Responses of phytoplankton and its satellite bacteria to exogenous ethanol

The response of phytoplankton and its satellite bacteria to various concentrations(0.01%-10%v/v)of ethanol is studied.To elucidate the effect of ethanol,single-strains of phytoplankton(SSP)culture,pure strains of satellite bacteria isolated from nonaxenic SSP cultures,and Escherichia coli were screened.Results indicate that ethanol could promote the growth and photo synthetic efficiency(F_(v)/F_(m))of S SP at 0.01%and the growth of satellite bacteria at 0.01%-1%.Nevertheless,ethanol inhibited the growth and F_(v)/F_(m)of SSP at 0.1%-1%,and killed bacteria and SSP at 10% concentration.Further investigation on a satellite bacterium(Mameliella alba)revealed that ethanol promotes growth by serving as a growth stimulant rather than a metabolic carbon source.The 16 S rRNA gene amplicon indicated that all nonaxenic S SP cultures harbor distinct satellite bacteria communities where the SSP culture of Skeletonema costatum,Phaeodactylum tricornutum,and Dunaliella bardawil were dominated by bacteria genera of Marivita(~80%),Dinoroseobacter(~47%),and Halomonas(~87%),respectively,indicating that every SSP cultures have their own distinct satellite bacterial community.The bacteria family Rhodobacteraceae was dominant in the two marine diatoms,whereas Halomonadaceae was dominant in the saline green microalga.Compared to their respective controls,the supply of 0.5% ethanol to SSP cultures promoted the growth of the satellite bacteria but did not cause a significant difference in species composition of satellite bacteria.Therefore,a low concentration of ethanol can promote the growth of bacteria in a non-selective way.This study enriched our knowledge about the effect of ethanol on aquatic microbes and provided a baseline for basic and applied biotechnological re search in the aquatic environment in the future.

Occurrence of viable but non-culturable(VBNC)pathogenic bacteria in tap water of public places

Viable but non-culturable(VBNC)bacteria have been detected in source water and effluent of drinking water treatment processes,leading to significant underestimation of viable cell counts.Limited information exists on VBNC bacteria in tap water,particularly in public places.To address this gap,a comprehensive nine-month study was conducted in a major city in south-eastern China,using culture-based and quantitative PCR with propidium monoazide(PMA)dye methods.Forty-five samples were collected from five representative public places(railway station,campus,hospital,shopping mall,and institution).The findings revealed that culturable bacteria represented only 0–17.51%of the viable 16S rRNA genes,suggesting that the majority of viable bacteria existed in an uncultured or VBNC state.Notably,opportunistic pathogens such as Escherichia coli,Enterococcus faecalis,Pseudomonas aeruginosa,Salmonella sp.,and Shigella sp.were primarily detected as VBNC cells,with concentrations ranging from 1.03×10^(0)to 3.01×10^(3),1.20×10^(0)to 1.42×10^(2),1.32×10^(0)to 8.82×10^(0),1.00×10^(0)to 6.71×10^(1),and 2.07×10^(0)to 1.93×10^(2)cell equivalent/100 mL,respectively.Culturable P.aeruginosa was observed in tap water after prolonged stagnation,indicating potential risks associated with bacterial regrowth.Spatial and temporal factors accounted for 17.1%and 26.0%,respectively,of the variation in tap water community structure during the sampling period,as revealed by 16S rRNA amplicon sequencing.This study provides quantitative insights into the occurrence of VBNC bacteria in tap water and highlights the need for more sensitive monitoring methods and microbial control techniques to enhance tap water safety in public locations.

Potential shift of bacterial community structure and corrosion-related bacteria in drinking water distribution pipeline driven by water source switching

As a result of pollution in the present water sources,cities have been forced to utilize cleaner water sources.There are few reports regarding the potential shift of bacterial community structure driven by water source switching,especially that of corrosion-related bacteria.Three types of finished water were used for simulation,the polluted source water from the Qiantang and Dongtiaoxi Rivers(China)was replaced by cleaner water from Qiandao Lake(China).Here,we discussed the transition effects through three simulated reactors.The bacterial characteristics were identified using the highthroughput sequencing and heterotrophic plate count method.It was observed that the level of culturable bacteria declined by 2–3 orders of magnitude after water source switching.The bacterial community released from the pipeline reactor was significantly different under different finished water,and it exhibited large variation at the genus level.Porphyrobacter(58.2%)and Phreatobacter(14.5%)clearly replaced Novosphingobium,Aquabacterium,and Cupriavidus as new dominant genera in system A,which could be attributed to the lower carbon and nitrogen content of the new water source.Although corrosion-inhibiting bacteria decreased after switching,they still maintained dominant in three reactors(6.6%,15.9%,and 19.7%).Furthermore,potential opportunistic pathogens such as Sphingomonas were detected.Our study shows that after transition to a high quality water source,the total culturable bacteria released was in a downtrend,which leads to a great reduction in the risk of bacterial leakage in the produced drinking water.