The hydroxyectoine gene cluster of the non-halophilic acidophile Acidiphilium cryptum

Abstract

Acidiphilium cryptum is an acidophilic, heterotrophic α-Proteobacterium which thrives in acidic, metal-rich environments (e.g. acid mine drainage). Recently, an ectABCDask gene cluster for biosynthesis of the compatible solutes ectoine and hydroxyectoine was detected in the genome sequence of A. cryptum JF-5. We were able to demonstrate that the type strain A. cryptum DSM 2389(T) is capable of synthesizing the compatible solute hydroxyectoine in response to moderate osmotic stress caused by sodium chloride and aluminium sulphate, respectively. Furthermore, we used the A. cryptum JF-5 sequence to amplify the ectABCDask gene cluster from strain DSM 2389(T) and achieved heterologous expression of the gene cluster in Escherichia coli. Hence, we could for the first time prove metabolic functionality of the genes responsible for hydroxyectoine biosynthesis in the acidophile A. cryptum. In addition, we present information on specific enzyme activity of A. cryptum DSM 2389(T) ectoine synthase (EctC) in vitro. In contrast to EctCs from halophilic microorganisms, the A. cryptum enzyme exhibits a higher isoelectric point, thus a lower acidity, and has maximum specific activity in the absence of sodium chloride.

Strangers in the archaeal world: osmostress‐responsive biosynthesis of ectoine and hydroxyectoine by the marine thaumarchaeon Nitrosopumilus maritimus

“…N. maritimus’ SCM1 EctC protein is 5.65, and hence closer to that of A. cryptum JF‐1; its salt‐sensitive properties (Fig. C and D) is thus consistent with the hypothesis put forward by Moritz and colleagues ().…”

“…N. maritimus’ SCM1 ectoine hydroxylase are very similar to those of a considerable number of previously characterized EctD proteins (eight enzymes in total) from members of the Bacteria (Bursy et al ., 2007; 2008; Widderich et al ., ). However, this situation is somewhat different for the ectoine synthase, an enzyme for which only two representatives have been kinetically characterized in some detail so far, namely the enzymes from H. elongata and Acidiphilium cryptum (Ono et al ., ; Moritz et al ., ). The ectoine synthase from H. elongata is a highly salt tolerant enzyme (Ono et al ., ), whereas both the EctC proteins from A. cryptum JF‐1 (Moritz et al ., ) and Ca.…”

“…C and D) are sensitive to high salt concentrations. Moritz and colleagues () suggested that these different sensitivities of the EctC enzymes from H. elongata and A. cryptum JF‐1 against high salt concentrations result from their different overall net‐negative charge (calculated isoelectric points: 4.87 and 6.03 for the EctC proteins from H. elongata and A. cryptum respectively). The calculated pI of the ‘ Ca .…”

Different strategies of osmoadaptation in the closely related marine myxobacteria Enhygromyxa salina SWB007 and Plesiocystis pacifica SIR-1

“…The preferential accumulation of hydroxyectoine has also been observed in other salt-stressed bacteria, such as Streptomyces coelicolor A3(2) and Virgibacillus salexigens (Sadeghi et al, 2014). Recently the ability to synthesize hydroxyectoine was also demonstrated in the acidophilic Acidiphilium cryptum, which displays only limited salt tolerance (Moritz et al, 2015). The authors concluded that hydroxyectoine, besides osmoadaptation, may serve other, hitherto unknown, functions.…”

Moderately Halophilic Bacterium Halomonas sp. AAD12: A Promising Candidate as a Hydroxyectoine Producer

“…Among them, ectoine and hydroxyectoine have been widely investigated [5]. The exceptional ability to protect enzymes against a variety of stress factors such as heating, freeze-thawing and freeze-drying places hydroxyectoine, a derivative of ectoine, in the heart of a number of studies [15,16].…”