Cyanobacterial Growth on Municipal Wastewater Requires Low Temperatures

Abstract

28Side-streams in wastewater treatment plants can serve as concentrated sources of nutrients 29 (i.e. nitrogen and phosphorus) to support the growth of photosynthetic organisms that ultimately 30 serve as feedstock for production of fuels and chemicals. However, other chemical characteristics 31 of these streams may inhibit growth in unanticipated ways. Here, we evaluated the use of liquid 32 recovered from municipal anaerobic digesters via gravity belt filtration as a nutrient source for 33 growing the cyanobacterium Synechococcus sp. strain PCC 7002. The gravity belt filtrate (GBF) 34 contained high levels of complex dissolved organic matter (DOM), which seemed to negatively 35 influence cells. We investigated the impact of GBF on physiological parameters such as growth 36 rate, membrane integrity, membrane composition, photosystem composition, and oxygen 37 evolution from photosystem II. At 37°C, we observed an inverse correlation between GBF 38 concentration and membrane integrity. Radical production was also detected upon exposure to 39 GBF at 37°C. However, at 27°C the dose dependent relationship between GBF concentration and 40 lack of membrane integrity was abolished. Immediate resuspension of strains in high doses of GBF 41 showed markedly reduced oxygen evolution rates relative to the control. Together, this suggests 42 that one mechanism responsible for GBF toxicity to Synechococcus is the interruption of 43 photosynthetic electron flow and subsequent phenomena. We hypothesize this is likely due to the 44 presence of phenolic compounds within the DOM. 45 46

Engineering photosynthetic production of L-lysine

“…Cyanobacteria growth media is commonly formulated with nitrate that is reduced to ammonia (serving as a sink for excess electrons) prior to assimilation ( McNeely et al, 2014 ). In contrast, when wild-type PCC 7002 is fed ammonia as a N-source, cells grow slower and display significant chlorosis ( Korosh et al, 2017 ). This can be overcome by providing an alternative electron sink such as biomass (providing elevated P CO2 ) or production of reduced compounds.…”

“…Given the cost of fertilizers, it is attractive to consider alternative sources of low-cost nitrogen and phosphate such as anaerobic digestor and/or municipal waste water streams Anaerobic digestion effluent from municipal wastewater has previously been used as a nutrient source for cyanobacterial cultivation and lactate production ( Hollinshead et al, 2014 ), but there are many potential toxicants that could limit its widespread adoption. We have previously demonstrated that a physiological adaptation at 27°C is necessary to allow growth of PCC 7002 in filtrate recycled from the gravity belt (GBF) of a local municipal water treatment plant ( Korosh et al, 2017 ). The GBF provides a nitrogen- (predominantly NH 4 + ) and phosphate-source.…”

“…Strains were grown in 250 ml baffled flasks with 50 mL Media A + with 1% CO 2 -enriched air at 150 rpm in a Kuhner ISF1-X orbital shaker. Growth on wastewater-derived nutrients was accomplished as described elsewhere ( Korosh et al, 2017 ). Briefly, filtrate from the anaerobic digester gravity belt filter (GBF), and effluent from the post-mainstream secondary treatment clarifier (secondary effluent) served as a diluent which was obtained from Nine Springs Wastewater Treatment Plant (Dane County, Wisconsin).…”

“…Direct photosynthetic production of L-lysine is an attractive process because it circumvents the need for harvesting, processing and fermentation of plant-derived sugars, by directly coupling lysine biosynthesis to photosynthesis. Cyanobacteria are attractive photosynthetic organisms for L-lysine production due to the availability of genetic tools, rapid growth rates, halotolerance, and ability to be grown on non-productive land with simple nutrient requirements ( Oliver and Atsumi, 2014 ; Pate et al, 2011 ) or wastestreams ( Korosh et al, 2017 ). Here, we report successful metabolic engineering strategies for production of L-lysine from a strain of the fast-growing Synechococcus sp.…”