Viral infection of bacteria causes release of dissolved organic matter (DOM), which is available for bacterial uptake. In aquatic environments, this virus-mediated transformation of living cells into dissolved and colloidal organic matter may be a quantitatively important process in the pelagic recycling of carbon and nutrients, but little is known about the amount, composition, or bioavailability of viral lysates. By using a model system of a marine bacterium (Cellulophaga sp.) and a virus specific to this bacterium, the present study provides a first quantification of the input of dissolved free and combined amino acids (DFAA and DCAA) and bacterial cell wall compounds following viral lysis. The DCAA constituted 51–86% of the total virus-mediated organic carbon release of 1087–1825 μg C l⁻¹ (estimated biomass of the lysed bacteria), whereas DFAA and glucosamine each accounted for 2–3% of total lysate-C. The viral particles themselves constituted 4–6% of the released organic carbon, and altogether, the applied analyses thus identified 53–92% of the released lysates. Approximately 12% of the identified compounds were derived from bacterial cell wall peptidoglycan, including various D-isomers of DFAA and DCAA, glucosamine and diaminopimelic acid (DAPA). Although a portion of this cell wall material may have entered the pool of refractory material, a significant fraction of some peptidoglycan-derived components, e.g. 83% of the released D-DFAA, were removed from the dissolved phase during the last part of the incubations, suggesting that part of the cell wall material were utilized by the developing virus-resistant Cellulophaga population. Therefore, we suggest that virus-mediated DOM is a source of a variety of organic compounds, which contribute significantly to the pool of rapidly recycling material in the ocean.

Extracellular peptidoglycan is commonly found in natural environments, yet little is known about its biodegradation in nature. We here describe a novel peptidoglycan-degrading bacterium, designated strain 332T, isolated from mesotrophic lake water in Denmark. The strain was a Gram-negative-staining, motile rod. It had chitinase and lysozyme activities, which are relevant to peptidoglycan degradation, and was capable of utilizing several mono- and disaccharides, amino acids and organic acids. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain 332T belonged to the genus Delftia. Fatty acids of the strain included C8 : 0 and C10 : 0, which are characteristic of the genus Delftia. The DNA G+C content of the strain was 65.3 mol%. A DNA–DNA hybridization value of 66.2 % was found between strain 332T and Delftia tsuruhatensis DSM 17581T. Based on differences in physiological and biochemical characteristics, the strain is considered to represent a novel species, for which the name Delftia lacustris sp. nov. is proposed. The type strain is 332T (=DSM 21246T =LMG 24775T). An emended description of Delftia tsuruhatensis is also presented.