Proposal for a method to estimate nutrient shock effects in bacteria

Genetic engineering of low-temperature polyhydroxyalkanoate production by Acidovorax sp. A1169, a psychrophile isolated from a subglacial outflow

In recent years, extremophilic microorganisms have been employed as producers of the microbial bioplastics polyhydroxyalkanoates (PHA), which are of great biotechnological value. Nevertheless, cold-loving or psychrophilic (cryophilic) bacteria have been neglected in this regard. Here, we present an investigation of the Arctic glacier-derived PHA producer Acidovorax sp. A1169. Biolog GEN III Microplates were used as a screening tool to identify the most suitable carbon substrate concerning PHA synthesis. The strain produced homopolymer poly(3-hydroxybutyrate) (PHB) most efficiently (2 g/L) at a temperature of 15 °C when supplied with fructose or mannitol as carbon sources with a substantial decrease of PHB biosynthesis at 17.5 °C. The PHB yield did not increase considerably or even decreased when carbon source concentration exceeded 10 g/L hinting that the strain is oligotrophic in nature. The strain was also capable of introducing 3-hydroxyvalerate (3HV) into the polymer structure, which is known to improve PHA thermoplastic properties. This is the first investigation providing insight into a PHA biosynthesis process by means of a true psychrophile, offering guidelines on polar-region bacteria cultivation, production of PHA and also on the methodology for genetic engineering of psychrophiles.

Evaluating the environmental microbiota across four National Health Service hospitals within England

Hospital surfaces contaminated with microbial soiling, such as dry surface biofilms (DSBs), can act as a reservoir for pathogenic micro-organisms, and inhibit their detection and removal during routine cleaning. Studies have recognized that such increases in bioburden can hinder the impact of disinfectants and mask the detection of potential pathogens. Cleanliness within healthcare settings is often determined through routine culture-based analysis, whereby surfaces that exhibit >2.5 colony-forming units (CFU) per cm² pose a risk to patient health; therefore, any underestimation could have detrimental effects. This study quantified microbial growth on high-touch surfaces in four hospitals in England over 19 months. This was achieved using environmental swabs to sample a variety of surfaces within close proximity of the patient, and plating these on to non-specific low nutrient detection agar. The presence of DSBs on surfaces physically removed from the environment was confirmed using real-time imaging through episcopic differential interference contrast microscopy combined with epifluorescence. Approximately two-thirds of surfaces tested exceeded the limit for cleanliness (median 2230 CFU/cm²), whilst 83% of surfaces imaged with BacLight LIVE/DEAD staining confirmed traces of biofilm. Differences in infection control methods, such as choice of surface disinfectants and cleaning personnel, were not reflected in the microbial variation observed and resulting risk to patients. This highlights a potential limitation in the effectiveness of the current standards for all hospital cleaning, and further development using representative clinical data is required to overcome this limitation.

Diluted conventional media improve the microbial cultivability from aquarium seawater

The cultivation of microbial species remains a primary challenge in microbiology and obtaining pure cultures is essential for the study of microbial physiology and function. When isolating microorganisms from aquaculture environments, Vibrio are the most dominate isolates on the media that are commonly used. In order to expand our ability to study microbial species, an easy-operation and low-cost medium that can reduce the interference of Vibrio strains and increase the cultivability of other bacteria is urgently needed. We compared viable cell counts on conventional media (CM; including Marine Agar 2216 and LB media) and diluted media (DM; including 1/10-Marine Agar 2216, 1/10-LB). We also assessed the diversity of cultivable microorganisms under high and low nutrient conditions by a plate-wash strategy coupled with high-throughput sequencing of the V4 hypervariable region of the 16S rRNA gene. The results show that microbial communities from DM, especially 1/10-Marine Agar 2216, are more diverse than those obtained from CM. Vibrio isolates were reduced on DM. PICRUSt analysis revealed that nutrient composition is a significant contributor to the diversity and function of the cultivable microbial communities. Bacteria grown on CM possess more pathogenic characteristics, whereas DM favors the growth of bacteria that have multiple metabolic functions. Collectively, our data provide strong evidence that dilution of CM influences the cultivability of bacteria from aquaculture seawater. It also supports that DM can expand the range of microbial species that can be cultivated. This study also provides insights for media design in microbial cultivation from aquaculture systems.

Low-frequency electromagnetic fields as an alternative to sanitize water of drinking systems in poultry production?

Low-frequency electromagnetic fields (LF-EMF) may present an alternative to conventional sanitation methods of water supply lines in animal production. The objective of this study was to evaluate the effect of the application of LF-EMF on bacterial concentrations and biofilms at scale-models of different drinking systems (circulating and non-circulating) conventionally used in poultry holdings. Treated systems were equipped with commercial devices producing pulsed electromagnetic signals of low frequency up to 10,000 Hz; max. 21 mT. Exposure of water to LF-EMF resulted in changes of the culturable bacterial counts, although with high standard deviations. Differing between systems types, LF-EMF treatment seemed to be responsible either for a limitation or for an increase of colony forming unit counts, with partly statistically significant differences, especially in early stages of treatment. In contrast, neither biofilm formation nor counts of cells suspended in water differed between treated and control lines over 28 days of experiment, as determined by fluorescence microscopy. Although this study indicates that LF-EMF may influence culturability of water microorganisms, no clear inhibitory effects on bacterial biofilm formation or on planktonic microbes by LF-EMF treatment were confirmed in the experiments.

A method for culturing Gram-negative skin microbiota

Background

Commensal Gram-negative (CGN) microbiota have been identified on human skin by DNA sequencing; however, methods to reliably culture viable Gram-negative skin organisms have not been previously described.

Results

Through the use of selective antibiotics and minimal media we developed methods to culture CGN from skin swabs. We identified several previously uncharacterized CGN at the species level by optimizing growth conditions and limiting the inhibitory effects of nutrient shock, temperature, and bacterial competition, factors that may have previously limited CGN isolation from skin cultures.

Conclusions

Our protocol will permit future functional studies on the influences of CGN on skin homeostasis and disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0684-9) contains supplementary material, which is available to authorized users.