Exploring the potential environmental functions of viable but non-culturable bacteria

Abstract

A conventional plate count is the most commonly employed method to estimate the number of living bacteria in environmental samples. In fact, judging the level of viable culture by plate count is limited, because it is often several orders of magnitude less than the number of living bacteria actually present. Most of the bacteria are in "viable but non-culturable" (VBNC) state, whose cells are intact and alive and can resuscitate when surrounding conditions are more favorable. The most exciting recent development in resuscitating VBNC bacteria is a bacterial cytokine, namely, the resuscitation-promoting factor (Rpf), secreted by Micrococcus luteus, which promotes the resuscitation and growth of high G+C Gram-positive organisms, including some species of the genus Mycobacterium. However, most of studies deal with VBNC bacteria only from the point of view of medicine and epidemiology. It is therefore of great significance to research whether these VBNC state bacteria also possess some useful environmental capabilities, such as degradation, flocculation, etc. Further studies are needed to elucidate the possible environmental role of the VBNC bacteria, rather than only considering their role as potential pathogens from the point view of epidemiology and public health. We have studied the resuscitation of these VBNC bacteria in polluted environments by adding culture supernatant containing Rpf from M. luteus, and it was found that, as a huge microbial resource, VBNC bacteria could provide important answers to dealing with existing problems of environmental pollution. This mini-review will provide new insight for considering the potentially environmental functions of VBNC bacteria.

Current Perspectives on Viable but Non-Culturable (VBNC) Pathogenic Bacteria

“…The resuscitation of VBNC state is not only important in the field of medicine, but also for several industrial processes to improve biodegradation and flocculation (105). Although a considerable amount of work is going on in this area, specific mechanism responsible for the transition of bacteria to the VBNC state or its revival to culturability remain obscure.…”

Optimization of protein production by Micrococcus luteus for exploring pollutant-degrading uncultured bacteria

“…Furthermore, in the M. luteus culture supernatant, several other proteins had been found to possess the same muralytic activity as Rpf protein (Mukamolova et al 2006). The resuscitation and stimulatory activities of proteins from M. luteus culture supernatant had been recently verified (Ding 2004; Su et al 2013; Su et al 2013). Therefore, for the purpose of resuscitating and stimulating VBNC or uncultured bacteria, proteins from M. luteus culture supernatant are more convenient and cost-effective than purified Rpf protein.…”

“…Rpf (activity at picomolar concentrations) could promote the resuscitation and growth of high G + C Gram-positive organisms, including Mycobacterium , Rhodococcus , Arthrobacter , Leifsonia, Bacillus , Nocardia , Kitasatospora and Streptomyces (Su et al 2013) . At present, more than 30 genes from various microorganisms coded for “Rpf-like” proteins were grouped into Rpf family (Telkov et al 2006).…”

Genetic characterization of <i>Salmonella</i> and <i>Shigella</i> spp. isolates recovered from water and riverbed sediment of the Apies River, South Africa

“…(qPCR) counts were respectively 65 to 1 571 and 11 to 51 times higher than that from cultured-based quantification. In a study by Su et al (2013), the high bacterial counts were attributed to viable but non-cultivable bacteria that are found in the environment. In another study, it was found that high qPCR counts may also result from DNA of dead cells in the environment (Wolffs et al, 2005).…”