Polyester production by halophilic and halotolerant bacterial strains obtained from mangrove soil samples located in Northern Vietnam

Abstract

This research article reports halophilic and halotolerant bacteria isolated from mangrove forests located in Northern Vietnam. Several of these bacteria were able to synthesize polyhydroxyalkanoates (PHAs). PHAs are polyesters stored by microorganisms under the presence of considerable amounts of a carbon source and deficiency of other essential nutrient such as nitrogen or phosphorous. Mangrove forests in Northern Vietnam are saline coastal habitats that have not been microbiologically studied. Mangrove ecosystems are, in general, rich in organic matter, but deficient in nutrients such as nitrogen and phosphorus. We have found about 100 microorganisms that have adapted to mangrove forests by accumulating PHAs. The production of polyesters might therefore be an integral part of the carbon cycle in mangrove forests. Three of the strains (ND153, ND97, and QN194) isolated from the Vietnamese forests were identified as Bacillus species, while other five strains (QN187, ND199, ND218, ND240, and QN271) were phylogenetically close related to the α-proteobacterium Yangia pacifica. These strains were found to accumulate PHAs in noticeable amounts. Polymer inclusions and chemical structure were studied by transmission electron microscopy and proton nuclear magnetic resonance (NMR) spectroscopy analyses, respectively. Strains ND153, ND97, QN194, QN187, ND240, and QN271 synthesized poly(3-hydroxybutyrate) (PHB) from glucose, whereas strains ND199 and ND218 synthesized poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from this carbohydrate. With the exception of strain QN194, the strains accumulated PHBV when a combination of glucose and propionate was included in the culture medium. The polymer yields and cell growth reached by one Bacillus isolate, strain ND153, and one Gram-negative bacterium, strain QN271, were high and worth to be researched further. For experiments performed in shake flasks, strain ND153 reached a maximum PHBV yield of 71 wt% and a cell dry weight (CDW) of 3.6 g/L while strain QN271 attained a maximum PHB yield of 48 wt% and a CDW of 5.1 g/L. Both strain ND153 and strain QN271 may only represent a case in point that exemplifies of the potential that mangrove forests possess for the discovery of novel halophilic and halotolerant microorganisms able to synthesize different types of biopolyesters.

A fed-batch fermentation process for poly (3-hydroxybutyrate-co-3-hydroxyvalerate) production by Yangia sp. ND199 using molasses as substrate

“…Maximum CDW of 6.37 g/l, P(3HB-co-3HV) content of 43.1 wt% and P(3HB-co-3HV) concentration of 2.75 g/l were obtained by Yangia after 60 h of cultivation. The results obtained from this experiment (when molasses was used as carbon source) are comparable with those of the previous report (when pure sugars, such as glucose, sucrose, fructose or glycerol as carbon substrate) [16], suggesting that molasses can be a good carbon substrate for P(3HB-co-3HV) production and the growth of Yangia sp. ND199.…”

“…Among them, strain Yangia sp. ND199 were found to synthesize the copolymer P(3HB-co-3BV) when grown on glucose or sucrose as carbon source [15,16]. In the present work, we undertaken to find strategies for improving the volumetric productivity of P(3HB-co-3HV) by Yangia sp.…”

Bioconversion of Commercial and Waste Glycerol into Value-Added Polyhydroxyalkanoates by Bacterial Strains

“…The advantage of using of halophilic microorganisms in PHA production systems is related to their ability to grow optimally at high salt concentrations. At determined concentrations of salt, the growth of nonhalophilic microorganisms is prevented, hence allowing a process without strict sterile conditions and reducing the inherent costs, such as the costs of the energy required for sterilizing the equipment for fermentation and culture media [22]. Recently, it was reported the production of PHB by moderately halotolerant Halomonas campisalis MCM B-1027, isolated from Lonar Lake, India.…”

Polymerase chain reaction-based screening method applicable universally to environmental haloarchaea and halobacteria for identifying polyhydroxyalkanoate producers among them

“…Halophiles mostly inhabit extreme environments like alkaline salt lakes, hypersaline soda lakes, solar saltern crystallizer ponds, natural brines, salt deposits, and salted foods (Ventosa 2006). However, few explorations have been done worldwide to isolate PHA-producing halophiles from different environmental niches like hypersaline soils of Egypt and mangrove forests of Vietnam (Hezayen et al 2010; Van-Thuoc et al 2012). In India, salt producing multi-pond solar salterns are situated in the states of Andhra Pradesh, Goa, Gujarat, Orissa, Tamil Nadu, and West Bengal.…”