Comparison of ectoine synthesis regulation in secreting and non-secreting strains of Halomonas

Strategies for the biological production of ectoine by using different chassis strains

As an amino acid derivative and a typical compatible solute, ectoine can assist microorganisms in resisting high osmotic pressure. Own to its long-term moisturizing effects, ectoine shows extensive applications in cosmetics, medicine and other fields. With the rapid development of synthetic biology and fermentation engineering, many biological strategies have been developed to improve the ectoine production and simplify the production process. Currently, the microbial fermentation has been widely used for large scaling ectoine production. Accordingly, this review will introduce the metabolic pathway for ectoine synthesis and also comprehensively evaluate both wild-type and genetically modified strains for ectoine production. Furthermore, process parameters affecting the ectoine production efficiency and adoption of low cost substrates will be evaluated. Lastly, future prospects on the improvement of ectoine production will be proposed.

Unusual deprivation of compatible solutes in Acinetobacter baumannii

The opportunistic human pathogen Acinetobacter baumannii is one of the leading causes of nosocomial infections. The high prevalence of multidrug-resistant strains, a high adaptability to changing environments and an overall pronounced stress resistance contribute to persistence and spread of the bacteria in hospitals and thereby promote repeated outbreaks. Altogether, the success of A. baumannii is mainly built on adaptation and stress resistance mechanisms, rather than relying on 'true' virulence factors. One of the stress factors that pathogens must cope with is osmolarity, which can differ between the external environment and different body parts of the human host. A. baumannii ATCC 19606^T accumulates the compatible solutes glutamate, mannitol and trehalose in response to high salinities. In this work, it was found that most of the solutes vanish immediately after reaching stationary phase, a very unusual phenomenon. While glutamate can be metabolized, mannitol produced by MtlD is excreted to the medium in high amounts. First results indicate that A. baumannii ATCC 19606^T undergoes a rapid switch to a dormant state (viable but non-culturable) after disappearance of the compatible solutes. Resuscitation from this state could easily be achieved in PBS or fresh medium.