Mineral Salt Broth Research Articles

Bioremediation of oil-contaminated water by bacterial consortium immobilized on environment-friendly biocarriers

Accidental oil spills in the Nile River represents a public health concern in Egypt. Bioremediation of oil-contaminated water is efficiently competitive and economically effective compared to mechanical and chemical methods. The current study aimed to: i) assess using environment-friendly materials as carriers for immobilizing oil-degrading bacteria and ii) evaluate applying these biocarriers for removal of oil from water in a batch experiment. Four bacterial strains Pseudomonas aeruginosa, Cronobacter sakazakii (recently named Enterobacter sakazakii), Klebsiella oxytoca and Bordetella bronchispetica were immobilized on grinded corn qgualh, Egyptian loofah, palm leaf raffia and sponge. Immobilizing bacterial consortium was carried out by incubating bacteria with carriers at 37°C with shaking at 120 rpm for three days. Biofilm formed on biocarriers was checked using scanning electron microscopy. Biocarriers with immobilized bacterial consortium were used for the removal of oil. Experiments were carried out in flasks each containing 100 ml of mineral salt broth fortified with 1 g/l light crude oil. Flasks were incubated at 37°C with shaking at 120 rpm for nine weeks. Total viable bacterial count and oil and grease were determined weekly. Oil and grease measurements showed a significant removal that reached 68.3, 71.5, 77.7 and 81% for grinded corn qgualh, Egyptian loofah, palm leaf raffia and sponge respectively. Flasks inoculated with sponge biocarriers showed rapid oil removal compared with other biocarriers. Gas chromatography-mass spectrometry (GC-MS) showed a percentage removal that reached 87% for compounds C11 to C32 in case of sponge carrier. Immobilizing bacteria on biocarriers showed a good biofilm formation. Immobilized bacterial consortium showed rapid and efficient oil removal in bioremediation processes. Sponge showed dense bacterial colonization and consequently biofilm formation compared with other biocarriers.

Isolation and Characterization of Hydrocarbon Utilizing Yeast (HUY) Isolates from Palm Wine

Hydrocarbon utilizing yeasts (HUY) were isolated from palm wine, a rich sugar substrate from a non-oil impacted environment using Bacto Bushnell Haas broth. The medium composed of 0.2 g MgSO4, 0.02 g CaCl2, 1 g KH2PO4, 1 g K2HPO4, 0.05 g FeCl2, 1 g/L NH4NO3, pH 7.2 ± 0.2) and mineral salt broth comprising of 4.4 g KH2PO4, 8 g NH4)2SO4, 2 g Na2HPO4.H2O, MgSO4.7H2O, 0.1g FeSO4, 0.01 g/L CaCl2, pH 4.5 ± 0.2) supplemented with palm wine (0.5%) and crude oil (1%). Yeasts isolated from an enriched medium and palm wine showed similarities. Yeast isolates were further screened for hydrocarbon degrading potentials using the Bacto Bushnell Haas broth containing 2,6- dichlorophenol indophenols as the indicator agent. The isolates were identified using microscopic, macroscopic, fermentation and molecular characteristics as Candida adriatica (ZIM 2468) and Candida taoyuanica (MYA-4700).

Isolation and Characterization of Hydrocarbon Utilizing Yeast (HUY) Isolates from Palm Wine

Several studies have reported on the capabilities of different yeasts to utilize hydrocarbons hence the need to ascertain the petroleum hydrocarbon biodegradation potential of yeast isolated from palm wine. The study aimed at isolation, characterization and testing of yeasts from palm wine for biodegradation of petroleum hydrocarbons. Hydrocarbon utilizing yeasts (HUY) were isolated from palm wine, a rich sugar substrate from a non-oil impacted environment using Bacto Bushnell Haas broth. The medium composed of 0.2 g MgSO4, 0.02 g CaCl2, 1 g KH2PO4, 1 g K2HPO4, 0.05 g FeCl2, 1 g/L NH4NO3, pH (7.2 ± 0.2) and mineral salt broth comprising of 4.4 g KH2PO4, 8 g (NH4)2SO4, 2 g Na2HPO4&#183H2O, MgSO4&#1837H2O, 0.1 g FeSO4, 0.01 g/L CaCl2, pH (4.5 ± 0.2) supplemented with palm wine (0.5%) and crude oil (1%). Yeasts isolated from an enriched medium and palm wine showed similarities. Yeast isolates were further screened for hydrocarbon degrading potentials using the Bacto Bushnell Haas broth containing 2, 6-dichlorophenol indophenols as the indicator agent. The isolates were identified using microscopic, macroscopic, fermentation and molecular characteristics as Candida adriatica (ZIM 2468) and Candida taoyuanica (MYA-4700).

