Transcriptional organization of the Azotobacter vinelandii algGXLVIFA genes: characterization of algF mutants.

Azotobacter vinelandii forms desiccation-resistant cysts which contain a high proportion of the exopolysaccharide alginate in their envelope. We have previously shown that the A. vinelandii alginate biosynthetic genes algA and algL are transcribed from a promoter located somewhere upstream of algL. In this study we sequenced the A. vinelandii algX, algL, algV, algI and algF genes located between algG and algA. We carried out primer extension analysis of the algG, algX and algL genes and detected transcription start sites upstream algG but not upstream algX or algL, implying that algG and algX form part of the previously identified algL-A operon. A promoter upstream algA was also detected; however, transcription of algA exclusively from this promoter is not sufficient for the AlgA levels required for alginate production. An algF mutant (AJ34) was constructed by insertion of the Omega-tetracycline cassette in the non-polar orientation. As expected, AJ34 produced unacetylated alginate. Viability of 35day old cysts formed by strain AJ34, but not of those formed by the wild type, was reduced, indicating that acetylation of alginate plays a role in cyst resistance to desiccation.