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Abstract

Chitin is the second most abundant renewable polysaccharide, as it is a component of the exoskeleton of many organisms and of the cell walls of numerous fungi. Most streptomycetes secrete a number of chitinases, hydrolyzing chitin to oligomers, chitobiose or N-acetylglucosamine which can be utilized as carbon or nitrogen source. The chitinases of several streptomycetes have been shown to have a modular arrangement comprising catalytic, substrate binding as well as linker domains. Moreover, during growth in the presence of chitin-containing substrates, many Streptomyces strains have been shown to secrete formerly unknown, small (about 200 aa) chitin binding proteins (CHBs) which lack enzymatic activity and specifically target and invade chitin. Several motifs, including the relative location and spacing of four tryptophan residues, are conserved in the investigated CHB types, CHB1 and CHB2. The affinity of CHB1 to crab shell chitin is two times higher than that of CHB2. Comparative studies of various generated mutant CHB1 proteins led to the conclusion that it is one of the exposed tryptophan residues that directly contributes to the interaction with chitin. On the basis of immunological, biochemical and physiological studies, it can be concluded that the CHBs act like a glue with which streptomycetes target chitin-containing samples or organisms. The ecological implications of these findings are discussed.

Bacterial Communities in the Gut and Reproductive Organs of Bactrocera minax (Diptera: Tephritidae) Based on 454 Pyrosequencing

“…Actinobacteria was another major member of the bacterial communities in the reproductive organs in our study. Actinobacteria exhibits diverse physiological and metabolic properties, such as the production of extracellular enzymes and the formation of a wide variety of secondary metabolites [36]. The additional species may represent low-abundance taxa present in some or all samples; however, they may become dominant under some special circumstances, as previously reported in coral hosts [37].…”

The gut microbiota in larvae of the housefly Musca domestica and their horizontal transfer through feeding

“…Arabinoxylans and β-glucans are polysaccharides in the cell wall of wheat bran and have a potential role in lowering the risk of type II diabetes, colorectal cancer and cardiovascular and diverticular diseases (Poutanen et al 2014). Actinobacteria has also been reported to exhibit diverse physiological and metabolic properties, such as the production of extracellular enzymes and the formation of a wide variety of secondary metabolites (Schrempf 2001). …”

Active invasion of bacteria into living fungal cells

“…We therefore assume that Cbp facilitates bacterial attachment to the fungal hyphae and renders the chitin matrix more accessible to chitinase degradation as it was proposed for family 33 Cbps. Small Cbps also promote the recognition and degradation of chitin by streptomycetes (Schrempf, 2001). Chitin-binding proteins could play a role in various close interactions where bacteria attach to the hyphal surface and form fibrillar structures, as in specific Streptomyces-Aspergillus (Siemieniewicz and Schrempf, 2007) and Paenibacillus-Fusarium co-cultures (Dijksterhuis et al, 1999).…”