Environmental organic carbon sources inhibit the predatory life of Halobacteriovorax vibrionivorans

Abstract:

[Background] The carbon sources required for the growth of Bdellovibrio-and-like organisms are mainly derived from the host, and the effects of various carbon sources in the environment remain to be explored. [Objective] The effects of different extracellular organic carbon sources on the predatory life of Halobacteriovorax vibrionivorans was investigated to provide a theoretical basis for subsequent research on the predation mechanism and microbiological control agent against pathogenic bacteria. [Methods] Vibrio alginolyticus was used as host strain, an absorbance-based assay with 96-well plates for cell lysis and double-layer plate method were applied to determine the effects of different carbohydrates, yeast extract and tryptone on the predatory growth of H. vibrionivorans Y22. Comparative experiments between nonviable heat-deactivated and viable hosts, artificial seawater and Tris-HCl (25 g/L NaCl) culture system, were adopted to explore possible growth mechanism of strain Y22, combined with genomic analysis of strain Y22 and its host strain. [Results] Strain Y22 had no phosphotransferase system and ABC transporters of sugars, and could not use extracellular carbohydrates as carbon sources; The host V. alginolyticus could utilize sucrose, maltose, mannitol for growth and produce acid, which lead to the decreased pH value of the artificial seawater co-culture system, thereby block the predation of strain Y22. Glucose could not only decrease the pH value of artificial seawater co-culture system, but also changed the cell characteristics of the host, thereby block the predation recognition process of strain Y22. The host could not grow with starch and α-lactose, and these carbon sources did not affect the predation of strain Y22. Strain Y22 contained protein, polypeptide and amino acid membrane transporter genes, which allowed it to utilize the host protein as carbon sources and nitrogen sources. Around 1?5 g/L external yeast extract and tryptone could inhibit the predation of strain Y22, and the predation-inhibiting effect was found to be dose dependent. When the concentration of yeast extract was over 4 g/L, and the concentration of tryptone was over 5 g/L, the predation phenomenon of strain Y22 was strongly inhibited and almost invisible. [Conclusion] Environmental carbohydrates will affect the metabolic activity of host bacteria, acidify the co-culture system, and change the cell characteristics of the host, which inhibit the predatory activity of H. vibrionivorans. H. vibrionivorans can absorb and utilize the environmental protein or peptide, by which its predatory growth will be inhibited. The results will provide further insights into the predation mechanism and antibacterial application of Halobacteriovorax.