Microbial responses to chitin and chitosan in oxic and anoxic agricultural soil slurries

Abstract

Abstract. Microbial degradation of chitin in soil substantially contributes to carbon cycling in terrestrial ecosystems. Chitin is globally the second most abundant biopolymer after cellulose and can be deacetylated to chitosan or can be hydrolyzed to N,N′-diacetylchitobiose and oligomers of N-acetylglucosamine by aerobic and anaerobic microorganisms. Which pathway of chitin hydrolysis is preferred by soil microbial communities is unknown. Supplementation of chitin stimulated microbial activity under oxic and anoxic conditions in agricultural soil slurries, whereas chitosan had no effect. Thus, the soil microbial community likely was more adapted to chitin as a substrate. In addition, this finding suggested that direct hydrolysis of chitin was preferred to the pathway that starts with deacetylation. Chitin was apparently degraded by aerobic respiration, ammonification, and nitrification to carbon dioxide and nitrate under oxic conditions. When oxygen was absent, fermentation products (acetate, butyrate, propionate, hydrogen, and carbon dioxide) and ammonia were detected, suggesting that butyric and propionic acid fermentation, along with ammonification, were likely responsible for anaerobic chitin degradation. In total, 42 different chiA genotypes were detected of which twenty were novel at an amino acid sequence dissimilarity of less than 50%. Various chiA genotypes responded to chitin supplementation and affiliated with a novel deep-branching bacterial chiA genotype (anoxic conditions), genotypes of Beta- and Gammaproteobacteria (oxic and anoxic conditions), and Planctomycetes (oxic conditions). Thus, this study provides evidence that detected chitinolytic bacteria were catabolically diverse and occupied different ecological niches with regard to oxygen availability enabling chitin degradation under various redox conditions on community level.

Genome sequencing and analysis of the first spontaneous Nanosilver resistant bacterium Proteus mirabilis strain SCDR1

“…Thus, although we did not detect chitinase genes in P. mirabilis SCDR1, the presence of Chitin-binding protein suggests that P. mirabilis SCDR1 has some mechanisms of protection against chitin and the chitosan antimicrobial effect. In addition, the presence of genes encoding for the members Chitosanase family GH3 of N, N′-diacetylchitobiose-specific 6-phospho-beta-glucosidase (EC 3.2.1.86), Beta N-acetyl-glucosaminidase (nagZ, beta-hexosaminidase) (EC 3.2.1.52), and Glucan endo-1, 4-beta-glucosidase (EC 3.2.1.-) in P. mirabilis SCDR1 suggests that it can hydrolyze chitosan to glucosamine [ 60 – 62 ]. This justifies the lack of antimicrobial effect of chitosan against P. mirabilis SCDR1.…”

Organic Farming Improves Soil Microbial Abundance and Diversity under Greenhouse Condition: A Case Study in Shanghai (Eastern China)

“…LEfSe analysis showed that the phyla Planctomycetes and Cyanobacteria were the preferential bacterial communities in OP soil. Members belonging to Planctomycetes have been reported as major groups to decompose heteropolysaccharide [39] and chitin [40] and are involved in the C cycle in soils, which might be related to the highest Ctot content being in OP soil. OTUs from Cyanobacteria are photoautotrophs and play key roles in biogeochemical processes in nature and improve the turnover of C and N in the soil [41].…”

Genome Analysis of Fimbriiglobus ruber SP5T, a Planctomycete with Confirmed Chitinolytic Capability

“…These cultured representatives, however, do not cover all planctomycete diversity in natural habitats. Recent molecular study of microbial degradation of chitin in an agricultural soil suggested involvement of Singulisphaera-like planctomycetes in this process (18). Additional evidence for the existence of chitinolytic planctomycetes was obtained in a metatranscriptome-based study of microbial populations driving biopolymer degradation in acidic peatlands (19).…”