Application of response surface methodology for rapid chrysene biodegradation by newly isolated marine-derived fungus Cochliobolus lunatus strain CHR4D.

For the first time, Cochliobolus lunatus strain CHR4D, a marine-derived ascomycete fungus isolated from historically contaminated crude oil polluted shoreline of Alang-Sosiya ship-breaking yard, at Bhavnagar coast, Gujarat has been reported showing the rapid and enhanced biodegradation of chrysene, a four ringed high molecular weight (HMW) polycyclic aromatic hydrocarbon (PAH). Mineral Salt Broth (MSB) components such as ammonium tartrate and glucose along with chrysene, pH and trace metal solution have been successfully optimized by Response Surface Methodology (RSM) using central composite design (CCD). A validated, two-step optimization protocol has yielded a substantial 93.10% chrysene degradation on the 4(th) day, against unoptimized 56.37% degradation on the 14(th) day. The results depict 1.65 fold increase in chrysene degradation and 1.40 fold increase in biomass with a considerable decrement in time. Based on the successful laboratory experiments, C. lunatus strain CHR4D can thus be predicted as a potential candidate for mycoremediation of HMW PAHs impacted environments.

English

Clarified sugar cane juice was evaluated as an alternative substrate for the batch production of polyhydroxyalkanoates (PHAs) by Alcaligenes latus , and a mineral salt broth was used as the control. The study included the physicochemical characterization of the juice, measurement of the fermentation kinetic parameters and identification of the polymer type by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Batch-type aerobic fermentations were performed (33°C at 200 rpm and pH 6.5-7 for 60 h) and set at 20 gL -1 of fermentable sugar and a carbon/nitrogen ratio of 28.3/1. A 10% v/v ratio of inoculum/substrate was used. The alternative substrate presented a greater concentration of magnesium and micronutrients such as Fe, B, Zn, Mg and Cu compared to the control. The biomass yield ( ) of the juice was 1.27 g.g -1 (0.414 g.g -1 in control medium), which was 69% more than the control medium; the product-substrate yield ( ) was 0.10 g.g -1 , which was similar to the control medium (0.15 g.g -1 control medium). The production of PHB was of 1.3 gL -1 , less than half of the concentration obtained in commercial substrate. Infrared spectroscopy indicated that the polymer obtained in the evaluated substrates was polyhydroxybutyrate (PHB). The clarified juice of sugar cane, without the addition of nutritional supplements can be used for the production of biomass of A. latus , first step in the production of PHB. Keywords: Alternative substrate, Alcaligenes latus, polymer, polyhydroxybutyrate (PBH), fermentation. African Journal of Biotechnology , Vol 13(40) 4019-4027

Antimicrobial Activity of a Bioemulsifier Produced by Serratia marcescens S10

This study was designed to evaluate the ability of bioemulsifier to inhibit the growth of some pathogenic microorganisms. Fourteen isolates belonged to Serratia sp. were collected and tested for their ability to produce bioemulsifier. Results showed that Serratia marcescens S10 (isolated from the gut of the American cockroach) had the highest ability to produce bioemulsifier, among 14 isolates belong to Serratia spp. and it had the ability to inhibit the growth of some microorganisms. The production of bioemulsifier was detected by determination of emulsification index (E24%), qualitative drop-collapse test, emulsification activity (E.A) and measuring the surface tension (S.T). The results of bioemulsifier produced by Serratia marcescens S10 cultivated in mineral salts broth containing olive oil were: E24%= 87%, E.A= 0.31 and reducing of surface tension from 65mN/m to 41.5mN/m. The bioemulsuifier was extracted by organic solvent (chloroform-methanol and diethylether) and antimicrobial activity (antibacterial and antifungal) of bioemulsifier was tested against some pathogenic microorganisms. Results revealed that bioemulsifier reduced the growth of bacteria (Lesteria spp., Salmonella spp., Klebsiella spp. and Staphylococcus aureus) and inhibited the growth of fungi (Candida albicans, Aspergillus niger and Geotricum spp.).

