Tohey Matsuyama

Listeria monocytogenes infiltrated the reticulate structure of a membrane filter and passed through a filter with pore sizes of 0.45 μm and 0.2 μm in 6 to 24 h and 5 to 6 days, respectively. Flagellar motility and expansive pressure generated by the growing bacterial population were indicated as the driving forces of infiltration.

Serrawettin W1 produced by Serratia marcescens is a surface active exolipid having various functions supporting behaviors of bacteria on surface environments. Through the genetic analyses of serrawettin‐less mutants of S. marcescens 274, the swrW gene encoding putative serrawettin W1 synthetase was identified. Homology analysis of the putative SwrW demonstrated the presence of condensation, adenylation, thiolation, and thioesterase domains which are characteristic for nonribosomal peptide synthetase (NRPS). NRPSs have been known as multi‐modular enzymes. Linear alignment of these modules specifying respective amino acids will enable peptide bond formation resulting in a specific amino acid sequence. Putative SwrW was uni‐modular NRPS specifying only L‐serine. Possible steps in this simple uni‐modular NRPS for biosynthesis of serrawettin W1 [cyclo‐(D‐3‐hydroxydecanoyl‐L‐seryl)₂] were predicted by referring to the ingenious enzymatic activity of gramicidin S synthetase (multi‐modular NRPS) of Brevibacillus brevis.

Serratia marcescens mutants defective in production of the red pigment prodigiosin and the biosurfactant serrawettin W1 in parallel were isolated by transposon mutagenesis of strain 274. Cloning of the DNA fragment required for production of these secondary metabolites with different chemical structures pointed out a novel open reading frame (ORF) named pswP. The putative product PswP (230 aa) has the distinct signature sequence consensus among members of phosphopantetheinyl transferase (PPTase) which phosphopantetheinylates peptidyl carrier protein (PCP) mostly integrated in the nonribosomal peptide synthetases (NRPSs) system. Since serrawettin W1 belongs to the cyclodepsipeptides, which are biosynthesized through the NRPSs system, and one pyrrole ring in prodigiosin has been reported as a derivative of L‐proline tethered to phosphopantetheinylated PCP, the mutation in the single gene pswP seems responsible for parallel failure in production of prodigiosin and serrawettin W1.

Proteus mirabilis forms a concentric-ring colony by undergoing periodic swarming. A colony in the process of such synchronized expansion was examined for its internal population structure. In alternating phases, i.e., swarming (active migration) and consolidation (growth without colony perimeter expansion), phase-specific distribution of cells differing in length, in situ mobility, and migration ability on an agar medium were recognized. In the consolidation phase, the distribution of mobile cells was restricted to the inner part of a new ring and a previous terrace. Cells composing the outer part of the ring were immobile in spite of their ordinary swimming ability in a viscous solution. A sectorial cell population having such an internal structure was replica printed on fresh agar medium. After printing, a transplant which was in the swarming phase continued its ongoing swarming while a transplanted consolidation front continued its scheduled consolidation. This shows that cessation of migration during the consolidation phase was not due to substances present in the underlying agar medium. The ongoing swarming schedule was modifiable by separative cutting of the swarming front or disruption of the ring pattern by random mixing of the pattern-forming cell population. The structured cell population seemed to play a role in characteristic colony growth. However, separation of a narrow consolidation front from a backward area did not induce disturbance in the ongoing swarming schedule. Thus, cells at the frontal part of consolidation area were independent of the internal cell population and destined to exert consolidation and swarming with the ongoing ordinary schedule.