Biodegradation of bioplastics in natural environments.

The actinomycete genus Gordonia has attracted much interest in recent years for a variety of reasons. Most species were isolated due to their abilities to degrade xenobiotics, environmental pollutants, or otherwise slowly biodegradable natural polymers as well as to transform or synthesize possibly

Biology of the Metabolically Diverse Genus Gordonia

Hydrocarbons are relatively recalcitrant compounds and are classified as high-priority pollutants. However, these compounds are slowly degraded by a large variety of microorganisms. Bacteria are able to degrade aliphatic saturated and unsaturated hydrocarbons via both aerobic and anaerobic pathways. Branched hydrocarbons and cyclic hydrocarbons are also degraded by bacteria. The aerobic bacteria use different types of oxygenases, including monooxygenase, cytochrome-dependent oxygenase and dioxygenase, to insert one or two atoms of oxygen into their targets. Anaerobic bacteria, on the other hand, employ a variety of simple organic and inorganic molecules, including sulphate, nitrate, carbonate and metals, for hydrocarbon oxidation.

A Comprehensive Review of Aliphatic Hydrocarbon Biodegradation by Bacteria

The popularity of fermented foods and beverages is due to their enhanced shelf-life, safety, functionality, sensory, and nutritional properties. The latter includes the presence of bioactive molecules, vitamins, and other constituents present in the initial food substrates. Many fermented foods also contain live microorganisms that may improve gastrointestinal health and provide other health benefits, including lowering the risk of type two diabetes and cardiovascular disease. The number of organisms in fermented foods can vary significantly, depending on how products were manufactured and processed, as well as conditions and duration of storage. In this review, we surveyed published studies in which lactic acid and other relevant bacteria were enumerated from the most commonly consumed fermented foods, including cultured dairy products, cheese, fermented sausage, fermented vegetables, soy-fermented foods, and fermented cereal products. Most of the reported data were based on retail food samples, rather than experimentally produced products made on a laboratory scale. Results indicated that many of these fermented foods contained 105-7 lactic acid bacteria per mL or gram, although there was considerable variation based on region and sampling time. In general, cultured dairy products consistently contained higher levels, up to 109/mL or g. Although few specific recommendations for what constitutes a relevant dose exist, the findings from this survey revealed that many fermented foods are a good source of live lactic acid bacteria, including species that reportedly provide human health benefits

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Fermented Foods as a Dietary Source of Live Organisms

The problems linked to plastic wastes have led to the development of biodegradable plastics. More specifically, biodegradable bioplastics are the polymers that are mineralized into carbon dioxide, methane, water, inorganic compounds, or biomass through the enzymatic action of specific microorganisms. They could, therefore, be a suitable and environmentally friendly substitute to conventional petrochemical plastics. The physico-chemical structure of the biopolymers, the environmental conditions, as well as the microbial populations to which the bioplastics are exposed to are the most influential factors to biodegradation. This process can occur in both natural and industrial environments, in aerobic and anaerobic conditions, with the latter being the least researched. The examined aerobic environments include compost, soil, and some aquatic environments, whereas the anaerobic environments include anaerobic digestion plants and a few aquatic habitats. This review investigates both the extent and the biodegradation rates under different environments and explores the state-of-the-art knowledge of the environmental and biological factors involved in biodegradation. Moreover, the review demonstrates the need for more research on the long-term fate of bioplastics under natural and industrial (engineered) environments. However, bioplastics cannot be considered a panacea when dealing with the elimination of plastic pollution.

Biodegradation of Wasted Bioplastics in Natural and Industrial Environments: A Review

Degradation of three kinds of bioplastics and their effects on microbial biomass and microbial diversity in soil environment were analyzed. The degradation rate of bioplastic in soil was closely related to the main components in the bioplastics. Poly (butylene succinate)-starch (PBS-starch) and poly (butylene succinate) (PBS) were degraded by 1% to 7% after 28 days in a soil with an initial bacterial biomass of 1.4 × 109 cells/g-soil, however poly lactic acid (PLA) was not degraded in the soil after 28 days. When the powdered-bioplastics were examined for the degradation in the soil, PBS-starch also showed the highest degradability (24.4% degradation after 28 days), and the similar results were obtained in the case of long-term degradation experiment (2 years). To investigate the effect of bacterial biomass in soil on biodegradability of bioplastics, PBS-starch was buried in three kinds of soils differing in bacterial biomass (7.5 × 106, 7.5 × 107, and 7.5 × 108 cells/g-soil). The rate of bioplastic degradation was enhanced accompanied with an increase of the bacterial biomass in soil. 16S rDNA PCR-DGGE analysis indicated that the bacterial diversity in the soil was not affected by the degradation of bioplastics. Moreover, the degradation of bioplastic did not affect the nitrogen circulation activity in the soil.