Degradation and transformation of anthracene by white-rot fungus Armillaria sp. F022

Characterization of anthracene metabolites produced by Armillaria sp. F022 was performed in the enzymatic system. The fungal culture was conducted in 100-mL Erlenmeyer flask containing mineral salt broth medium (20 mL) and incubated at 120 rpm for 5-30 days. The culture broth was then centrifuged at 10,000 rpm for 45 min to obtain the extract. Additionally, the effect of glucose consumption, laccase activity, and biomass production in degradation of anthracene were also investigated. Approximately, 92 % of the initial concentration of anthracene was degraded within 30 days of incubation. Dynamic pattern of the biomass production was affected the laccase activity during the experiment. The biomass of the fungus increased with the increasing of laccase activity. The isolation and characterization of four metabolites indicated that the structure of anthracene was transformed by Armillaria sp. F022 in two routes. First, anthracene was oxidized to form anthraquinone, benzoic acid, and second, converted into other products, 2-hydroxy-3-naphthoic acid and coumarin. Gas chromatography-mass spectrometry analysis also revealed that the molecular structure of anthracene was transformed by the action of the enzyme, generating a series of intermediate compounds such as anthraquinone by ring-cleavage reactions. The ligninolytic enzymes expecially free extracellular laccase played an important role in the transformation of anthracene during degradation period.

Effect of Microbes, Npk Fertilizer and Cow Dung on the Biodegradation of Polycyclic Aromatic Hydrocarbons from Abattoir Wastes in Nigeria

The biodegradation of polycyclic aromatic hydrocarbons by associated microorganisms were studied. Soil and waste water samples were collected from four abattoirs located at Egbu and Ogbe in Imo state, Trans-Amadi and Ahoada in Rivers State. Likewise, surface water and sediment samples from Otamiri River and Oginigba Creek adjoined to Egbu and Trans-Amadi abattoirs, respectively were collected using standard methods. The ability of hydrocarbon utilizing bacteria and fungi to biodegrade polycyclic aromatic hydrocarbons (PAHs) was carried out by growing the isolates in a mineral salt broth amended with PAHs and nutrients (NPK fertilizer and cow dung). Levels of polycyclic aromatic hydrocarbons (PAHs) left after incubation were determined using Gas chromatographic method. Results showed that soil samples from various abattoirs had high concentrations of PAHs ranging from 0.176 mg/kg at Ahoada abattoir to 2.44 mg/kg at Egbu abattoir. In a 21-day biodegradation test, there was a drop in the initial concentration of PAHs used as control from 0.03 mg/l to 0.024 mg/l. There was loss of low molecular weight PAHs than the high molecular weight components. It is evident from the study that both mixed cultures of bacteria and fungi can biodegrade polycyclic aromatic hydrocarbons. Results from this study have shown that abattoir wastes have high pollution strength and thus should be treated before being discharged into the environment. Of note is the fact that the microorganisms isolated from the abattoirs are potential agents of remedying environments impacted by polycyclic aromatic hydrocarbons (PAHs).

Biodegradation of Polycyclic Aromatic Hydrocarbons by Associated Microbes from Abattoir Wastes in the Niger Delta, Nigeria

The biodegradation of polycyclic aro matic hydrocarbons by associated microorganisms were studied. Soil and waste water samp les were co llected fro m four abattoirs located at Egbu and Ogbe in Imo state, Trans-Amad i and Ahoada in Rivers State. Likewise, surface water and sediment samples fro m Otamiri River and Og inigba Creek adjoined to Egbu and Trans-Amadi abattoirs, respectively were co llected using standard methods. The ability of hydrocarbon utilizing bacteria and fungi to biodegrade polycyclic aro matic hydrocarbons (PAHs) was carried out by growing isolates in a mineral salt broth amended with PAHs. Levels of polycyclic aro matic hydrocarbons (PAHs) left after incubation were determined using Gas chromatographic method. Results showed that soil samples fro m various abattoirs had high concentration of PAHs which ranged fro m 0.176 mg/kg fro m Ahoada abattoir to 2.44 mg/ kg fro m Egbu abattoir. In a 21-day biodegradation test, there was a drop in the init ial concentration of PAHs used as control fro m 0.03 mg/l to 0.024 mg/l. Test results showed decrease in the concentration of PAHs with increase in exposure time. There was observable loss of low molecular weight PAHs than the high mo lecular weight co mponents. It is evident fro m the study that both mixed cultures of bacteria and fungi can biodegrade polycyclic aro matic hydrocarbons. Results fro m this study have shown that abattoir wastes have high pollution strength and thus should be treated before being discharged into the environment. Thus bacteria and fungi isolated fro m and within the abattoirs are potential agents of remedying environ ments impacted by polycyclic aro mat ic hydrocarbons (PAHs).

