The Succession of Bacterial Community Attached on Biodegradable Plastic Mulches During the Degradation in Soil

Despite the increasing application of biodegradable plastic mulches (BDMs) in agriculture, the colonization and succession of the attached microbial community on BDMs during their degradation processes remain poorly characterized. Here, we buried four types of commonly used BDMs, including pure polylactic acid (PLA), pure polybutylene adipate terephthalate (PBAT), and two mixtures of PLA and PBAT (85:15 and 15:85 w/w), and one classic polyethylene (PE) mulch in soil for 5 months. Both plastic components and incubation time significantly shaped the β-diversities of microbiota on the plastic mulches (p < 0.001). Meanwhile, the microbial compositions and community structures on BDMs were significantly different from PE mulch, and when excluding PE mulch, the microbiota varied more with time than by the composition of the four BDMs. The orders Burkholderiales and Pseudonocardiales were dominant on most BDMs across different time points. The genus Ramlibacter was revealed as a common biomarker for both PLA and PBAT by random-forest model, and all biomarkers for the BDMs belonged to the dominant order Burkholderiales. In addition, degradation-related and pathogen-related functional taxa were enriched in all mulches among all 40 functional groups, while surprisingly, potential pathogens were detected at higher levels on BDMs than PE. For community assembly on all mulches, the drift and dispersal processes played more important roles than selection, and in particular, the contribution of stochastic drift increased during the degradation process of BDMs while selection decreased, while the opposite trend was observed with PE mulch. Overall, our results demonstrated some degradation species and pathogens were specifically enriched on BDMs, though stochastic processes also had important impacts on the community assembly. It suggested that, similar to conventional plastic mulch, the increased usage of BDMs could lead to potential hazards to crops and human health.

Assessing Biodegradability of PVA/Starch Based Composite Films Reinforced With Long Chain Fatty Acid Grafted Barley Husk

The main objective of this study is the preparation of poly (vinyl alcohol) PVA/starch based composite films reinforced with barley husk and grafted barley husk (prepared using lauric acid, palmitic acid and arachidic acid) for packaging applications and assessment of their biodegradability. The biodegradability test of the films was performed by measuring weight loss of the films after degradation in soil under natural environmental conditions and by measuring evolved carbon dioxide (CO2) during degradation under aqueous aerobic environment containing activated sludge. Physico-chemical variation in the films after degradation were observed using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The composite films containing barley husk showed highest degradation in soil (70 % after 180 days) as well as in aqueous aerobic medium (58.83 % after 30 days). The results of scanning electron microscopy showed the formation of cracks and holes over the surface of the composite films after degradation. The degradation of the films occurred inside the composite films, not only on their surface. The incorporation of starch and barley husk in PVA matrix enhanced the degradation rate of films.

Draft Genome Sequence of Rhodococcus erythropolis VKPM Ac-1659, a Putative Oil-Degrading Strain Isolated from Polluted Soil in Siberia

The draft genome sequence of Rhodococcus erythropolis Ac-1659, a putative oil-degrading strain, is reported. This genome sequence may provide better insights into the diversity and evolution of the genes responsible for hydrocarbon degradation in soil microorganisms.