Alkalicaulis satelles gen. nov., sp. nov., a novel haloalkaliphile isolated from a laboratory culture cyanobacterium Geitlerinema species and proposals of Maricaulaceae fam. nov., Robiginitomaculaceae fam. nov., Maricaulales ord. nov. and Hyphomonadales ord. nov

Diverse aerobic anoxygenic phototrophs synthesize bacteriochlorophyll in oligotrophic rather than copiotrophic conditions, suggesting ecological niche

While investigating aerobic anoxygenic phototrophs (AAP) from Lake Winnipeg's bacterial community, over 500 isolates were obtained. Relatives of 20 different species were examined simultaneously, identifying conditions for optimal growth or pigment production to determine features that may unify this group of phototrophs. All were distributed among assorted α-Proteobacterial families including Erythrobacteraceae, Sphingomonadaceae, Sphingosinicellaceae, Acetobacteraceae, Methylobacteriaceae, and Rhodobacteraceae. Major phenotypic characteristics matched phylogenetic association, including pigmentation, morphology, metal transformations, tolerances, lipid configurations, and enzyme activities, which distinctly separated each taxonomic family. While varying pH and temperature had a limited independent impact on pigment production, bacteriochlorophyll synthesis was distinctly promoted under low nutrient conditions, whereas copiotrophy repressed its production but enhanced carotenoid yield. New AAP diversity was also reported by revealing strains related to non-phototrophic Rubellimicrobium and Sphingorhabdus, as well as spread throughout Roseomonas, Sphingomonas, and Methylobacterium/Methylorubrum, which previously only had a few known photosynthetic members. This study exemplified the overwhelming diversity of AAP in a single aquatic environment, confirming cultivation continues to be of importance in microbial ecology to discover functionality in both new and previously reported cohorts of bacteria as specific laboratory conditions were required to promote aerobic bacteriochlorophyll production.

Prosthecate aerobic anoxygenic phototrophs Photocaulis sulfatitolerans gen. nov. sp. nov. and Photocaulis rubescens sp. nov. isolated from alpine meromictic lakes in British Columbia, Canada

Seven Gram-negative flagellated and subsequent prosthecate bacteria were isolated from meromictic Mahoney Lake and Blue Lake in British Columbia, Canada. Each became pink-red after 1-2 weeks of incubation, containing bacteriochlorophyll a incorporated into light harvesting and reaction center pigment-protein complexes. They did not grow anaerobically under illuminated conditions, supporting their identification as obligate aerobic anoxygenic phototrophs (AAP). All isolates preferred high salinity and BL14^T tolerated up to 6.5% NaCl or 16.0% Na₂SO₄. In addition to phenotypic differences, analysis of 16S rRNA gene sequences found both strains BL14^T and ML37^T were related to Alkalicaulis satelles, G-192^T by 98.41 and 98.84%, respectively, and distantly associated to members of the non-phototrophic genus Glycocaulis profundi, ZYF765^T (95.59 and 95.36%, respectively) within the newly recognized Maricaulales order of α-Proteobacteria. BL14^T and ML37^T contained photosynthetic operons of 46,143 and 46,315 bp, where genes of BL14^T were uniquely split into two distal operons. Furthermore, A. satelles was not originally published as an AAP, but was also found in this work to contain a similar 45,131 bp fragment. The distinct morphological features, physiological traits and genomic analysis including average nucleotide identity and digital DNA:DNA hybridization of circularized genomes supported the proposal of new genus and species Photocaulis sulfatitolerans gen. nov. sp. nov., type strain BL14^T and Photocaulis rubescens sp. nov. type strain ML37^T.

New Alphaproteobacteria Thrive in the Depths of the Ocean with Oxygen Gradient

We survey here the Alphaproteobacteria, a large class encompassing physiologically diverse bacteria which are divided in several orders established since 2007. Currently, there is considerable uncertainty regarding the classification of an increasing number of marine metagenome-assembled genomes (MAGs) that remain poorly defined in their taxonomic position within Alphaproteobacteria. The traditional classification of NCBI taxonomy is increasingly complemented by the Genome Taxonomy Database (GTDB), but the two taxonomies differ considerably in the classification of several Alphaproteobacteria, especially from ocean metagenomes. We analyzed the classification of Alphaproteobacteria lineages that are most common in marine environments, using integrated approaches of phylogenomics and functional profiling of metabolic features that define their aerobic metabolism. Using protein markers such as NuoL, the largest membrane subunit of complex I, we have identified new clades of Alphaproteobacteria that are specific to marine niches with steep oxygen gradients (oxycline). These bacteria have relatives among MAGs found in anoxic strata of Lake Tanganyika and together define a lineage that is distinct from either Rhodospirillales or Sneathiellales. We characterized in particular the new ‘oxycline’ clade. Our analysis of Alphaproteobacteria also reveals new clues regarding the ancestry of mitochondria, which likely evolved in oxycline marine environments.

Maricaulis alexandrii sp. nov., a novel active bioflocculants-bearing and dimorphic prosthecate bacterium isolated from marine phycosphere

An aerobic, Gram-stain-negative, straight or curved rods and dimorphic prosthecate bacterium designated as strain LZ-16-1^T was isolated from phycosphere microbiota of routinely laboratory-cultured and highly-toxic marine dinoflagellate Alexandrium catenella LZT09. Strain LZ-16-1^T produces active bioflocculanting exopolysaccharides (EPS). Cells were dimorphic with non-motile prostheca, or non-stalked and motile by a single polar flagellum. Growth occurred at 10-40 °C, pH 5-9 and 1-8% (w/v) NaCl, with optimum growth at 25 °C, pH 7-8 in the presence of 2-4% (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain LZ-16-1^T was affiliated to the genus Maricaulis, and closely related to M. parjimensis MCS 25^T (99.5%) and M. virginensis VC-5^T (99.0%). However, based on genome sequencing and phylogenomic calculations, the average nucleotide identity (ANI) and digtal DNA-DNA genome hybridization (dDDH) values between strains LZ-16-1^T and its closest relative, M. parjimensis MCS 25^T were only 85.0 and 20.9%, respectively. The dominant fatty acids of strain LZ-16-1^T were summed feature 8, C_16:0, C_17:0, C_18:0, C_18:1 ω9c and summed feature 9. Major polar lipids were sulfoquinovosyl diacylglycerol, six glycolipids, one unidentified phospholipid and one unidentified polar lipid. The predominant isoprenoid quinone was Q-10. The DNA G + C content calculated from the genome was 63.6 mol%. Physiological and chemotaxonomic characterizations further confirmed the distinctiveness of strain LZ-16-1^T from other Maricaulis members. Thus, strain LZ-16-1^T represents a novel species of the genus Maricaulis, for which the name Maricaulis alexandrii sp. nov. (type strain LZ-16-1^T = KCTC 72194^T = CCTCC AB 2019006^T) is proposed.