Biological activities of compounds from Piper species

It is well established that secondary metabolites play an important role in plant chemical defense. In an effort to find natural herbicides research on plant growth regulatory activity of secondary metabolites has received more and more attention recently. The genus Piper has been an important source for useful secondary metabolites.^ Crude extracts from Piper species inhibited gram-positive bacteria and higher plant growth under laboratory conditions. Bioassay-guided isolation and purification lead to the identification of safrole, a phenylpropene, as the responsible agent for the inhibitory activity. Safrole was found to leach from naturally fallen leaves with water. Mechanisms of plant growth inhibition by safrole were investigated. Disassociation of cell membrane from cell walls was determined to be a major cause.^ Phenylpropenes structurally similar to safrole had similar phytogrowth inhibitory activity. It is postulated that phenylpropanoids are an important group of naturally occurring secondary metabolites in plant-plant interactions. ^

The 4-aza-S-ribosyl-L-homocysteine derivatives and the related gamma-lactam and azahemiacetal analogs: Synthesis, inhibition and quorum sensing activity

Quorum sensing (QS) is a population-dependent signaling process bacteria use to control multiple processes including virulence, critical for establishing infection. There are two major pathways of QS systems. Type 1 is species specific or intra-species communication in which N-acylhomoserine lactones (Gram-negative bacteria) or oligopeptides (Gram-positive bacteria) are employed as signaling molecules (autoinducer one). Type 2 is inter-species communication in which S-4,5-dihydroxy-2,3-pentanedione (DPD) or its borate esters are used as signaling molecules. The DPD is biosynthesized by LuxS enzyme from S-ribosylhomocysteine (SRH). Recent increase in prevalence of bacterial strains resistant to antibiotics emphasizes the need for the development of new generation of antibacterial agents. Interruption of QS by small molecules is one of the viable options as it does not affect bacterial growth but only virulence, leading to less incidence of microbial resistance. Thus, in this work, inhibitors of both N-acylhomoserine lactone (AHL) mediated intra-species and LuxS enzyme, involved in inter-species QS are targeted. The γ-lactam and their reduced cyclic azahemiacetal analogs, bearing the additional alkylthiomethyl substituent, were designed and synthesized targeting AHL mediated QS systems in P. aeruginosa and Vibrio harveyi. The γ-lactams with nonylthio or dodecylthio chains acted as inhibitors of las signaling in P. aeruginosa with moderate potency. The cyclic azahemiacetal with shorter propylthio or hexylthio substituent were found to strongly inhibit both las and rhl signaling in P. aeruginosa at higher concentrations. However, lactam and their azahemiacetal analogs were found to be inactive in V. harveyi QS systems. The 4-aza-S-ribosyl-L-homocysteine (4-aza-SRH) analogs and 2-deoxy-2-substituted-S-ribosyl-L-homocysteine analogs were designed and synthesized targeting Bacillus subtilis LuxS enzyme. The 4-aza-SRH analogs in which oxygen in ribose ring is replaced by nitrogen were further modified at anomeric position to produce pyrrolidine, lactam, nitrone, imine and hemiaminal analogs. Pyrrolidine and lactam analogs which lack anomeric hydroxyl, acted as competitive inhibitors of LuxS enzyme with KI value of 49 and 37 µM respectively. The 2,3-dideoxy lactam analogs were devoid of activity. Such findings attested the significance of hydroxyl groups for LuxS binding and activity. Hemiaminal analog of SRH was found to be a time-dependent inhibitor with IC50 value of 60 µM.

Diversity of Vancomycin Genes in Sub-tropical Soils

With the increased antibiotic exposure from anthropogenic sources, soil microbes are an ever-increasing ecological pool of resistant bacteria. This is the case with bacterial resistance to vancomycin through transfer of van-resistance genes by transposons. Studies show that bacterial species other than enteroccoci harbor genetic-like elements such as the Tn1546 transposon containing vancomycin-resistant genes. Overuse and misuse of antibiotics in hospital settings and agricultural practices have led to an increase in transferability of vancomycin-resistant genes among microbes. The objective of this project is to analyze the diversity of these genes found in the soil microbes from Miami-Dade County. Bacterial isolates were Gram-stained and the Kirby-Bauer antibiotic disk diffusion test was performed to determine the degree of resistance. Results showed that all bacterial isolates were resistant to penicillin at the 10 µg concentration and most were susceptible to varying vancomycin concentrations (10 µg, 20 µg, and 30 µg). A 1465 bp fragment was amplified from the 16S rDNA gene using 27F and 1492R universal primers from the multi-antibiotic resistant bacteria and sequenced to identify the isolates. Three Gram-negative bacteria genera were identified with the closest phylogenetic match to: Pseudomonas sp., Stenotrophomonas sp., Xanthomonas sp., as well as two Gram-positive bacteria genera: Bacillus sp. and Brevibacillus sp. The isolates’ vanA and vanB genes were amplified using the respective primers. Ongoing work is underway to sequence and compare these known van resistant genes, with the goal of revealing intrinsic vancomycin resistance present in soil bacteria.