The study describes the effect of aerobic conditions on the proteome of homofermentative lactic acid bacterium Lacticaseibacillus rhamnosus CM MSU 529 grown in a batch culture. Aeration caused the induction of the biosynthesis of 43 proteins, while 14 proteins were downregulated as detected by label-free LC-MS/MS. Upregulated proteins are involved in oxygen consumption (Pox, LctO, pyridoxine 5’-phosphate oxidase), xylulose 5-phosphate conversion (Xfp), pyruvate metabolism (PdhD, AlsS, AlsD), reactive oxygen species (ROS) elimination (Tpx, TrxA, Npr), general stress response (GroES, PfpI, universal stress protein, YqiG), antioxidant production (CysK, DkgA), pyrimidine metabolism (CarA, CarB, PyrE, PyrC, PyrB, PyrR), oligopeptide transport and metabolism (OppA, PepO), and maturation and stability of ribosomal subunits (RbfA, VicX). Downregulated proteins participate in ROS defense (AhpC), citrate and pyruvate consumption (CitE, PflB), oxaloacetate production (AvtA), arginine synthesis (ArgG), amino acid transport (GlnQ), and deoxynucleoside biosynthesis (RtpR). The data obtained shed light on mechanisms providing O₂-tolerance and adaptation to aerobic conditions in strain CM MSU 529. The biosynthesis of 39 from 57 differentially abundant proteins was shown to be O₂-sensitive in lactic acid bacteria for the first time. To our knowledge this is the first study on the impact of aerobic cultivation on the proteome of L. rhamnosus.

The iron-oxidizing system of a moderately thermophilic, extremely acidophilic, gram-positive mixotroph, Sulfobacillus sibiricus N1^T, was studied by spectroscopic, high-performance liquid chromatography and inhibitory analyses. Hemes B, A, and O were detected in membranes of S. sibiricus N1^T. It is proposed that the electron transport chain from Fe²⁺to O₂is terminated by 2 physiological oxidases: aa₃-type cytochrome, which dominates in the early-exponential phase of growth, and bo₃-type cytochrome, whose role in iron oxidation becomes more prominent upon growth of the culture. Both oxidases were sensitive to cyanide and azide. Cytochrome aa₃was more sensitive to cyanide and azide, with K_ivalues of 4.1 and 2.5 µmol·L^–1, respectively, compared with K_ivalues for cytochrome bo₃, which were 9.5 µmol·L^–1for cyanide and 7.0 µmol·L^–1for azide. This is the first evidence for the participation of a bo₃-type oxidase in ferrous iron oxidation. The respiratory chain of the mixotroph contains, in addition to the 2 terminal oxidases, a membrane-bound cytochrome b₅₇₃.

Lacticaseibacillus rhamnosus CM MSU 529 was grown in a batch culture under intensive aeration in the presence of 38 µM hemin and 18 µM vitamin K2

Methylamine dehydrogenase (MADH) and azurin were purified from the periplasmic fraction of the methylamine-grown obligate methylotroph Methylobacillus flagellatus KT. The molecular mass of the purified azurin was 16.3 kDa, as measured by SDS–PAGE, or 13 920 Da as determined by MALDI–TOF mass spectrometry. Azurin of M. flagellatus KT contained 1 copper atom per molecule and had an absorption maximum at 620 nm in the oxidized state. The redox potential of azurin measured at pH 7.0 by square-wave voltammetry was +275 mV versus normal hydrogen electrode. MADH reduced azurin in the presence of methylamine, indicating that this cupredoxin is likely to be the physiological electron acceptor for MADH in the electron transport chain of the methylotroph. A scheme of electron transport functioning in M. flagellatus KТ during methylamine oxidation is proposed.