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A small receptor molecule composed of a porphyrin core with tetrakis-ammonium glycine pickets (liptin 3e) appears to target anionic phosphatidylglycerol (PG) lipid head groups through multifunctional binding-pocket complementarity. Although a major component of bacterial cell membranes, PG is not widely found in animal cells, making PG potentially selective for bacterial targeting. Growth of microbial isolates was monitored in liquid cultures treated with liptin 3e by dilution plate counts and turbidity. Inhibition of growth by liptin 3e was observed for the ESKAPE human pathogens (Enterobacter aerogenes, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterococcus faecium), Escherichia coli, Mycobacterium smegmatis, Streptococcus sobrinus, and methicillin-resistant S. aureus (MRSA), with certain species suppressed at <1 μg/mL (sub-μM) concentrations. Prolonged lag phases were observed, although cell viability was mainly unaffected, suggesting that liptin treatment caused bacteriostasis. Cultures treated with liptin 3e eventually recovered, resumed growth, and reached the same final densities as untreated cultures. Growth of the fungus Candida albicans was not appreciably inhibited by liptin 3e. If liptins exhibit bacteriostasis through broad extracellular binding to PG head groups, thereby disrupting cellular processes, liptins may be considered for development into preclinical drug candidates or be useful as a targeting system for molecular beacons or antibacterial drugs., (© 2023. Institute of Microbiology, Academy of Sciences of the Czech Republic, v.v.i.)

Hygroscopic salts at Mars' near-surface (MgSO 4 , (per)chlorates, NaCl) may form brines by absorbing moisture from the atmosphere at certain times through the process of deliquescence. We have previously shown strong bacterial growth in saturated MgSO 4 (∼67% w/v as epsomite) at room temperature, and growth was observed at the MgSO 4 eutectic point (43% w/v at -4°C). Here, we have investigated the growth of salinotolerant microbes ( Halomonas, Marinococcus, Planococcus ) from Hot Lake, Washington; Basque Lake, British Columbia; and Great Salt Plains, Oklahoma under deliquescing conditions. Bacterial cultures were grown to mid-log phase in SP medium supplemented with 50% MgSO 4 (as epsomite), 20% NaClO 3 , or 10% NaCl (w/v), and small aliquots in cups were dried by vacuum desiccation. When the dried culture was rehydrated by the manual addition of water, the culture resumed growth in the reconstituted brine. When desiccated cultures were maintained in a sealed container with a brine reservoir of the matching growth medium controlling the humidity of the headspace, the desiccated microbial culture evaporites formed brine by deliquescence using humidity alone. Bacterial cultures resumed growth in all three salts once rehydrated by deliquescence. Cultures of Halomonas sp. str. HL12 showed robust survival and growth when subjected to several cycles of desiccation and deliquescent or manual rehydration. Our laboratory demonstrations of microbial growth in deliquescent brines are relevant to the surface and near-subsurface of cold arid worlds like Mars. When conditions become wetter, hygroscopic evaporite minerals can deliquesce to produce the earliest habitable brines. Survival after desiccation and growth in deliquescent brines increases the likelihood that microbes from Earth, carried on spacecraft, pose a contamination risk to Mars.

Growing algae in darkness for biodiesel production eliminates the challenges of evaporation and light penetration reported for open ponds and the costs and fouling that plague photobioreactors. The current study demonstrated that Chlorella kessleri str. UTEX 263 could grow heterotrophically in the dark on pure sugars or lignocellulosic hydrolysates of plant biomass. Hydrolysates of a prairie grass native to Kansas, Big bluestem ( Andropogon gerardii ), supported the growth of C. kessleri in the dark. Nitrogen limitation stimulated the accumulation of biodiesel lipids by 10-fold in heterotrophic cultures grown on pure sugars or Big bluestem hydrolysate. Limiting P in the growth medium also was shown to increase cellular lipid accumulation in C. kessleri . Iron limitation was not sufficient to increase cellular lipid content. Crude biomass extracts may have levels of N that can't be easily removed, which are high enough to relieve N limitations in growth media. This initial study suggests that P might be more easily removed from biomass extracts than N for increasing cellular lipid production by nutrient limitation and further that native prairie grasses are potentially suitable as sources of lignocellulosic sugars.

Liquid water on Mars might be created by deliquescence of hygroscopic salts or by permafrost melts, both potentially forming saturated brines. Freezing point depression allows these heavy brines to remain liquid in the near-surface environment for extended periods, perhaps as eutectic solutions, at the lowest temperatures and highest salt concentrations where ices and precipitates do not form. Perchlorate and chlorate salts and iron sulfate form brines with low eutectic temperatures and may persist under Mars near-surface conditions, but are chemically harsh at high concentrations and were expected to be incompatible with life, while brines of common sulfate salts on Mars may be more suitable for microbial growth. Microbial growth in saturated brines also may be relevant beyond Mars, to the oceans of Ceres, Enceladus, Europa and Pluto. We have previously shown strong growth of salinotolerant bacteria in media containing 2 M MgSO 4 heptahydrate (~50% w/v) at 25 °C. Here we extend those observations to bacterial isolates from Basque Lake, BC and Hot Lake, WA, that grow well in saturated MgSO 4 medium (67%) at 25 °C and in 50% MgSO 4 medium at 4 °C (56% would be saturated). Psychrotolerant, salinotolerant microbes isolated from Basque Lake soils included Halomonas and Marinococcus , which were identified by 16S rRNA gene sequencing and characterized phenetically. Eutectic liquid medium constituted by 43% MgSO 4 at -4 °C supported copious growth of these psychrotolerant Halomonas isolates, among others. Bacterial isolates also grew well at the eutectic for K chlorate (3% at -3 °C). Survival and growth in eutectic solutions increases the possibility that microbes contaminating spacecraft pose a contamination risk to Mars. The cold brines of sulfate and (per)chlorate salts that may form at times on Mars through deliquescence or permafrost melt have now been demonstrated to be suitable microbial habitats, should appropriate nutrients be available and dormant cells become vegetative.

