A chemically defined medium containing 18 amino acids, inorganic salts, rhamnose, choline, and ferric pyrophosphate has been developed. The final concentrations of salts and amino acids were modeled after yeast extract. This medium supported the growth of four serogroups of Legionella pneumophila. Growth in shake cultures at 37 degrees C produced a lag time of approximately 5 h and a generation time of 4 h with a maximum growth yield of 10 9 colony-forming units per ml. A soluble brown pigment was observed in the stationary phase of growth. The optimal pH was 6.3. Rhamnose and choline were stimulatory; arginine, serine, threonine, cysteine, valine, and methionine were essential. Supplemental iron was not required to attain maximum growth, but iron deprivation caused an extended lag phase.

Background: Understanding cellular mechanism of communication is the main goal of systems biology. Unicellular yeasts are effective model to understand the molecular interactions that generate cell polarity induced by external inputs. The mechanisms of many extracellular stimuli are induced by complexes of cell surface receptors, G proteins. The mechanisms of many extracellular stimuli are induced by complexes of cell surface receptors, G proteins and mitogen activated protein (MAP) kinase complexes. Many components, their interrelationships, and their regulators of these mechanisms were initially identified in yeast. A complex web of sensing mechanisms and cooperation among signaling networks such as a cyclic adenosine monophosphate dependent protein kinase, mitogen-activated protein kinase cascade and 5-adenosine monophosphate activated protein kinase induce various changes in physiology, cell polarity, cell cycle progression and gene expression to achieve differentiation. Ras-cAMP pathway explained in yeast model with signalling function of the oncogenic mammalian Ras protein. So studies on yeast cells may enlighten some underlying mechanism which will be beneficial to understand the mechanisms of disease.

Background: Quorum sensing is a cell-to-cell communication, which is extensively observed in bacteria. This process allows the cell to detect, analyze, share and act upon various environmental stimuli based on cell density. The molecular aspect of this process is the secretion and detection of chemical signaling molecules called autoinducers (AIs), which act upon the gene expression. The quorum sensing signaling pathway is specifically observed only bulk population or in other words, the quorum sensing is effective only in high cell density. The quorum sensing circuit in the bacterial population is widely studied under the following heading; quorum sensing in Gram positive bacterium, Quorum sensing in Gram negative bacterium and the Quorum sensing with respect to Interkingdom communication. These models are studied using the widely studied models like Vibrio fischeri in Gram negative QS circuit, Staphylococcus aureus in Gram positive QS circuit and Vibrio harveyi. This review paper details the introduction of quorum sensing and their gene level explanation and how they effect on the virulence of a particular species of bacteria. This paper also throws light on the realization that the bacteria has the capable of performing coordinated activities that was so long contributed to the eukaryotic cell performance.