which are needed in large amounts over a short period of time (9, 10). Based on morphological and physiological criteria, the fourth instar of R. americana larvae has been divided into six periods (11). The first indication of DNA puff formation is the appearance of a fast-green staining band between two orcein (+) bands at the chromosomal sites ofthese puffs early in period 4 (ref. 12; unpublished data). Amplification and puffformation are subsequently maximal at different times for each site and are also dependent on the position of the cell within the gland (13, 14). The largest puffs are found in region 2 of the B chromosome and in regions 3 and 8 of the C chromosome. The B2 puffis formed preferentially in the first 50 cells of the gland in period 5, whereas C3 attains its largest size in the middle and distal section of the gland in period 6. The C8 puff is similar in all regions and is also maximal in period 6. As the larvae progress from period 3 to period 4; there is a dramatic change in the pattern of RNA and protein synthesis. This consists of an inhibition of rRNA synthesis (15) and the synthesis of new poly(A)+RNA species (7,8). This is accompanied by inhibition of the synthesis of certain peptides and the synthesis jtg of unfractionated RNA from the salivary glands of periods 3 and 5 larvae, was fractionated by electrophores...

No abstract

No abstract

Cyclic lipopeptides are produced by a soil Bacillus megaterium strain and several other Bacillus species. In this work, they are detected both in the Bacillus intact cells and the cells culture medium by MALDI-TOF mass spectrometry. The cyclic lipopeptides self-assemble in water media producing negatively charged and large aggregates (300–800 nm of mean hydrodynamic radius) as evaluated by dynamic light scattering and zeta-potential analysis. The aggregate size depends on pH and ionic strength. However, it is not affected by changes in the osmolarity of the outer medium suggesting the absence of an internal aqueous compartment despite the occurrence of low molecular weight phospholipids in their composition as determined from inorganic phosphorus analysis. The activity against a sensitive Bacillus cereus strain was evaluated from inhibition halos and B. cereus lysis. Essential features determining the antibiotic activity on susceptible Bacillus cereus cells are the preserved cyclic moiety conferring cyclic lipopeptides resistance to proteases and the medium pH. The aggregates are inactive per se at the pH of the culture medium which is around 6 or below. The knock out of the sensitive cells only takes place when the aggregates are disassembled due to a high negative charge at pH above 6.