ABSTRACT
Extracellular pili-like structures (PLS) produced by cyanobacteria have been poorly explored. We have done detailed topographical and electrical characterisation of PLS in Nostoc punctiforme PCC 73120 using transmission electron microscopy (TEM) and conductive atomic force microscopy (CAFM). TEM analysis showed that N. punctiforme produces two separate types of PLS differing in their length and diameter. The first type of PLS are 6-7.5 nm in diameter and 0.5-2 µm in length (short/thin PLS) while the second type of PLS are ~20-40 nm in diameter and more than 10 µm long (long/thick PLS). This is the first study to report long/thick PLS in N. punctiforme. Electrical characterisation of these two different PLS by CAFM showed that both are electrically conductive and can act as microbial nanowires. This is the first report to show two distinct PLS and also identifies microbial nanowires in N. punctiforme. This study paves the way for more detailed investigation of N. punctiforme nanowires and their potential role in cell physiology and symbiosis with plants.
Subject(s)
Nanowires/ultrastructure , Nostoc/ultrastructure , Nostoc/physiologyABSTRACT
Identification of extracellular conductive pilus-like structures (PLS) i.e. microbial nanowires has spurred great interest among scientists due to their potential applications in the fields of biogeochemistry, bioelectronics, bioremediation etc. Using conductive atomic force microscopy, we identified microbial nanowires in Microcystis aeruginosa PCC 7806 which is an aerobic, photosynthetic microorganism. We also confirmed the earlier finding that Synechocystis sp. PCC 6803 produces microbial nanowires. In contrast to the use of highly instrumented continuous flow reactors for Synechocystis reported earlier, we identified simple and optimum culture conditions which allow increased production of nanowires in both test cyanobacteria. Production of these nanowires in Synechocystis and Microcystis were found to be sensitive to the availability of carbon source and light intensity. These structures seem to be proteinaceous in nature and their diameter was found to be 4.5-7 and 8.5-11 nm in Synechocystis and M. aeruginosa, respectively. Characterization of Synechocystis nanowires by transmission electron microscopy and biochemical techniques confirmed that they are type IV pili (TFP) while nanowires in M. aeruginosa were found to be similar to an unnamed protein (GenBank : CAO90693.1). Modelling studies of the Synechocystis TFP subunit i.e. PilA1 indicated that strategically placed aromatic amino acids may be involved in electron transfer through these nanowires. This study identifies PLS from Microcystis which can act as nanowires and supports the earlier hypothesis that microbial nanowires are widespread in nature and play diverse roles.
Subject(s)
Microcystis , Nanowires , Synechocystis , Computational Biology/methods , Fimbriae Proteins/chemistry , Fimbriae Proteins/genetics , Fimbriae Proteins/metabolism , Fimbriae, Bacterial/physiology , Fimbriae, Bacterial/ultrastructure , Microcystis/physiology , Microcystis/ultrastructure , Microscopy, Atomic Force , Models, Molecular , Protein Conformation , Synechocystis/physiology , Synechocystis/ultrastructureABSTRACT
Production of nitric oxide (NO) and the presence of NO metabolism genes, nitrous oxide reductase (nosZ), nitrous oxide reductase regulator (nosR) and nitric oxide reductase (norB) were identified in the plant-associated bacterium (PAB) Azospirillum brasilense SM. NO presence was confirmed in all overexpressing strains, while improvement in the plant growth response of these strains was mediated by increased NO and indole-3-acetic acid (IAA) levels in the strains. Electron microscopy showed random distribution to biofilm, with surface colonization of pleiomorphic Azospirilla. Quantitative IAA estimation highlighted a crucial role of nosR and norBC in regulating IAA biosynthesis. The NO quencher and donor reduced/blocked IAA biosynthesis by all strains, indicating their common regulatory role in IAA biosynthesis. Tryptophan (Trp) and l-Arginine (Arg) showed higher expression of NO genes tested, while in the case of ipdC, only Trp and IAA increased expression, while Arg had no significant effect. The highest nosR expression in SMnosR in the presence of IAA and Trp, along with its 2-fold IAA level, confirmed the relationship of nosR overexpression with Trp in increasing IAA. These results indicate a strong correlation between IAA and NO in A. brasilense SM and suggest the existence of cross-talk or shared signaling mechanisms in these two growth regulators.
Subject(s)
Azospirillum brasilense/genetics , Azospirillum brasilense/metabolism , Indoleacetic Acids/metabolism , Nitric Oxide/metabolism , Sorghum/microbiology , Arginine/metabolism , Azospirillum brasilense/growth & development , Bacterial Proteins/genetics , Biofilms/growth & development , Gene Expression Regulation, Bacterial , Membrane Proteins/genetics , Microscopy, Electron, Scanning , Nitric Oxide/isolation & purification , Plant Roots/microbiology , Plant Roots/ultrastructure , Signal Transduction , Sorghum/growth & development , Tryptophan/metabolismABSTRACT
A remarkable diastereoselective synthesis of some novel arylthiazolyl pyrazoline derivatives 3(a-l) is displayed which were evaluated for their in vitro antimicrobial activities. In particular, compounds 3e, 3g & 3l (MIC 12.5 µg /ml) showed good activity against S. aureus and compounds 3b & 3j (MIC 12.5 µg / ml) against B. subtilis. Compounds 3g, 3i, 3j (MIC 12.5 µg/ ml) and 3l (MIC 6.25 µg / ml) also displayed excellent antifungal activity against C. albicans. Of all the synthesized compounds, 3g and 3e exerted a wide range of antibacterial activities against entire tested gram positive (S. aureus and B. subtilis) and gram negative (E. coli and P. aeruginosa) bacterial strain except P. aeruginosa.