Production and cross-feeding of nitrite within Prochlorococcus populations

Prochlorococcus is an abundant photosynthetic bacterium in the oligotrophic open ocean where nitrogen (N) often limits the growth of phytoplankton. Prochlorococcus has evolved into multiple phylogenetic clades of high-light (HL) adapted and low-light (LL) adapted cells. Within these clades, cells encode a variety of N assimilation traits that are differentially distributed among members of the population. Among these traits, nitrate (NO3-) assimilation is generally restricted to a few clades of high-light adapted cells (the HLI, HLII, and HLVI clades) and a single clade of low-light adapted cells (the LLI clade). Most, if not all, cells belonging to the LLI clade have the ability to assimilate nitrite (NO2-), with a subset of this clade capable of assimilating both NO3- and NO2-. Cells belonging to the LLI clade are maximally abundant at the top of the nitracline and near the primary NO2- maximum layer. In some ecosystems, this peak in NO2- concentration may be a consequence of incomplete assimilatory NO3- reduction by phytoplankton. This phenomenon is characterized by a bottleneck in the downstream half of the NO3- assimilation pathway and the concomitant accumulation and release of NO2- by phytoplankton cells. Given the association between LLI Prochlorococcus and the primary NO2- maximum layer, we hypothesized that some Prochlorococcus exhibit incomplete assimilatory NO3- reduction. To assess this, we monitored NO2- accumulation in batch culture for 3 Prochlorococcus strains (MIT0915, MIT0917, and SB) and 2 Synechococcus strains (WH8102 and WH7803) when grown on NO3- as the sole N source. Only MIT0917 and SB accumulated external NO2- during growth on NO3-. Approximately 20-30% of the NO3- transported into the cell by MIT0917 was released as NO2-, with the balance assimilated into biomass. We further observed that co-cultures using NO3- as the sole N source could be established for MIT0917 and a Prochlorococcus strain that can assimilate NO2- but not NO3-. In these co-cultures, the NO2- released by MIT0917 was efficiently consumed by its partner strain during balanced exponential growth. Our findings highlight the potential for emergent metabolic partnerships within Prochlorococcus populations that are mediated by the production and consumption of the N cycle intermediate, NO2-.

Single-Cell Time-Lapse Observation Reveals Cell Shrinkage upon Cell Death in Batch Culture of Saccharomyces cerevisiae

Cells display various behaviors even though they originate from a clonal population. Such diversity is also observed in cell survival in the stationary phase of Saccharomyces cerevisiae .

CHARACTERISATION OF A MEMBER OF THE GENUS CELLULOSIMICROBIUM AS A DEGRADER OF 2,4-DICHLOROPHENOXYACETIC ACID

On the basis of the cultural, morphological, physiological and biochemical features, the taxonomic position of the NPZ-121 strain (isolated from the soil contaminated with chemical waste in Ufa (Russia)) as belonging to the species Cellulosimicrobium funkei was specified. In a batch culture the dynamics of growth of the strain C. funkei NPZ-121 and utilization of 2,4-dichlorophenoxyacetic acid at a concentration of 100 mg/l were described. For 11 days the culture used up to 69% of the substrate from the initial value. The ability of the strain to metabolize 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was revealed previously. Thus, the polysubstrate activity to chlorinated phenoxyacetic acids of the NPZ-121 strain was established.

Bacterial Cellulose Synthesis by Gluconacetobacter xylinus: Enhancement via Fed-batch Fermentation Strategies in Glycerol Media

Bacterial cellulose (BC) is an abundant polysaccharide, which is secreted by several genera of bacteria. It has remarkable characteristics, which include high purity, high tensile strength, high biocompatibility and non-toxic. The main feature that differentiates BC and plant cellulose (PC) is the absence of contaminants such as lignin, hemicellulose and pectin. However, the main drawbacks in producing BC are low yield and expensive carbon source. Due to that, this study was carried out to enhance BC volumetric productivity in fed-batch operation mode using glycerol as a carbon source. BC was produced in fill-and-draw and pulse-feed fed-batch cultures of Gluconacetobacter xylinus DSM 46604 in a 3-L bench-top bioreactor. The fed-batch fermentation trials were conducted in agitated and aerobic conditions at 30 ºC. For fill-and-draw fed-batch culture, a total of 24.2 g/L of BC accumulated in the bioreactor after 9 days, which corresponded to a yield and productivity of 0.2 g/g and 2.69 g/L/day, respectively. Pulse-feed fed-batch fermentation resulted in a yield and volumetric productivity of 0.38 g/g and 2.71 g/L/day, respectively. The pulse-feed fed-batch culture proved to be a better fermentation system for utilizing glycerol, which is a low-cost and abundant carbon source. HIGHLIGHTS Komagataeibacter species, which were formerly known as Acetobacter or Gluconacetobacter is one of the Gram-negative BC producers that secretes a large quantity of BC microfibrils extracellularly One of the main challenges in bacterial cellulose (BC) production is low productivity and high processing cost As fed-batch fermentation is one of the operation modes in bioprocess that can control the microbial growth rate, this operation mode is conducted to enhance the yield of BC, substrate consumption and also volumetric productivity Fill-and-draw and pulse feed fed-batch culture were conducted to enhance yield and volumetric productivity. The pulse-feed fed-batch culture resulted to be a favorable operation mode for utilizing glycerol, which is a low-cost and abundant carbon source GRAPHICAL ABSTRACT

Removal of Toxic Volatile Compounds in Batch Culture Prolongs Stationary Phase and Delays Death of Escherichia coli

The mechanisms controlling entry into and exit from death phase in the bacterial life cycle remain unclear. While bacterial growth studies in batch cultures traditionally focus on the first three phases during incubation, two additional phases, death phase and long-term stationary phase, are less understood. Although there are a number of stressors that arise during long-term batch culture, including nutrient depletion and the accumulation of metabolic toxins such as reactive oxidative species, their roles in cell death are not well-defined. By manipulating environmental conditions of Escherichia coli incubated in long-term batch culture through chemical and mechanical means, we investigated the role of volatile metabolic toxins in modulating the onset of death phase. Here, we demonstrate that with the introduction of substrates with high binding affinities for volatile compounds, toxic byproducts of normal cell metabolism, into the headspace of batch cultures, cells display prolonged stationary phase and delayed entry into death phase. Addition of these substrates allows cultures to maintain a high cell density for hours to days longer than cultures incubated under standard growth conditions. A similar effect is observed when the gaseous headspace in culture flasks is continuously replaced with sterile air, mechanically preventing the accumulation of metabolic byproducts in batch cultures. We establish that toxic compound(s) are produced during exponential phase, demonstrate that buildup of toxic byproducts influence entry into death phase, and present a novel tool for improving high density growth in batch culture that may be used in future research, industrial, or biotechnology applications. IMPORTANCE Bacteria, such as Escherichia coli , are routinely used in the production of biomaterials because of their efficient and sustainable capacity for synthesis of bioproducts. Industrial applications of microbial synthesis typically utilize cells in stationary phase, when cultures have the greatest density of viable cells. By manipulating culture conditions to delay the transition from stationary phase to death phase, we can prolong stationary phase on a scale of hours to days, thereby maintaining the maximum density of cells that would otherwise quickly decline. Characterization of the mechanisms that control entry into death phase for the model organism Escherichia coli not only deepens our understanding of the bacterial life cycle, but also presents an opportunity to enhance current protocols for batch culture growth and explore similar effects in a variety of widely used bacterial strains.