Effects of low-shear modeled microgravity on a microbial community filtered through a 0.2-μm filter and its potential application in screening for novel microorganisms

Novel method for screening probiotic candidates tolerant to human gastrointestinal stress

Tolerance to human gastrointestinal stressors is crucial for probiotics to exhibit their health benefits; however, there is no standardised method for screening their stress tolerance. In this study, we proposed a novel method for screening probiotic candidates tolerant to human gastrointestinal stress-gastrointestinal tolerance assay and culture (GTA-C) method-using black polyethylene terephthalate (PET) non-woven fabric as a scaffold to modify the specialized cellulose film (SCF) method. The modified SCF method showed excellent pH-based diffusion of medium components, had minimal effect on the growth of Escherichia coli K12, and improved the visibility of the colonies. Analysis of kimchi samples cultured using the SCF and modified SCF methods revealed that the modified method diversified the cultured bacteria. GTA in a simulated human fasting state using the modified SCF method showed that acid stress significantly affected the growth of four bacteria used as probiotics and that tolerance to acid stress may be species-dependent. Screening of probiotics in kimchi samples resulted in the identification of lactic acid bacteria tolerant to human gastrointestinal stress during fasting. Our results indicate that the modified SCF method (GTA-C method) is useful for screening probiotics resistant to the gastrointestinal environment during fasting.

Effect of intermittent opening of breathable culture plugs and aeration of headspace on the structure of microbial communities in shake-flask culture

In this study, we found that opening breathable culture plugs for 30 s during periodic and aseptic sampling affects the community structure of cultured soil microbes. Similar effects were observed using an automatic aeration flask system that mimics aseptic opening of the breathable culture plug during sampling, but without interruption in shaking. Thus, the observed changes in the microbial consortia appear to be due exclusively to the intermittent ventilation of the flask headspace. To elucidate the mechanism driving this phenomenon, we monitored CO₂ and O₂ concentrations in both headspace and culture broth using the new system termed as circulation direct monitoring and sampling system. The data show that the CO₂ concentration in the culture broth temporarily decreased with the CO₂ concentration in the headspace, strongly suggesting that the effect of intermittent ventilation of the headspace on the microbial consortia depends on CO₂. Importantly, the data also imply that environmental variables during shake flask culture, especially CO₂ concentration, is important for screening aerobic microorganisms.