Osmoadaptation in halophilic and alkaliphilic methanotrophs

Abstract

By using (1)H- and (13)C-NMR spectroscopy, an accumulation of sucrose and two cyclic amino acids [ectoine (1,4,5, 6-tetrahydro-2-methyl-4-pyrimidine carboxylic acid) and 5-oxoproline (pyrrolidone carboxylic acid)] was detected in the halotolerant methanotrophs Methylobacter alcaliphilus 20Z and Methylobacter modestohalophilus 10S. The organic solute pool was found to increase upon raising the NaCl concentration. In M. alcaliphilus 20Z, the intracellular level of the total solutes was shown to be sufficient to balance the osmotic pressure of the medium, whereas in M. modestohalophilus 10S their content was several times lower. Additionally, phosphatidylglycerol and phosphatidylcholine were predominant cell phospholipids in salt-adapted M. alcaliphilus 20Z. However, no phosphatidylcholine was found in M. modestohalophilus 10S, and the portion of phosphatidylglycerol increased while phosphatidylethanolamine decreased upon elevated external NaCl concentrations. Regularly arranged glycoprotein surface layers (S-layers) of hexagonal and linear (p2) symmetry were observed on the outer cell walls of M. alcaliphilus 20Z and M. modestohalophilus 10S. The S-layer in M alcaliphilus 20Z consisting of tightly packed, cup-shaped subunits was lost during growth at pH 7.2 (the lowest possible pH) in the absence of NaCl. Hence, osmoadaptation in the methanotrophs studied involves structure/function alterations of cell envelopes and changes in the chemical composition of membranes as well as de novo synthesis of compatible solutes.

Identification and Characterization of EctR1, a New Transcriptional Regulator of the Ectoine Biosynthesis Genes in the Halotolerant Methanotroph Methylomicrobium alcaliphilum 20Z

“…These results suggested a specific interaction between EctR1 and the promoter regions of the ectABC-ask and ectR1 genes. (20,40,60,80, and 160 pmol) were added to the probe. For the competition assay, an unlabeled specific DNA was added to the reaction mixture after incubation with the labeled fragment.…”

“…The halotolerant obligate methanotroph Methylomicrobium alcaliphilum 20Z is capable of growth at a salinity as high as 2 M NaCl (19). It was demonstrated that in response to the elevated salinity of the growth medium, M. alcaliphilum cells accumulate ectoine as a major osmoprotective compound (20). The ectoine biosynthesis pathway in M. alcaliphilum 20Z is similar to the pathway employed by halophilic/halotolerant heterotrophs and involves three specific enzymes: diaminobutyric acid (DABA) aminotransferase (EctB), DABA acetyltransferase (EctA), and ectoine synthase (EctC) (7,21,24,30,32,49).…”

Methylocapsa acidiphila gen. nov., sp. nov., a novel methane-oxidizing and dinitrogen-fixing acidophilic bacterium from Sphagnum bog.

“…Preparation of thin sections and electron microscopy were done as described previously (Khmelenina et al, 1997(Khmelenina et al, , 1999. For freeze-fractured preparations, exponentially growing cells were collected and frozen in liquid propane cooled to k196 mC with liquid nitrogen.…”

Methylotrophic Autotrophy in Beijerinckia mobilis

“…2A and B). Thin sections of these cells were prepared and examined using the procedure described by Khmelenina et al (18). Major differences were observed between cells grown in nitrogen-sufficient and nitrogen-free media ( Fig.…”