Abstract
Viable but nonculturable (VBNC) bacteria, which maintain the viability with loss of culturability, universally exist in contaminated and non-contaminated environments. In this study, two strains, Rhodococcus sp. TG13 and TN3, which were isolated from PCB-contaminated sediment and non-contaminated sediment respectively, were investigated under low temperature and oligotrophic conditions. The results indicated that the two strains TG13 and TN3 could enter into the VBNC state with different incubation times, and could recover culturability by reversal of unfavourable factors and addition of resuscitation-promoting factor (Rpf), respectively. Furthermore, the gene expression variations in the VBNC response were clarified by Illumina high throughput RNA-sequencing. Genome-wide transcriptional analysis demonstrated that up-regulated genes in the VBNC cells of the strain TG13 related to protein modification, ATP accumulation and RNA polymerase, while all differentially expressed genes (DEGs) in the VBNC cells of the strain TN3 were down-regulated. However, the down-regulated genes in both the two strains mainly encoded NADH dehydrogenase subunit, catalase, oxidoreductase, which further verified that cold-induced loss of ability to defend oxidative stress may play an important role in induction of the VBNC state. This study further verified that the molecular mechanisms underlying the VBNC state varied with various bacterial species. Study on the VBNC state of non-pathogenic bacteria will provide new insights into the limitation of environmental micro-bioremediation and the cultivation of unculturable species.
Highlights
The genus Rhodococcus plays a significant role in the fields of environmental bioremediation and industrial biotechnology [1]
Total cell counts remained constant at the initial level (107 cells/mL). These results demonstrated that the strains TG13 and TN3 could enter the Viable but nonculturable (VBNC) state under the present conditions
These results indicated that for resuscitation from VBNC state, the strain TN3 needed extracellular bacterial proteins, but the strain TG13 could be achieved by a simple reversal of the unfavourable factors
Summary
The genus Rhodococcus plays a significant role in the fields of environmental bioremediation and industrial biotechnology [1]. The pollutant-degrading abilities of many species have been widely used for the biodegradation of xenobiotic compounds which are recalcitrant with. Transcriptome Analysis of VBNC State in Rhodococcus remarkable stability and toxicity, including various herbicides, nitroaromatics, chloroaromatics and polychlorinated biphenyls (PCBs) [2]. Various bacterial strains of the genus Rhodococcus represent an abundant part of indigenous bacterial communities in contaminated localities [3]. The versatile degradative potential of Rhodococcus species and their ability to persist in adverse conditions make them suitable industrial microorganisms for bioremediation of contaminated sites. Isolating and culturing difficult-to-culture or VBNC bacteria, searching for new Rhodococcus species, and understanding their related function and genotype have become increasingly more important
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