Inorganic polyphosphate (polyP), a polymer of hundreds of phosphate (Pi) residues, accumulates in Escherichia coli in response to stresses, including amino acid starvation. Here we show that the adenosine 5'-triphosphate-dependent protease Lon formed a complex with polyP and degraded most of the ribosomal proteins, including S2, L9, and L13. Purified S2 also bound to polyP and formed a complex with Lon in the presence of polyP. Thus, polyP may promote ribosomal protein degradation by the Lon protease, thereby supplying the amino acids needed to respond to starvation.

Two chemotactic transducer genes (termed pctB and pctc) and an open reading frame (orfl) were found in the -flanking region which was previously identified as a chemotactic transducer gene in Ps0udomonas eeruginosa. The pctB and pcK: genes encode predicted polypeptides of 629 and 632 amino acids, respectively. Overall, PctB and Pctc had 81 and 75% amino acid identities with PctA, respectively. A null mutant strain PCT2, which contained a deletion in the entire pctC, orfl, pctA and pctB genes, did not show chemotaxis towards all 20 commonly occurring Loamino acids. This mutant strain also failed to respond to amino acid catabolites (cadaverine, baminobutyrate and putrescine) that are strong attractants for the wild-type strain PAOl. To study the role of each gene product in L-amino acid taxis, plasmids harbouring the pctC, orfl, pctA, or pets genes were constructed and introduced into strain PO2 by transformation. The orfl gene did not complement the defect in chemotaxis of strain -2.The pctA gene restored the ability of strain PCT2 to respond to 18 L-amino acids, suggesting that PctA plays a major role in detecting L-amino acids in P. a0ruglnosa. The pctB and pctC genes complemented the defect in chemotaxis to only seven (Ala, Arg, Glu, Lys, Met, Tyr, Gln) and two (His, Pro) Lamino acids, respectively.

The marine bacterium Pseudoalteromonas sp. strain A28 was able to kill the diatom Skeletonema costatum strain NIES-324. The culture supernatant of strain A28 showed potent algicidal activity when it was applied to a paper disk placed on a lawn of S. costatum NIES-324. The condensed supernatant, which was prepared by subjecting the A28 culture supernatant to ultrafiltration with a 10,000-M w -cutoff membrane, showed algicidal activity, suggesting that strain A28 produced extracellular substances capable of killing S. costatum cells. The condensed supernatant was then found to have protease and DNase activities. Two Pseudoalteromonas mutants lacking algicidal activity, designated NH1 and NH2, were selected after N-methyl-N-nitrosoguanidine mutagenesis. The culture supernatants of NH1 and NH2 showed less than 15% of the protease activity detected with the parental strain, A28. The protease was purified to homogeneity from A28 culture supernatants by using ion-exchange chromatography followed by preparative gel electrophoresis. Paper-disk assays revealed that the purified protease had potent algicidal activity. The purified protease had a molecular mass for 50 kDa, and the N-terminal amino acid sequence was determined to be Ala-Thr-Pro-Asn-Asp-Pro. The optimum pH and temperature of the protease were found to be 8.8 and 30°C, respectively, by using succinyl-Ala-Ala-ProPhe-p-nitroanilide as a substrate. The protease activity was strongly inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate, antipain, chymostatin, and leupeptin. No significant inhibition was detected with EDTA, EGTA, phenanthroline or tetraethylenepentamine. These results suggest that Pseudoalteromonas sp. strain A28 produced an extracellular serine protease which was responsible for the algicidal activity of this marine bacterium.There have recently been discussions concerning the roles of marine bacteria in algal bloom dynamics (7,15,22). Marine bacteria may both promote and regulate algal blooms (6, 9). The fact that marine bacteria selectively promote bloom formation by algal species has recently been reported (10). On the basis of laboratory experiments, it has also been reported that some bacteria are able to inhibit the growth of red-tide algae (12). In general, bacteria that inhibit algal growth are effective through direct or indirect attack (2, 17). For example, the gliding bacterium Cytophaga sp. strain J18/M01 effectively kills diatoms and raphidophytes when it is added to algal cultures but not when filtrate alone is added (direct attack) (12). Indirect attacks are thought to be chemically mediated (17). Recent studies have demonstrated the presence of bacteria that lyse algal cells by producing extracellular substances (2, 8). Alga-lytic bacteria have also been found in coastal environments where harmful algal blooms often occur (2, 8, 12-14, 17, 19, 23). It is therefore possible that bacteria having algicidal effects are involved in the termination and decomposition of algal blooms. However, virtually nothing is known...

N-Octanoyl cyclopentylamide (C8-CPA) was found to moderately inhibit quorum sensing in Pseudomonas aeruginosa PAO1. To obtain more powerful inhibitors, a series of structural analogs of C8-CPA were synthesized and examined for their ability to inhibit quorum sensing in P. aeruginosa PAO1. The lasB-lacZ and rhlA-lacZ reporter assays revealed that the chain length and the ring structure were critical for C8-CPA analogs to inhibit quorum sensing. N-Decanoyl cyclopentylamide (C10-CPA) was found to be the strongest inhibitor, and its concentrations required for half-maximal inhibition for lasB-lacZ and rhlA-lacZ expression were 80 and 90 M, respectively. C10-CPA also inhibited production of virulence factors, including elastase, pyocyanin, and rhamnolipid, and biofilm formation without affecting growth of P. aeruginosa PAO1. C10-CPA inhibited induction of both lasI-lacZ by N-(3-oxododecanoyl)-L-homoserine lactone (PAI1) and rhlA-lacZ by N-butanoyl-L-homoserine lactone (PAI2) in the lasI rhlI mutant of P. aeruginosa PAO1, indicating that C10-CPA interferes with the las and rhl quorum-sensing systems via inhibiting interaction between their response regulators (LasR and RhlR) and autoinducers.Pseudomonas aeruginosa is a gram-negative bacterium capable of infecting insects, plants, animals, and humans (29). It is one of the most frequently isolated bacteria in nosocomial infections (6). As an opportunistic human pathogen, it colonizes immunocompromised hosts and mechanically ventilated patients. Most notably, cystic fibrosis patients are particularly susceptible to chronic infections by P. aeruginosa, which is a leading cause of mortality in this population (13). The capacity of this bacterium to cause such diverse infections is due to the production of a plethora of virulence factors (38).It has been shown that P. aeruginosa employs quorum sensing in the regulation of genes encoding extracellular virulence factors (35). Quorum sensing is an intercellular communication system that allows bacteria to control gene expression in a cell population density-dependent manner. P. aeruginosa possesses two quorum-sensing systems termed las and rhl. The las and rhl quorum-sensing systems are comprised of the LuxRI homologs LasRI and RhlRI, respectively (9). The LuxI homologs LasI and RhlI are responsible for the synthesis of the las and rhl signals, N-(3-oxododecanoyl)-L-homoserine lactone (PAI1) (Fig. 1) and N-butanoyl-L-homoserine lactone (PAI2; Fig. 1), respectively. PAI1 activates the LuxR-type transcription factor LasR, and in turn LasR-PAI1 induces the production of LasB elastase, LasA protease, alkaline protease, exotoxin A, and LasRI (10, 11, 32, 37). The las quorum-sensing system is also required for the development of P. aeruginosa biofilms (5). PAI2 cooperates with the cognate regulator RhlR to enhance the production of rhamnolipid, pyocyanin, LasB elastase, hydrogen cyanide, and cytotoxic lectins (1,20,25,41). The las quorum-sensing system regulates the rhl quorum-sensing system at the transcriptional and posttranscrip...

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