Athalassohaline waters that are rich in divalent ions are good analogues for the chemical environments of Mars and the ocean worlds. Sulfate salts, along with chlorides, are important in Mars regolith with Ca, Fe, Mg, and Na counterions. Certain lakes in the Pacific Northwest are saturated with MgSO 4 as epsomite. Here we report on the microbial community of Basque Lake, BC, a group of playas that is saturated with MgSO 4 . More than 60 bacterial isolates were obtained from Basque Lake soils by enrichment culture and repetitive streak-plating using media containing 10% (~ 1.7 M) NaCl or 50% (~ 2 M) MgSO 4 . Most of the isolates (~ 75%) were Gram-positive, motile, and produced endospores. Isolates related to Marinococcus halophilus and Virgibacillus marismortui dominated the collection. Halomonas and Salinivibrio were Gram-negative genera found at Basque Lake. Nearly all of the Basque Lake isolates grew at 50% MgSO 4 , with 65% growing at 60% MgSO 4 . Several isolates could grow in saturated (67%) MgSO 4 (a w  = 0.90). All of the isolates grew at 10% NaCl with 70% growing at 20% salinity (~ 3.5 M NaCl; a w  = 0.82). Basque Lake isolates grew better at basic pH than acidic pH, with 80% growing at pH 9 and 30% growing at pH 10. Only 20% of the isolates grew at pH 5. Numerical taxonomy dendrograms based on 44 phenetic characteristics showed a strong correspondence to phylogenetic trees constructed from 16S rRNA gene sequences. Pyrosequencing of 16S rRNA gene sequences from direct DNA extracts of Basque Lake soils recovered predominantly Proteobacteria (60%), Firmicutes (11%), and unclassified bacteria (27%). Microbes capable of growth under the extreme chemical conditions of Mars are a particular concern for forward planetary protection should they contaminate a spacecraft.

Small streams exert great influences on the retention and attenuation of nitrogen (N) within stream networks. Human land use can lead to increased transport of dissolved inorganic N compounds and downstream eutrophication. Microbial activity in streams is important for maintaining an actively functioning N cycle. Chronically high N loading in streams affects the rates of the central processes of the N cycle by increasing rates of nitrification and denitrification, with biota exhibiting decreased efficiency of N use. The LINXII project measured N-cycle parameters in small streams using 15 NO 3 - tracer release experiments. We concurrently measured N 2 fixation rates in six streams of three types (agricultural, pristine, and urban prairie streams) as part of this broader study of major N-cycle processes. Nitrogen fixation in streams was significantly negatively correlated with nitrate levels, dissolved inorganic N levels, and denitrification rates. Algal mat and leaf litter samples generally exhibited the highest rates of N 2 fixation. The abundance of nifH genes, as measured by real-time PCR, was marginally correlated with N 2 -fixation rates, but not to other N-cycle processes or stream characteristics. The nifH sequences observed were assigned to cyanobacteria, Deltaproteobacteria, Methylococcus, and Rhizobia. Seasonal changes, disturbances, and varying inputs may encourage a diverse, flexible, stable N 2 -fixing guild. Patchiness in the streams should be considered when assessing the overall impact of N 2 fixation, since algal biomass exhibited high rates of N 2 fixation.

Sucretolerant microbes grow in the presence of sugar concentrations high enough to substantially lower water activities. Natural habitats high in sugars are mainly limited to dried fruit, floral nectar, honey, sugarcane, and associated soils. Organisms that tolerate extremes of solute concentration, high enough to lower water activities, might not be expected in common oligoosmotic soils. We report on the isolation of sucretolerant bacteria from common soils using media supplemented with 50% sucrose (a w 0.91) and their physiological characterization and identification by 16S rRNA gene phylogeny. Fifteen of these sucretolerant isolates from common soils were related to four Bacillus spp. A Lysinibacillus and a Microbacterium (actinomycete) also were collected. All grew at 50% sucrose and 13 grew at 60% sucrose. Most probable number counts were used to determine the abundance of sucretolerant microbes in several common soil types, including agricultural, managed turf, and native prairie. Microbial abundance (with fungicides) was about 10 5 and 10 3 cells g -1 soil in media containing 50 or 70% sucrose, respectively. The abundances of sucretolerant bacteria in common soils mirror those of halotolerant bacteria that grow at 10 and 20% NaCl. However, there is not a correlation between halotolerance and sucretolerance in our isolates, nor can predictions be made based on taxonomy. Specific solute effects may be at work, rather than biological responses to a single physicochemical parameter such as a w . The occurrence of spore-forming sucretolerant bacteria in common soils has relevance to forward planetary protection and astrobiology. Extraterrestrial habitable regions are defined in part by tolerance to high solute concentrations and osmotolerant soil microbes may contaminate spacecraft.