Opposing effects of NaCl on reversibility and thermal stability of halophilic β-lactamase from a moderate halophile, Chromohalobacter sp. 560

Structure of a highly acidic β-lactamase from the moderate halophile Chromohalobacter sp. 560 and the discovery of a Cs(+)-selective binding site

Environmentally friendly absorbents are needed for Sr(2+) and Cs(+), as the removal of the radioactive Sr(2+) and Cs(+) that has leaked from the Fukushima Nuclear Power Plant is one of the most important problems in Japan. Halophilic proteins are known to have many acidic residues on their surface that can provide specific binding sites for metal ions such as Cs(+) or Sr(2+). The crystal structure of a halophilic β-lactamase from Chromohalobacter sp. 560 (HaBLA) was determined to resolutions of between 1.8 and 2.9 Å in space group P31 using X-ray crystallography. Moreover, the locations of bound Sr(2+) and Cs(+) ions were identified by anomalous X-ray diffraction. The location of one Cs(+)-specific binding site was identified in HaBLA even in the presence of a ninefold molar excess of Na(+) (90 mM Na(+)/10 mM Cs(+)). From an activity assay using isothermal titration calorimetry, the bound Sr(2+) and Cs(+) ions do not significantly affect the enzymatic function of HaBLA. The observation of a selective and high-affinity Cs(+)-binding site provides important information that is useful for the design of artificial Cs(+)-binding sites that may be useful in the bioremediation of radioactive isotopes.

Isolation and characterization of gram-positive biosurfactant-producing halothermophilic bacilli from Iranian petroleum reservoirs

Background:

Petroleum reservoirs have long been known as the hosts of extremophilic microorganisms. Some of these microorganisms are known for their potential biotechnological applications, particularly production of extra and intracellular polymers and enzymes.

Objectives:

Here, 14 petroleum liquid samples from southern Iranian oil reservoirs were screened for presence of biosurfactant‐producing halothermophiles.

Materials and Methods:

Mixture of the reservoir fluid samples with a minimal growth medium was incubated under an N₂ atmosphere in 40°C; 0.5 mL samples were transferred from the aqueous phase to agar plates after 72 hours of incubation; 100 mL cell cultures were prepared using the MSS-1 (mineral salt solution 1) liquid medium with 5% (w/v) NaCl. The time-course samples were analyzed by recording the absorbance at 600 nm using a spectrophotometer. Incubation was carried out in 40°C with mild shaking in aerobic conditions. Thermotolerance was evaluated by growing the isolates at 40, 50, 60 and 70°C with varying NaCl concentrations of 5% and 10% (w/v). Halotolerance was evaluated using NaCl concentrations of 5%, 10%, 12.5% and 15% (w/v) and incubating them at 40°C under aerobic and anaerobic conditions. Different phenotypic characteristics were evaluated, as outlined in Bergey's manual of determinative bacteriology. Comparing 16S rDNA sequences is one of the most powerful tools for classification of microorganisms.

Results:

Among 34 isolates, 10 demonstrated biosurfactant production and growth at temperatures between 40°C and 70°C in saline media containing 5%‐15% w/v NaCl. Using partial 16S rDNA sequencing (and amplified ribosomal DNA restriction analysis [ARDRA]) and biochemical tests (API tests 20E and 50 CHB), all the 10 isolates proved to be facultative anaerobic, Gram-positive moderate thermohalophiles of the genus Bacillus (B. thermoglucosidasius, B. thermodenitrificans, B. thermoleovorans, B. stearothermophilus and B. licheniformis), exhibiting surface-active behaviors.

Conclusions:

General patterns include decreasing the thermotolerance with increasing the salt concentrations and also more halotolerance in the aerobic environment compared with anaerobic conditions. The results demonstrated that Iranian petroleum reservoirs enjoy a source of indigenous extremophilic microorganisms with potential applications in microbial enhanced oil recovery and commercial enzyme production.

Halophilic beta-lactamase as a new solubility- and folding-enhancing tag protein: production of native human interleukin 1alpha and human neutrophil alpha-defensin

The amino acid composition of halophilic enzymes is characterized by an abundant content of acidic amino acid, which confers to the halophilic enzymes extensive negative charges at neutral pH and high aqueous solubility. This negative charge prevents protein aggregation when denatured and thereby leads to highly efficient protein refolding. Beta-lactamase from periplasmic space of moderate halophile (BLA), a typical halophilic enzyme, can be readily expressed as a native, active form in Escherichia coli cytoplasm. Similar to other halophilic enzymes, BLA is soluble upon denaturation by heat or urea treatments and, hence, can be efficiently refolded. Such high solubility and refolding efficiency make BLA a potential fusion partner for expression of aggregation-prone heterologous proteins to be expressed in E. coli. Here, we succeeded in the soluble expression of several "difficult-to-express" proteins as a BLA fusion protein and verified biological activities of human interleukin 1alpha and human neutrophil alpha-defensin, HNP-1.