Assessment of the Local Isolate ability Nocardia asteroids for production of biosurfactants and utilize Crude Oil and use mutation technology by Laser Irradiation for enhancement of their efficiency

he present study was performed to assess the ability of local isolate Nocardia asteroids to produce bioemulisifers and utilize crude oil at three concentrations (0.5,1,2) % on blue mineral salt agar and mineral salt broth. Four parameters were used to detect the production of the bioemulisifers: Diameter of dark blue halo around the colonies, the time of appearance, emulisification activity of supernatant, hydrophobicity of cell surface of suspension.The local isolate was subjected to mutation by laser irradiation at different exposure times (2,4,6,8,10,12)minutes. In this study the ability of both non mutated and mutated local isolate had been tested to utilize crude oil in soil sample was monitored through six weeks Results obtaind could be summarized as follows: The local isolate has shown the ability to emulsify crude oil as the sole carbon and energy source by bioemulisification, depending on four parameters, bioemulisifers production reaching maximum after utilizing 2% crude oil. Significant increase in production of bioemulisifers reaching maximum after, (6) minutes from exposure to Laser, depending on four parameters. Significant increase in total number of the cells in soil sample contaminated with 2% crude oil after the addition of bacterial filtrate of non mutated and mutated of local isolate.

Aerobic and anaerobic de-epoxydation of mycotoxin deoxynivalenol by bacteria originating from agricultural soil

One hundred and fifty soil samples collected from different crop fields in southern Ontario, Canada were screened to obtain microorganisms capable of transforming deoxynivalenol (DON) to de-epoxy DON (dE-DON). Microbial DON to dE-DON transformation (i.e. de-epoxydation) was monitored by using liquid chromatography-ultraviolet-mass spectrometry (LC-UV-MS). The effects of growth substrates, temperature, pH, incubation time and aerobic versus anaerobic conditions on the ability of the microbes to de-epoxydize DON were evaluated. A mixed microbial culture from one composite soil sample showed 100% DON to dE-DON biotransformation in mineral salts broth (MSB) after 144h of incubation. Treatments of the culture with selective antibiotics followed an elevated temperature (50°C) for 1.5h considerably reduced the microbial diversity. Partial 16S-rRNA gene sequence analysis of the bacteria in the enriched culture indicated the presence of at least six bacterial genera, namely Serratia, Clostridium, Citrobacter, Enterococcus, Stenotrophomonas and Streptomyces. The enriched culture completely de-epoxydized DON after 60h of incubation. Bacterial de-epoxydation of DON occurred at pH 6.0-7.5, and a wide array of temperatures (12-40°C). The culture showed rapid de-epoxydation activity under aerobic conditions compared to anaerobic conditions. This is the first report on microbial DON to dE-DON transformation under aerobic conditions and moderate temperatures. The culture could be used to detoxify DON contaminated feed and might be a potential source for gene(s) for DON de-epoxydation.

Chlorothalonil degradation by Ochrobactrum lupini strain TP-D1 and identification of its metabolites

Chlorothalonil (2, 4, 5, 6-tetrachloroisophthalonitrile, TPN) has been widely used as a wide-spectrum fungicide in China and other countries, and is considered to be an important soil and water contaminant. Here we report the isolation and characterization of a novel TPN-degrading bacterial strain TP-D1 from a heavily TPN-polluted soil in Henan Province, China, and identified it as a strain of Ochrobactrumlupini based on 16S rRNA gene sequence analysis and its morphological, biochemical, and physiological characteristics. Strain TP-D1 could degrade 90.4 and 99.7% of TPN after 4- and 7-day incubation in mineral salt broth with 50 mg TPN l−1 and in autoclaved soil with 50 μg TPN g−1, respectively. Two new metabolites, methyl 2, 5, 6-trichloro-3-cyano-4-methoxy-benzoate (metabolite C) and methyl 3-cyano-2, 4, 5, 6-tetrachlorobenzoate (metabolite D), were detected besides previously reported 4-hydroxy-2, 5, 6-trichloroisophthalonitrile (TPN-OH, metabolite A). This result suggests that the cyano-group in TPN could be converted into amide groups by strain TP-D1, and reveal the biodegradation mechanism of TPN in soil.