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Degradation of Bioplastics in Soil and Their Degradation Effects on Environmental Microorganisms

Thirty-six bacteria that degraded long-chain hydrocarbons were isolated from natural environments using long-chain hydrocarbons (waste car engine oil, base oil or the c-alkane fraction of base oil) as the sole carbon and energy source. A phylogenetic tree of the isolates constructed using their 16S rDNA sequences revealed that the isolates were divided into six genera plus one family (Acinetobacter, Rhodococcus, Gordonia, Pseudomonas, Ralstonia, Bacillus and Alcaligenaceae, respectively). Furthermore, most of the isolates (27 of 36) were classified into the genera Acinetobacter, Rhodococcus or Gordonia. The hydrocarbon-degradation similarity in each strain was confirmed by the 2,6-dichlorophenol indophenol (2,6-DCPIP) assay. Isolates belonging to the genus Acinetobacter degraded long-chain normal alkanes (n-alkanes) but did not degrade short-chain n-alkanes or cyclic alkanes (c-alkanes), while isolates belonging to the genera Rhodococcus and Gordonia degraded both long-chain n-alkanes and c-alkanes.

Phylogenetic analysis of long-chain hydrocarbon-degrading bacteria and evaluation of their hydrocarbon-degradation by the 2,6-DCPIP assay.

Two microorganisms (NDKK48 and NDKY76A) that degrade long-chain cyclic alkanes (c-alkanes) were isolated from soil samples. Strains NDKK48 and NDKY76A were identified as Rhodococcus sp. and Gordonia sp., respectively. Both strains used not only normal alkane (n-alkane) but also c-alkane as a sole carbon and energy source, and the strains degraded more than 27% of car engine base oil (1% addition).

Degradation of Car Engine Base Oil by Rhodococcus sp. NDKK48 and Gordonia sp. NDKY76A

The degradation pathways for cyclic alkanes (c-alkanes) in Rhodococcus sp. NDKK48 were investigated. Strain NDKK48 used dodecylcyclohexane as a sole carbon and energy source, and five metabolites in the dodecylcyclohexane degradation pathway were detected by gas-chromatography/mass spectra. The metabolites were identified as cyclohexanecarboxylic acid, cyclohexylacetic acid, 1-cyclohexene-1-acetic acid, 4-dodecylcyclohexanol, and 4-dodecylcyclohexanone. The strain degrades dodecylcyclohexane via a ring oxidation pathway and an alkyl side chain oxidation pathway. Cyclohexanecarboxylic acid was further oxidized to muconic acid via 1-cyclohexene-1-carboxylic acid and benzoic acid, and the muconic acid was finally used by strain NDKK48 for growth. Methylcyclohexane and cyclohexane were co-oxidized with hexadecane by strain NDKK48. Methylcyclohexane was degraded via a ring oxidation pathway, and the degradation pathway contained part of the Baeyer-Villiger oxidation for ring cleavage. Cyclohexane was also degraded by the same pathway as methylcyclohexane. Thus, strain NDKK48 has two pathways for the complete degradation of c-alkanes.

Degradation pathways of cyclic alkanes in Rhodococcus sp. NDKK48.

The lactic acid bacterial flora in commercial and homemade Funazushi (fermented crucian carp and rice) were investigated. Funazushi is a fermented fish product that continues to be produced in the traditional style in Japan. Lactic acid bacteria in four commercial and five homemade Funazushi were enumerated. The viable counts of commercial samples ranged from 3.0 × 10 to 2.7 × 10 cfu/g, with an average of 2.4 × 10 cfu/g, while the viable counts of homemade samples ranged from 2.0 × 10 to 2.6 × 10 cfu/g, with an average of 1.3 × 10 cfu/g. Twenty-seven lactic acid bacteria isolates were obtained from the commercial samples, and identified as Streptococcus salivarius, Lactobacillus buchneri, and Lactobacillus parabuchneri. Forty-eight isolates were obtained from the homemade samples, and identified as Lactobacillus plantarum, Lb. buchneri, Lactobacillus alimentarius, Lactobacillus farciminis, Lactobacillus acidipiscis, and Lactobacillus casei. Lb. buchneri was the predominant species in commercial Funazushi, while Lb. plantarum and Lb. buchneri were the predominant species in the homemade products.

Kenzo Kubota

Papers

Degradation of Bioplastics in Soil and Their Degradation Effects on Environmental Microorganisms

Phylogenetic analysis of long-chain hydrocarbon-degrading bacteria and evaluation of their hydrocarbon-degradation by the 2,6-DCPIP assay.

Degradation of Car Engine Base Oil by Rhodococcus sp. NDKK48 and Gordonia sp. NDKY76A

Degradation pathways of cyclic alkanes in Rhodococcus sp. NDKK48.

Isolation and Identification of Lactic Acid Bacteria in Traditional Fermented Sushi, Funazushi, from Japan