No abstract

Microbial biofilms are ubiquitous. In marine and freshwater ecosystems, microbe-mineral interactions sustain biogeochemical cycles, while biofilms found on plants and animals can range from pathogens to commensals. Moreover, biofouling and biocorrosion represent significant challenges to industry. Bioprocessing is an opportunity to take advantage of biofilms and harness their utility as chassis for biocommodity production. Electrochemical bioreactors have numerous potential applications, including wastewater treatment and commodity production. The literature examining these applications has demonstrated that the cell-surface interface is vital to facilitating these processes. Therefore, it is necessary to understand the state of knowledge regarding biofilms’ role in bioprocessing. This mini-review discusses bacterial biofilm formation, cell-surface redox interactions, and the role of microbial electron transfer in bioprocesses. It also highlights some current goals and challenges with respect to microbe-mediated bioprocessing and future perspectives.

Polyhydroxybutyrate (PHB) is a bio-based, biodegradable alternative to petroleum-based plastics. PHB production at industrial scales remains infeasible, in part due to insufficient yields and high costs. Addressing these challenges requires identifying novel biological chassis for PHB production and modifying known biological chassis to enhance production using sustainable, renewable inputs. Here, we take the former approach and present the first description of PHB production by two prosthecate photosynthetic purple non-sulfur bacteria (PNSB), Rhodomicrobium vannielii and Rhodomicrobium udaipurense. We show that both species produce PHB across photoheterotrophic, photoautotrophic, photoferrotrophic, and photoelectrotrophic growth conditions. Both species show the greatest PHB titers during photoheterotrophic growth on butyrate with dinitrogen gas as a nitrogen source (up to 44.08 mg/L), while photoelectrotrophic growth demonstrated the lowest titers (up to 0.13 mg/L). These titers are both greater (photoheterotrophy) and less (photoelectrotrophy) than those observed previously in a related PNSB, Rhodopseudomonas palustris TIE-1. On the other hand, we observe the highest electron yields during photoautotrophic growth with hydrogen gas or ferrous iron electron donors, and these electron yields were generally greater than those observed previously in TIE-1. These data suggest that non model organisms like Rhodomicrobium should be explored for sustainable PHB production and highlights utility in exploring novel biological chassis.

Recent attempts to sequence regions of the Rhodomicrobium vannielii ATCC 17100 genome revealed discrepancies with the previously published genome. We report the revised draft genome sequences of the type strains Rhodomicrobium vannielii ATCC 17100 and Rhodomicrobium udaipurense JA643. These revisions will facilitate genetic studies of phototrophic metabolism in these bacteria.