Effect of carbon, nitrogen sources and inducers on ligninolytic enzyme production by Morchella crassipes

The effect of different carbon, nitrogen sources and inducers on growth and ligninolytic activity by Morel mushroom Morchella crassipes was investigated. The maximum growth was observed in mineral salts broth containing glucose as the carbon source and sodium nitrate as the nitrogen source. Among the inducers, chemical inducers inhibited the growth whereas in natural substrates, growth was not affected much. Manganese peroxidase and lignin peroxidase activity were not detected in the medium with different carbon and nitrogen sources, whereas laccase activity varied depending on carbon source (0.7–3.48 U/ml). Among the inducers, natural inducers resulted in an increase in the enzyme activities. Maximum laccase activity was observed in rice straw (12. 6 U/ml) followed by ABTS (11.6 U/ml); Manganese peroxidase activity was maximum in rice straw (14.32 U/l) wheat straw (12.16 U/l) and phenol red (15 U/l) as the inducers, whereas for Lignin peroxidase activity, rice straw (22 U/l), wheat straw (16 U/l) and veratrylalcohol (20 U/l) served as the best inducers.

Characterization of phenanthrene degradation by strain Polyporus sp. S133

Polyporus sp. S133, a fungus collected from contaminated soil, was used to degrade phenanthrene, a polycyclic aromatic hydrocarbon, in a mineral salt broth liquid culture. A maximal degradation rate (92%) was obtained when Polyporus sp. S133 was cultured for 30 days with agitation at 120 r/min, as compared to 44% degradation in non-agitated cultures. Furthermore, the degradation was affected by the addition of surfactants. Tween 80 was the most suitable surfactant for the degradation of phenanthrene by Polyporus sp. S133. The degradation rate increased as the amount of Tween 80 added increased. The rate in agitated cultures was about 2 times that in non-agitated cultures. The mechanism of degradation was determined through the identification of metabolites; 9,10-phenanthrenequinone, 2,2′-diphenic acid, phthalic acid, and protocatechuic acid. Several enzymes (manganese peroxidase, lignin peroxidase, laccase, 1,2-dioxygenase and 2,3-dioxygenase) produced by Polyporus sp. S133 were detected during the incubation. The highest level of activity was shown by 1,2-dioxygenase (187.4 U/L) after 20 days of culture.

Comparative production of ligninolytic enzymes by Phanerochaete chrysosporium and Polyporus sanguineus

The aim of the present study was to compare the effect of a wide range of culture conditions on production of ligninolytic enzymes by Polyporus sanguineus and Phanerochaete chrysosporium. Lignin peroxidase production by P. sanguineus was comparable with that of P. chrysosporium, although the culture conditions giving the highest yield varied greatly between the two fungi. Highest yield of manganese peroxidase by P. sanguineus obtained in 0.5% malt extract medium and peptone or malt extract supplemented mineral salts broth could not be surpassed by P. chrysosporium in any of the optimization experiments. In addition to lignin peroxidase and manganese peroxidase, P. sanguineus also produced laccase, which was best expressed in malt extract medium supplemented with sugarcane bagasse.

Biodegradation of chrysene, an aromatic hydrocarbon by Polyporus sp. S133 in liquid medium

Polyporus sp. S133, a fungus collected from contaminated-soil was used to degrade chrysene, a polycyclic aromatic hydrocarbon (PAH) in a mineral salt broth (MSB) liquid culture. Maximal degradation rate of chrysene (65%) was obtained when Polyporus sp. S133 was incubated in the cultures supplemented with polypeptone (10%) for 30 days under agitation of 120 rpm, as compared to just 24% degradation rate in non-agitated culture. Furthermore, the degradation of chrysene was affected by the addition of carbon and nitrogen sources as well as kind of surfactants. The degradation rate was increased with increase in added amount of carbon and nitrogen sources, respectively. The degradation rate in agitated cultures was enhanced about 2 times higher than that in non-agitated cultures. The degradation mechanism of chrysene by Polyporus sp. S133 was determined through identification of several metabolites; chrysenequinone, 1-hydroxy-2-naphthoic acid, phthalic acid, salicylic acid, protocatechuic acid, gentisic acid, and catechol. Several enzymes (manganese peroxidase, lignin peroxidase, laccase, 1,2-dioxygenase and 2,3-dioxygenase) produced by Polyporus sp. S133 were detected during the incubation. The highest enzyme activity was shown by 1,2-dioxygenase (237.5 U l −1) after 20 days of incubation.

