Extracellular polymer substance synthesized by a halophilic bacterium Chromohalobacter canadensis 28

Abstract

Halophilic microorganisms are producers of a lot of new compounds whose properties suggest promising perspectives for their biotechnological exploration. Moderate halophilic bacterium Chromohalobacter canadensis 28 was isolated from Pomorie salterns as an extracellular polymer substance (EP) producer. The best carbon source for extracellular polymer production was found to be lactose, a sugar received as a by-product from the dairy industry. After optimization of the culture medium and physicochemical conditions for cultivation, polymer biosynthesis increased more than 2-fold. The highest level of extracellular polymer synthesis by C. canadensis 28 was observed in an unusually high NaCl concentration (15% w/v). Chemical analysis of the purified polymer revealed the presence of an exopolysaccharide (EPS) fraction (14.3% w/w) and protein fraction (72% w/w). HPLC analysis of the protein fraction showed the main presence of polyglutamic acid (PGA) (75.7% w/w). EPS fraction analysis revealed the following sugar composition (% w/w): glucosamine 36.7, glucose 32.3, rhamnose 25.4, xylose 1.7, and not identified sugar 3.9. The hydrogel formed by PGA and EPS fractions showed high swelling behavior, very good emulsifying and stabilizing properties, and good foaming ability. This is the first report for halophilic bacterium able to synthesize a polymer containing PGA fraction. The synthesized biopolymer shows an extremely high hydrophilicity, due to the simultaneous presence of PGA and EPS. The analysis of its functional properties and the presence of glucosamine in the highest proportion in EPS fraction clearly determine the potential of EP synthesized by C. canadensis 28 for application in the cosmetics industry.

High bioreactor production and emulsifying activity of an unusual exopolymer by Chromohalobacter canadensis 28

“…A lag phase lasted of about 6 h for all rates, followed by an exponential phase until 18‐24 h of cultivation time and a stationary phase until 48 h, as monitored by cease of cell growth. Such a way, the polymer production was shorten twofold in comparison with batch cultures (96 h) [10]. Growth of C. canadensis 28 varied in OD 660 range 5.6 (600 rpm) and 6.2 (900 rpm) (Figure 1A).…”

“…A halophilic bacterium C. canadensis 28 was isolated from a crystallizer pond of Pomorie salterns (42°35′33“N, 27°37′21″E), Burgas Bay, Black Sea, Bulgaria and deposited in NBIMCC (WDCM № 135) under the number 8924 [10]. The strain synthesized EP consisting of PGA (72% w/w) and EPS (14.3% w/w) fractions where the monomeric molar composition of the EPS was found to be: 36.7% glucosamine; 32.3% glucose; 25.4% rhamnose; 1.7% xylose, and 3.9% unidentified sugar.…”

“…The composition of the medium providing highest EP yield was determined in our previous study [10]. Colonies were transferred to 20 mL of culture medium in 100 mL shake flask and incubated for 72 h at 30°C, then the cells were transferred into 100 mL fresh medium and incubated for 20 h up to OD of 2‐2.5 at 660 nm.…”

“…The carbohydrate content was determined using the phenol/sulfuric acid method with glucose as standard [13]. Protein concentration consisting mainly from polyglutamic acid [10] was determined by Lowry test using bovine serum albumin as a standard. EP content was estimated as a sum from EPS and protein content.…”

“…In our previous studies, a halophilic bacterium Chromachalobacter canadensis was established to produce an unusual EP containing both EPS and γ‐polyglutamic acid (PGA) fractions and reported as the first halophilic bacterium able to produce PGA [10]. The limited knowledge on the effect of agitation and aeration on biomass and EP production by halophiles has determined the main aim of the current work, namely to study the EP biosynthesis by C. canadensis 28 in different mass and oxygen transfer conditions in a laboratory bioreactor.…”