Comparison of two assay procedures for lignin peroxidase

The most widely accepted assay for detecting lignin peroxidase, based on the oxidation of veratryl alcohol to veratraldehyde, suffers from some drawbacks. At 310 nm, the wavelength at which the assay is performed, some other materials like lignins, quinonic compounds and aromatics also exhibit strong absorbance thus interfering with the estimation when present in the media. The present study reports the lignin peroxidase production by some white rot fungi under different nutritional conditions. The veratryl alcohol oxidation assay procedure for lignin peroxidase has been compared with another method based on the oxidation of the dye azure B involving absorbance measurements in the visible range. The latter method proved to be much more advantageous over the veratryl alcohol oxidation method, in media supplemented with malt extract, lignin preparations and agricultural residues. The enzyme production by veratryl alcohol assay could be detected only in mineral salts broth. By the azure B assay the enzyme activity was detected in all the media tested. The supplements gave varied response in different media. Veratryl alcohol enhanced the enzyme production in malt extract broth and mineral salts malt extract broth. Among the lignin preparations Indulin AT increased the lignin peroxidase titres from 2 to 20 fold in different fungi. Similarly, wheat straw supplemented in mineral salts broth and malt extract broth, separately, strongly stimulated the lignin peroxidase production. The above studies revealed that azure B assay may act as a substitute or equivalent method.

Laccase production by some white rot fungi under different nutritional conditions

The role of laccase in ligninolysis has been disputed but it still seems to have an important place in the reactions. Trametes versicolor has been the organism of choice for laccase production. The present paper reports laccase production by Phlebia fascicularia, P. floridensis and Dichomitus squalens. Enzyme production in mineral salts broth, malt extract broth and in the presence of various supplements showed that P. floridensis and D. squalens were better laccase producers than T. versicolor. Different lignin preparations and natural agricultural residues gave the best enzyme production, except with T. versicolor. The studies underline the need to explore more organisms to fully exploit the potential of laccase-producing fungi.

Phenotypic characteristics and composition of rhizobia associated with woody legumes growing in diverse Kenyan conditions

Over 480 rhizobia were isolated from root nodules of woody legume and herbaceous trap host species grown in soils collected from 12 different Kenyan sites. The isolates were differentiated by growth and morphological characteristics, intrinsic antibiotic resistance (IAR) and salt (NaCl) tolerance levels (STL) when grown on yeast mannitol mineral salts agar and broth media. The bulk of the isolates (91%) were watery, milky-translucent and curdled milk types with moderate to copious extracellular polysaccharide (EPS). The rest were creamy or white opaque with little to moderate EPS production. Overall, they showed a wide range of growth rates: very fast-growing (mean generation time 1.6–2.5 h), fast-growing (2.8–4.8 h), intermediate between fast- and slow-growing (5.6–5.7 h) and slow- and very slow-growing (6.4–8.8 h). The isolates were tentatively grouped into Rhizobium spp., to include very fast, fast and intermediate (acid-producing) types; and Bradyrhizobium spp., to include very slow, slow and intermediate (alkali-producing) types. Bradyrhizobium spp. were more sensitive to antibiotics (40 μg mL-1) than Rhizobium spp., contrary to the general opinion which indicates that they are normally resistant. Cluster analysis based on sensitivity responses of IAR and STL could not distinguish Rhizobium spp. from Bradyrhizobium spp., neither was there any association by site nor host of isolation except for those isolates trapped with Phaseolus vulgaris at Kibwezi. Our data demonstrated a high diversity of tropical rhizobia associated with trees.

Further studies on biodegradation of aliphatic poly(ester‐amides)

AbstractTwo types of aliphatic poly(ester‐amides) (PEAs) were subjected to microbial degradation in basal mineral salt broth, under the attack of a yeast, Cryptococcus laurentii, at 20°C. PEA‐I copolymers were made by the anionic ring‐opening copolymerization of ϵ‐caprolactone and ϵ‐caprolactam, whereas PEA‐II copolymers were synthesized by a two‐step polycondensation reaction of hexanediol‐1,6, hexanediamine‐1,6, and adipolyl chloride. These copolymers were found to be readily degradable under biotic conditions, based on weight loss, GPC, NMR spectroscopy, and tensile property measurements. Compared to abiotic hydrolysis, biodegradation occurred much faster under milder conditions. Furthermore, NMR spectroscopic analysis proved that the biodegradation of poly(ester‐amides) involves the enzymatic hydrolysis of ester groups on the backbones of polymers into acid and hydroxyl groups. No breakdown of amide bonds was observed under the given biotic conditions. © 1993 John Wiley & Sons, Inc.